The Strangest of Spiders

In the comments to an earlier post, I promised to write a post sometime on micro-spiders. As alluded to in that post, some of the smallest spiders are mind-bogglingly tiny - the smallest known male spider, Patu digua, reaches all of 0.37 mm in length as an adult, but at least one other species known as yet only from females could potentially have a male even smaller. If one of these spiders crawled into your ear while you were sleeping, it could probably slip into your Eustachian tubes and tap on the back of your eyeballs. But even more remarkable than their small size is the bizarre morphologies on show among the micro-spiders. And no group of micro-spiders is more bizarre than the Archaeidae.

Archaeids are a bit bigger than Patu, but still pretty small - the largest examples reach about six millimetres. The name "Archaeidae", of course, means "old", and archaeids received their name because they were first described in 1854 from fossils in Baltic amber from northern Europe. In Europe, the archaeids are long gone (they may have disappeared along with the amber forests), but nearly thirty years after their initial description living examples were found in Madagascar. They are also known from Australia, while a specimen from Cretaceous Burmese amber has been placed in a living genus from South Africa and Madagascar (Penney, 2003). A species has also been described from the Jurassic of Kazakhstan, but it is uncertain whether this species is an actual archaeid or belongs to another micro-spider family such as Pararchaeidae.

Many micro-spiders show relatively long chelicerae (the fangs and their base) relative to body size, but in Archaeidae this is taken to the extreme, as can well be seen in the photo by Jeremy Miller at the top of this post. Because the trochanter (base) of the chelicerae is a rigid structure, lengthening them in spiders requires that the carapace as a whole be raised, otherwise the fangs would not be able to get anywhere near the mouth. Archaeids have developed a long "neck" supporting the eyes and chelicerae. The distinct shape of the cephalothorax together with the long chelicerae gives them an unmistakeable profile, and one common name used for the group is "pelican spiders". Despite their small size, archaeids are active hunters and voracious exclusive predators of other spiders (another common name is "assassin spiders"). It has been suggested that the lengthened chelicerae are directly related to their araneophagous diet, allowing them to strike their prey without getting too close, but as I already noted archaeids are not the only small spiders with lengthened chelicerae (though they are still the most dramatic), and I'd be interested to know if there is a correlation between small size and long chelicerae.



I'd also like to share this diagram from Wood et al. (2007) showing a molecular-derived phylogeny of the endemic Madagascan genus Eriauchenius. As can be seen, there is a fair amount of variation in the thickness of the "neck" (the darkness of the bars reflects the mean carapace height/length ratio for whichever group they subtend), and it had been suggested that those species with a particularly slender neck formed a derived clade. Wood et al. (2007) found that this does not appear to be the case, with at least two extreme narrow-neck groups - E. workmani in one and E. gracilicollis and E. lavatenda in the other - at quite divergent points in the tree. I also looks to me like at least one group - E. tsingyensis and its allies - may have gone the other way. To paraphrase a Rocky Horror Picture Show audience member - that spider has no neck.

REFERENCES

Penney, D. 2003. Afrarchaea grimaldii, a new species of Archaeidae (Araneae) in Cretaceous Burmese amber. Journal of Arachnology 31 (1): 122-130.

Wood, H. M., C. E. Griswold & G. S. Spicer. 2007. Phylogenetic relationships within an endemic group of Malagasy ‘assassin spiders’ (Araneae, Archaeidae): ancestral character reconstruction, convergent evolution and biogeography. Molecular Phylogenetics and Evolution 45 (2): 612-619.

Linnaeus' Legacy: Legs Eleven

The next edition of Linnaeus' Legacy, the taxonomy and systematics blog carnival, will be coming up shortly at The Other 95%. Last month's edition at A DC Birding Blog matched its host by holding lots of birds, so my challenge to you all would be to try to make this month follow suit and bring out the marine invertebrates. Submissions can be directed to Eric Heupel via eric.heupel at gmail.com, or use the BlogCarnival submission form.

More Juvenilia

Chris M at The Echinoblog has put up a list of odd things that sit in his laboratory, and notes that people look askance at the pile of toilet paper (a vital tool in drying specimens). Well, I can top that:



K-Y jelly is actually fantastic stuff for preparing temporary slide mounts. It's transparent, it holds things in place reasonably well (though it does heat up and start flowing a bit if you leave it under the light for too long) and it's water-soluble, so you can just take a specimen preserved in alcohol out of its vial and put it straight onto the slide then return it straight to the vial when finished without needing to wash or prepare it in any way. Putting the specimen in alcohol on a concave slide is still preferable, because alcohol is more optically clear than K-Y, but alcohol won't hold the specimen at an angle in any way if you need to look at the specimen in a particular position. Seeing as how this is invertebrate systematics we're talking about, the thing I most commonly need to look at on a slide are reproductive organs. Which leads to an actual exchange that took place:

Colleague: "Why do you have K-Y jelly in your office?"

Me: "I use it for mounting... I mean, I put genitalia in it... Crap."

Offhand, I have also now discovered that if you do an image search for K-Y jelly, it pays to have the SafeSearch option turned on.

Ye Gods I'm Immature

Sometimes when naming a species, it pays to be careful...

In 1954, Roewer described a new species of harvestman named Metagagrella mysoreana (so named, I assume, because it came from Mysore). Metagagrella has since been synonymised with the older genus name Psathyropus, but most of the appropriate new combinations have not yet appeared in print. I was just entering in names for the Psathyropus section of the Palpatores nomenclator, which requires me to form said new combinations. However, because Psathyropus is a masculine name, I had to correct species name genders.

Yep.

Psathyropus mysoreanus.

The fact that I giggled when I realised shows just how much of a child I am.

Inevitable Spandrels on a Biology Blog

Nearly thirty years ago, a paper was published that almost every student of evolutionary science will end up reading at some point in their career. Despite being only eighteen pages long and containing no original research, many people see it as marking something of a revolution in biology. Like many a revolutionary document, it says little of substance that is not completely obvious, but entire books have been written that derive their subject matter directly from it. I speak of Gould and Lewontin's 1979 paper "The spandrels of San Marco and the Panglossian paradigm: a critique of the adaptationist programme".

In architectural terminology, a "spandrel" is the space formed where two arches meet each other, or where an arch meets a wall. The title of Gould and Lewontin's paper refers to such structures spaced around the dome in the Basilica di San Marco in Venice which sits on four arches (technically, the Venice structures are pendentives rather than spandrels, but this terminological error is irrelevant to Gould and Lewontin's argument). The iconography decorating the dome radiates towards those four pendentives. An observer completely ignorant of the requirements of architectural stability might feel that their focal significance in the iconography indicates that the pendentives were specifically designed to support the iconography, but this is simply not the case. Rather, the pendentives are simply a side-effect of building a stable dome, and the iconography has been designed to take advantage of their presence rather than vice versa. Gould and Lewontin used the Basilica di San Marco as a metaphor to criticise the over-reliance in evolutionary biology on adaptation as an explanation for characters of organisms. Wasn't it possible, claimed Gould and Lewontin, that at least some features of organisms were not selective traits in their own right, but merely biological "spandrels", architectural side-effects of the development of other traits?

Let me give a couple of examples. One that Gould and Lewontin refer to themselves involves the famous midget arms of Tyrannosaurus rex. Much speculation has taken place on what the function of these relatively tiny appendages could have been - props in raising the animal up from a lying position, grappling hooks in mating, etc. but as pointed out by G & L these "explanations" all rather missed the point. Tyrannosaurus did not evolve its tiny arms de novo, but inherited them from a proportionately longer-armed ancestor. While Tyrannosaurus arms could well have fulfilled any or all of the functions ascribed to them, none of the suggestions actually explained why Tyrannosaurus arms became so small in the first place. This may well have been a consequence of the rest of the animal increasing in size faster than the arms did, in which case the question is not "why did the arms become small", but "why did the rest of the dinosaur get so big?". Gould later brought up another example - giant pandas have an enlarged protruding wrist-bone on their forelimbs that functions as a crude thumb in manipulating the bamboo they eat. They also possess a similar enlarged ankle-bone on their hindlimbs that serves no obvious purpose, and indeed may be something of a nuisance. Gould suggested that the enlarged bone on the hindlimbs was a side-effect of the development of that on the forelimbs, due to the same processes underlying patterning in the development of both sets of limbs.

