Like, Wow. Just... Wow.

This is something I saw this morning at Small Things Considered, that I though was just so spectacularly brilliant that I just had to copy it:



One hundred and sixty-seven species of ciliate, artfully arranged and all drawn to scale, from the gigantic Stentor to the sinuous Homalozoon to the infinitesimal Cinetochilum. The image comes from here, where not only can you see it in its full glory, but you'll find the key to the numbering that tells you what each one of these marvels is. The species are partially arranged in line with their chosen habitats - those towards the top left are found in the open water column in lakes, those around the centre of the bottom are anaerobes, while the others make their homes among sediment. And there's even little extra bits of detail hidden within - see if you can find the Chilodonella crawling along the Epistylis stalk, for instance. Enjoy!

Then if you're in the mood for more details on ciliates, including comments on their mind-blowingly complicated genetic system, take a look at my earlier posts here and here. And if anyone is feeling really generous and wants to get this printed out as a wall poster for me...

More Things in Heaven and Ocean

Following on from the post just put up on xenophyophores, I couldn't pass on without mentioning these fellows:



This is Haeckel's (1889) plate of members of the Ammoclathrinidae, taken from here. Haeckel described members of this family* among his "Deep-Sea Keratosa", the other examples of which have since been identified as xenophyophores (and not, as Haeckel thought they were, sponges). Like xenophyophores, ammoclathrinids had coverings constructed from foreign objects, and when I wrote the page on xenophyophores for Palaeos.com, I interpreted ammoclathrinids as being xenophyophores. True, Haeckel had originally identified separate cells inside his ammoclathrinids, but I suggested that this could have been an artefact caused by his use of acid to prepare the specimens, and they might have originally been coenocytic. However, when I wrote that I was working from Tendal's (1972) recounting of Haeckel's work, and hadn't seen the original description. Looking at it now, I have to admit that the illustrations in Haeckel's plate look very different from xenophyophores.

*Which he called Ammoconidae, but this name was changed by Tendal (1972) for reasons of preoccupation.

Unfortunately, Haeckel's original material no longer exists (it seems likely that he pulled it apart in the process of describing it), and no-one has ever laid eyes on a recognisable ammoclathrinid since. The nature of these organisms, therefore, is a complete mystery. Such a situation is more common than you may think, particularly in microbiology. The protistological literature is littered with examples of organisms seen and described by someone looking down a microscope in the 1800s, and never recorded since. It might be tempting to wonder whether the original describer ever really saw what they thought they saw at all, but that may be ignoring one of the major issues in microbiology itself - the world is very, very large, and the things being looked for a very, very small. If comparatively large mammal species can elude attention for numbers of years, how much more so can tiny micro-organisms? Or something like Ammoclathrinidae, lurking somewhere in the little-explored deep sea?

REFERENCES

Haeckel E. 1889. Report on the Deep-Sea Keratosa. Report on the Scientific Results of the Voyage of H. M. S. Challenger during the years 1873–76. Zoology 32 (part 82): 1–92.

Tendal, O. S. 1972. A monograph of the Xenophyophoria (Rhizopodea, Protozoa). Galathea Report 12: 7-99.

Living with Poo - A New Xenophyophore

Scattered individuals of the xenophyophore Reticulammina labyrinthica. Image from Ocean Planet.

And if you don't know what a xenophyophore is, then shame on you! Xenophyophores are sessile deep-sea protists that often reach comparatively gigantic sizes. One species, Stannophyllum venosum (which looks something like half a plate sitting on its edge), can be nearly a foot across (Tendal, 1972). Images from deep-sea submersibles have shown that xenos can be spectacularly abundant, carpeting the ocean floor in some places.

Xenophyophores are sometimes referred to as the largest unicellular organisms, but as I've mentioned before, that's arguably not entirely appropriate. Rather, xenophyophores have a coenocytic or hyphal organisation, with numerous nuclei scattered throughout long branching cytoplasmic tubes. The name "xenophyophore" means "bearer of foreign objects", and refers to the external test of the organism, which it constructs by cementing together objects it collects from the sediment around it - sand grains , for instance, or shells of other organisms - using a polysaccharide cement. The xenos also sequester their faecal pellets, which they may also integrate into their skeleton. Different species of xeno can be distinguished by the nature and arrangement of the foreign particles in the test (they are often quite picky about what they use), and the proportion of foreign particles to cement or faecal pellets. The species Cerelasma massa, for instance, differs from other xenos in using no foreign particles whatsoever, but only cement and its own faecal pellets - hence also being a contender for the title of most disgusting organism in existence. Species that use a high proportion of foreign particles in their construction are generally quite rigid, while those using more cement are softer.


