What is a Daddy-Longlegs?

"Daddy-longlegs" is one of the worst animal names there is. The name is widely used and generally recognised, but causes endless confusion because it is applied to no less than three very different animals. In a brief attempt at disambiguation, these are the animals involved:

First are harvestmen of the order Opiliones (picture from UMMZ). Harvestmen are often confused with spiders, but the body is not divided into a cephalothorax and abdomen, the opisthosoma (the posterior part of the body corresponding to the abdomen) is externally segmented, the chelicerae (mouthparts) are pincers rather than fangs, and harvestmen do not produce silk. The name "daddy-longlegs" as applied to harvestmen usually refers to the group known as "long-legged harvestmen" (Palpatores). There is some uncertainty about whether Palpatores are a monophyletic group, but that's a subject for another time.

Second are spiders of the family Pholcidae (picture is from Iziko Museums of Cape Town - the object the spider is holding is the egg-sac, which is carried by the female until the eggs hatch). Pholcids are true spiders, and so have a divided body, an unsegmented abdomen, fangs, and produce silk. Here in Australia and New Zealand, the 'daddy-longlegs' that are almost ubiquitously found in houses (particularly bathrooms) are pholcids, most often the introduced Pholcus phalangioides. Offhand, there is a common belief that daddy-longlegs (either pholcids or Opiliones) are "the most poisonous spiders in existence, but their fangs are too small to pierce human skin". I have come across this story many times, and have even been assured of it by people who really should know better. This story is absolute bunkum. The University of California, Riverside site has more info.

Finally, the third group accused of being 'daddy-longlegs' are crane flies of the family Tipulidae (picture from Wikipedia). Crane flies look a bit like giant mosquitoes, but they are not blood-suckers. They are a large family - the adults are nectarivores or do not feed, while the larvae, commonly called leatherjackets, feed on vegetation. Crane flies are easily distinguished from the other 'daddy-longlegs' - the wings are a bit of a give-away.

Five Things for Brian Switek

Brian Switek from his blog Laelaps* has sent me five questions to answer as part of a circulating blog-connecting thingy. If you want to be connected to it, I'll explain in a moment, but first the questions.

*Brian has named his blog Laelaps in reference to the dinosaur genus by that name, now known as Dryptosaurus due to the name being preoccupied by a mite. He has not named it after the actual genus Laelaps, which are bloodsucking parasites of rodents (and occassionally humans). Pictures of the dinosaur "Laelaps" are pretty abundant online, so for a change of pace I've shown a picture of the mite Laelaps (picture comes from CSIRO).

1) What got you interested in evolution/biology?

It's a little hard to recall exactly - I've had at least a vague interest in animals for as long as I remember - my mother informs me my first word as a baby was "duck" (and I've never even considered the possibility that, growing up as I did on a farm in New Zealand, she may have misheard me). The main reason for my interest, I think, was probably the names. I've always had a fascination for how words fit together, and it was probably the names in my dinosaur books that first grabbed my attention. Who can fail to be impressed by the sound of Parasaurolophus? And by the time I discovered Opisthocoelicaudia, there was no saving me.

2) Now that you’ve told me about your oldest book, what’s your favorite book?

Hmmm... not sure. One book that I've found that there seems to be no limit to how many times I can read it is Catch-22. I, too, would like to know how to buy eggs for seven cents apiece in Crete and sell them at a profit for five cents in Malta. Other books I own that I value quite highly are The Book of the New Sun by Gene Wolfe, Galapagos and Slaughterhouse-5 by Kurt Vonnegut, and Hard-boiled Wonderland and the End of the World by Haruki Murakami.

3) Given your studies, do you have a favorite arachnid?

It almost goes without saying that I have a soft spot for the harvestman Pantopsalis phocator, the first species I ever named myself (Taylor, 2004) [spot the blatant self-promotion]. The only dampener to my enthusiasm is that, to be perfectly honest, I have never yet laid eyes on a live specimen of that or any other Pantopsalis, only corpses in vials. I have found other members of the same family, but in my enthusiasm at finally recovering specimens I gave them no time to escape and chucked them straight into ethanol. One of the large harvestmen would still be on top of my list of things I would like to encouter in the wild. There are few arachnids that I wouldn't like to at least give the time of day to (well, I might be convinced to steer clear of scabies mites).

4) If you could travel anywhere in the world, where would you go and what would you do there?

Everywhere and everything? There is no shortage of places I would like to go. I spent a year of my life in Japan in high school, and I would quite like to go back there with Jack so I can show him around. We're hoping to go to Thailand next year, which I've always wanted to do. I suppose I've always wanted to go to the Siberian taiga - there's something about the idea of standing in a forest and thinking that that particular patch of forest stretches halfway around the freakin' planet.... If that doesn't make you feel absolutely minuscule, I don't know what would.

On the other hand, my enthusiasm for travelling to the Great Pyramids has been dampened slightly since I tracked them down on Google Earth and discovered that the city goes right up to them. The photos may look like they're sitting in the middle of open desert, but if the person taking the photo had turned two degrees further to his left, he would have gotten a face full of someone's laundry.

5) Do you have any pet peeves when it comes to having chosen science as a profession (i.e. non-science folk not understanding why you would want to study what you do, hoops you have to jump through for research, anything at all) ?

I suppose the thought that really causes me worry at nights is the whole uncertainty of it all career-wise. I honestly have little idea what's going to happen once I've finished my PhD. Australia's currently having a bit of a boom in science, and I'm just praying that continues (or that somewhere else is having a boom).

In terms of peeves, some of the security and safety restrictions in recent years have reached the point of ridiculousness. I recently found that I probably wouldn't be able to borrow vital type specimens from Germany because the restrictions on shipping alcohol have become such that the museum is afraid that they don't have enough of a guarantee that the specimens will arrive and be returned safely. Postal services have decided they do not want to shoulder the explosive risk posed by two mL of 70% ethanol.

Now that I've answered Brian's questions, here are the rules if you want to join in, copied verbatim from Brian's page:

1. Leave me a comment saying anything random, like [the food you hate most in all the world]. Something random. Whatever you like.
2. I respond by asking you five personal questions so I can get to know you better.
3. You will update your [blog] with the answers to the questions.
4. You will include this explanation and offer to ask someone else in the post.
5. When others comment asking to be asked, you will ask them five questions.

Have fun.

Links and Piccies and other stuff

I've been shifting a few things around, and I'd just like to point them out. Firstly, I've added a set of links to other biology blogs, and I'd like to be able to add more. Get in touch with me if you've got a site you'd like to have linked. Also, if for whatever reason you'd prefer me not to link to your site, ask and the link shall be removed at once, no questions asked.

One thing that has been bugging me is that I haven't been including many pictures in Catalogue of Organisms. I realise it's a bit of an ask for people to want them to slog through dense text by a dense writer without any pretty pictures to lighten the mood, but I have had two reasons for their previous absence. One is Time - it takes a while to write the posts, let alone track down pictures to illustrate them. The other is Ability - I write most of my posts while at uni, and the *&^%$# Mac I use here doesn't seem to let me upload pictures in Netscape (the button for doing so simply doesn't show up). I've just discovered I can do so in Safari, though Safari isn't so good for editing the text. I promise I'll try to include more pictures in future, but I emphasise the word try. Again, while I will endeavour to only use publicly available pictures appropriately, if you come across a picture you don't think I should have, let me know and it'll be gone.

And while I'm at it, is there anything else people think I'm doing wrong? All opinions will be heard, considered, then acted on or binned as the whim takes me.

