(Belated) Taxon of the Week: The Bishop's Mitra

Mitra cardinalis. Photo from Sydney Shell Club.

The marine gastropods of the genus Mitra get their genus name (as well as their common name of 'mitre shells') from the resemblance of many species, at certain angles, to the pointy hat of a bishop (and indeed, the species names Mitra episcopalis, M. pontificalis and M. papalis all appear to be floating around out there). They are fairly middling-sized shells - three or four centimetres long would seem to be a respectable Mitra size - and most of them are slender and pointed at one end (the technical term is 'fusiform', and the discription 'cigar-shaped' gets bandied about regularly). Members of the subgenus Strigatella, however, are shorter, more globular animals.

Mitra are members of the family Mitridae, which is in term a family of the Neogastropoda. Neogastropods have been featured at this site before (here and here), albeit without having been identified as such, and there is a fair probability that if you go looking for gastropods on a trip to the beach that the first one you find will be a neogastropod. This is not so much because neogastropods are that much more abundant than other marine gastropods (although they are a fairly speciose bunch) as because neogastropods tend to be a lot more active than other gastropods, and are much more likely to be visibly on the move while other gastropods are sitting clamped to rocks. And the reason for the greater mobility of neogastropods is a matter of diet.


Mitra idae. Note the siphon protruding in front of the shell. Photo from Wikipedia.

The ancestral diet for gastropods was a reliable, if somewhat unexciting, scraped meal - algae rasped off rocks, or the fruits of scavenging. As a result, mobility is not at much of a premium for most gastropods - it doesn't take much speed to chase down a patch of algae - and the only reason to move is to get to the next patch of algae. Neogastropods, however, tired of this diet and went for something a little more exiting - they became active predators. Mobile neogastropods at the beach are on the hunt for prey (or, alternatively, pre-deceased animals to scavenge off). One of the most distinctive features of neogastropods to the casual observer is their elongate siphon, which in live animals can usually be seen extended from the front of the shell (which has a distinct notch or anterior extension for it to extend through), waving back and forth as the animal moves, sniffing for any appetising scents. The radula (the tongue-like structure covered with teeth in the mouth of a gastropod) has become adapted to the predatory life-style, with the number of teeth reduced but each individual tooth much larger and sharper. The fusiform body-shape as seen in most Mitra also appears well-suited to mobility, and is shared by a significant proportion of neogastropods.


Mitra mitra everting its proboscis. Photo from here, where they've made the mistake of thinking this individual is swallowing a worm.

Members of the family Mitridae possess a particularly elongate proboscis, often longer than the rest of the animal. Running along the inside of the proboscis is the radula and a muscular rod called the epiproboscis, which can be even further extended. Mitrids are specialist feeders on sipunculan worms, which live buried in sediment or burrowed into corals (Taylor, 1989), and the epiproboscis is used to capture their prey. Suggestions that it is used to inject digestive enzymes into the prey for external digestion are incorrect, as the prey is usually swallowed directly without allowing time for digestion (Taylor, 1989) The method used by Mitra idae to capture a sipunculan was described by West (1990), and as the morphology of the epiproboscis is fairly constant within the Mitridae other species probably use the same or a very similar method. After locating a sipunculan with its siphon, the gastropod would extend its proboscis until it contacted the worm, then the epiproboscis to grab onto the worm. The first move of the Mitra would then be to try and suck the worm directly out of its burrow. If this failed (which I suspect would be the norm), it would then use its radula to rasp a hole through the worm's skin before inserting the epiproboscis through the hole. The epiproboscis would entwine itself around the worm's viscera and grab directly onto its intestines. The viscera would then be hauled out through the hole in the sipunculan's skin and slurped down the waiting proboscis. Once the Mitra had pulled as much of the worm's guts out as it could, it would close its proboscis over the remaining husk and finish drawing the worm out from its hole. Insertion and retraction of the epiproboscis took a little under ten seconds. The whole process, from initial insertion to final withdrawal, could take up to twenty minutes.

REFERENCES

Taylor, J. D. 1989. The diet of coral-reef Mitridae (Gastropoda) from Guam; with a review of other species of the family. Journal of Natural History 23: 261-278.

West, T. L. 1990. Feeding behavior and functional morphology of the epiproboscis of Mitra idae (Mollusca: Gastropoda; Mitridae). Bulletin of Marine Science 46 93): 761-779.

Keeping an Eye on Inflation

Neofelis diardi, the "new" clouded leopard species (actually first described in 1823, but later sunk into synonymy until recently resurrected) that has become something of a poster child for arguments on the worth of recent vertebrate species splits. Photo from Tet Zoo.

Normally, there'd be a Taxon of the Week post here on a Monday, but due to various circumstances that won't be happening today. Instead, here's something I've been sitting on for a few days now:

Sangster, G. (in press) Increasing numbers of bird species result from taxonomic progress, not taxonomic inflation. Proceedings of the Royal Society of London Series B.

Despite the widespread (and, I should note, entirely valid) complaints about the decline of taxonomy as a field of research, a person unfamiliar with the dynamics of the field might possibly be forgiven if, on a cursory glance, they saw it as stronger than ever. The number of new taxa, particularly species, being described every day has not appreciably slowed down - indeed, new species are probably debuting faster than ever. In many cases, study of a "species" once believed widespread has lead to the recognition of multiple species, each occupying a different part of the originally-recognised taxon's "range". This latter pattern is particularly noticeable in studies on vertebrates. Often, the new "species" were previously recognised as "subspecies" before their promotion. This has led to the accusation that such cases are examples of taxonomic inflation.


Lesser bird of paradise, Paradisaea minor. Birds of paradise have become one of the prime examples of conflict between the Biological and Phylogenetic Species Concepts. Most authors claiming to follow the BSC have recognised about forty species of bird of paradise (and that total is possibly oversplit, considering the high interfertility of the recognised species), but applications of the PSC to the family have suggested more than ninety species. Photo by stboed.

For those of you unfamiliar with the term, the term "taxonomic inflation" refers to situations where names, but not the content, of taxa change as a result of their elevation in rank. When the term is used, it usually carries the disparaging implication that this is change simply for the sake of change without any underlying gain in information, and hence unnecessary at best and a misleading waste of everyone's time at worst*. Taxonomic inflation has also been cited as a problem with the use of the Phylogenetic Species Concept (PSC) rather than the Biological Species Concept (BSC) (see here for an earlier post of mine on the subject). Many authors have complained that the rise in recognised species is bad news for conservation, as it increases the number of required conservation targets.

*Personally, I (and others before me) would argue that taxonomic inflation is an inevitable side-effect of our current use of a rank-based classification. As I complained last week, an unfortunate side-effect of the pinning of our ranking system on certain primary ranks leads to the belief (whether concious or subconcious) that those ranks should be used for the most "significant" taxa. Now, imagine that I'm a researcher spending five years working on a particular family of organisms. As a result of my research, I find that my "family" of interest renders another "family" paraphyletic. Assuming that I prefer a classification recognising all-monophyletic taxa, I have two options - either I can subsume my "family" of interest into the other family, or I can divide up the other "family" in order to maintain the distinctiveness of my research family. It all depends on my perception of the relative significance of the taxa - and what do you think that might be, considering into what I've been investing the last five years of my life?