Unarguable as this all might seem, a certain frustration tends to set in towards the end of a reading of "Spandrels", as one eventually feels the need to rejoin with a "So what's your point, Vanessa?" Gould and Lewontin claimed, probably accurately, that over-atomising organism traits might lead to the failure to recognise linkage between features - looking at the spandrels only without considering the entire dome - and called for a whole-organism approach. But in practice, a certain degree of atomisation is necessary if our understanding is to go anywhere at all. It would seem ridiculous to claim that we cannot explain the evolution of the eye without also understanding the evolution of the big toe. Also, at the risk of stating a truism, we cannot possibly know everything about an organism, otherwise we would not be conducting the research in the first place.

Also, there is no way of distinguishing a priori a trait that has arisen as a result of being selectively advantageous from one that has "piggy-backed" on something else. It could well be argued that selective function for a given trait is a more fruitful base assumption that non-function because that is the basis that leads to further research, while assuming non-function is a bit of a show-stopper. As a result, while the concept of biological "spandrels" has caused a great deal of debate over the years on a theoretical basis, it is arguable whether it has had much direct practical effect. A similar fate befell another related Gould neologism, when Gould and Vrba (1982) coined the term "exaptation" for an organismal trait that had been co-opted for another use, just as the pendentives had been co-opted for use in decoration, in contrast to "adaptations" that had evolved specifically for the function they currently fulfilled. The distinction never caught on because, while it might seem theoretically significant, in practice it was fairly pointless. After all, evolution does not create things entirely from whole cloth but works through the alteration of pre-existing features, so all "adaptations" are at some level "exaptations".

Nevertheless, if the "Spandrels" paper had been so pointless as I've just implied, it wouldn't hold the iconic position in modern biology that it does. And agin like many another revolutionary document, this wasn't so much as a direct result of its own propositions, but of the effect it had on how people saw everything else. Gould and Lewontin were protesting against the assumption they saw in many biology studies that an adaptive function for any given trait must be in there somewhere, and if one could not be found it merely meant that we hadn't looked hard enough. As a result, the corollary assumption arose all too often that if an adaptive explanation could be derived for something, then it must be true. Gould and Lewontin argued that mere plausability was not sufficient support in itself for a proposition, because the possibility always existed that an equally plausible explanation had been overlooked - a logical error Voltaire had parodied in 1759 when he had his Dr. Pangloss in Candide, ou l'Optimisme argue that the nose had developed for the purpose of holding up spectacles. It was the recognition that adaptationist hypotheses were hypotheses that required further investigation as much as any other scientific proposition that was Gould and Lewontin's ultimate legacy to biology.

REFERENCES

Gould, S. J., & R. C. Lewontin. 1979. The spandrels of San Marco and the Panglossian paradigm: a critique of the adaptationist programme. Proceedings of the Royal Society of London Series B – Biological Sciences 205: 581-598.

Gould, S. J., & E. S. Vrba. 1982. Exaptation; a missing term in the science of form. Paleobiology 8 (1): 4-15.

The Calcareous Heart

Fossil cockle (Cardium), end-on to show the heart-shape formed by the two valves of these bivalves. Photo from the Humboldt State University Natural History Museum.

For me, the crux of what I do here at Catalogue of Organisms lies in the Taxon of the Week posts (I don't know if anybody else would agree with me, but it's my site, so I think I have more say in the matter). Every week I take a taxon chosen more or less at random (I have a big list of taxa on my computer at home that I move through cyclically) and find something to write on it. The idea behind this, of course, is that there is no group of organisms which is not deeply fascinating in its own way. Nevertheless, there was one group of organisms for which I knew it would be only a matter of time before they got their time in the sun, a time that would force me to make a confession that violates every standard of Catalogue of Organisms. This week's highlight taxon is the bivalve subfamily Cardiinae - and much as I hate to admit it, bivalves are almost undoubtedly the most boring organisms on the planet.

So spectacularly dull are bivalves, in fact, that their monotony almost becomes their main fascination. Like turtles and linguloid brachiopods, bivalves found something they were good at early on in their history and largely stuck to it*. Representatives are known from the very earliest Cambrian that would pass unremarked if mixed in with a collection of modern taxa. The vast majority of bivalves are passive filter feeders. While some live attached to hard substrates (mussels and oysters) or free-living on the surface of the sediment (e.g. scallops), probably the most common way of life in the class is buried in the sediment with only the siphons protruded above the surface to draw in and expel water and particulate matter. The internal anatomy of such burrowing bivalves has been reduced to three major components - gonad, gills for filtering, and the muscular foot used for digging. Despite their supposed ancestry from properly encephalised ancestors, bivalves have jettisoned all traces of an actual head as unnecessary frippery**, and gone for a more decentralised nervous system.

*I'll admit, there are exceptions. Oysters are somewhat odd. And one relatively small bivalve group, the anomalodesmatans, seemingly threw caution to the winds and has turned out almost all of the real freaks of the bivalve worlds, including active predators such as the cuspidariids, and the cylindrical "flower-pots" of the clavagellids. If bivalves were a distinguished well-to-do line of British nobility, anomalodesmatans would be the young ne'er-do-wells that fled the family home and joined a hippy commune.

**Cavalier-Smith (1998) suggested that the headless bivalves actually represented the ancestral condition for molluscs, while encephalisation had occurred independently in the clade containing the remaining molluscs from other encephalised animals. At present, this is something of a minority view, with most authors seeing the shell-less, wormlike aplacophorans as more likely to resemble the ancestral molluscs.


Acanthocardia tuberculata. Photo by Hans Hillewaert.

The bivalve family Cardiidae includes two superficially quite distinct groups of animals, the burrowing cockles and the tropical reef-dwelling giant clams (though the animal that we used to collect and eat under the name of "cockle" in New Zealand, Austrovenus stutchburyi, actually belongs to a quite different family, the Veneridae). Despite the apparent difference between these two groups (and indeed, giant clams were once included in their own separate family and even superfamily), phylogenetic analysis has established that the giant clams represent a derived subgroup of the cockles nested in a cluster of more standard cockle subfamilies known as the CFTL lineage (for Clinocardiinae-Fraginae-Tridacninae-Lymnocardiinae; Schneider, 2002). Schneider & Carter (2001) and Schneider (2002) demonstrated that the subfamily Cardiinae as previously recognised was paraphyletic with regard to the CFTL clade (the two groups together forming a clade called eucardiids) and restricted the Cardiinae to a smaller monophyletic group containing the genera Cardium, Bucardium, Vepricardium, Dinocardium, Chesacardium, Planicardium, Acanthocardia and Schedocardia. Nevertheless, only three characters supported this more restricted Cardiinae clade in the analysis of Schneider (2002), two of which are actually reversed or indeterminate for subclades within the Cardiinae.