Yet another passerine 'family'

I discovered yesterday via Creagrus that the stitchbird (Notiomystis cincta) has been elevated to 'new monotypic family' status in a recent paper in the Australian Journal of Zoology (Driskell et al., 2007). This has been in the works a little while - a preliminary paper a year ago reported on its unexpected position (Ewen et al., 2006). Stitchbirds are a highly vulnerable species of passerine from the North Island of New Zealand - I say 'vulnerable' rather than 'endangered' because I believe populations are fairly healthy in the very few areas they are found, but they could easily fall victim if those areas were invaded by introduced predators - the only surviving natural population is on Little Barrier Island, but they have been re-introduced on Tiritiri Matangi Island and the Karori Wildlife Sanctuary in Wellington. I was fortunate enough to see both males and females at Karori last year while I was unsuccessfully trying to find harvestmen. The male is a quite attractive little bird with a black head with white streaks on the cheeks (the image here is by Michael Szabo, and comes via GrrlScientist. In the past, the stitchbird has been included in the family Meliphagidae (honeyeaters - superfamily Meliphagoidea), but the genetic data analysed by the two papers shows that it is actually sister-group to the endemic New Zealand family Callaeidae (wattlebirds - superfamily Corvoidea)*. The Callaeidae + Notiomystis clade makes for a nice little endemic New Zealand radiation - though only four genera and a maximum of six species** are known, all genera are quite distinct from each other.

*The wattlebirds are referred to as Callaeidae or Callaeatidae, and I must confess I haven't a clue which is correct. The type genus is Callaeas.

**I say "maximum of six" because authors differ whether the two taxa each in Callaeas (kokakos) and Philesturnus (saddlebacks) are species or subspecies - current opinion favours the former.

A little background here so you know what I'm talking about - the Passeriformes are the perching birds, and are the largest of the generally recognised bird orders. Traditionally, Passeriformes have been divided between Oscines (songbirds) and suboscines - it's the Oscines that concern us at the moment. In the past, Oscines were divided into a large number of families, but most were relatively small with the vast majority of species included in a few giant cosmopolitan families such as Muscicapidae (flycatchers) and Sylviidae (warblers). While it was long realised that this situation wasn't entirely satisfactory, it more or less persisted until the appearance of the DNA-DNA hybridisation studies of Sibley & Ahlquist (Sibley & Ahlquist, 1990) completely overturned the boat.

Sibley & Ahlquist identified a major split in the Oscines into two clades. The shocking part was that these clades were almost totally unexpected - rather than lining up with the previously recognised families, Sibley and Ahlquist recognised a division between mostly Australasian oscines (Corvida) and the mostly Holarctic Passerida. Genera that were once regarded as fairly closely related were placed on opposite sides of the divide, with massive morphological convergences implicated. Further testing has refined the idea slightly (Ericson et al., 2002; Barker et al., 2004), such that while the Passerida has remained monophyletic, the 'Corvida' are now regarded as paraphyletic with regard to the Passerida. As things currently stand, the Menurae (lyrebirds and scrub-birds) are the basalmost Oscines (as originally predicted by morphology), followed by a small clade of Climacteridae (Australian woodcreepers) + Ptilonorhynchidae (bowerbirds), then the Meliphagoidea (honeyeaters and fairy wrens), then the Passerida (most Holarctic songbirds) sister to the Corvoidea (mostly Australasian songbirds, as well as a number of non-Australasian taxa such as crows and shrikes). The upshot of all this is that to move the stitchbird from Meliphagoidea to Corvoidea is a fairly significant shift.

I do have one quibble with this paper, though, which effectively amounts to a quibble about the current state of passerine taxonomy as a whole. As more and more taxa are shifted about on the passerine tree, the general response has been to divide them into smaller and smaller families. Yes, the idea of a "family" rank doesn't really mean anything, and ultimately the recognition of such is entirely arbitrary, but there are still pragmatic implications to what gets recognised as a "family" and what doesn't, because this is a rank often used in assessing diversity. Why should Notiomystis get its own "family"? Recognising a monotypic family tells us nothing about its relationships. In my opinion, it would have been far more informative to expand the concept of Callaeidae and place Notiomystis as its basalmost member. But as I already said, the recognition of family rank is entirely arbitrary, and there is ultimately no obligation to accept my option over the authors'.

REFERENCES

Barker, F.K., A. Cibois, P. Schikler, J. Feinstein, and J. Cracraft. 2004. Phylogeny and diversification of the largest avian radiation. Proceedings of the National Academy of Sciences of the USA 101: 11040-11045.

Driskell, A., L. Christidis, B. J. Gill, W. E. Boles, F. K. Barker & N. W. Longmore. 2007. A new endemic family of New Zealand passerine birds: adding heat to a biodiversity hotspot. Australian Journal of Zoology 55: 73-78.

Ericson, P. G. P., L. Christidis, M. Irestedt & J. A. Norman. 2002. Systematic affinities of the lyrebirds (Passeriformes: Menura), with a novel classification of the major groups of passerine birds. Molecular Phylogenetics and Evolution 25: 53-62.

Ewen, J. G., I. Flux & P. G. P. Ericson. 2006. Systematic affinities of two enigmatic New Zealand passerines of high conservation priority, the hihi or stitchbird Notiomystis cincta and the kokako Callaeas cinerea. Molecular Phylogenetics and Evolution 40 (1): 281-284.

Sibley, C. G., & J. E. Ahlquist. 1990. Phylogeny and Classification of Birds: a Study of Molecular Evolution. Yale Univ. Press: New Haven (CT).

Taxon of the Week: Capra - the goats

At least one member of the genus Capra will be familiar to most people - the domestic goat Capra hircus. The goats are a mostly Palaearctic genus of alpine bovid, easily recognised by their distinctive large, ornamented horns. Different sources disagree on just how many species there are, but species are divisible into five distinct 'horn groups' (theres a good picture of all five in Pidancier et al., 2006, if you have access).

The bezoar (Capra aegagrus), the ancestor of domestic goats, has long, laterally-compressed, scimitar-shaped horns. The ibex group (Capra ibex and others) also has scimitar-shaped horns, but oval or subtriangular in cross-section with transverse ridges on the front - it is this group that causes problems taxonomically, with some authors recognising a single species and others recognising a number of geographically isolated species. The Pyrenean ibex (Capra pyrenaica) has lyre-shaped triangular horns. The eastern tur (Capra cylindricornis) has subtriangular horns curving in an open spiral. The most spectacular horns of all probably belong to the markhor (Capra falconeri) which has massive corkscrewing horns - go to Tetrapod Zoology and scroll down the page to see a photo showing just how unbelievable these appendages are. There are variations within these groups, of course - the western tur (Capra caucasica) has less well-developed transverse ridges on its horns than other members of the ibex group, while the extinct Portuguese ibex (Capra pyrenaica lusitanica) had horns with less of a backwards sweep than the other subspecies of Capra pyrenaica (see The Extinction Website).

Hybridisation between Capra species is apparently not uncommon. The webpage for a 2000 IUCN Workshop on Caprinae Taxonomy refers to hybrids between domestic goats and wild species such as Nubian ibex (Capra nubiana), "Asiatic ibex" (I'm not sure if this is supposed to refer to Siberian ibex [Capra sibirica] or one of the two tur species) and markhor being bred in order to improve stock. Pidancier et al. (2006) suggest that hybridisation may explain why relationships in Capra inferred from mitochondrial cytochrome b (which is maternally inherited) contradict those inferred from Y-chromosome sequences (which are paternally inherited) and morphology. In the former case, the Siberian ibex is sister to all other species, while in the latter, the division is between a clade formed of the markhor, bezoar and domestic goat and a clade of the ibexes and turs. The Pyrenean ibex is very close related to the Alpine ibex (Capra ibex) - most individuals were even identical in Y-chromosome data - and despite its autapomorphic horn form appears to be a fairly recent derivation from the ibex (I'd also say that the nested position of the Pyrenean ibex and the eastern tur among the more typical ibex forms makes it all the more logical to recognise the isolated ibex populations as separate species). One individual of the eastern tur actually clustered among bezoar sequences from the same location rather than with other tur sequences, providing another possible case of hybridisation (though personally, I'd want to have this checked against the possibility of misidentification or mix-up).

REFERENCES

Pidancier, N., S. Jordan, G. Luikart & P. Taberlet. 2006. Evolutionary history of the genus Capra (Mammalia, Artiodactyla): discordance between mitochondrial DNA and Y-chromosome phylogenies. Molecular Phylogenetics and Evolution 40 (3): 739-749.

The Phylogenetic Species Concept: is there such a thing as too much?