Variation in appearance between different populations of giraffe, Giraffa spp. Usually recognised as a single species, G. camelopardalis, recent authors have suggested giraffes should be divided between a number of species. Image from The Barcode Blog.

The new paper by Sangster responds to the claim that the increase in recognised vertebrate species is due solely to the increased popularity of the PSC, and does not reflect any net increase in our taxonomic understanding (invertebrate taxonomy has been less affected by this debate, because invertebrate systematists have, for the most part, been less inclined to recognise "subspecies" [with the notable exception of lepidopterists]). According to Sangster, if this claim is true, it leads to four predictions: (1) the increase in recognised species would have not begun until the introduction of the PSC in the early 1980s*; (2) most taxonomic changes would be based on reinterpretations of old data rather than on collection of new data; (3) most taxonomic splits would be based on specifically PSC-related criteria such as diagnosability and reciprocal monophyly to each other and other taxa, as opposed to less specifically PSC-related criteria such as degree of difference ("too different" to be the same species, or "too similar" to be different species), differences in adaptive zone (e.g. lowland vs montane taxa) or reproductive isolation; and (4) new taxonomic splits would be biased towards members of charismatic groups (in which there may be more of a vested interest in raising their conservation profile). To test these predictions, Sangster surveyed taxonomic proposals affecting taxon rank published in seven major ornithological journals (such as The Auk and Ibis) between 1950 and 2007 - whether proposals recommended a split (subspecies becoming species) or lump (species becoming subspecies), and what were the criteria cited as support for the proposal.

*The date is inexact because a number of variants on the PSC were proposed by different authors.



The results of Sangster's survey showed that the increase in the percentage of taxonomic proposals recommending splits rather than lumps (shown in the graph above from the paper) had been continuous over the time period surveyed, and the rate of increase had not significantly changed in the 1980s (indeed, there had been a slight downturn in the 2000s, though probably not a significant one). 76.4% of taxonomic proposals over the period covered had been supported by new data rather than based on reinterpretation of old data, and proposals for splits were significantly more likely to be based on new data than proposals for lumps (84.6% vs 64.2%). Prior to the introduction of the PSC, 71.7% of proposed splits were based on new data - post-PSC, 93.9% of them were. Only 10.3% of proposed splits overall were based solely on reinterpretation of old data using PSC-related criteria.

The most common criterion for a proposal was diagnosability, followed by reproductive isolation. The least commonly used criteria related to reciprocal monophyly. All criteria were more likely to lead to splits than lumps, though "degree of difference" had the smallest difference in propensity. Proposals based only on PSC-related criteria were more likely to lead to a split than those based only on non-PSC criteria, with the latter more likely to propose a lump than a split. There was no correlation between the increase of species in a family and the charisma of that family, but there was a correlation between the number of splits and the number of polytypic species (i.e. species divided into subspecies) in that family.


The two storm petrel species breeding on the Azores, of which Oceanodroma monteiroi was only described last year in Bolton et al. (2008), from which comes this figure. Though very similar, the two species breed at different times of the year.

Sangster concludes that the accusation that recent increases in species number are based solely on reinterpretation of old data is grossly unfounded. Proposed changes aren't taxonomic "inflation", they're taxonomic "progress". However, as much as I personally like his conclusion, it must be admitted that Sangster is potentially setting up a strawman here. Taxonomic research does not exist in a vacuum, and an author is not very likely to go about revising the taxonomy of a group unless they are working on that group already. The increase in the proportion of taxonomic changes supported by new data might indeed reflect changes in researcher practice - or it may reflect the journals becoming more discerning about what manuscripts they will accept for publication (still, for the reader it may not really matter whether the increased rigour is being driven by the researcher or the publisher).

On the other hand, Sangster brings up the very important point that many of these "new" species aren't really new at all. During the early 1900s, vertebrate taxonomy went through a period of significant lumping. Sangster cites the point that while Sharpe recognised 18,939 species of bird in 1909, Mayr & Amadon recognised only 8590 in 1951 - less than half Sharpe's total. The justification for this lumping was often unclear (they were in a time period when a researcher's authority was generally taken for granted, rather than their being required to show their working), and many current taxonomists feel that in many cases the lumping went too far (for a concrete example, see Darren Naish's post from a few years back on babirusas). Many proposed splits are arguably correcting the excesses of the past.

Finally, on a personal level, I wouldn't particularly care even if the species increase was based on a change in species concept, because as I've explained before (see the first post linked to at the top of this one), I'm a much greater fan of the PSC than of the impractical-to-test, everyone-says-they-follow-it-but-pretty-much-no-one-actually-does mess that is the Biological Species Concept. The conservation and PR argument cited above - that the PSC somehow leads to there being "too many" species - completely fails to impress me, because I don't think that scientific investigation should be directly influenced by political concerns. Once you have the information, then you can work out what to do about it, but changing your working information to what you want it to be first is just not on.

42

Here are the answers to yesterday's quiz:

1. Current rank-based taxonomy is based on seven primary ranks. Which two were not used by Linnaeus?

Okay, that was an easy one to start off with. Linnaeus didn't use "families" or "phyla" (and for animals, he only recognised six "classes" - mammals, birds, amphibians [including reptiles], fish, insects [including other arthropods] and "worms" [pretty much anything soft and squishy, and not necessarily even worm-like]).

2. What are the five codes of biological nomenclature currently in action?

Mike Keesey even had the titles - International Code of Zoological Nomenclature, International Code of Botanical Nomenclature, International Code of Nomenclature of Bacteria (now the International Code of Nomenclature of Prokaryotes, in light of the increasing tendency not to refer to archaebacteria as 'Bacteria'), International Code of Virus Classification and Nomenclature, and International Code of Nomenclature of Cultivated Plants. The last one, if you were wondering, covers the registration of names for varieties bred in horticulture, such as a cauliflower Brassica oleracea 'Snow Ball'.



3. Name one group of organisms not governed by any of these five codes.

Since the bacterial code went its separate way from the botanical code, fossil prokaryotes have been left effectively homeless. The botanical code no longer regulates prokaryotes except for Cyanobacteria (so those fossil prokaryotes identified as cyanobacteria would still be regulated), while the bacterial code is effectively inapplicable to non-living taxa (it requires deposition of a sample of the living type strain in at least two collections in two different countries for a taxon to be valid). Mike's guess that stem-biotes were the organisms in question is therefore partially correct, because it is possible (albeit probably not ever demonstrable) that a fossil prokaryote could be a stem-biote.

4. What is the earliest publication using binomial nomenclature to be currently recognised by the ICZN?

This was meant to be a trick question, but sadly no-one fell for the trick. While the 10th edition of Linnaeus' Systema Naturae, published in 1758, is the official starting point for binomial nomenclature under the ICZN, Andreas Johansson correctly pointed out that one earlier publication, Clerck's 1757 Svenska Spindlar uti sina hufvud-slågter indelte samt under några och sextio särskildte arter beskrefne och med illuminerade figurer uplyste - Aranei Svecici, descriptionibus et figuris æneis illustrati, ad genera subalterna redacti, speciebus ultra LX determinati (usually referred to simply as Aranei Svecici, for obvious reasons), has been accepted by the ICZN as admissible (and officially takes priority over Linnaeus). You can read the entirety of Aranei Svecici online through this site.