The new xenophyophore species Shinkaiya lindsayi. In the long section, the central white strands are the xenophyophore's cytoplasm, while the black strands are strings of faecal pellets. Figure from Lecroq et al. (2009).

Yesterday saw the publication of a new xenophyophore species, Shinkaiya lindsayi (the genus is named, offhand, after the submersible that was used to collect the type specimen) by Lecroq et al. (2009). One of the most significant features of the new paper is that it includes a molecular phylogenetic analysis of the new species. Xenophyophores have been sequenced on one occasion before, by Pawlowski et al. (2003), who placed the species Syringammina corbicula among basal Foraminifera. It is good to see that Lecroq et al. place Shinkaiya as the sister to Syringammina, and the two together fit in the same position among forams originally found by Pawlowski et al.. The closest relative to xenophyophores identified is a foram called Rhizammina, which is also sessile, constructs a test of foreign matter, and even sequesters faecal pellets in a similar manner to xenophyophores.

This is a noteworthy achievement - these are not easy organisms to sequence. Not only is there a shortage of accessible material, but xenos and forams both tend to have large numbers of bacteria and other micro-organisms living around them, just aching to contaminate DNA samples (the very first molecular phylogenetic analysis of a foram, for instance, suggested a close relationship between forams and dinoflagelates, only to have it later shown that the sequence analysed belonged not to the foram but to parasitic micro-organisms living in the foram*). So the fact that Lecroq et al.'s results are not only well-supported, but make a lot of intuitive sense morphologically, makes this a very nice study indeed.

*Still, if the recently suggested SAR clade is correct, there is a certain irony to this - forams may be somewhat related to dinoflagellates after all.


Haeckel's (1889) illustrations of species of Stannophyllum, including the gigantic S. venosum at the bottom. Stannophyllum belongs to a family of xenophyophores called stannomids that differ from other xenos such as Shinkaiya (called psammetids) in having reinforcing threads (probably made of mucopolysaccharides) running through their tests. Stannomids are more plate-like, upright and flexible than the lumpy psammetids. Image via here (Haeckel referred to xenophyophores as "Deep-Sea Keratosa", as he was under the impression that they were sponges).

REFERENCES

Haeckel E. 1889. Report on the Deep-Sea Keratosa. Report on the Scientific Results of the Voyage of H. M. S. Challenger during the years 1873–76. Zoology 32 (part 82): 1–92.

Lecroq, B., A. J. Gooday, M. Tsuchiya & J. Pawlowski. 2009. A new genus of xenophyophores (Foraminifera) from Japan Trench: morphological description, molecular phylogeny and elemental analysis. Zoological Journal of the Linnean Society 156: 455-464.

Pawlowski, J., M. Holzmann, J. Fahrni & S. L. Richardson. 2003. Small subunit ribosomal DNA suggests that the xenophyophorean Syringammina corbicula is a foraminiferan. Journal of Eukaryotic Microbiology 50: 483-487.

Tendal, O. S. 1972. A monograph of the Xenophyophoria (Rhizopodea, Protozoa). Galathea Report 12: 7-99.

Southern Moss (Taxon of the Week: Ptychomitrium muelleri)

There don't seem to be any images of Ptychomitrium muelleri available online, so here's another Ptychomitrium species, P. gardneri from China. Photo by Li Zhang.

Mosses are often treated as the poor relation in plant diversity. Popular presentations of plant evolution often tend to have even more of a Scala Natura-esque slant to them than presentations of animal evolution, and so mosses and other non-vascular plants get glossed over as mere stepping stones to their more upright "descendants", if they even warrant a mention at all. This is, of course, complete rubbish - mosses have a very respectable diversity of species (about 10,000, according to Tree of Life). I've met a few moss researchers over the years, and a more devoted following a taxon could not hope for.

Ptychomitrium muelleri is a haplolepidous moss of the family Ptychomitriaceae (I'll explain what that means in a minute). It grows to a maximum height of one and a half centimetres, and if the type specimens are any indication, prefers to grow on rocks. Ptychomitrium mosses seem to be found more or less worldwide, but Ptychomitrium muelleri itself is found in south-eastern Australia, New Caledonia, southern South America and southernmost Africa. What is interesting about this species' distriution is that it was thought to be endemic to Australia until very recently when Cao et al. (2001) established that species described from each of the other localities were conspecific with P. muelleri. As a result, P. muelleri has what might be described as a classic "Gondwanan" distribution, but I rather doubt that Gondwana had anything to do with it. After all, moss spores are very light and extremely easily dispersed, and surely it is no coincidence that all the localities where P. muelleri can be found lie roughly along the same wind belt.