A recent editorial in the open-access journal PLoS Biology (you can tell it's online because of the acronym title ;-P ) comments on the recent widespread adoption of the Phylogenetic Species Concept as opposed to the Biological Species Concept, and the resulting 'taxonomic inflation' in the number of recognised species around the world. The authors feel that this is a Bad Thing, because increased number of species by definition means more endangered taxa, which means less effective conservation. This is not the first time this point has been made, and I feel the need to put my own oar in on the subject. To do this, I'm going to have to address the two arguments that are really at stake here - I'm going to call them the idealistic and the pragmatic sides of the argument.

The idealistic point is that we should not be using the Phylogenetic Species Concept in recognising species. I wrote a page on Palaeos a while back explaining some species concepts, and I'll refer you there if you want a more detailed description. For now, it'll suffice to say that the 'Biological Species Concept' (BSC) defines a species as a cluster of individuals 'potentially interbreeding to produce viable, fertile offspring', while the 'Phylogenetic Species Concept' (PSC) defines a species as the 'smallest diagnosable population of organisms sharing a distinct pattern of descent'. The latter concept has also been referred to as the LITU (Least Inclusive Taxonomic Unit) by authors who do not necessarily feel that an LITU is equivalent to a 'species'.

One side-effect of using the PSC rather than the BSC is that the latter is indeed generally predisposed to recognise more species. Under the PSC, there is really no place for the concept of 'subspecies' because, after all, if a population can be distinguished as a subspecies then it fulfils the requirements for a species. For vertebrates in particular the subspecies rank has a long history of use, and so application of the PSC results in all those subspecies becoming recognised as species. [Invertebrate workers have, on the whole, been less inclined to recognise subspecies (with the notable exception of lepidopterologists), so this is less of an issue there. I'm not familiar enough with the situation in plants to comment.] Also, there is no theoretical lower limit on how fine distinctions between 'species' can be, so long as those distinctions are accurate.

The BSC, however, has its own problems. Despite being the most commonly quoted species concept, it is usually recognised more in the breach than the practice. The requirements for actually testing whether populations can interbreed soon become prohibitive, and the BSC is difficult to apply in the case of populations that are separated geographically (to ask a strawman question, are two individuals 'potentially interbreeding' if they're never going to meet?) Recognising species using the BSC, therefore, generally depends on the individual author's own subjective judgements about whether or not two populations are conspecific.

In my opinion, the balance weighs overall in favour of the Phylogenetic Species Concept. In practice, the PSC is more objective and falsifiable than the BSC. As an extreme example of taxonomic inflation, the authors of the PLoS Biology editorial refer to Merriam's 1918 classification of North American brown bears into 82 species, and quote George Gaylord Simpson's critique that the distinguishing characters of these species were so finely defined that "On such a system twin bear cubs could be of different species". There are two replies to this: (1) why not recognise 82 species if there are 82 distinguishable populations?, and (2) Simpson's complaint indicates that Merriam's species would not be valid under the PSC, because the PSC requires that a species be a population (the 'distinct pattern of descent' referred to above). If a character varies within a population to the extent that it overlaps with other populations, it is not usable in distinguishing them as species.

In regards to the pragmatic side of the argument, the PLoS authors have more of a point. As the number of species supposedly requiring conservation increases, funds to conserve them become more stretched and the effectiveness of conservation goes down. However, the practicalities deriving from species recognition should be divorced from species recognition itself. Populations of organisms exist in nature independently of whether or not humanity chooses to recognise them, and the role of science is to try and identify what is, not what should be. It is true that as the number of recognised species increases, it becomes increasingly evident that we will not be able to conserve them all. Nevertheless, the appropriate response is probably to try and work out how to direct funds in such a way that the maximum amount of biodiversity is saved. This will probably require some sort of prioritising of conservation targets rather than attempting to save everything, and thinking in terms of ecosystems and taxon groups rather than individual species. It is still better that we keep a clearer view of what is out there than masking diversity within expansive categories.

Taxon of the Week: Phocidae

Still with the mammals. This week's highlighted subject is the Phocidae - the earless or 'true' seals. Phocidae are quite easily distinguishable from the Otariidae (sea lions and fur seals) by the absence of external ears (hence the name, duh) and the inability to turn their hind flippers under the body and use them in locomotion out of the water. This means that while otariids are still reasonably mobile on land, phocids are decidedly clumsy critters, reduced to a sort of humping, slug-like movement (Wikipedia claims that this is referred to as galumphing, which makes for the second time this week I've had to invoke Carroll [he left it dead, and with its head, he went galumphing back] and admit that I'd always imagined galumphing slightly differently - some of you may even recall the performance of The Jabberwocky on an episode of The Muppet Show, where Scooter rendered galumphing as a sort of jerky stomp with the word 'galumph' intoned at every step). Put them in the water, though, and phocids are magical.

The Phocidae are divided into two subfamilies, the 'Northern Hemisphere' Phocinae and the 'Southern Hemisphere' Monachinae. The inverted commas are there because the Monachinae do include a small number of Northern Hemisphere species, including the type genus Monachus (the monk seals). While it has been suggested in the past that Monachinae might be paraphyletic with regard to Phocinae (reported in Walsh & Naish, 2002), modern studies both molecular and morphological are fairly unanimous that the two subfamilies are monophyletic (Arnason et al., 2006; Davis et al., 2004).

Because I'm more familiar with them (being a Southern Hemispherean myself) I'm going to concentrate on the Monachinae. If you want to read about phocines, which are the classic white-pup-aren't-I-just-so-goddamn-cute-you want-to-hit-me-with-a-club seals, I recommend you go here and scroll down to Darren Naish's post on the Baikal seal. The Monachinae probably aren't as speciose as the Phocinae (it's a little difficult to tell, as the number of species in the Phocinae goes up and down from reviewer to reviewer) but are arguably more diverse in form. Living species are divided into three tribes - Monachini (Monachus), Miroungini (Mirounga, the elephant seals) and Lobodontini (Antarctic seals). The first two tribes only include one genus each in the modern fauna, but also include fossil genera.

Monachus (the monk seals) is the basalmost clade of monachines, and the only tropical/subtropical genus of Phocidae. There are three species with widely separated distributions - one each in the Mediterranean (Monachus monachus), Caribbean (M. tropicalis) and Hawaii (M. schauinslandi), though the Caribbean species is now extinct and the other two are endangered. Most references to monk seals I've come across mention their small size, but the Monachus Guardian website indicates that all are over two metres in length, demonstrating once again that size is a relative thing.

Mirounga are the two elephant seals - the Northern Pacific Mirounga angustirostris and the circum-Antarctic M. leonina. Elephant seals are so-called for two reasons - the males have a large inflatable proboscis that is used to make loud roaring noises, and because they are absolutely huge. Wikipedia cites a size of nearly 2.3 tonnes, with a recorded maximum of 5 tonnes. Elephant seals are also the most terrestrially capable of all Phocidae (Walsh & Naish, 2002). Back in New Zealand, elephant seals make the news every few years or so when one makes its way inland, including one dubbed 'Humphrey' that was present intermittently over a period of five years and was famed for his attachment to a herd of cows. Fantastic quote of the day about elephant seals inland - Although popular with locals and visitors, the impact of an amorous, two tonne male elephant seal on cars and other structures is significant (Harcourt, 2001).

The Lobodontini are the most diverse group of monachines, including the crabeater seal (Lobodon carcinophagus), Weddell seal (Leptonychotes weddellii), leopard seal (Hydrurga leptonyx) and Ross seal (Ommatophoca rossi). The Ross seal is a particularly obscure animal, little seen and restricted to the Antarctic. The leopard seal is the real star member of this group, though - a sleek super-predator that can be over 3.5m long and 400kg, able to eliminate about 2.5% of an Adelie penguin colony in a single season (Harcourt, 2001 - that's leopard seals as a whole, of course, not a single individual). Hydrurga is also known for its ability to extend its neck quite some distance from its body. Notably from this factoid, it is probably closely related to the fossil long-necked seal Acrophoca, inspiration of a whole swath of lake-monster theories.

And that's the Phocidae for this week. Now I really should get around to working on my conference poster....

REFERENCES

Arnason, U., A. Gullberg, A. Janke, M. Kullberg, N. Lehman, E. A. Petrov & R. Väinölä. 2006. Pinniped phylogeny and a new hypothesis for their origin and dispersal. Molecular Phylogenetics and Evolution 41 (2): 345-354.