5. When and what was the earliest formal zoological nomenclatural code proposed? What was the earliest botanical code?

Mike did refer to the 1842 Strickland Code, but unfortunately for Mike the object of the Strickland Code was zoology, not botany. As I previously alluded to at the beginning of an earlier post, botanists at the time rejected the idea of extending the Strickland code to cover their territory (the open-access article linked to at that post also transcribes a large part of the Strickland Code, for anyone interested in reading it). The first Botanical code to be formally adopted was the Lois de la Nomenclature Botanique published by Alphonse de Candolle in 1867. Ironically, while the zoologists had a twenty-five-year head-start over the botanists in establishing a code, it was the botanists that actually paid attention to theirs, while the Strickland Code ending up largely falling by the wayside. As such, botanical nomenclature ended up becoming a lot more stabilised a lot earlier than zoological nomenclature.

6. What do the letters 'VP' and 'AL' mean as part of a bacterial name?

Originally, bacteria were dealt with using the Botanical Code, but as time went by it became increasingly clear that the provisions of that code were not suitable for working with prokaryotes (which are mostly distinguished by chemical rather than physical characteristics), with thousands of excess names for bacterial taxa having been proposed for which no-one had the slightest idea to what they referred, and eventually a separate Bacterial Code was established. Those bacterial taxa that had been well-characterised were listed in the Approved Lists of Bacterial Names, published in 1980, and any taxa from before 1980 that were not on the Approved Lists were effectively null or void. Any bacterial name published after 1980, in order to be valid, had to be either published or validated in the International Journal of Systematic Bacteriology (now the International Journal of Systematic and Evolutionary Microbiology). To indicate the mode of validation, the full citation for a bacterial name will have the letters 'AL' or 'VP' as a superscript against the publication date - 'AL' indicates a name was on the Approved Lists (in which case it takes priority from the original date of publication), while 'VP' (for 'Valid Publication') indicates that it was validated by publication in the IJSEM (in which case it is dated from it appeared in that journal, no matter how much earlier the name may have appeared elsewhere).



7. Kathablepharis and Katablepharis are different spellings for the name of the same organism. Each is the one spelling that must be used, while the other spelling is invalid. Explain.

Mike was halfway there with this one - Katablepharis is a protist that has been treated by different authors using both the zoological and botanical codes. Its name was originally published as Kathablepharis by Skuja in 1939, but the correct Latinisation should have been Katablepharis. In such cases, the botanical code requires that the name be corrected, but the zoological code requires that the original spelling be maintained. Hence the correct name of this organism ended up being spelt differently depending on which code it was being treated under.

8. The name Oedicnemidae was published by Gray in 1840. The name Burhinidae was published by Mathews in 1912. Both refer to the same family, for which the valid name is Burhinidae. Why?

Okay, take a deep breath. This one gets a little involved, but the situation it refers to is actually not that uncommon. Genus- and species-level nomenclature can be confusing enough, but sometimes family-level nomenclature is just plain evil.

It used to be the tradition that when the type genus of an animal family was synonymised with another genus, the name of the family also changed to match. So when Oedicnemus was synonymised with Burhinus, Oedicnemidae became known as Burhinidae. Where this gets confusing is that the altered name continued to take its priority from the original name - so the name Burhinidae would be treated as dating from 1840, when Oedicnemidae was published, even though the name Burhinidae itself never actually existed until 1912. When the modern Zoological Code was first published in 1961 (well, before that, even), it was realised that this was far too complicated and confusing a way to do things (especially in cases of debated synonymy), and so the current rule was introduced that family names were determined only by their own priority, and the synonymy of its type genus did not affect the validity of a family name. However, because the ICZN does not mess with past actions when introducing new rules, if a family name was changed under the old tradition before 1960, it retained the new name. So the then-current name Burhinidae stayed Burhinidae, and didn't have to revert to the probably long-forgotten name Oedicnemidae.

9. If two or more taxa have the same name, and fall under the scope of the same code, then their names are homonyms, and only one can be valid. Pupa affinis Rossmaessler 1839, Pupa affinis Aradas & Maggione 1843 and Pupa affinis (Adams 1855) are all names for animals, but they are not considered homonyms. How is this possible?

Mike got this one right off the bat. The three names are not counted as homonyms because they are not actually in the same genus - they are in three different genera that had each been named Pupa. The genus names have to be corrected because they are homonyms, but the species that were published in association with those genera can keep their original names.



Picture credits (from top to bottom): Dante being examined on theology in heaven, from Il Paradiso, via here.

The Beaver's Lesson, from The Hunting of the Snark.

Examition of a Witch, by T. H. Matteson, via here.

"Lojban" from xkcd.

Satan in Heaven, from Paradise Lost, via here.

Completely Frivolous Taxonomy Quiz

For no good reason, here's a set of trivia questions about biological taxonomy and nomenclature. Excuse the possible zoological bias - I am a zoologist, after all. How many can you answer? They start off easy, but (hopefully) they get trickier.

1. Current rank-based taxonomy is based on seven primary ranks. Which two were not used by Linnaeus?

2. What are the five codes of biological nomenclature currently in action?

3. Name one group of organisms not governed by any of these five codes.

4. What is the earliest publication using binomial nomenclature to be currently recognised by the ICZN?

5. When and what was the earliest formal zoological nomenclatural code proposed? What was the earliest botanical code?

6. What do the letters 'VP' and 'AL' mean as part of a bacterial name?



7. Kathablepharis and Katablepharis are different spellings for the name of the same organism. Each is the one spelling that must be used, while the other spelling is invalid. Explain.

8. The name Oedicnemidae was published by Gray in 1840. The name Burhinidae was published by Mathews in 1912. Both refer to the same family, for which the valid name is Burhinidae. Why?

9. If two or more taxa have the same name, and fall under the scope of the same code, then their names are homonyms, and only one can be valid. Pupa affinis Rossmaessler 1839, Pupa affinis Aradas & Maggione 1843 and Pupa affinis (Adams 1855) are all names for animals, but they are not considered homonyms. How is this possible?



Picture credits (from top to bottom): Tweedle Dum from Alice Through the Looking Glass, via here.

Satan in Hell from L'Inferno, via here.

The Ship of Fools by Hieronymus Bosch, via here.

Hey, Old Taxo! My Genus is Better than Yours!

In the children's picture book The Kuia and the Spider by New Zealand author Patricia Grace, an elderly woman (kuia in Maori) is challenged by a spider living in her kitchen, who keeps saying to her, "Hey, old woman! My weaving/cooking/etc. is better than yours!" Each successive challenge leads to frantic competition, as the woman and the spider try to outdo each other ("cooking" for the spider, of course, refers to the process of catching, wrapping and breaking down flies). However, each of these competitions ends in an effective draw - they only way they could end, because neither competitor is willing to admit the other's superiority in these ultimately subjective comparisons.