Within the Cardiinae, the type genus Cardium (the name means "heart", and undoubtedly refers to the shape of the shell) might appear at first glance to be the largest, by a considerable margin, but I'm unsure how reliable this is. One of the side-effects of the aforementioned tendency towards monotony of bivalves in general was that in the earlier days of taxonomic study a large number of bivalve genera were placed into a rather small number of genera - names such as Nucula, Mytilus, Venus and, yes, Cardium were used to cover levels of diversity that modern authors would regard as entire families or even larger groups (to complicate matters further, many earlier bivalve workers showed an unenviable lack of imagination with regard to species names that, especially in those days before easily searchable taxonomic indices, have made bivalve taxonomy in many cases a mind-bending morass of homonymies). As a result, probably more than half of the cardiids, of almost all subfamilies, have passed through Cardium at some point in their taxonomic history, and it would not be at all surprising if a number of unrevised species that should belong elsewhere are still lurking within. For instance, a quick search online shows that one still comes along references to the common cockle of Britain as Cardium edule - this species actually belongs to the genus Cerastoderma, and is actually a member of the Lymnocardiinae, more closely related to the giant clams than to the Cardiinae (Schneider & Carter, 2001). The situation becomes even worse when fossil taxa are considered. As currently constituted, the Cardiinae date back to the late Palaeocene. The eucardiids were actually hit pretty hard by the end-Cretaceous extinction, but this was overlooked for a great many years due to the assignment to more recent genera of members of the Cretaceous eucardiid subfamily Profraginae, which lies outside the purely Caenozoic eucardiid crown group (Schneider, 2002). Evolutionarily speaking, cockles in their modern sense are actually a fairly recent group.

REFERENCES

Schneider, J. A. 2002. Phylogeny of cardiid bivalves (cockles and giant clams): Revision of the Cardiinae and the importance of fossils in explaining disjunct biogeographical distributions. Zoological Journal of the Linnean Society 136: 321-369.

Schneider, J. A., & J. G. Carter. 2001. Evolution and phylogenetic significance of cardioidean shell microstructure (Bivalvia, Mollusca). Journal of Paleontology 75: 607-643.

Is Taxonomy a Science?

A couple of days ago, I referred to the point that the dividing line between the sciences and the humanities is not particularly clear, and there are some forms of research that do not fall clearly on one side of that divide. Taxonomy, the practice of classifying and characterising organisms, has been described as one such practice. So it is worth asking - is taxonomy a science?

First, of course, one needs to establish what exactly science is, a topic that has taken up entire volumes. One of the main characteristics of science, though, is the use of the scientific method. Hopefully, you would have had this explained to you in high school, probably as a scientist constructs a hypothesis about something, devises an experiment to test that hypothesis, then finds whether the results of the experiment support the initial hypothesis, refining the hypothesis as needs be (for instance, a hypothesis that hydrogen and oxygen combine to form water may be tested by burning hydrogen in oxygen and finding whether water is produced). Lather. Rinse. Repeat. For many branches of science, however, this is not really an option. In studies such as phylogeny, astronomy or geology, we generally can't directly experiment on our subjects as such. To use Stephen Jay Gould's metaphor, we can't rewind the tape of time, fiddle with the parameters, and see how things could have turned out. Nevertheless (contrary to what some have said), the scientific method is still applicable to these studies, but instead of directly experimenting on the object of study, the method goes somewhat more like this - the researcher will collect a body of observations, construct a hypothesis that explains the observations, then collect further observations and see whether the initial hypothesis still explains the available body of observations (for instance, observations that koalas are only ever seen eating eucalyptus leaves leads to the hypothesis that they have a diet solely composed of such leaves, which may then be tested by continued observations on koala diet). These two methods may be referred to as the experimental or "hard" scientific method and the observational or "soft" scientific method. Needless to say, the two methods blend into each other (is a developmental geneticist staining embryos to find where a certain gene product is expressed conducting experiments or observations?), and are not exclusive.

As a discipline, taxonomy can actually be divided into two distinct but interleaving components - systematics is the identification of relationships between organisms, while nomenclature is the process of determining what the various groupings of organisms identified by systematics should be called. Nomenclature, it should be stressed, is not a scientific process. The name Homo sapiens is not science, just as the equation "E = mc²" is not science. The process by which Einstein established that energy was equivalent to mass multiplied by the speed of light squared was science, but there was no inherent reason why the resulting equation had to be expressed in the format used. Had Einstein used a completely different set of symbols (say, "۞☺۝۩^♫"), it could have still meant exactly the same thing. Similarly, the name given to a taxon is simply the linguistic tag used to identify that taxon, not the taxon itself. Once a particular tag has been established for a particular taxon, it is in every researcher's best interest to continue using that tag rather than inventing a completely new tag every time that taxon is referred to but this is a question of communication, not of science.

Systematics, on the other hand, is a scientific process - most of the time. Imagine I have a collection of unsorted arachnid specimens in front of me (which, as it happens, I pretty much do). I divide these specimens into smaller clusters whose components are morphologically more similar to each other than to specimens in other clusters. For the sake of argument, say I decide that these clusters represent separate species. These species are then able to be tested. I may look at further specimens to see if the boundaries between my various species remain constant, or whether there are specimens that blur the boundaries between clusters. I may use alternative data sources, such as genetics or biogeography, to see if my clusters remain consistent across methods. But while my initial division may be able to be tested scientifically, did it represent a scientific process itself? You might argue that it did not - that it involved a purely subjective judgement about similarities between specimens on my part. What about species that have been erected on the basis of single specimens, and so cannot be said to have been properly tested? I might reply that my own experience, and what I've learnt from the experience of others*, may have taught me a great deal about what kind of characters are likely to be reliable in distinguishing taxa. But is this a scientific progress, or an application of learning? What is the difference?

*In the past I've complained about the errors of past workers such as Carl-Friedrich Roewer complicating the taxonomy of harvestmen that I work on. At the same time, it cannot be stressed enough that I can only criticise the work of my predecessors because I have the published experience of later workers to draw on - Hickman, Martens, Staręga, the Goodnights, even Roewer himself. This is what Isaac Newton was referring to when he noted that "If I have seen farther it is by standing on the shoulders of giants".

In the end, I have to fall back on a quote from Bonde (1977) that I've used before: "An important aspect of any species definition whether in neontology or palaeontology is that any statement that particular individuals (or fragmentary specimens) belong to a certain species is an hypothesis (not a fact)". In my initial establishment of a species (especially if said species is only based on a single or very few specimens) I am essentially proposing a hypothesis that may be tested at a later date. The hypothesis itself may arguably not be science, but the scrutiny it will later be held up to almost certainly will be.

REFERENCES

Bonde N. 1977. Cladistic classification as applied to vertebrates. In Major Patterns in Vertebrate Evolution (M. K. Hecht, P. C. Goody, & B. M. Hecht, eds.) pp. 741-804. Plenum Press: New York.

A Brief Moment of Politics

I don't normally do politics here - this is a biology blog, not a politics blog - but some things can't be allowed to pass by unnoticed. A prominent international figure recently made the following statement:

Russia is a state that is unfortunately using the one tool that it has always used … when it wishes to deliver a message, and that's its military power. That's not the way to deal in the 21st century.

The speaker? Condoleeza Rice.

Now, is this funny? Or horrible? Or is it horribly funny?

But Is It Art?

Just a footnote to the last post - I realise a number of people who read this live in America (you poor, poor, sorry people) and I don't know how familiar Ab Fab is to American audiences. So if there are any of you who haven't seen the segment I referred to, here's the part quoted courtesy of YouTube:



Of course, as YouTube has been blocked at uni to stop students from simply downloading stuff all day, and I live in one of the sections of Perth where we can only have a dial-up connection at home because the phone-lines can't carry broadband, this took half an hour of buffering to check I had the right one-minute segment. I hope you appreciate it.

Art is Science, Science is Art

Guardando nel suo Figlio con l'Amore
che l'uno e l'altro etternalmente spira
lo primo e ineffabile Valore
quanto per mente e per loco si gira
con tant' ordine fé, ch'esser non puote
sanza gustar di lui chi ciò rimira.

Gazing on His Son with the Love
the One and the Other eternally breathe forth,
the inexpressible and primal Power
made with such order all things that revolve
that he who studies it, in mind and in space,
cannot but taste of Him.

---Dante Alighieri, Il Paradiso, Canto X, English translation by Robert & Jean Hollander, via the Princeton Dante Project.