Davis, C. S., I. Delisle, I. Stirling, D. B. Siniff & C. Strobeck. 2004. A phylogeny of the extant Phocidae inferred from complete mitochondrial DNA coding regions. Molecular Phylogenetics and Evolution 33 (2): 363-377.

Harcourt, R. G. 2001. Advances in New Zealand mammalogy 1990-2000: Pinnipeds . Journal of the Royal Society of New Zealand 31 (1): 135-160.

Walsh, S., & D. Naish. 2002. Fossil seals from Late Neogene deposits in South America: a new pinniped (Carnivora, Mammalia) assemblage from China. Palaeontology 45 (4): 821-842.

Why Do We Bother?

`I don't REJOICE in insects at all,' Alice explained, `because I'm rather afraid of them -- at least the large kinds. But I can tell you the names of some of them."
`Of course they answer to their names?' the Gnat remarked carelessly.
`I never knew them do it.'
`What's the use of their having names,' the Gnat said, `if they won't answer to them?'
`No use to THEM,' said Alice; `but it's useful to the people who name them, I suppose. If not, why do things have names at all?'--Lewis Carroll, Alice Through the Looking Glass

I recently came across a comment reported on The Voltage Gate questioning why we bother distinguishing insects and arachnids. Jeremy Bruno has commented on it himself there, but I'm going to put my own oar in. I'm taking the liberty of repeating the main body of the original comment:

Why spiders SHOULD be considered "insects". Or at least a sub-category of insects. Exo-skeleton. Multiple legs. Creepy crawly. And if it quacks like a duck, people. So for some stuffy scientists, biologists, zoologists, paleantolgists, etc, to come up with artificial nit-picky labelings and distinctions, to make spiders a totally different species, like "arachnids", is silly. Why can't "aranchids" simply be considered a TYPE of "insect"??? (As well as scorpions, or dust mites, or whatever else.) The average person (and even insect and animal lover) doesn't generally in practical purposes separate spiders from the category of "bugs" or "insects". Why?? Cuz even though there ARE SOME basic differences here and there (like 8 legs instead of 6, two body segments instead of three, and claw jaw munching distinctions, whatever blah blah, those are just hair-splitting differences in the overall picture of it. Cuz again, just who came up with these uptight definitions of these things in the first place. When you see a spider in your bathtub (and I like spiders, by the way), you automatically think "bug" or "insect" or "creepy crawly" not "aracnid". So let's lose the silliness already on this subject.

Now, if I was really being nit-picky, I would reply that arachnids are not a separate 'species' from insects, but many thousands of species; that scorpions and dust-mites are arachnids; the presence above of at least three different spellings of arachnid; but all that would be merely pettiness and not replying to the main meat of the argument, wouldn't it?

And if it quacks like a duck, people.

It does not. Alright, I may be slightly biased by the fact that I work on arachnids, but I find the distinctions between arachnids and insects far more significant than the differences between most vertebrates (which is not surprising because they've probably been distinct for longer). Which brings me onto my next point:

...even though there ARE SOME basic differences here and there (like 8 legs instead of 6, two body segments instead of three, and claw jaw munching distinctions, whatever blah blah, those are just hair-splitting differences in the overall picture of it.

These differences are hair-splitting? Good thing I didn't have a mouthful of soft-drink when I read that, because the dry-cleaning bill would have been drastic. Arachnids are only insects, and the differences between them are minor. Dogs are only newts, and the differences are even less significant. After all, dogs and newts have the same number of legs, the same basic body arrangement, and even process their food in much the same way, so why do we bother to distinguish them?

So for some stuffy scientists, biologists, zoologists, paleantolgists [sic], etc, to come up with artificial nit-picky labelings and distinctions, to make spiders a totally different species, like "arachnids", is silly.

I've already pointed out that the differences are not artificial. As for the labels - all labels are artificial. Distinct categories of things exist all around us, and it is ourselves who decide whether a given category receives a name and what that name is. The importance of a name does not lie in the name itself, but in the concepts it communicates. Communication is the key here. In the general human mode of perception, something doesn't really exist until it's been given a name.

Why can't "aranchids" [sic] simply be considered a TYPE of "insect"???

Dude, what's with the capitals and multiple exclamation points? Anyway, as follows on from the previous point, there is not inherent reason why insects can't be arachnids, because the names for categories are ultimately arbitrary. And yet the simple fact is that people have come to an agreement that the name 'insect' shall be used for a category that excludes arachnids, meaning that whenever I hear someone referring to an 'insect' I automatically feel confident that what they are talking about has six legs, three tagmata (not segments - the insect body actually has many more than three segments) instead of two, mandibles rather than chelicerae, two compound eyes, and a whole host of other features. If I wanted to refer to animals with a chitinous exoskeleton, jointed legs, and any other feature shared by arachnids and insects, I could just say 'arthropods', because that's what convention has decided that group should be called.

Every discipline has its own set of terminology that becomes automatic over time. If I was considering mechanics, I might decide that there was no point in distinguishing spanners and screwdrivers - both are made of metal, both are used to tighten/loosen things, both hurt if you drop them on your toe. So long as I didn't need to talk to anyone else about spanners and screwdrivers, it wouldn't matter a damn what I called them in my own head. But if I needed to ask someone to fetch me one, it might be best for me to defer to convention.

When you see a spider in your bathtub (and I like spiders, by the way), you automatically think "bug" or "insect" or "creepy crawly" not "aracnid".

I don't. I might if I didn't know what an arachnid or an insect was, but that doesn't mean that I'm correct, only that I don't know the difference. To use another analogy, I personally know nothing about cars, and couldn't tell one car from another to save myself (someone asked me recently what kind of car my boyfriend owns, and I replied "a red one"). This does not mean that there is no difference between a Honda Accord or Holden Kingswood or Aston Martin or whatever, only that I personally don't know to recognise them.

As I said, communication is the key. Ultimately our names for the things around us are dictated by nothing more than convention, but we try to agree on what they mean because that's how we know that the heck we're all talking about.

Buddenbrockia: The Gift that Keeps on Giving

A few days ago, I commented on the recent publication by Jiménez-Guri et al. (2007) on the basal myxozoan and parasitic worm Buddenbrockia (I'd recommend reading that post before this one - see Pharyngula for another good post on the same paper). I really should have held my tongue just a little longer, because just today I received notice of yet another paper on Buddenbrockia (Morris & Adams, 2007), and it makes the creature even cooler than I realised. Which is a big thing, because I already thought Buddenbrockia was a very cool little animal.

Firstly, I'll briefly cover the 'relationships of the Myxozoa' section, because there's not too much to say there. Morris and Adams support the idea of Buddenbrockia and Myxozoa as basal bilaterians, in a similar grade (though not necessarily clade) with Acoela and Mesozoa. However, they defer to past analyses in this, and their points against a cnidarian position for Buddenbrockia (primarily possession of muscle blocks and Hox genes) were both dealt with by Jiménez-Guri et al., with the former present in some cnidarians and the latter shown to be contamination (ironically, Morris and Adams note the similarity of one 'myxozoan' Hox gene to vertebrates and suggest the possibility of lateral transfer). That said, Jiménez-Guri et al. did not include any Acoela, which lie outside the Protostomia + Deuterostomia clade, in their analysis, and I feel that the possibility cannot be ruled out that their inclusion may have affected the result. As always in science, there is the prospect of further testing.

The really interesting part of Morris and Adams, however, lies in their detailed description of Buddenbrockia's development, which is bizarre and incredible and makes me all the more sympathetic to earlier researchers who did not even recognise myxozoans as animals. Buddenbrockia reproduces by means of spores (produced asexually, as far as I can tell - I haven't come across any reference to cross-fertilisation methods) that accumulate in the central cavity of the worm until it bursts open, releasing the spores into the host's coelom from whence they are ejected by the host into the surrounding water. It is not clear how exactly the spores infect a new host, but when we see them next they have hatched into unicellular amoeboids (the pre-saccular phase) within the basal lamina of the host. Note that I said unicellular - on PZ Myers' post linked to above, David Marjanović corrected him on the point that myxosporeans aren't really ever unicellular in the strict sense but syncytial (large multinucleate mass without individual cells, also called plasmodial). Nevertheless, Buddenbrockia unicells do have only a single nucleus. Because of the laminal connection between individual zooids in Bryozoa, it is possible that Buddenbrockia infection can spread through a colony at this stage.