As my regular readers will probably be aware, I'm not a big fan of rank-based classifications (see here for one of my earlier rants on the subject. The ultimate problem with rank-based taxonomy is that the urge to inject some sort of "reality" into the concept of ranks is irresistible. Defenders of the rank system claim that this is not a problem - ranks only indicate relative positions, and it does not matter that a "genus" of insects is not directly comparable to a "genus" of mammals, because that's not the point of ranks. Unfortunately, they then forget this point themselves - instantaneously, even:

Everyone accepts that Linnaean ranks are subjective, and yet there is no benefit in abandoning ranks because they have proved to be of such value to users of classifications, and genera and families, for example, act as valuable surrogates for species in large−scale evolutionary and ecological studies. (Benton, 2007)

If ranks are subjective (as supposedly everyone says they are), then higher ranks cannot possibly act as surrogates for species for the simple reason that one author's rank-ometer may be (and, in practice, usually is) calibrated differently from another author's.

The point I really wanted to make today, though, is another aspect of the fallacy of thinking of ranks as "real". The current taxonomic ranking system, as we all know, is anchored on the principle that Kind People Can Often Find Good Sex. The seven ranks referred to by that mnemonic are the primary and more or less mandatory ranks of the system, while all other more optional ranks are conceptualised in their relationship to the primary seven. Unfortunately, this leads directly to the idea that taxa at those "primary" ranks are somehow more significant than taxa at the "subsidiary" ranks. Take this comment made recently on the Taxacom mailing list:

Ideological extinction is the fate of autophyletic (descendant groups recognized at same taxonomic level as ancestor) taxa, and of paraphyletic taxa split into non-recognition. Although taxa of high visibility (Aves, polar bears) seem immune to ideological extinction, many groups simply disappear from classification because they were embedded in an ancestral group of the same rank. In my own field, bryology, three families (Ephemeraceae, Cinclidotaceae, and Splachnobryaceae) have been sunk in a recent influential phylogenetic classification into one larger one (Pottiaceae) without discussion because they were autophyletic in previously published molecular trees; their names do not appear anywhere in the classification, which offers no synonymy.

The author of the comment, Richard Zander, is complaining that the subsumation of the three smaller families into the larger family obscures the distinctiveness of the three smaller groups. There is no particular reason why this should be so - if the taxa originally labelled by those three names are still good taxa, then they should still be perfectly recognisable whatever rank they are put at. The only reason why it should make a difference that they have lost their status as separate families is if there is some particular significance to being a "family" as opposed to a subfamily, tribe or whatever. If ranks are truly only relative, and there's no real significance to them, then why are you complaining?

REFERENCES

Benton, M. J. 2007. The PhyloCode: beating a dead horse? Acta Palaeontologica Polonica 52 (3): 651-655. (Thank you to David Marjanović for pointing this out to me.)

Multifarities Most Horrid (Taxon of the Week: Braconidae)

Braconid wasp of the subfamily Aphidiinae laying an egg in a hapless aphid. Photo from BioMed Central.

We all know that J. B. S. Haldane is supposed to have remarked that God seemed to have an "extraordinary fondness for beetles". What Haldane may not have realised was the possibility that the beetles were just a means to an end. As the current rate of taxonomic description is considered, some researchers have come to the suspicion that the true objects of the Creator's affection are not beetles, but parasitoid wasps*. Which, when you consider the natures of parasitoid wasps, kind of explains some things about life.

*Personally, I'm still taking the long odds and backing the nematodes.


Microgastrinae larvae emerging from a host caterpillar. Photo from here.

The Braconidae are just one of the stupidly diverse lineages of Hymenoptera (another group, the Proctotrupomorpha, was covered at this site here). According to ToLWeb (in 2004), there are some 12,000 described species of braconids, with estimates of up to 50,000 in total. Braconids form the living sister group to the similarly diverse Ichneumonidae, though braconids tend to be smaller in size (still, some of them are more than big enough). Braconids include both exoparasitic and endoparasitic taxa, parasitoids of eggs, larvae or adult insects, and a small number of gall-forming plant-parasitic taxa for added variety. The usual opinion is that the exoparasitic taxa represent the ancestral lifestyle for the family, but the actual phylogeny of the family is still being hammered out (and the "usual opinion" may yet turn out to be the wrong opinion). About forty subfamilies are currently recognised, but most authors (e.g. Shi et al., 2005) divide those subfamilies between three main lineages, the cyclostomes, microgastroids and helcionoids, with some subfamilies of uncertain position relative to the three. The microgastroids and helcionoids are all koinobiont endoparasitoids (after the wasp has laid its eggs in the host, the host continues to grow and develop), while the cyclostomes include both exoparasitoids and endoparasitoids, with exoparasitoids usually paralysing the host before laying their eggs (Wharton, 1993). The microgastroids are fastidious in their tastes, restricting their diet to Lepidoptera (Murphy et al., 2008), while helcionoids attack a wide variety of hosts, including hemimetabolous as well as holometabolous insects. Early phylogenetic studies suggested that the cyclostomes (which possess a distinctive mouthpart morphology) were paraphyletic with regard to the other braconids, but more recent studies support a monophyletic cyclostome clade (Shi et al., 2005). The monophyly of a microgastroid + helcionoid clade is supported by molecular data (Shi et al., 2005), but remains short on morphological support (Quicke et al., 1999).


An individual of the genus Atanycolus (subfamily Braconinae in the cyclostome group). Photo by Richard Bartz.

The Aphidiinae are the largest group of braconids to not fit comfortably within the three-way division. Aphidiinae are parasitoids of aphids. Morphological data supports a relationship between aphidiines and the cyclostome group (Quicke et al., 1999), but the molecular analysis of Shi et al. (2005) suggested a relationship between the Aphidiinae and the Euphorinae, members of the helcionoids. The intriguing feature of this result is that Aphidiinae and Euphorinae both have the unusual characteristic (for insect parasitoids) of parasitising adult hosts rather than larvae - albeit with different host ranges in the two subfamilies. Euphorinae were probably originally parasitoids of beetles, but some species have since become parasitoids of hosts as diverse as grasshoppers or Psocoptera. (A more recent combined morphological and molecular study whose authors argued against an Aphidiinae-Euphorinae relationship in favour of an Aphidiinae-cyclostome connection [Zaldivar-Riverón et al., 2006] actually did not test anything either way, because the authors' choice of taxa and outgroup effectively forced an a priori cyclostome position).


An adult of Microgastrinae. Photo by Scott Justis.

Finally, some would think it rather remiss of me to write about braconids without making some mention of polydnaviruses, but I don't see why I should when a much better description of such things than I could produce has already been written by Merry Youle at Small Things Considered. After you read the main article there, though, make sure you scroll down the comments to Merry's description of the differences between polydnaviruses in Braconidae and Ichneumonidae suggesting the independent origins of the polydnavirus system in the two families. As well as the differences described by Mary, it also turns out that polydnaviruses are not characteristic of braconids as a whole, but are in fact only found within the microgastroid clade (Wharton, 1993), so an independent origin from ichneumonid polydnaviruses has phylogenetic as well as biochemical support.

REFERENCES

Murphy, N., J. C. Banks, J. B. Whitfield & A. D. Austin. 2008. Phylogeny of the parasitic microgastroid subfamilies (Hymenoptera: Braconidae) based on sequence data from seven genes, with an improved time estimate of the origin of the lineage. Molecular Phylogenetics and Evolution 47 (1): 378-395.

Quicke, D. L. J., H. H. Basibuyuk & A. P. Rasnitsyn. 1999. Morphological, palaeontological and molecular aspects of ichneumonoid phylogeny (Hymenoptera, Insecta). Zoologica Scripta 28 (1-2): 175-202.