I have probably been remiss in not mentioning that this week (since Saturday, in fact) is National Science Week in Australia. To mark the week, I was considering presenting daily posts on five of the foundations that I think underly the concept of science - Mathematics, Language, Art, Enquiry and Skepticism. Obviously, this didn't end up happening - if nothing else, I'm not really knowledgeable enough to comment on most of them (it's probably better I leave such things to people such as John Wilkins who are more likely to actually know what they're talking about). I would like to present one of those ideas, though, flawed as my reasoning might be - the relation between Science and Art.

In that incredible human ability to devise false dichotomies that I've spoken of before, people often imagine "the Sciences" and "the Arts" as two distinct entities, often imagined to be at odds with each other in some way. As with so many other such distinctions, this is complete rubbish. For all that they may differ in method, the ultimate aims of science and art are practically identical - the investigation and description of the world in which we find ourselves living. Interest in either field engages similar qualities - creativity, the desire to investigate and challenge boundaries, and ultimately the desire to communicate about one's findings/products with others.



Art, like Science, is a difficult concept to define, and one question that tends to come up repeatedly is how an empty room with a flickering light bulb, a statue of the Virgin Mary ensheathed in a condom, or a couple of buckets of paint dribbled randomly over a canvas by Jackson Pollock qualifies as "art". Part of the explanation is that there is more to a work of art than simply the piece itself. The movie Memoirs of a Geisha refers to such an artwork - "At the temple, there is a poem called "Loss" carved into the stone. It has three words, but the poet has scratched them out. You cannot read Loss, only feel it." The viewer's experience of the artwork is as integral to that work as the physical object itself. In the Kurt Vonnegut novel Bluebeard, the artist Rabo Karabekian keeps his last and most spectacular artwork locked up in a barn, concealed from all others until it is only revealed after his death. The obvious question is whether, had it never been found, the piece would have even qualified as art as all. I would also cite the example of an episode of Absolutely Fabulous in which Edina decides to invest in art in order to establish a legacy. At the gallery, she makes it clear that she has no interest in the artistic intention of the works, only in their monetary value, so the gallery manager immediately sells her a pile of the more rubbishy abstract works - a pile of planks of wood lying against the wall, a stack of empty jam jars, a mobile constructed of coat-hangers. Later, she attempts to explain the pieces to Patsy (really, only reading out what it says in the brochure): "This is the materialisation of the psychotic's dream deciphered by a clairvoyance... hangers, it's hangers". Without the viewer engaging the artwork as an artwork, it ceases to be one - the pile of coat-hangers is merely a pile of coat-hangers. Similarly, the ultimate value of science lies in communication. Research that is conducted in private and never made public might as well have never been done at all. Just as an artist prepares their work and presents it for the appreciation and criticism of their peers, so a scientist prepares and presents their publications.

Last week I referred to Ernst's Haeckel's luxurious 1899-1904 work Kunstformen der Natur ("Artforms of Nature"), which deliberately blurred the boundary between a scientific and an artistic work. As reflected in the quote at the top of this post, one of Western Civilisation's most enduring works of Art, La Commedia of Dante Alighieri, stressed the importance of rational enquiry as long ago as the 1300s. I have spoken to a number of fellow scientists - both professional and amateur - who have described their interest in reading firsthand the works of past researchers such as Owen, Cuvier, Darwin, Cope and Marsh. In many cases, the practical significance of these works has arguably decreased over time, as their premises have been improved or superceded by later workers, but their significance and interest as historical compositions turns them into artworks in their own way.

Amaurobioidea: Rummaging through a Wastebasket

A representative of the strikingly-coloured Nicodamidae from Australia. Photo by Nick Monaghan. While such spiders were previously identified as Nicodamus bicolor, there are no less than 23 species in seven genera that have previously been included under that name.

One term that you may come across in discussions of phylogeny is the concept of a "wastebasket" taxon. As the name suggests, a wastebasket taxon is one into which authors tend to throw everything that they can't really deal with. Often, a wastebasket will include the members of a group that are relatively unspecialised, often primitive, and united less by their shared characters than their lack of distinct features to connect them to one or another of the specialised subgroups that the author may recognise within the parent group. Phalangodidae among short-legged harvestmen, Sylviidae among passerine birds and Perciformes among spiny-finned fishes are all examples of taxa that have become wastebaskets in the past. Some wastebasket taxa are explicitly established as such, like the 'Deuteromycota' that included asexual fungi before techniques were developed that made it significantly easier to relate asexual and sexual fungal taxa. More often, though, a taxon originally based on a certain combination of features will develop into a wastebasket over time as phylogenetic studies show that the original basis characters for that taxon represent plesiomorphies (ancestral characters). This week's highlight taxon, the spider superfamily Amaurobioidea, perhaps belongs to the latter group.


Tegenaria gigantea (Agelenidae). Photo from Wikipedia. Agelenids build funnel-shaped webs and are apparently often called some variant of "funnel spiders" in North America, but such names are likely to cause confusion here in Australia with a certain notorious mygalomorphs. Some species of Tegenaria such as the hobo spider are also known for being toxic, but nowhere near as toxic as the Australian funnel-web.

In an earlier post, I included a quick overview of basal spider phylogeny, going as far down as the clade Araneoclada that unites those spiders that have only a single pair of book lungs (ancestrally, at least - many families of Araneoclada have lost the book lungs entirely, or evolved tracheae in their place). Members of the Araneoclada are further divided between the Haplogynae and the Entelegynae, originally based on the presence (Entelegynae) or absence (Haplogynae) in females of paired copulatory ducts opening on a sclerotised plate called the epigyne. While the absence of such ducts in the Haplogynae is obviously a primitive character and no longer regarded as uniting them, the group has funnily enough been supported as monophyletic based on a number of other characters (except for a small number of 'haplogyne' taxa that are phylogenetically entelegynes) (Coddington & Levi, 1991). However, the Amaurobioidea belong to the Entelegynae, which is by far the larger of the two clades. Within the Entelegynae, the primary division was long based on whether or not a species possessed a cribellum, a plate-like structure among the spinnerets that bears hundreds of tiny silk-producing spigots. As these spigots exude silk simultaneously, the spider uses a specialised arrangement of bristles on the fourth pair of legs to weave them together to form a woolly thread (see here for a more detailed description). Because this woolly thread is composed of multiple tangled strands, it can effectively entangle prey such as small insects that get caught among the strands. Unfortunately, as knowledge of entelegyne spiders improved it became clear that possession of a cribellum did not define a phylogenetically coherent group. A number of cases were identified of pairs of taxa clearly related by other characters in which one taxon possessed a cribellum and the other did not. The eventual conclusion was that the cribellum was an ancestral character for the Entelegynae (as also supported by its presence in one haplogyne family, the Filistatidae) that had been lost on numerous occassions.


Ctenus floweri (Ctenidae), from Singapore. Photo by David Court. Ctenids are active hunters.

In general, the Amaurobioidea included cribellate spiders with unbranched abdominal median tracheae, as opposed to Dictynoidea with branched abdominal median tracheae (Coddington & Levi, 1991). Families that have been assigned to Amaurobioidea include (among others) Amaurobiidae, Agelenidae, Ctenidae, Amphinectidae and Nicodamidae, but relatively little unites these families. Most of them are generally ground-dwellers (which may explain the common name of one of the best-known members, the hobo spider Tegenaria agrestis). Many members build small sheet-webs, but others are active hunters. Both the characters referred to above have since been shown to represent plesiomorphies of larger clades, with the alternative conditions arising multiple times. The phylogenetic analysis of entelegyne spiders by Griswold et al. (1999) found the 'Amaurobioidea' to fall within a clade that was sister to the clade including the orb-weavers, but the same clade included the Dictynoidea and Lycosoidea (wolf spiders and such) nested within 'amaurobioids'. Indeed, not even the type family of Amaurobiidae was monophyletic, with some members closer to the lycosoids while others were closer to the agelenoids. The Amaurobioidea, it seems, was a bust.