The unicells then push their way through the host muscle tissue and aggregate together under the peritoneum. And when I say aggregate, I mean they are packed. Morris and Adams use the term 'pseudosyncytium' to describes how the cells are pressed so close together that it becomes nigh on impossible to distinguish individual cells, if indeed they remain individual cells (Morris & Adams were unable to satisfactorily resolve this question). The host cells surrounding the pseudosyncytium react strongly, encapsulating the pseudosyncytium within cytoplasmic extensions and necrotic cells. It is from this 'pseudocapsule' as the authors call it that the mature worm develops.

Now comes one really cool point - this does not happen the same way in every host species. In most host species, the mature parasite develops muscle blocks and forms the worm-like form we've been discussing so far. In Cristatella, the muscle blocks never develop, and the mature Buddenbrockia forms an ovoid sac, the Tetracapsula form (believed once upon a time to be a separate taxon). Morris & Adams' observations are of the worm form, and that's what we'll continue to explore.

Within the pseudocapsule, the individual unicells form junctions with each other, and start growing out into the host coelom as the 'worm'. Fibres are extruded from the pseudosyncytium that anchor it to the surrounding host cells. Within the worm, the pseudosyncytial cells differentiate into an outer layer of ectoderm and two inner layers of mesendoderm. The worm hollows out as it grows and a fibrous lamina develops between the mesoderm and endoderm. The endoderm develops into spore-producing cells, while the mesoderm forms the muscle blocks.

The muscle blocks develop from the base of the worm at the pseudosyncytium. One of the more unusual suggestions about Buddenbrockia muscle develop is that it may involve the co-option of host myofibres. If correct, this suggestion may explain why Buddenbrockia doesn't develop muscle tissue in all host species, as maturation of Buddenbrockia in Cristatella (as well as development of the closely-related Tetracapsuloides, which also doesn't develop muscles) takes place entirely in the coelom rather than in the cell wall. It also correlates with Buddenbrockia's unusual develop of muscle blocks within already-differentiated mesoderm. However, Morris & Adams didn't find any direct evidence for host co-option.

Eventually, the mature worm is released from the coelom wall to become the free worm we all know and love. Whether the worm is released from the pseudosyncytium which remains behind to generate other worms, or whether the pseudosyncytium comes free with the worm and is resorbed is currently unknown, though Morris & Adams cite past observations of worms with scalloped ends as suggesting the latter option.

As I already noted, the malacosporean (Buddenbrockia + Tetracapsuloides) lifecycle with multiple individuals coming together to form a single mature form is completely unlike any other class of animal. In many ways, it is more reminiscent of the slime moulds, a point noted by Morris & Adams, particularly the so-called 'cellular slime moulds'. Cellular slime moulds are now regarded as forming two separate groups - the dictyostelids in Amoebozoa and the acrasids in Heterolobosea. Neither of these groups is related to myxozoans (or, for that matter, to each other), so this form of life cycle has evolved independently in all three. It would be fascinating to see if the separate unicells aggregating together all derive from a single infective spore multiplying at the unicellular stage, or whether the products of multiple infections with different genetic identities can form a single pseudosyncytium. Aggregation of different genetic 'individuals' can happen in slime moulds - such chimaeras seem to be at a functional disadvantage to genetically pure aggregates, but this may be compensated for by the ability to form a larger colony (Foster et al., 2002). For Buddenbrockia, living in a soup of host-supplied nutrients with no need to move particularly far, the functional restrictions on chimaera formation might be even less.

REFERENCES

Foster, K. R., A. Fortunato, J. E. Strassmann & D. C. Queller. 2002. The costs and benefits of being a chimera. Proceedings of the Royal Society of London Series B – Biological Sciences 269: 2357-2362.

Jiménez-Guri, E., H. Philippe, B. Okamura & P. W. H. Holland. 2007. Buddenbrockia is a cnidarian worm. Science 317: 116-118.

Morris, D. J., & A. Adams. 2007. Sacculogenesis of Buddenbrockia plumatellae (Myxozoa) within the invertebrate host Plumatella repens (Bryozoa) with comments on the evolutionary relationships of the Myxozoa. International Journal for Parasitology 37 (10): 1163-1171.

(Possibly) The World's Smallest Tetrapods

The subject of today's post are proturans. Proturans are rather unique little hexapods (though not, by the currently used definition, insects) that are apparently widespread despite being rarely seen (Imadaté, 1991). I have to confess that I've never seen one yet in my time in entomology - I was reminded of them because one of my co-workers briefly thought he might have found one (but alas, not to be - it was probably some form of beetle larva). The title for the post derives from the fact that, despite being hexapods, proturans are functionally quadrapedal. They lack antennae, and instead the first pair of legs is held up and in front of the body as sensory organs. Christopher Tipping has a page with some neat pictures - in particular, check out the 1907 drawing at the top of the page like something on the cover of an Edgar Rice Burroughs book.

Protura show a number of other unique features as well. They are the only insects to increase the number of abdominal segments over their life. And perhaps most notable of all, their spermatozoa are completely unlike any other hexapod (Baccetti et al., 1973). The proturan spermatozoon is non-motile, varying from a complicated twisted helical structure (Acerentulus traegardhi and Acerentomon majus) to a simple mammalian-blood-cell-like torus (Eosentemon transitorium). In those species that retain an axoneme (the flagellar 'skeleton') it shows an abnormal arrangement of microtubules. In the vast majority of eukaryotes, the axoneme has a '9 + 2' arrangement - nine pairs of microtubules around the outside and two single microtubules in the centre (this is also the same arrangement as in spirochaetes, a clade of spiral bacteria, which has lead to rather controversial suggestions that the eukaryote flagellum may be derived from symbiotic spirochaetes - a suggestion I happen to be rather skeptical of). In contrast, proturan axonemes show a whole range of arrangements - 12 + 0, 13 + 0, 14 + 0 or even 9 + 9 + 2. Such unique features have lead to suggestions that proturans may not even be related to insects (there was an article in Simonetta & Conway Morris, 1991, that I recall, but i haven't been able to find the specific reference), but as they are undoubtedly unique derived features of proturans they are completely uniformative as to outside relationships.

In terms of actual phylogenetic relationships, proturans are entognathous (that is, the mouthparts are recessed into a capsule under the head). Most authors have united them with the Collembola (springtails) in a clade called Ellipura, but most of the supposed characters of this clade reflect character losses, which are generally regarded as less trustworthy due to the higher chance of homoplasy. A couple of recent papers did not support the Ellipura grouping (Giribet et al., 2004; Luan et al., 2005), instead placing Protura with Diplura, but the former paper also found an unexpected polyphyletic arrangement of hexapods relative to crustaceans which requires further investigation.

REFERENCES

Baccetti, B., R. Dallai & B. Fratello. 1973. The spermatozoon of Arthropoda. XXII. The '12+0', '14+0' or aflagellate sperm of Protura. J. Cell Sci. 13: 321-335.

Giribet, G., G. D. Edgecombe, J. M. Carpenter, C. A. D’Haese & W. C. Wheeler. 2004. Is Ellipura monophyletic? A combined analysis of basal hexapod relationships with emphasis on the origin of insects. Organisms, Diversity and Evolution 4: 319-340.

Imadaté, G. 1991. Protura. In The Insects of Australia (CSIRO) pp. 265-268. Melbourne University Press.

Luan, Y.-X., J. M. Mallatt, R. D. Xie, Y.-M. Yang & W.-Y. Yin. 2005. The phylogenetic positions of three basal-hexapod groups (Protura, Diplura, and Collembola) based on ribosomal RNA gene sequences. Molecular Biology and Evolution 22: 1579-1592.

Taxon of the week: Marmotini

Okay, I admit, last week's entry for Taxon of the Week was a little, well, weak. Basically I didn't feel like writing on monkeys at the time. This week's entry is much better - squirrels. Specifically, the mostly North American ground squirrels - Marmotini (see here for some pictures and an article).