Shi, M., X. X. Chen & C. van Achterberg. 2005. Phylogenetic relationships among the Braconidae (Hymenoptera: Ichneumonoidea) inferred from partial 16S rDNA, 28S rDNA D2, 18S rDNA gene sequences and morphological characters. Molecular Phylogenetics and Evolution 37 (1): 104-116.

Wharton, R. A. 1993. Bionomics of the Braconidae. Annual Review of Entomology 38: 121-143.

Zaldivar-Riverón, A., M. Mori & D. L. J. Quicke. 2006. Systematics of the cyclostome subfamilies of braconid parasitic wasps (Hymenoptera: Ichneumonoidea): a simultaneous molecular and morphological Bayesian approach. Molecular Phylogenetics and Evolution 38 (1): 130-145.

Remarkable Things

Yesterday was indeed a day for remarkable things. It started when I walked into the bathroom and found a winged male embiopteran sitting on the wall above the toilet cistern. Not the usual place where one would expect to find an embiopteran. It continued when I was informed of the publication of not one but two papers of note on harvestmen.


Lateral view of the male of Neopantopsalis thaumatopoios with most of the legs removed (because there's a limit to how much I'm willing to draw). Even for harvestmen, species of Neopantopsalis have stupidly long appendages. This figure was used in Taylor & Hunt (2009). The scale bar equals a millimetre.

The first is of note on a more personal level - my paper on the new genus Neopantopsalis has come out in Zootaxa (Taylor & Hunt, 2009). This is the first of the three major papers that will be coming out of my PhD - the other two (which I'm still in the process of writing) will cover the genera Megalopsalis and Spinicrus, respectively, as well as the phylogeny of the family Monoscutidae as a whole (or, at least, as much of it as I can reliably make out - long-legged harvestmen aren't exactly brimming over with phylogenetically useful characters). But now that the Neopantopsalis paper has completed the review process and made it into print, I can safely say that I'm not entirely happy with it. I began working on it when I found that Glenn Hunt, the last major worker on Australian harvestmen, had designated a specimen in the Queensland Museum as the type of a new species that he had unfortunately never published before he passed away (in recognition of this, I included Glenn as a second author on my manuscript). This species, it turned out, was one of a well-defined group of species found in Queensland and northern New South Wales - the group now labelled by the name Neopantopsalis. Unfortunately, distinguishing individual species within Neopantopsalis threatened to become an overwhelming task. Individual variation in almost every character was the norm rather than the exception, and in more than one case I was left at a loss to decipher whether I was dealing with a species complex or a complex species. Eventually realising that I could end up spending my entire doctorate working on this one genus (which would not be ideal), I was forced to cut my losses, pick out some well-defined exemplars that could stand in for the overall diversity, and put an appropriate manuscript together as best I could so I could move on to the next topic. So if anyone with a penchant for arachnid systematics with connections to the Queensland region is ever looking for something to do, there's a very widespread genus there still begging to be given the attention it really requires.


The fossil remains of Mesobunus martensi, the better-preserved of the two recent finds. Figure from Huang et al. (in press).

The other paper I learnt of yesterday has perhaps got a broader appeal - the first Jurassic harvestman fossils (Huang, Selden & Dunlop, in press, 2009). Harvestmen are purely terrestrial, not particularly vagile and mostly very delicately built. As a result, their fossil record can only be described as pitiful. There's a couple of fossils from the Devonian, a small collection from the Carboniferous, a couple from the Cretaceous and a small smattering from the Cenozoic (mostly amber) (Dunlop, 2007). However, the few fossils that we do have are quite remarkable in light of how incredibly unremarkable they are. Most fossil harvestmen are almost indistinguishable from taxa living today. Even the very oldest known harvestman, Eophalangium sheari from the Rhynie Chert, would probably fail to raise a single eyebrow if reanimated and released into the modern environent. The origin of harvestmen could not have been all that long before the time of Rhynie Chert, because it wasn't that long before then that there wasn't even a terrestrial environment for there to be harvestmen in. Harvestmen, it seems, are the ultimate retroactive conservatives - if it was good enough 400 million years ago, it's good enough today.

The two new Jurassic fossils, coming from Daohuguo in China, do not buck this trend in the least. Indeed, so similar to modern long-legged harvestmen are they that Huang et al. even assign the better-preserved of the two, Mesobunus martensi, to the modern family Sclerosomatidae (this is the family that includes the genera Gagrella and Leiobunum). They do this on the basis of "the extremely elongate legs, a single tarsal apotele [claw], a pediform [leg-like] pedipalp, and, particularly, the fusion of the first five opisthosomal tergites into a single dorsal plate". They also note the presence of what may (or may not) be pseudoarticulations in femora of the fourth pair of legs, which (if present) would not only place Mesobunus in the Sclerosomatidae, but also within the subfamily Gagrellinae within the Sclerosomatidae. The long legs, simple claw and leg-like pedipalps are plesiomorphies for the harvestman superfamily Phalangioidea (and quite possibly for a larger subgroup of harvestmen), so are not really significant. The dorsal scute and possible pseudoarticulations are more interesting - but, unfortunately, not conclusive. A similar dorsal scute is found in other harvestmen in other suborders (such as the genus Ischyropsalis), and also (though less sclerotised) in some members of the eupnoan family Monoscutidae (notably the genus *ahem*, which however doesn't have very long legs*). Femoral pseudoarticulations are also not unique to Sclerosomatidae - for instance, they have recently been recorded in two species of Monoscutidae by - oh, will you look at that - Taylor & Hunt (2009). So while it is true that Sclerosomatidae is the only living family that shows the exact combination of characters seen in Mesobunus, none of the characters individually is unique. Or to turn that around, while I'm not entirely convinced that Mesobunus is a sclerosomatid, I can't exactly show that it's not a sclerosomatid either. Unfortunately, a rock-solid identification with Sclerosomatidae would probably require examination of features such as the genitalia or spiracles - both highly unlikely to be visible in a fossil.

*I say "ahem" because it's in press as we speak.


Reconstructions of Mesobunus from Huang et al. (in press).

If we accept for the present that Mesobunus is a sclerosomatid, that has some interesting implications for harvestman biogeography. The Phalangioidea can be roughly divided into two morphological groups, a mostly Northern Hemisphere group containing the families Phalangiidae and Sclerosomatidae, and a Southern Hemisphere group containing the families Neopilionidae and Monoscutidae*. The Phalangiidae + Sclerosomatidae group is well supported by a few good characters (most notably the structure of the spiracle) and is more than likely a good clade. The characters uniting the Southern Hemisphere families, on the other hand, are probably plesiomorphies, so this group is quite possibly paraphyletic with regard to the Northern clade (though exact relationships are currently unknown). Similar patterns, with Northern Hemisphere taxa nested among Southern Hemisphere taxa, have been observed in many groups of organisms, and it has often been suggested to indicate a Gondwanan ancestry for those groups. Birds, butterflies... there was a period when it seemed almost everything came from Gondwana. Usually, such Gondwanan ancestries were suggested to be related to the mass extinction at the end of the Cretaceous - with the Northern Hemisphere more heavily affected by the end-Cretaceous meteor impact than the South (which is entirely plausible if the Chicxulub crater in Mexico is the site of the impact), Southern Hemisphere taxa were able to radiate at the beginning of the Cenozoic and repopulate the devastated Northern Hemisphere.