Coming up - science and art, whether taxonomy is science, why family names are so awful, micro-spiders, and Parapseudoleptomesochrella almoravidensis.

REFERENCES

Coddington, J. A., & H. W. Levi. 1991. Systematics and evolution of spiders (Araneae). Annual Review of Ecology and Systematics 22: 565-592.

Griswold, C. E., J. A. Coddington, N. I. Platnick & R. R. Forster. 1999. Towards a phylogeny of entelegyne spiders (Araneae, Araneomorphae, Entelegynae). Journal of Arachnology 27: 53-63.

Get Kunstformen!

As a corrolary of preparing the last post, I also discovered that a scan of the entirety of Haeckel's Kunstformen der Natur on the BioLib site is available here. Be warned, though - that link leads directly to a file some 130 Mb in size, so only click on it if you really want it. Not to mention the significant amount of potentially productive time lost as you sit gazing stunned at Haeckel's spectacular artworks. Check out the dinoflagellates on page 131, the octocorals on page 145, the radiolarians on page 182, the demonic boxfish on page 182... hell, almost any of the plates will do. Though I have to admit that some of the things on page 403 are a little divergent from reality.

E Pluribus Unum

For many people, the name "Ernst Haeckel" is most associated with slightly dodgy illustrations of vertebrate embryos that have doomed his memmory to be quote-mined by people with an agenda to push for all eternity. For others, though, the epitome of Haeckel's work lies in the many spectacular illustrations of invertebrates and protozoa he produced in such works as his reports on the biological material collected by the HMS Challenger expedition, and his 1899-1904 Kunstformen der Natur ("Artforms in Nature"). With their awe-inspiring detail and spectacular presentation, the plates he produced are more than just technical illustrations, they are true works of art. Perhaps among the greatest of his productions were the plates of siphonophores, an example of which is shown above. Baroque tentacled horrors, they loom out of the page threatening to engulf Dunwich. I wouldn't be able to tell you whether Lovecraft had ever seen one of Haeckel's illustrations to inspire him in his descriptions of the twisted hybrid offspring of Yog-Sothoth, but the resemblance is uncanny.

Siphonophores are planktonic cnidarians (the group that includes corals and jellyfish), distantly related to hydras (a good online reference on siphonophores has been put together by Casey Dunn). The most familiar member of the group is Physalia, the Portuguese man of war (so-called because of a supposed resemblance to that form of ship), but on the whole Physalia is not very typical of the order. All siphonophores are colonial, in their way - incomplete budding leads to the production of a colony of generally large numbers of metabolically interconnected zooids that are developmentally homologous to the more independent polyps of other cnidarians. However, the individual zooids of siphonophores are each highly specialised for separate divided functions such as feeding, reproduction or motility, meaning that siphonophore zooids are incapable of living independently of the colony. Perhaps more than any other group of organisms, the siphonophores challenge the question of what defines an individual or a colony, which has led to their description as "superorganisms".

Siphonophores have been divided into three main groups, the Cystonectae, Physonectae and Calycophorae, but the phylogenetic analysis of Dunn et al. (2005) found calycophores to be nested within physonects, the two together forming a clade they named the Codonophora. Cystonects (which include Physalia) form the sister-group to the codonophores, and share a colony morphology characterised by a division between a terminal pneumatophore (float) and the siphosome, the region of the colony containing feeding and reproductive zooids coming off a central stalk (in Physalia the central stalk is relatively short, but other siphonophores will have exceedingly long colonies). In the "physonects", the pneumatophore and siphosome are separated by the nectosome, a region of generally bell-shaped zooids called nectophores specialised for motility. In the calycophores, the pneumatophore has been lost and the colony is composed of the nectosome and siphosome. The illustration at the top of the post represents the physonect Physophora hydrostatica - the pneumatophore is the bulb-shaped structure at the top, with the zooids of the nectosome between the pneumatophore and the tentacle-like structures representing the top of the siphosome. These latter structures are not actually tentacles (the tentacles are the filaments radiating from the siphosome) but palpons, zooids whose function remains unknown but has been suggested to be related to excretion or defense. Underneath the palpons are the gonophores, the reproductive zooids, with separate male and female forms (males and females may both be present in a single colony, or there may be colonies of separate sexes). The large funnels like the horn of an old gramophone are gastrozooids, the feeding individuals. The clubbed side-branches on the trailing tentacles are tentilla, and contain concentrations of nematocysts for capturing prey. Most codonophores (but not cystonects) also have shield-like gelatinous bracts protecting the siphosome. Cystonects also have structures called gonodendra, which are concentrations of gonophores, palpons and also specialised nectophores that can propel a detached gonodendron through the water. Many codonophores are bioluminescent - the bracts may contain luminescent cells, and at least one member of the genus Erenna has flashing red tentilla that probably function as lures. The Physonecta illustrated above has only one iteration of the siphosome, but in other forms (such as the one illustrated below in another Haeckel plate) the clusters of palpons, gastrozooids and gonophores may form iterative elements that repeat continuously down the growing stem.



Despite what can only be described as their inherent coolness, siphonophores as a group are poorly known. Like other planktonic cnidarians, their gelatinous structure makes them quite frail and difficult to collect. The entire colony may be only loosely connected by the slender stem, such as in the example just above. Some siphonophores reach spectacularly large sizes - species of Apolemia may be more than 30 m in length, yet only a few centimetres in diameter. Attempts to net such specimens using conventional means would be lucky to retrieve anything more than disassociated mush.

REFERENCES

Dunn, C. W., P. R. Pugh & S. H. D. Haddock. 2005. Molecular phylogenetics of the Siphonophora (Cnidaria), with implications for the evolution of functional specialization. Systematic Biology 54: 916-935.

Haeckel, E. 1899-1904. Kunstformen der Natur. Bibliographisches Institut: Leipzig & Wien.

It's Baaack!

After a brief hiatus, the palaeontology blog carnival The Boneyard has returned and can be found at Laelaps. But take care - Amphicyon is guarding it...

Sacred Monkeys

Hanuman langurs - photo by Kamal Kumar Dua. Though identified on the source site as Semnopithecus entellus, this taxon has been divided between up to seven species in recent publications.

Todays' Taxon of the Week is the primate genus Semnopithecus. Once again, that's a sentence that's a bit easier to glibly write than it is to define. Semnopithecus includes the langurs, and together with the surelis (Presbytis) and leaf monkeys (Trachypithecus) forms a generally-accepted clade within the Colobinae, a group that also includes the colobus and odd-nosed monkeys and is characterised by a number of adaptations to a higher proportion of leaves in their diet than most other primate groups - most notably, a division of the enlarged stomach into an upper neutral region and a lower acid region, with leaves being broken down by fermenting bacteria in the upper region. Within the langur clade, however, there has been disagreement on the best way to treat the three subgroups taxonomically. Some authors have included all three groups in Presbytis, others have restricted Presbytis to the surelis and combined the langurs and leaf monkeys as Semnopithecus, while others have recognised three separate genera. Because this is purely a question of ranking and there doesn't seem to be any disagreement that langurs and leaf monkeys are more closely related to each other than either are to surelis, there is no "correct" answer here. For the purposes of this post, I'm going to treat langurs and leaf monkeys as two subgenera of Semnopithecus, for no reason whatsoever other than it allows me to cover both groups, though it is worth noting that the phylogenetic analysis of Osterholz et al. (2008) did not confirm the monophyly of Trachypithecus relative to Semnopithecus sensu stricto.