[As an aside, I saw Bridge to Terabithia with Jack this Saturday just been, which presented me with a bit of a biogeographic quandary. The movie looked very much like it had been filmed in New Zealand - I recognised the vegetation. Though the intended setting was not specified, I'm guessing it was somewhere in the American Midwest. A couple of scenes featured squirrels, obviously filmed in America (New Zealand animal importation laws expressly forbid importing squirrels under any circumstances). However, in one scene where the main character traps and releases an animal that has been attacking his family's greenhouse, the animal in question is a brushtailed possum - not, to my knowledge, present in North America, but very much present in New Zealand. Sometimes, I have to admit, I wish I didn't realise these things so I could just ignore it and enjoy the movie.]

The Marmotini are one of the few clades of squirrels to make it to North America, along with the flying squirrel genus Glaucomys and the genera Tamiasciurus and Sciurus*. There are five genera - the more arboreal Tamias (chipmunks) and the terrestrial Ammospermophilus, Spermophilus, Marmota (marmots) and Cynomys (prairie dogs) - though some authors divide up some of these genera, notably Tamias and Spermophilus (which is probably paraphyletic). Tamias, Spermophilus and Marmota include Eurasian members, while Ammospermophilus and Cynomys are solely North American. I haven't been able to find what are the specific morphological characters uniting this clade (reading between the lines in Callahan & Davis (1982), I suspect they're genitalic characters), but it is also recovered with molecular phylogenies (Mercer & Roth, 2003). All Marmotini hibernate during winter to some extent (A. Watts).

*There is another genus present in North America, Microsciurus, but Mercer & Roth (2003) find it to be nested within Sciurus.

Perhaps the most interesting features I've come across in a quick scan of the Marmotini are their reproductive patterns and their sociality. Marmotini produce large litters of relatively small cubs or pups or whatever a baby squirrel is called, and apparently have the smallest size at weaning relative to adult size (see here).

Marmota and Cynomys both contain species that live socially. All species of Cynomys are social and form larger colonies than Marmota, of which there are some non-social species (in line with the common name of 'prairie dog', the name Cynomys translates as 'dog-mouse'). These two genera form a clade relative to the other Marmotini, but it is debatable whether sociality has appeared multiple times within the clade or whether it has appeared once and then been lost in the non-social marmots - the nested position of the solitary Marmota monax within marmots suggests to me that the latter may be more likely (Cardini et al., 2005).

REFERENCES

Callahan, J. R., & R. Davis. 1982. Reproductive tract and evolutionary relationships of the Chinese rock squirrel, Sciurotamias davidianus. Journal of Mammalogy 63 (1): 42-47.

Cardini, A., R. S. Hoffmann & R. W. Thorington Jr. 2005. Morphological evolution in marmots (Rodentia, Sciuridae): size and shape of the dorsal and lateral surfaces of the cranium. Journal of Zoological Systematics and Evolutionary Research 43 (3): 258-268.

Mercer, J. M., & V. L. Roth. 2003. The effects of Cenozoic global change on squirrel phylogeny. Science 299: 1568-1572.

The return of Buddenbrockia

In a previous post I briefly mentioned the mysterious worm Buddenbrockia plumatellae Schröder 1910, listed by Haszprunar et al. (1991) as an "extant problematicum", and alluded to how the true identity of this critter was rather unexpectedly resolved a few years back (Okamura et al., 2002). Further work on the position of Buddenbrockia appeared this past Friday in Science and adds a further small twist to the tale (Jiménez-Guri et al., 2007).

Buddenbrockia is a parasite of freshwater bryozoans, small, sessile, colonial animals that are sometimes referred to as 'moss animals' for little apparent reason ('moss animals' happens to be the English translation of 'Bryozoa'). After Schröder first described it in 1910, he suggested two years later that it was related to nematodes due to its mesodermal muscle blocks. A relationship to trematodes (flukes) was suggested around the same time by Braem (Okamura et al., 2002).

Okamura et al. (2002) examined the ultrastructure of Buddenbrockia, and found that it possessed an inner and outer layer of cells separated by the aforementioned muscle blocks, of which there are four arranged around the body. There is no through gut. Most significantly, the outer cell layers (the mural cells) contained polar capsules. Polar capsules are rounded organelles containing a tightly coiled filament that can be ejected at great speed. The polar capsules of Buddenbrockia were very similar to those of Tetracapsula, a basal member of the Myxozoa (and also a bryozoan parasite).

In my earlier post, I referred to Myxozoa as the least animal-like of animals, and I unreservedly stand by that statement. Myxozoa are parasites and fall into two classes. The class Malacosporea contains the aforementioned Tetracapsula (and now Buddenbrockia) and are parasites of bryozoans and fish. The class Myxosporea is considerably larger and are parasites of fish and annelid worms. As an interesting aside, the Myxosporea was previously divided between two classes of superficially very distinct appearance, the fish-parasitic Myxosporea and the annelid-parasitic Actinosporea. This distinction was removed in the mid-1980s when it was shown that spores of the myxosporean Myxobolus fed to tubificid annelids developed into the actinosporean Triactinomyxon (Wolf & Markiw, 1984). The two 'classes', therefore, represent different stages in the myxosporean life cycle.

So derived are myxosporeans relative to other animals that until fairly recently they were not even recognised as animals at all, being instead classified with the parasitic protozoa (Sporozoa and Microsporidia). Myxosporeans contain very few cells, and are contained completely within the cells of the host for part of the life cycle. A connection with animals was first suggested on the basis of the presence in myxosporeans of collagen, and on the near-identical ultrastructure of the myxosporean polar capsule with the cnidarian nematocyst (stinging cell) (see here for more details).

Even after myxozoans were recognised as animals, however, their position within the animal kingdom proved very hard to establish. Obviously, the ultrastructural similarities supported a connection with the cnidarians (the parasitic cnidarian Polypodium [not to be confused with the fern genus Polypodium] was particularly suggested as a close relation). However, some molecular studies supported a connection with bilaterians, most notably the reported presence in myxozoans of bilaterian-like Hox genes.

When Okamura et al. (2002) published their ultrastructural study of Buddenbrockia, they felt that its worm-like structure supported a bilaterian relationship for myxozoans, and highlighted previous molecular studies connecting myxozoans to nematodes. Jiménez-Guri et al.'s (2007) publication, however, turns this on its head, and returns Myxozoa to a position with the Cnidaria. This was done through a Bayesian phylogenetic analysis of some 129 proteins in 47 animals (plus 13 opisthokont outgroups) in a range of higher taxa. Buddenbrockia proved to have a significant branch length (easily the longest on the tree). interestingly, parsimony analysis (which is very vulnerable to long-branch attraction) of the data set resulted in Buddenbockia associating with a clade of nematodes + platyhelminthes, the other long-branch taxa analysed. It is likely that long-branch attraction has also been the culprit for such associations in the past.

And those bilaterian-like Hox genes? Well, the authors of the current study managed to isolate the supposed myxozoan Hox genes from host species that were not even infected with myxozoans. They were unable to isolate them from myxozoan samples that had been scrupulously cleared of any host tissue. Therefore, the supposed myxozoan Hox sequences represent contamination from the hosts, and are not myxozoan at all.

REFERENCES

Haszprunar, G., R. M. Rieger & P. Schuchert. 1991. Extant "problematica" within or near the Metazoa. In The Early Evolution of Metazoa and the Significance of Problematic Taxa (A. M. Simonetta & S. Conway Morris, eds.) pp. 99-105. Cambridge University Press.

Jiménez-Guri, E., H. Philippe, B. Okamura & P. W. H. Holland. 2007. Buddenbrockia is a cnidarian worm. Science 317: 116-118.

Okamura, B., A. Curry, T. S. Wood & E. U. Canning. 2002. Ultrastructure of Buddenbrockia identifies it as a myxozoan and verifies the bilaterian origin of the Myxozoa. Parasitology 124: 215-223.

Wolf, K., & M. E. Markiw. 1984. Biology contravenes taxonomy in the Myxozoa: new discoveries show alternation of invertebrate and vertebrate hosts. Science 225: 1449-1452.