*Phalangiidae extend into the Southern Hemisphere in Africa, and Sclerosomatidae in South America, but in both cases it seems likely that these are more recent invasions from Northern Hemisphere ancestors.

The problem with a Gondwanan origin for the Phalangioidea, however, is that it implies a rather recent derivation for the Northern Hemisphere clade, within the last hundred million years or so, which seems a little out of kilter with the sedate rate of harvestman evolution suggested by the fossil record (most Eocene amber fossils [including Phalangioidea], for instance, can be assigned not only to modern families but even to modern genera). On the other hand, if sclerosomatids were present in the Middle Jurassic of China as suggested by Mesobunus, then that indicates that the modern phalangioid families had diverged before Gondwana had even properly divided from the rest of Pangaea, and some other explanation is required for modern phalangioid distribution.

REFERENCES

Dunlop, J. A. 2007. Paleontology. In Harvestmen: The Biology of Opiliones (R. Pinto-da-Rocha, G. Machado & G. Giribet, eds) pp. 247-265. Harvard University Press: Cambridge (Massachusetts).

Huang, D., P. A. Selden & J. A. Dunlop (in press, 2009). Harvestmen (Arachnida: Opiliones) from the Middle Jurassic of China. Naturwissenschaften.

Taylor, C. K., & G. S. Hunt. 2009. New genus of Megalopsalidinae (Arachnida: Opiliones: Monoscutidae) from north-eastern Australia. Zootaxa 2130: 41-59.

Of Taxonomy and Rabbis

A couple of weeks ago, Mike Keesey brought up a point where, it seems, the ICZN doesn't actually say what everyone has always thought it says. The tone of the ensuing discussion reminds me of a story that a Jewish friend of mine once told me. It concerns a disagreement that the famous rabbi Akiba ben Joseph* once had with a group of other rabbis on a point of law (hush up if you've heard this one before).

*Well, to be honest, I'm not sure if it was actually Akiba that was the subject of the story. It might have been some other influential figure. For the sake of maintaining a narrative, let's just say it was Akiba.

Anywho, the argument had apparently been raging for some time - Akiba holding out for one interpretation, all the other rabbis in the room holding to the other - and had evidently reached something of an impasse. Eventually, frustrated at his failure to get his point across successfully, Akiba exclaimed that if he was in the right, then the tree standing at the door of the synagogue should uproot itself and walk away. Amazingly, this is exactly what happened at that very moment. But the other rabbis were unimpressed by this miracle - after all, they demanded to know, what would a mere tree know of the Holy Law? Akiba then made another oath, that his correctness should be demonstrated by the river running outside the synagogue turning back on itself, and flowing uphill. Again, the river did this very thing (and according to the story, it still does today). But once more the other rabbis only scoffed - what does a river know of the Holy Law?



His frustration at a peak, Akiba appealed to the highest authority he knew of, exclaiming that if he was in the right, G-D himself would speak in his favour. And at the point, the clouds opened, a light shone down from the sky, and a great voice could be heard - "Rabbi Akiba is right!" Hearing this voice, the other rabbis turned to face the heavens, and spoke as one:

"And as for you - stay out of this!"

Saintly Harvestmen (Taxon of the Week: Equitius)

Features of Equitius formidabilis. Basically, a lot of spikes. From Hunt (1985).

The Australian harvestman genus Equitius was first named by the French arachnologist Eugene Simon in 1880. Now there was nothing particularly odd about that - for many years in the late 1800s, Simon was not so much an arachnologist as the arachnologist, achieving a reputation none of his contemporaries could match, and possibly none of his successors either (apparently, the Muséum National d'Histoire Naturelle still has his chair and desk on display). Simon used classical names for many of his genera, and Equitius was such a genus - there are numerous personages in Roman history by the name of Equitius, including an early Catholic saint. In this case, unfortunately, Simon seems to have dropped the ball somewhat in terms of getting the word out, because in 1903, the British researcher Pocock described a very similar species as belonging to a new genus, Monoxyomma. Then the baton was taken up by arachnology's favourite bête noire, Roewer, who in 1915 and 1931 added further genera, distinguished (as usual for Roewer) by the most superficial of features*, to the list. It wasn't until 1985 that the Australian Glenn Hunt combined all these genera into a single one, Equitius, found in southern Queensland and New South Wales.

*Hunt (1985) was later to refer to specimens for which the Roewerian system would have identified oneside as Equitius, and the other as Monoxyomma.

Equitius is a member of the Triaenonychidae, a family of Laniatores or short-legged harvestmen. Laniatores generally tend to be rather spiky, heavily-armoured creatures, but some triaenonychids have a tendency to be particularly baroque, with high spines ornamenting the eyemound and abdomen, and large spiny pedipalps in the males. The greatest diversity of triaenonychids has been described from Australasia (though southern Africa is fast catching up), and in my experience triaenonychids are the easiest harvestmen to find in New Zealand. That is, assuming that you can see them - they can readily be found by lifting logs and stones in moist areas, but the usual triaenonychid response when disturbed is to ball up their legs and freeze, at which point they become very difficult to spot against the background. Even if you do spot them, they still have the defense of the distinctive harvestman odour, which has on at least one occasion nearly (I stress nearly) fooled me into thinking that an individual I'd found was both dead and in a reasonably advanced state of decay.


An individual of a North American triaenonychid species, Fumontana deprehendor. Fumontana is something of a biogeographic enigma - despite its Appalachian distribution, it appears to be more closely related to Southern Hemisphere triaenonychids than to other North American species (which are quite possibly not correctly assigned to Triaenonychidae). Photo from the Marshal Hedin Lab.

One intriguing feature of a number of triaenonychid genera is the occurrence of male dimorphism, with one male form failing to develop the enlarged pedipalps and other secondary sexual characteristics of the other male form. In many similar cases in other animals, such male dimorphism is related to trade-offs between attractiveness to females and overall vitality, but it has not been demonstrated if that is the case with triaenonychids. Glenn Hunt studied the development of effeminate males in Equitius doriae for his PhD thesis, but unfortunately only the abstract was ever published (Hunt, 1981). Hunt found that effeminate males became dormant over winter an instar earlier than normal males, suggesting that dimorphism in this genus may be as much a matter of environmental factors as anything else.

REFERENCES

Hunt, G. S. 1981. Male dimorphism and geographic variation in the genus Equitius Simon (Arachnida, Opiliones). Dissertation Abstracts International B 41: 4375.

Hunt, G. S. 1985. Taxonomy and distribution of Equitius in eastern Australia (Opiliones: Laniatores: Triaenonychidae). Records of the Australian Museum 36: 107-125.