No consensus seems to exist on the number of species within Semnopithecus. The langurs may represent as little as one or as many as seven species, depending on how the various populations around the Indian subcontinent are divided up. The leaf monkeys are even worse - Trachypithecus is the largest generic grouping in the Colobinae, and includes more than ten species scattered through south-east Asia. Many leaf monkey populations are poorly studied and species boundaries within the group are often unclear. Osterholz et al. divided Trachypithecus into fifteen species in five species groups as apparently recognised by Groves (2001) (which I haven't read), one of which (the Semnopithecus vetulus group with two species found in Sri Lanka and southernmost India) they found to cluster polyphyletically within Semnopithecus sensu stricto and transferred into the latter genus as a result. The Trachypithecus pileatus group, found on the boundary between the Indian subcontinent and south-east Asia, clustered with Semnopithecus in analysis of mitochondrial DNA but with Trachypithecus in analysis of Y chromosome data, leading Osterholz et al. to suggest the possibility of ancient hybridisation in the origin of the group.


The golden langur (Trachypithecus geei). Photo from bhutanonline.net.

Most leaf monkeys live in small groups of about six to eighteen individuals (Brandon-Jones, 1984). Compared to some other primates, colobines apparently show relatively little social interaction among members of a troop (though still being fairly social compared to many other mammals, of course), which Brandon-Jones (1984) suggested may be an indirect consequence of their diet. Almost all colobines include a certain proportion of young leaves in their diet, but few can eat a significant amount of mature leaves. As this is fairly low-nutrition fare, colobines must spend a higher proportion of their time feeding than other primates, while the scattered distribution of young shoots requires individuals to spread themselves fairly thinly through a foraging site. Most colobines do eat fruit and other plant parts in addition to leaves, and langurs have a fairly varied diet that also includes such things as insects, roots, gum and sap. Indeed, langurs are noted for being able to readily stomach toxin-bearing foods such as Strychnos fruit that other herbivorous mammals would find inedible or even fatal. Langurs may be found in larger groups than leaf monkeys, with up to seventy individuals recorded in a troop (the largest size referred to by Brandon-Jones is a group of 120 individuals, though this may have been a temporary cluster of troops seeking water rather than a single troop). This may reflect their more varied diet, and/or it may reflect the fact that langurs are looked on favourably in most parts of India due to their supposed connection with the monkey god Hanuman (indeed, the name Semnopithecus means "sacred monkey") and are tolerated by humans or even actively encouraged and fed. Langur social structure varies significantly between different areas, possibly also as a result of food availability and population density. Like lions in Africa, langur troops are based on related females, with male offspring being evicted as they reach maturity, often forming nomadic all-male clusters. In some areas, breeding troops may include a number of mature males co-existing relatively peacefully, but in many areas most troops generally include only a single mature male. Also like lions, eviction of the incumbent male by another male in single-male areas is also often followed by the entering male killing any young already present in the troop in order to favour the raising of his own young. Interestingly, females who are pregnant at the time of takeover will engage in "pseudo-oestrus" behaviour - to completely anthropomorphise things, they fake sexual interest in order to induce the invading male to accept their offspring as his own. Production of young in all colobines often involves their being "shared around" between members of a troop, and females will often "borrow" and nurse the young of other females.

REFERENCES

Brandon-Jones, D. 1984. Colobus and leaf monkeys. In All the World’s Animals: Primates (D. Macdonald, ed.) pp. 102-113. Torstar Books: New York.

Groves, C. P. 2001. Primate Taxonomy. Smithsonian Institution Press: Washington.

Osterholz, M., L. Walter & C. Roos. 2008. Phylogenetic position of the langur genera Semnopithecus and Trachypithecus among Asian colobines, and genus affiliations of their species groups. BMC Evolutionary Biology 8: 58.

Viruses upon viruses

Mimivirus. From Mimiviridae.

So, naturalists observe, a flea
Has smaller fleas that on him prey;
And these have smaller still to bite ’em;
And so proceed ad infinitum.

--Jonathan Swift, 1733, On Poetry, a Rhapsody

I've commented before on the hazards of making generalisations in biology, because no sooner do you think you've found a hard and fast rule than something comes along to break it. Seemingly basic questions have a way of becoming insanely difficult. Such as how do we decide whether or not something is alive? It may seem obvious at first glance - you may be fully confident that you yourself are alive, while the bloated gaseous corpse of a particularly unfortunate raccoon is most definitely not alive*. However, in making this argument you are glossing over the point that you are only considering extremes on the spectrum - as one gets closer and closer to the border between "alive" and "not alive", you may find it harder to confidently assign something to one or the other of your supposedly exclusive categories. Viruses have long been a classic example of such a difficult prospect. Viruses reproduce and disperse like more standard living organisms, but are generally regarded as not alive they do not do so independent of their host (but then, arguably neither do intracellular parasites such as Chlamydia and Microsporidia), and indeed they have to integrate themselves fully into their host's genome as part of doing so (which, admittedly, Chlamydia and Microsporidia do not). Is a virus alive or not alive? To what extent, if any, does it even make a difference?

*It's when I use phrases such as "bloated gaseous corpse" that it becomes obvious that I read way too much Mervyn Peake in my youth**.

**Not my misspent youth, I should point out. I tried to misspend it, but I don't think I ever really got the hang of misspending.

A few years ago, this still didn't seem like that much of an issue. Because viruses do not maintain a separate organismal identity throughout their reproductive cycle, it may be easier to imagine them as independently dispersing genetic fragments rather than discrete organisms in their own right. But then Mimivirus came along and, to use Scott Adams' phrase, demanded a "paradigm shift without a clutch". Mimivirus, a parasite of the amoebozoan Acanthamoeba, was the largest known virus to date when first described in 2003 (La Scola et al., 2003). So large is it that it is actually visible using an optical microscope and was apparently originally mistaken for a bacterium. When Mimivirus first infects its host, it releases its genetic material into the host cytoplasm. The viral DNA travels into the host nucleus (where it may or may not begin replicating) before travelling out again and inducing the formation of a separate "viral factory" that produces the progeny viruses (Suzan-Monti et al., 2007). However, with a genome of some 1.2 million base pairs, Mimivirus carries considerably more genetic material than many parasitic prokaryotes. It even carries genes to produce its own translation RNAs (Raoult et al., 2004). Phylogenetic analysis of the Mimivirus tRNA genes gave a position on the eukaryote stem outside the three standard domains of living organisms, leading to the implication that this might be some sort of surviving "progenote" (though I am personally skeptical - Mimivirus is different enough from prokaryotes and eukaryotes that even if the analysis is theoretically valid, long-branch effects are bound to be an issue). If Mimivirus is to be dismissed as not an organism in its own right, then it is as close to being one as one can possibly get, and trying to argue for either possibility carries a distressingly high risk of brain implosion.

A paper currently sitting in the advance online section of Nature (La Scola et al., in press 2008) carries the confusion even further. The authors of the paper were investigating a newly-discovered close but even larger relative of Mimivirus that they had dubbed Mamavirus in view of its size. In the process of doing so, they noticed a much smaller virus in association with Mamavirus that was eventually dubbed Sputnik. At first, Sputnik was assumed to be another Acanthamoeba pathogen, but further investigation established that Sputnik would only replicate in amoeboids that were also infected with mimivirids. In fact, Sputnik replicates in the mimivirid viral factories. Its presence is associated with the production of misformed mimivirids, and causes a 70% reduction in production of infectious Mimivirus. The conclusion of the researchers is unprecedented but almost inevitable - Sputnik is a virus that parasitises another virus.

Of course, it's not so simple and straightforward. Perhaps one could argue that Sputnik is not so much attacking the Mimivirus directly as hijacking the replicative framework produced by the amoebozoan host that the Mimivirus is inducing. But then, one could make similar (and perhaps similarly facetious) arguments about almost any case of hyperparasitism involving more unequivocal living organisms, or many other trophic relationships - if a lion kills a zebra then eats the zebra's stomach and intestines, is it eating the zebra or the grass ingested by the zebra? If there is one rule in biology, it is that life does not take kindly to clear-cut definitions.