Parcelling plastids

The Table of Contents alert for a bright, shiny new issue of Protist arrived in my e-mail box today. This is a journal I can usually rely on to supply something worthy of note (often some things), and today's was no exception. Right near the beginning of the issue, we receive a new class of heterokont (Horn et al., 2007).

So many new chromist classes have appeared in recent years that they're almost becoming routine (see Filling in the Gaps for another post of mine on one, which also includes an overview of the heterokonts). Today's subject has been dubbed Synchromophyceae, and contains a single new species, Synchroma grande, scraped off marine rocks on the coast of the Canary Islands (perhaps not the most unpleasant place to do field work). Synchroma is a photosynthetic amoeboid that forms a meroplasmodium (a network of individual cells connected by branching and anastomosing [fusing together where they meet] reticulopodia). Meroplasmodial forms are extremely rare in chromists - the only other chromist that exhibits this body form is the haptophyte Reticulosphaera japonensis (Cavalier-Smith et al., 1996). The main cell body is contained in a flattened lorica, which is adpressed to the substrate and is more or less circular on a flat surface. In reproduction, one daughter cell remains sessile in the lorica, while the other is released as a migratory cell. Migratory and floating cells are fusiform, with axopodia extending from the anterior and posterior ends. Sessile cells could also spontaneously convert to migratory cells by hatching out of their lorica. At no stage in the life-cycle were flagella present.

Phylogenetic analysis of Synchroma demonstrated that it is part of the Ochrophyta, the photosynthetic heterokont clade. Both rbcL and 18S rDNA maximum likelihood trees placed Synchroma as sister to the Chrysophyceae + Synurophyceae clade, but support in both cases was relatively low. The absence of a girdle lamella in Synchroma's chloroplasts supports its exclusion from either of those two classes.

The most interesting feature of Synchroma, however, lies in the arrangement of chloroplasts in the cell. As I mentioned previously, the chromist chloroplast is believed to be derived from an endosymbiotic red alga in a secondary endosymbiosis. As a result, the chromist chloroplast is surrounded by four membranes that represent (from the inside out) the original cyanobacterium's external cell membrane, the vacuolating membrane of the primary host, the primary host's external cell membrane, and the vacuolating membrane of the secondary host. There is some debate about whether the chloroplasts of all chromist groups (and those of their putative sister group, the alveolates) derive from a single endosymbiotic event, or have been independently derived from multiple events. The majority of authors currently favour the former option, or at least that the number of events was quite few. However, Synchroma has a unique arrangement of chloroplasts in regard to surrounding membranes. Each individual chloroplast is surrounded by two membranes, and then multiple chloroplasts are clustered in packages contained by the remaining two membranes. Horn et al. suggest in passing that Synchroma may preserve an ancestral stage in the endosymbiotic process, after the loss of the eukaryotic endosymbiont's nucleus but before the separation of the endosymbiont's chloroplasts (after all, there is no reason why the eukaryotic endosymbiont would have necessarily had only one chloroplast per cell). In light of the derived position of Synchroma within the chromists, if this is indeed an ancestral state it makes the idea of a single endosymbiosis event rather unlikely, because this would require that the ancestral state was lost repeatedly in all other chromist groups. However, I feel that it is much more likely that the other explanation suggested by Horn et al. for Synchroma's unusual chloroplasts is correct - that it is a derived state resulting from an abnormal division pattern. The possibility that within chromists cryptophytes, haptophytes and heterokonts have gained their chloroplasts independently is not completely unbelievable, but the idea that multiple hterokont groups have done the same seems to be pushing it a little. Especially as all members of this undoubtedly monophyletic clade possess red algal-derived chloroplasts - if they derived them independently, why shouldn't at least some have green algal chloroplasts?

REFERENCES

Cavalier-Smith, T., M. T. E. P. Allsopp, M. M. Häuber, G. Gothe, E. E. Chao, J. A. Couch & U.-G. Maier. 1996. Chromobiote phylogeny: the enigmatic alga Reticulosphaera japonensis is an aberrant haptophyte, not a heterokont. European Journal of Phycology 31 (3): 255-263.

Horn, S., K. Ehlers, G. Fritzsch, M. C. Gil-Rodríguez, C. Wilhelm & R. Schnetter. 2007. Synchroma grande spec. nov. (Synchromophyceae class. nov., Heterokontophyta): an amoeboid marine alga with unique plastid complexes. Protist 158 (3): 277-293.

Taxon of the Week: Anthropoidea

I hardly feel that this group needs much introduction. The Anthropoidea (the name means 'man-like') are the monkeys, and everyone knows what a monkey is (Groucho Marx supposedly once claimed that the word 'duck' was the funniest in the English language, but I'm sure that the word 'monkey' mustn't be far behind). Modern-day anthropoids fall into two clades, the New World Platyrrhini (New World monkeys) and the Old World Catarrhini (Old World monkeys and apes, including humans). There is also a handful of fossil taxa that probably fall outside the crown group such as Parapithecidae and Eosimiidae. It seems pretty clear that the Anthropoidea were Old World in origin, possibly Asian (Beard & Wang, 2004). How the ancestors of the Platyrrhini managed to turn up in South America is something of a mystery - it seems most likely that they dispersed there from Africa, but how they managed to cross the Atlantic remains an open question (Schrago & Russo, 2003). However they did it, it is possible that the ancestors of the South American caviomorph rodent radiation arrived the same way at the same time (Schrago & Russo, 2003).

Anthropoids are fairly easy to recognise, or at least the modern ones are. The eyes are more vertically-positioned than in other primates, among other features. At some point, the ancestors of anthropoids also lost the ability to produce ascorbic acid (vitamin C), which is why we have to receive it from our diet (apparently the only other animals to suffer from this deficiency are guinea pigs). It has even been suggested that this loss has been a major factor in anthropoid evolution, as mutation increases in the absence of ascorbate's antioxidant effect (Challem, 1997). However, the rate of evolution of the hominoid (humans and apes) branch, at least, seems to have been reduced relative to other primates (Tëtushkin, 2003).

REFERENCES

Beard, K. C. & J. Wang. 2004. The eosimiid primates (Anthropoidea) of the Heti Formation, Yuanqu Basin, Shanxi and Henan Provinces, People's Republic of China. Journal of Human Evolution 46 (4): 401-432.

Challem, J. 1997. Did the loss of endogenous ascorbate propel the evolution of Anthropoidea and Homo sapiens? Medical Hypotheses 48: 387-392.

Schrago, C. G., & C. A. M. Russo. 2003. Timing the origin of New World monkeys. Molecular Biology and Evolution 20 (10): 1620-1625.

Tëtushkin, E. Ya. 2003. Rates of molecular evolution of primates. Genetika 39 (7): 869-887 (transl. Russian Journal of Genetics 39 (7): 721-736.

Love Hurts

People generally know distressingly little about insects. The gossip section of the weekly telly guide with the paper on Saturday mentioned a comment by Jerry Seinfeld on an upcoming movie of his featuring bees: "Other insects are just kind of crawling around. They don't have the sophistication of the bee. They have no crime, they have no drugs, they have no rape. A little rape, but it's not that bad." Leaving aside the question of the propriety of these comments, I have one word to say about their accuracy: bedbugs. Welcome to the world of Traumatic Insemination.

Male bedbugs (Cimicidae) have a sharpened intromittent organ (or if you prefer, a great spike on their knob). The usual means of entry is ignored in mating - rather, the female genital tract is only used in egg-laying (Stutt & Siva-Jothy, 2001). Instead, the male uses his sharpened organ to pierce through the female's body wall and inject semen directly into the body cavity.

Males and females do not always have the same aims in sexual reproduction. Because the limits on reproduction rates for males are relatively minimal, it is generally in the interest of males to maximise their insemination rate, in order to maximise the number of offspring they produce. Females, on the other hand, are more likely to have a maximum reproductive rate limited by the number of offspring they can safely produce in a given time period. Therefore, it is more advantageous for them to limit fertilisation to the best males to maximise the health of their offspring. As well as the obvious restrictions a female can place on fertilisation by limiting the ability of males to mate with her, the genital tract of females often has adaptations to 'test' sperm. The genital tract itself may be hostile to sperm survival (by being highly acidic, for instance). There may be structures such as a bursa copulatrix that store and/or digest sperm, limiting their access to further parts of the tract.