More on Drosophila and Sophophora

Before I start this post, a public service announcement. This month, a group of bloggers have joined together to present an initiative called Silence is the Enemy. The aim of this initiative is to raise awareness about the epidemic of sexual assualt faced by women in war-torn parts of Africa, and also to raise awareness about the issues of sexual assault in general. As part of this campaign, all those websites connected to it will be donating their proceeds from the month of June to Médecins Sans Frontières, which is working as we speak to bring aid and comfort to women affected by sexual assault (as well as bringing aid in countless other ways to people around the world who would otherwise be unable to obtain proper medical treatment). Contributing sites include The Intersection, On Becoming a Domestic and Laboratory Goddess, Bioephemera, Adventures in Ethics and Science, Aetiology, Neurotopia, The Questionable Authority and Drugmonkey. Every time you visit one of those sites in the coming month, you help to raise revenue for an extremely important cause. So visit early, visit often.

Now, on to today's post:

Some of you may remember this post from over a year ago, when the proposal was put before the ICZN to make Drosophila melanogaster the type species of the genus Drosophila. For this post, I'm going to take that other post as read. At the present point in time, the ICZN has not yet voted on that application. But this does not mean that things have been sitting unremarked - quite to the contrary.

As well as publishing applications to the ICZN and their results, the Bulletin of Zoological Nomenclature also publishes comments from the general taxonomic public on cases being considered, allowing other workers to put forward their arguments for whether the commission should accept or deny an application. To be quite honest, this is usually the dullest part of the Bulletin. The majority of applications are fairly straightforward, and it is fairly uncommon for comments to say anything much more extensive than either "sounds good to me!" or "No sir, I don't like it"*. The Drosophila case, however, has inspired a barrage of commentary in the pages of the Bulletin to a level that has probably never been seen there before. The June 2008 issue of the Bulletin included nearly fourteen pages of commentary on the application. Some of these "comments" bordered on being full articles - Prigent (in the June 2008 issue), for instance, filled up three full pages ("no sir, I don't like it"), while McEvey et al. (also June) put their names on two and a half pages ("no sir, I don't like it, but it should probably happen anyway"). [Disclaimer: I haven't yet seen the March 2009 issue of the Bulletin, but apparently it's got even more comments to read.] So what have been the main points raised for and against the proposal?

*This is not to say that the comments are completely pointless - for a start, they're probably the primary means for the commissioners to gauge the popularity or otherwise of an application. Still, the vast majority of them are not particularly likely to become citation classics.

A common complaint has been that supporting the decision would be to support a particular classification or method of classification (or, to put it another way, "Oh noes! They be taking my paraphylum!") As stated by Thompson et al. (June 2008):

The proposal declares that the current concept of Drosophila is 'paraphyletic' and thus 'violates modern systematic practice'. That practice is cladistics or Hennigian systematics. For followers of 'evolutionary' systematics or phenetics, paraphyletic taxa are acceptable. Then there are the issues of the utility of large and small taxa (i.e. lumping vs splitting). We feel strongly that the Commission should not be endorsing one classification paradigm over another.

Some of you may have been struck by the gratuitous conflations of phylogenetic and taxonomic methodologies in the second and third sentences there*, but let's ignore those for now and move on, shall we? It would indeed be a strong violation of the ICZN's principles to judge between paradigms (though I've previously questioned the possibility of a truly paradigm-free nomenclatorial system). In this case, however, the Commission is being asked to do no such thing. Those authors who wished to retain Drosophila melanogaster and D. funebris (the current type species) within a single genus, whether paraphyletic or not, would still be perfectly free to do so - from their perspective, the case is largely irrelevant. Even if an author wised to divide up Drosophila by non-cladistic means, then odds are that they would still end up wanting to place D. melanogaster and D. funebris, because the two species are about as different from each other as any taxa within Drosophila could be - that's why they've been placed in separate subgenera in the first place - and then we'd be facing the exact same question. Indeed, it could be argued (whether validly or not) that the current situation is the one impeding taxonomic freedom, because no-one has been willing to take the step of removing D. melanogaster from Drosophila. So overall, the "no paradigm endorsement" argument is dead in the water from the outset.

*I'm not sure that a phenetically-derived classification really can be said to "permit" paraphyly - it's more that for phenetics, questions of monophyly vs. paraphyly vs. polyphyly become irrelevant.

The second major argument is that changing the type species increases the amount of taxonomic instability rather than decreasing it. Unlike the first argument, this one actually has some legs. As I mentioned in the earlier post, the current subgenus Drosophila is considerably larger than the subgenus Sophophora to which D. melanogaster belongs. Therefore, making D. melanogaster the type species of Drosophila potentially means that more individual species will end up undergoing name changes than if the type species remained D. funebris. Also, while D. melanogaster is the most commonly used Drosophila species in research, it is not the only species used in research. A significant number of other species have also come under the microscope, and some of these other model species (such as D. virilis and D. mojavensis) belong to subgenus Drosophila rather than Sophophora. On the other hand, many more model species (such as D. simulans and D. yakuba) are also members of Sophophora, so changing the type species preserves their names in their current combinations as well.

From a purely taxonomic viewpoint (as many commenters have stated), the answer is a simple one - the current situation is clearly valid under the rules, nomenclatural changes are a perfectly valid part of an developing taxonomic system, there ain't nothing wrong with Sophophora melanogaster, whaddya complaining about? Unfortunately, the reason why this case was proposed in the first place was that such a change does not only affect taxonomists. The case is most elegantly summarised, I think, by McEvey et al.:

The binomen Sophophora melanogaster would continue to convey a precise meaning, and in this sense there would be no confusion. [However] With respect to nomenclatural instability, there may be considerable reluctance to adopt the unfamiliar binomen Sophophora melanogaster and many would, no doubt, continue using Drosophila melanogaster, Drosophila or just melanogaster. And this would be confusing. Information retrieval would be hampered.

Thompson et al. claim that such fears of confusion are overblown, and specifically cite the case of the mosquito Aedes aegypti, widely studied as a major disease vector, which has been renamed and almost universally accepted as Stegomyia aegypti in recent taxonomic revisions. This was perhaps the most comic moment in the affair to date, because as pointed out by van der Linde et al. in the December 2008 Bulletin, Aedes-errr-Stegomyia aegypti provides a very strong argument in favour of the application. Taxonomists have mostly accepted the name Stegomyia aegypti, but almost everyone else working on the beast - ecologists, parasitologists, epidemiologists - has rejected it, and continues to use the name Aedes aegypti. A wide rift has developed between the two sides, making communication between disciplines increasingly difficult. One should never underestimate the holding power a name can have if it somehow catches the public's imagination. After all, we still witness the occasional trotting out of Brontosaurus, a name that was in proper use for less than twenty-five years and was sunk into synonymy more than a hundred years ago.

So ultimately the question is whether preserving the names of a smaller number of economically significant taxa is more important than preserving those of a much larger number of taxa of less direct significance to humans. And I have to admit, I'm glad I'm not one of the people having to make an actual decision on this one.

REFERENCES

Linde, K. van der, G. Bächli, M. J. Toda, W.-X. Zhang, T. Katoh, Y.-G. Hu & G. S. Spicer. 2008. Comment on the proposed conservation of usage of Drosophila Fallén, 1823 (Insecta, Diptera). Bulletin of Zoological Nomenclature 65 (4): 304-307.

McEvey, S. F., M. Schiffer, J.-L. Da Lage, J. R. David, F. Lemeunier, D. Joly, P. Capy & M.-L. Cariou. 2008. Comment on the proposed conservation of usage of Drosophila Fallén, 1823 (Insecta, Diptera). Bulletin of Zoological Nomenclature 65 (2): 147-150.