More has been written on the Sputnik virus at Living the Scientific Life.

REFERENCES

La Scola, B., S. Audic, C. Robert, L. Jungang, X. de Lamballerie, M. Drancourt, R. Birtles, J.-M. Claverie & D. Raoult. 2003. A giant virus in amoebae. Science 299: 2033.

La Scola, B., C. Desnues, I. Pagnier, C. Robert, L. Barrassi, G. Fournous, M. Merchat, M. Suzan-Monti, P. Forterre, E. Koonin & D. Raoult (in press, 2008) The virophage as a unique parasite of the giant mimivirus. Nature.

Raoult, D., S. Audic, C. Robert, C. Abergel, P. Renesto, H. Ogata, B. La Scola, M. Suzan & J.-M. Claverie. 2004. The 1.2-megabase genome sequence of Mimivirus. Science 306: 1344-1350.

Suzan-Monti, M. B. La Scola, L. Barrassi, L. Espinosa & D. Raoult. 2007. Ultrastructural characterization of the giant volcano-like virus factory of Acanthamoeba polyphaga Mimivirus. PLoS ONE 2(3): e328.

Linnaeus' Legacy #10: The Warbler Has Landed

Linnaeus' Legacy #10 is up at A DC Birding Blog. This month's keywords: a gull still looks like a gull, grammatical complexities, the first few billion years, gigantic ostracod, ticky land snail, specimens sitting in jars, friendly animals, larid not a Larus, ring species, enigmatic eclectus, eastern and western, not easy being green, wood warblers.

In Which I Reveal Just How Much of a Freak I Am

It's all there in the subtitle to this site. In the last few days I've decided to set myself a task that will probably be ridiculously time-confusing, gut-wrenchingly futile and will doubtless cause me to become even older before my time than I already am. But it's something that hasn't been done since 1923, and I think the time is ripe for it to be done again. I'm thinking of compiling an index for all described taxa of long-legged harvestmen. With a few thousand species involved, this is no small task.

But the thing is, and this is the freakish part, I actually really like nomenclature. Nomenclature is the specific part of the taxonomic process where the researcher sifts through the assortment of available names and works out which is the correct name to use for the organism sitting before them. It is important to distinguish the identification of the correct nomenclature from the identification of the organism itself - the nature of the specimen won't somehow magically change if the name attached to it does. Nomenclature is simply the system of labels that researchers have agreed to use in order to allow communication. As such, many people seem to regard the identification of the appropriate label as a somewhat arduous and uninspiring task, but personally I find it can be quite a lot of fun. As frustrating as past confusions can be, there is also something appealing in the challenge of sorting them out.

As a group, harvestmen have their share of nomenclatural challenges. I've just linked to my post on the mess that is Gagrella in which I just scratched the surface. There are no less than five taxa laying claim to the name Gagrella bispinosa as a result of its repeated use as a subspecific name. The oldest harvestman genus, Phalangium, was originally used by Linnaeus for pretty much any arachnid that wasn't a spider or a scorpion, leading to a fair number of homonyms spread between a number of orders. These are the sort of things I'd like to delve into for the next few years. Sure it's a big call, but if you can't be a little hubristic as a grad student, when can you be?

Life Before it had Facial Features

Fossil cyanobacteria of the form taxon Myxococcoides minor from the Bitter Springs Formation of Australia. Photo from UCMP.

On a Monday morning when I am feeling every little nuance of the fact that it's a Monday morning, it seems appropriate to discuss a section of organismal diversity whose study seems pretty severely crippled before it has even begun. I speak of the study of fossil bacteria, and the subject of today's Taxon of the Week post is the Proterozoic fossil taxon Myxococcoides.

Myxococcoides is a small (1-35 µm) spherical to ellipsoidal fossil without distinctive ornamentation or other visible features found either singly or in loose colonies without an enclosing sheath or other distinct colony shape. It is an oft-repeated, but perhaps little appreciated, fact that bacteria were around and about long before a few of them considered getting together and making a eukaryote. I mean really long before. The earliest evidence of bacteria in the fossil record dates back nearly four billion years, while the earliest unequivocal evidence for eukaryotes is only about 850 million years old* (Cavalier-Smith, 2002). In other words, fully three-quarters of the history of life on this planet is represented only by prokaryotes. Only members of a species with severely anthropocentric delusions of grandeur would imagine that biodiversity did nothing in all that time except twiddle its thumbs and wait for the nucleus to develop, but there are some serious hurdles to understanding what was happening for the first three billion years of life.

*It will probably come as no surprise that the earliest date for eukaryotes is rather debatable - Cavalier-Smith (2002) gives a brief, if somewhat partisan, review. The 850 Mya date represents the earliest appearance of protist fossils of eukaryote cell size and complex cell morphology that implies the existence of a well-developed microfilament skeleton to hold it all in place. Certain fossils dating back as far as 1200 Mya or even 2100 Mya have been identified as eukaryotes, such as the putative "red alga" Bangiomorpha. However, these taxa have fairly simple cell morphologies and their identification as eukaryotes rather than prokaryotes rests on relatively few characters such as cell size. As argued by Hofmann (1976), supposed 'nuclei' in fossil cells may represent degradational artefacts where cytoplasm has become detached from the surrounding cell wall. While prokaryote cells are generally much smaller than eukaryote cells, bacteria can occassionally reach considerable sizes - the largest known bacterium, the sulphur-oxidizing Thiomargarita namibiensis, has cells almost a millimetre in diameter, a size that, as pointed out by Schütt (2003), is more than twice that of the smallest known spiders, which is a great piece of information to bring up at parties (technically, some actinobacteria such as Streptomyces are arguably even larger, but have a fungus-like filamentous hyphal morphology). It is therefore a perilous activity to label Proterozoic fossils as eukaryotes on the basis of size alone, especially as it is not unlikely that bacteria may have occupied a number of niches prior to the appearance of eukaryotes from which they were later excluded.

Lacking as they do the well-developed eukaryote cytoskeleton, the morphology of most prokaryotes is decidedly simple, with the majority of taxa conforming to the basic rod or sphere. For instance, Thermoproteus and Mycobacterium are both rod-shaped prokaryotes with colonies formed through snapping division that may be morphologically almost indistinguishable despite one being a archaebacterium and the other a Gram-positive eubacterium. Instead, bacterial taxa are generally distinguished by features of their genetics, biochemistry and physiology - all features that, of course, are generally completely unavailable when studying fossilised remains. As a result, taxa based on fossilised bacteria are doomed to be form taxa or morphotaxa - labels to indicate a particular morphology without necessarily indicating the actual relationships of the fossils involved. To complicate matters further, a single living morphology may potentially give rise to multiple fossil 'taxa' due to the level of degradation prior to preservation, as shown in the figure below from Hofmann (1976) of various stages of degradation from a Myxococcoides-like morphology.



Needless to say, the relationships of forms such as Myxococcoides to modern taxa is difficult if not impossible to establish. Most Precambrian fossil bacteria have been found in association with stromatolites and interpreted as cyanobacteria. They have then been assigned to modern orders on the basis of colony morphology, so forms without defined colony structures such as Myxococcoides have been assigned to the Chroococcales. However, phylogenetic analysis of recent taxa has shown that the Chroococcales (not surprisingly seeing as it was defined solely on negative characters) is a strongly paraphyletic assemblage from which filamentous forms have arisen polyphyletically (Litvaitis, 2002).

So why, some of you may be asking yourselves at this point, should we study fossil bacteria at all? Well, the simple fact is that, murky as it is, the bacterial fossil record remains our main window into three billion years of evolution. Some distinctive probable cyanobacterial groups, such as the family Aphralysiaceae (Vachard et al., 2001), have been identified solely from fossils, while others, such as the stromatolite-forming Entophysalidaceae, held far more ecological significance in the past than presently. If, as alluded to above, forms such as Grypania and Bangiomorpha represent prokaryotes convergent on eukaryotes that were later replaced by actual eukaryotes, then such diversity would have remained unknown except through the fossil record. Three billion years is a long time to miss out on.