It is suspected that traumatic insemination evolved in males to bypass these restrictions on the part of the females. A good demonstration of this is seen in bugs of the family Nabidae, where entry into the female is still by the genital tract, but the sharpened intromittent organ pierces the wall of the bursa copulatrix (Tatarnic et al., 2006). Experimental evidence has shown that in traumatic inseminations the fertilisation advantage is held by the last males to mate with a female (Stutt & Siva-Jothy, 2001).

Nevertheless, females are not without defenses. While female bedbugs show a surprising lack of behavioural defenses against mating, they have developed an entirely novel paragenital system called the spermalege. In the common bedbug (Cimex lectularius), the external part of the spermalege is a special notch and a thickened part of the cuticle. Internally, there is a pocket filled with cells that receives the male ejaculate. Morrow & Arnqvist (2003) demonstrated that traumatic insemination through the spermalege had relatively little effect on the health of the recipient females. However, if the body wall was pierced anywhere else the female's survival rate was severely compromised. The internal part of the spermalege probably fulfils the sperm-killing role of the usual genital tract, as well as reducing the direct exposure of the female body cavity to potentially harmful ejaculate (Morrow & Arnqvist, 2003).

Different genera of bedbugs show a wide range of variation in the complexity of the paragenital system, from species entirely lacking one to species in which the system is exceedingly complex. In at least one genus, Afrocimex, a spermalege is present in both males and females (Tatarnic et al., 2006). It has been suggested that the presence of a spermalege in males defends against damage from homosexual matings - male bedbugs apparently tending to stab first and check suitability afterwards.

REFERENCES

Morrow, E. H., & G. Arnqvist. 2003. Costly traumatic insemination and a female counter-measure in bed bugs. Proceedings of the Royal Society of London Series B - Biological Sciences 270: 2377-2381.

Stutt, A. D., & M. T. Siva-Jothy. 2001. Traumatic insemination and sexual conflict in the bed bug Cimex lectularius. Proceedings of the National Academy of Sciences of the USA 98 (10): 5683-5687.

Tatarnic, N. J., G. Cassis & D. F. Hochuli. 2006. Traumatic insemination in the plant bug genus Coridromius Signoret (Heteroptera: Miridae). Biology Letters 2: 58-61.

The fall of Rafflesiales

I have to make a confession - I probably won't be covering a huge number of plants (in the sense of embryophytes) on this blog. This is, I admit, a pretty huge omission. After all, plants are a pretty significant chunk of phylospace, and pretty damn influential in shaping our environment. But compared to animals, plants are scary and complicated and I just don't know all that much about them. That said, I thought I should rectify my previous deficiencies by giving some plants the time of day. I'm not going to completely break with precedent, though - I'm looking at another group of parasites, the "Rafflesiales".

Until very recently, Rafflesiales was an order of holoparasites (i.e. they derive all their nutrition from their host, as opposed to hemiparasites such as mistletoes that still have leaves and produce some of their own nutrients) on roots of other flowering plants. Their main claim to fame lies in the genus Rafflesia, well-known as producers of the largest flowers in the world - Wikipedia gives the largest as over 100 cm in diametre and up to 10 kg in weight. I would be interested to know why they produce such ridiculously huge flowers. There just doesn't seem to be much point. When not flowering or fruiting, Rafflesiales are pretty much invisible, as they are otherwise entirely contained within the host.

I say "until very recently" because the Rafflesiales has, of recent years, fallen apart. This is not particularly surprising. Parasitic taxa of all varieties often show a great reduction in complexity, as organs related to nutrient gathering, production and processing lose their function - the host supplies all those things ready-made. Internal parasites are particularly notable in this regard. No need for a protective dermis of your own when you're safely contained within another organism's. No need for eyes, ears, nostrils - what are you going to see, hear, smell (that you would want to smell, at least)? Pretty much the only thing that the devoted endoparasite needs to do for itself is reproduce, and so many become little more than balls of gonad.*

*Seriously, no pun intended. I didn't even realise I'd written that at first.

Reduction in complexity often means loss of the characters that unite a parasitic clade with its non-parasitic sister group. And simplified characters come to resemble each other despite their different origins. Hence the previous unification of the families of 'Rafflesiales', and their sometimes-suggested connection with the Balanophorales, another group of reduced root-parasites (James Reveal seems to have phrased it best, though I'm not sure he meant quite the same thing as I do - "wherever go the Rafflesiales so go the Balanophorales").

The first molecular study that broke apart the Rafflesiales was Barkman et al. (2004). Barkman et al. looked at two genera of Rafflesiaceae (Rafflesia and Rhizanthes) as well as Mitrastema, another genus previously included in Rafflesiales. The two Rafflesiaceae clustered together, and appeared closely related to the Malpighiales, a large order of the flowering plant subclass Rosidae. In contrast, Mitrastema appeared as a member of the Ericales, in the subclass Asteridae. The remaining two families, Apodanthaceae and Cytinaceae, were added to the investigation by Nickrent et al. (2004). Cytinaceae was associated with Malvales (Rosidae). Apodanthaceae differed in its placement within Rosidae depending on which gene was examined, but it was never close to Rafflesiaceae (they may yet be related to Cytinaceae).

Nickrent et al. found that the peculiarities of 'rafflesialean' molecular evolution interfered with phylogenetic resolution. All the 'Rafflesiales' showed whacking great branch lengths, and when analysed under maximum parsimony, which is rather vulnerable to long-branch attraction (the tendency of long branches to randomly attach to each other), the Rafflesiales appeared as a near-monophlyetic clade. In one of the genes used by Nickrent et al., atp1, the Apodanthaceae clustered with Leguminosae, the host family of one of the Apodanthaceae. Because this result was in conflict with those from other genes, Nickrent et al. suggested that it represented lateral gene transfer from the host to the parasite. The occurrence of lateral (aka horizontal) gene transfer in eukaryotes is a subject of much debate, but it has been demonstrated to occur at least occasionally in flowering plants (Bergthorsson et al., 2003).

Most recently, Davis et al. (2007) investigated the specific position of Rafflesiaceae proper within Malpighiales, and found it to be actually nested within the Euphorbiaceae. This is a decidedly unexpected result, as Euphorbiaceae as a whole produce relatively minute flowers. Davis et al.'s result was unlikely to be simply long-branch attraction, because the other cluster on their tree to show accelerated evolutionary results was not Euphorbiaceae but the branch including Clusiaceae and Podostemaceae (the latter are aquatic plants that also show extreme reduction in complexity, to the point where they barely resemble flowering plants at all)*. I'm waiting in anticipation for Davis et al.'s results to be tested further.

*In recent years, there has been an increasingly distressing trend for articles to appear in high-impact journals with only the briefest of summaries of results in the actual printed journal, with the greater proportion of hard data, methods, etc. buried in online supplementary material (where it generally becomes inacessible after a couple of years). Davis et al. (2007) is actually one of the most extreme examples of this, with the printed article only a single page, with the supplementary info 424 pages long (fairness does compel me to admit that 415 pages of that are sequence alignments).

REFERENCES

Barkman, T. J., S.-H. Lim, K. Mat Salleh & J. Nais. 2004. Mitochondrial DNA sequences reveal the photosynthetic relatives of Rafflesia, the world's largest flower. Proceedings of the National Academy of Sciences of the USA 101 (3): 787-792.

Bergthorsson, U., K. L. Adams, B. Thomason & J. D. Palmer. 2003. Widespread horizontal transfer of mitochondrial genes in flowering plants. Nature 424: 197-201.

Davis, C. C., M. Latvis, D. L. Nickrent, K. J. Wurdack & D. A. Baum. 2007. Floral gigantism in Rafflesiaceae. Science 315: 1812.

Nickrent, D. L., A. Blarer, Y.-L. Qiu, R. Vidal-Russell & F. E. Anderson. 2004. Phylogenetic inference in Rafflesiales: the influence of rate heterogeneity and horizontal gene transfer. BMC Evolutionary Biology 4: 40. (online here).