Prigent, S. R. 2008. Comment on the proposed conservation of usage of Drosophila Fallén, 1823 (Insecta, Diptera). Bulletin of Zoological Nomenclature 65 (2): 137-140.

Thompson, F. C., N. L. Evenhuis, T. Pape & A. C. Pont. 2008. Comment on the proposed conservation of usage of Drosophila Fallén, 1823 (Insecta, Diptera). Bulletin of Zoological Nomenclature 65 (2): 140-141.

Focus on a Fern (Taxon of the Week: Polystichum vestitum)

The New Zealand fern Polystichum vestitum. Photograph by Alan Liefting.

For only the second time, the Taxon of the Week is going to be a single species. But while my earlier attempt at writing a Taxon of the Week post was hampered somewhat by a shortage of information about the species concerned, I'm happy to say that's not so much of a problem this time. And I'm also happy to say that for this post, I'm going home.

Polystichum vestitum (Forst.) Presl 1836, the prickly shield fern, is one of New Zealand's most abundant fern species. It's found in almost every corner of the country, including the Chatham and subantarctic islands, and even reaches as far south as Macquarie Island*. It is, however, restricted to the New Zealand biogeographic region - references in early sources to its presence in South America seem to represent confusion with Polystichum chilense (Looser, 1948). Polystichum vestitum is able to handle a greater deal of direct sun than other forest ferns, and is able to persist in cleared areas (Olsen, 2007). Mature specimens are about a metre in height and have a semi-tree fern growth habit, with a short trunk formed by the upright rhizome. Polystichum species are known as "shield ferns" because the stipes of the leaves are covered with glossy scales.

*Macquarie Island represents a obscure but interesting piece of the Great Trans-Tasman Rivalry. A small, windswept island halfway to Antarctica, almost untroubled by humans since the declines of sealing and whaling removed pretty much every reason why anyone would ever want to go there, Macquarie is biogeographically related to other subantarctic islands belonging to New Zealand, but is itself owned by Australia (in fact, it's technically part of the state of Tasmania, making Tasmania the third-longest Australian state north to south after Western Australian and Queensland). As a result, it's often covered in natural history works (such as bird field guides) for both countries. Despite having no trees, Macquarie Island is also notable for having been home to the world's southern-most parrot species, the parakeet Cyanoramphus erythrotis, until the effects of introduced animals caused their sudden decline and extinction in the late 1800s (according to Taylor, 1979, they survived dogs, they survived cats, but they were eventually undone by the rabbits**).

**The arrival of rabbits meant that the island was able to support higher populations of cats and also-introduced weka than it had previously, increasing the amount of predation by those species on parakeets beyond what the parakeet population could handle.


Another shot of Polystichum vestitum from NZ Plant Pics.

The scales of Polystichum vestitum are quite variable, and some authors have suggested that more than one species might be concealed under this name. Specimens found on the main islands of New Zealand have teardrop-shaped scales with broad bases and smooth edges, and with a glossy dark brown central region surrounded by a light brown margin. In many specimens from the Chatham and subantarctic islands, the scales become much longer, with a long trailing tip to the teardrop, and the dark brown centre disappears to leave an entirely light brown scale. In many Chatham Island specimens, the scales also develop notable marginal projections. However, these divergent morphologies are not universal in the outlying populations - instead, the populations vary from specimens with fully divergent morphologies to ones almost indistinguishable from mainland individuals. Analysis of the variation within Polystichum vestitum by Perrie et al. (2003b) failed to find clear divisions between the variants. When the variants were analysed using AFLP*** data, the fully divergent specimens from the Chatham Islands did cluster together, but with only low support, while the remaining specimens (including less divergent Chatham Island specimens) did not. Perrie et al. therefore recommended against recognising the divergent specimens as a distinct species or variety. However, it is remarkable that the level of variation in the small area of the Chatham Islands should be greater than that seen through mainland New Zealand. Perhaps an early population of P. vestitum became established on the Chathams and was partway into evolving into a new species but a second wave of colonisation from the mainland slowed things down? Multiple colonisations of the Chathams from the mainland have been demonstrated for another fern species, Asplenium hookerianum (Shepherd et al., 2009).

***Amplified Fragment Length Polymorphism - a method of observing variation in the sizes of the fragments that extracted DNA is chopped into by restriction enzymes. AFLP data is arguably a much rougher means of molecular analysis than full sequence comparison, but it has the distinct advantages of being much quicker and having a fraction of the cost, and hence also allowing comparison of a greater number of genes/alleles and individuals than would often be feasible with full sequencing.


The underside of a Polystichum vestitum leaf, showing the bicoloured scales. Photo by Larry Jensen.

In fact, the whole question of fern dispersal is an interesting one - as in, how much of it goes on? Ferns, of course, reproduce by means of spores which, being very small and light, could easily be carried long distances - perhaps even across oceans. It has therefore been suggested that distance has not been a major barrier in fern evolution. Brownsey (2001) suggested that most New Zealand ferns were derived from recent and common dispersals between Australia and New Zealand. In contrast, an AFLP analysis of Polystichum by Perrie et al. (2003a) found that the New Zealand species clustered in a clade, suggesting that they could possibly be derived from a single dispersal event. Interestingly, the closest relatives of the New Zealand clade were species from Lord Howe Island, which is positioned between Australia and New Zealand. Perrie et al. (2003a) also found specimens of another New Zealand species, Polystichum silvaticum, clustered together but were nested within specimens of Polystichum vestitum. This is in contrast to the results of Perrie et al. (2003b), which found a large distance between data from P. vestitum and P. silvaticum (but without data from other Polystichum species to provide a root). P. silvaticum shares the character of bicoloured scales with P. vestitum, but differs from it (and other Polystichum species) in lacking an indusium, a membrane that covers and protects young developing spores. Is it possible that P. silvaticum represents a derivative of P. vestitum?

And as a final aside, let me return to those subantarctic populations of Polystichum vestitum. On the Snares Islands, clumps of P. vestitum are apparently the preferred cover for nests of the Snares Island snipe, Coenocorypha huegeli (Miskelly, 1999). Why, you may ask, do snipes prefer to nest under ferns? As it turns out, birds on the Snares that nest higher up apparently lose a lot of eggs or chicks to petrels. Petrels don't eat the other birds, but they also nest under cover in the area - and petrels are notoriously bad at making landings. Touchdown for a petrel seems to basically involve throwing itself at the ground and hoping that there is enough vegetation to cushion its descent. Any nest in the way of a plummeting petrel is turned into kindling. In this situation, a nice sturdy fern is a ground-nesting birds friend, catching the petrels before they scramble your eggs.

REFERENCES

Brownsey, P. J. 2001. New Zealand's pteridophyte flora — plants of ancient lineage but recent arrival? Brittonia 53 (2): 284-303.

Looser, G. 1948. The ferns of southern Chile (conclusion). American Fern Journal 38 (3): 71-87.

Miskelly, C. M. 1999. Breeding ecology of Snares Island Snipe (Coenocorypha aucklandica huegeli) and Chatham Island Snipe (C. pusilla). Notornis 46: 207-221.

Olsen, S. 2007. Encyclopedia of Garden Ferns. Timber Press.

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