REFERENCES

Cavalier-Smith, T. 2002. The neomuran origin of archaebacteria, the negibacterial root of the universal tree and bacterial megaclassification. International Journal of Systematic and Evolutionary Microbiology 52: 7-76.

Hofmann, H. J. 1976. Precambrian microflora, Belcher Islands, Canada: significance and systematics. Journal of Paleontology 50 (6): 1040-1073.

Litvaitis, M. K. 2002. A molecular test of cyanobacterial phylogeny: Inferences from constraint analyses. Hydrobiologia 468: 135-145.

Schütt, K. 2003. Phylogeny of Symphytognathidae s.l. (Araneae, Araneoidea). Zoologica Scripta 32 (2): 129-151.

Vachard, D., M. Hauser, R. Martini, L. Zaninetti, A. Matter & T. Peters. 2001. New algae and problematica of algal affinity from the Permian of the Aseelah Unit of the Batain Plain (East Oman). Geobios 34 (4): 375-404.

Linnaeus' Birding

The next edition of Linnaeus' Legacy will be appearing at A DC Birding Blog in a few days' time. I've already received a number of submissions for the carnival, and if you want a piece of the action get submission in to me on gerarus at westnet.com.au, your host John (empidonax at gmail.com), or use the submission form at Blog Carnival. A reminder, too, that we're still looking for a host for September.

Inevitable Moles in a Lonely Universe

In 1989, the book Wonderful Life by Stephen Jay Gould made its triumphant appearance - of all the many writings by that prolific author, it was to become perhaps the most famous of all*. In this exploration of (then-)recent advances in our understanding of the animals making up the Cambrian explosion, the relatively rapid appearance of the distant ancestors of most living major animal groups, Gould argued extensively for the role of contingency and chance in evolution. If we were somehow able to turn time back to the Cambrian then let it run all over again, claimed Gould, then we would not see a repeat of the same evolutionary history. Major groups of organisms in our modern environment might fail to appear, while other groups that are currently minor and marginal might diversify to take their place. In particular, humans or intelligent life in general might never come to be.

*Something I find quite surprising - I personally find Wonderful Life rather drekky and overblown, and its arguments ultimately rather weak. To quote Moe Szyslak in the angel episode of The Simpsons (in which Gould actually made a guest appearance, "How about you stop telling us what it ain't, and start telling us what it am?"

Central to this argument of Gould's was his interpretation of the studies on animals from the Canadian Burgess Shale by Simon Conway Morris. Gould argued that very few of the animals present in the Burgess Shale could be definitely associated with taxa that survived the Cambrian, while most of the Burgess animals represented isolated lines that would eventually go extinct. Were one to look at the Burgess fauna in the absence of knowledge about future events, there would be no way of distinguishing which taxa were to survive and which would not. As it turned out, Gould's interpretation of Conway Morris' work was to rankle quite significantly with Conway Morris himself, who has since written two books that essentially counter Gould's book. In the 1998 The Crucible of Creation, Conway Morris attacked Gould's characterisation of the Burgess taxa as phylogenetically isolated oddballs, arguing instead that most were identifiable as stem-taxa showing connections to modern animals. While far more scientifically rigorous than Gould's Wonderful Life, The Crucible of Creation does suffer significantly from the constant shadow of Conway Morris' evident ire at Gould's 'misappropriation' of Conway Morris' work - Richard Fortey was later to comment in his 2000 book Trilobite! that he had "never encountered such spleen in a book by a professional".

I haven't yet read Conway Morris' second book of reply, the 2003 Life's Solution: Inevitable Humans in a Lonely Universe, but I would like to comment on its basic premise. In Life's Solution, Conway Morris addressed Gould's contention that the course of evolution was contingent on past history and essentially unpredictable. Instead, Conway Morris uses the prevalence of convergent evolution, the independent evolution of similar characters in unrelated organisms occupying similar habitats, to argue that selection pressures result in a relatively small number of potentially viable forms, and that even if Earth's history were rerun then a roughly similar assemblage of organisms would result. There might not be humans in exactly the form we now them, but intelligent, self-aware organisms of some kind would eventually appear.

Of course, both Gould's and Conway Morris' propositions are not directly empirically testable - there is no way of actually rerunning the course of evolution. However, convergent evolution is a widely prevalent phenomenon that we can examine and stimate its effect on the form of organisms. Convergent evolution seems to be the result of strong selective pressures - when a certain habitat or lifestyle strongly favours a certain morphology.

Moles, for instance, are definitely inevitable, at least among mammals. At least three different groups of living mammals have independently adopted a burrowing lifestyle - the Holarctic true moles, the African golden moles and the Australian marsupial moles. All three groups have developed a very similar morphology - reduced or lost eyes, dense fur, compact body with short limbs and spade-like forelimbs. Among fossil mammals, the marsupial (or at least metatherian) Necrolestes and the erinaceid Proterix have also been interpreted as burrowers with a very mole-like morphology. Even at least one group of burrowing insects, the mole crickets, went through a similar development of shortened limbs and spade-like forelimbs.

Cacti are fairly inevitable. A number of groups of plants inhabiting arid habitats - most notably various members of the Euphorbiaceae as well as the cacti proper - have evolved thickened water-storing stems with the loss or reduction of functional leaves to reduce water loss. Interestingly, the alteration of leaves to spines has occurred on numerous occassions, and it has been suggested that as well as the obvious benefit of protection, spines may help promote the condensation of moisture onto the plant as dew.

Lice, I'm sorry to say, seem to be inescapable. As well as the lice proper, a number of other insect groups have become ectoparasites living among the fur or feathers of other animals, such as a number of families of flies (including the sheep ked and bat flies) and the earwig Hemimerus. All such groups show a loss of wings, reduction of sensory organs such as eyes and antennae, and development of a flattened morphology that is probably less able to be squashed or scratched off by the host.

On the other hand, antelope are not inevitable. While the primary cursorial grazers of Eurasia and Africa are slender-legged quadrupeds, in Australia their niche is occupied by the bipedal kangaroos. I am not sure why kangaroos became jumping bipeds rather than running quadrupeds, but my suspicion is that their arboreal ancestry (phylogenetic analyses suggest that kangaroos descend from a possum-like ancestor) meant that the ancestral kangaroos started out with a difference in length between hind- and forelimbs. The point is that in this case two very different morphologies have developed to cope with very similar niches.

And humans? Well, it is my personal opinion that we have no reason to regard humans as inevitable. Invoking convergent evolution to claim the inevitability of humans runs up against the major stumbling block that we have no other examples of convergence on the human form. Questioning whether intelligence and self-awareness were destined to arrive as a result of selective pressure demands that we answer the insanely difficult yet crucial questions of how we define "intelligence" and "self-awareness", and how we would recognise them once defined. So difficult are these questions that yours truly is going to be a complete weasel and avoid them (I've spent enough time on this post already), but I will rather weakly point out that most behaviours cited as evidence for self-awareness in humans, such as figurative language and the production of art, are as yet unknown in other organisms when not encouraged by direct human intervention (but refer back to the recognition problem above). How is one to claim convergent evolution to support the existence of something for which no convergences are known?

A coda. In Kurt Vonnegut's 1985 novel Galapagos, a small boatload of people are shipwrecked on the Galapagos islands at about the same time as a plague wipes out humanity in the rest of the world. Over the course of the following million years, the descendants of this small group of shipwrecked survivors lose many of the features that have generally been regarded as the keys to what make us human but which are no longer selectively advantageous in their new environment, such as manual dexterity and large brains. Instead, humans become seal-like animals, covered in dense water-repellent fur with flippers for swimming and catching fish. It doesn't really matter what you're talking about - whether or not it's a good thing really depends on circumstance.