The diagram of a moss life cycle above has been stole from Palaeos.com. For the nonce, the important details are these - mosses, like other plants, are multicellular at both the haploid and diploid stages of the life cycle, but unlike vascular plants, the larger, dominant stage of the life cycle is the haploid gametophyte. When a female gametophyte is fertilised, the diploid sporophyte remains attached to the gametophyte and grows a spore-filled capsule that eventually breaks open (after the loss of the protective calyptra) to release the spores. Around the mouth of the capsule is a ring of "teeth", the peristome. In basal mosses, the peristome is made up of entire cells, but in the class Bryopsida, the arthrodontous mosses (which includes the larger part of the mosses), the teeth are reduced to cell wall remnants. Most of the bryopsid lineages have two rows of teeth in the peristome, an outer and an inner, but Ptychomitrium belongs to a group called the Haplolepideae or Dicranidae which have only the inner row of teeth. The haplolepidous mosses form a monophyletic clade within the Bryopsida.


Ptychomitrium polyphyllum from Scotland, showing the calyptra on the left capsule and the exposed peristome on the right. Photo from here.

Most of the features separating moss taxa are microscopic and relate to such things as cell arrangement (which is my weaselly method of saying that I don't understand a word of them), but Ptychomitrium is distinguished by having a mitrate calyptra (and those unsure what "mitrate" means might want to look at the Taxon of the Week post of two weeks ago) with characteristic lobes around the lower edge (Hernández-Maqueda et al., 2008, compare it to a Hawaiian skirt). Ptychomitrium muelleri has (amongst other features) lingulate (tongue-shaped, I'm guessing) leaves with smooth margins, and ovoid capsules.

REFERENCES

Cao, T., S. Guo & Y. Zhang. 2001. Distribution of Ptychomitrium muelleri (Bryopsida), with its synonyms. The Bryologist 104 (4): 522-526.

Hernández-Maqueda, R., D. Quandt, O. Werner & J. Muñoz. 2008. Phylogeny and classification of the Grimmiaceae/Ptychomitriaceae complex (Bryophyta) inferred from cpDNA. Molecular Phylogenetics and Evolution 46 (3): 863-877.

Knocked Off the Perch (Taxon of the Week: Percidae)

The rainbow darter, Etheostoma caeruleum, a representative of the North American radiation of small and often colourful freshwater fish known as darters. This species breeds on fast gravel riffles, where pairs mate with the female half buried in the gravel so the eggs are automatically covered over (Reeves, 1907). Photo by Jim McCormac.

Okay, this post has been delayed again. It's been an unusual week, is all I can say. I'd tell you all about, but I have very good reasons to believe that that would be extremely dull.

In earlier posts, I have ranted in a rather esoteric manner about my distaste with the commonly recognised fish order "Perciformes", really a random multi-paraphyletic assemblage of the more generalised members of the clade Percomorpha. In the recent partial reclassification of the Percomorpha by Li et al. (2009), the name "Perciformes" was ditched entirely, and the clade containing the family Percidae was instead called Serraniformes (suggesting, offhand, that some sort of taxonomic karma is dooming this taxon to be associated with confusing names - the family Serranidae as commonly recognised itself seems likely to be polyphyletic, and a number of "serranids" are not guaranteed Serraniformes). But even before the Perciformes of common use were recognised as a wastebasket assemblage (if, indeed, there ever really was such a time), Percidae was always a slightly odd choice for the type family. The Percidae, the perches and darters, are not particularly average Perciformes.

Among the percomorphs, percids are unusual for one main reason - they're almost entirely freshwater (a few European species stray into brackish waters, but only one species - Sander marinus, the estuarine perch of the Black and Caspian Seas - is a permanent resident in them). While the percomorphs have achieved true world dominance in the upper parts of the ocean, including the vast majority of coastal and surface-pelagic fish species, they have never made such significant inroads into fresh water. A few percomorph lineages have been very successful in fresh water, such as the Cichlidae, the Anabantiformes and various members of the Smegmamorpha*. But in contrast to their surface-marine monopoly, percomorphs have to share dominance of the fresh-water environment with members of the clade Otophysi - Cypriniformes, Characiformes and Siluriformes.

*No, honestly, it's a real name.


The zander, Sander lucioperca, a much larger Eurasian percid. Photo from EoL.

The Serraniformes also include the Trachinidae (weevers), the circum-Antarctic notothenioids and the majority of what were the Scorpaeniformes. Relationships within the Serraniformes are yet to be hammered out, but the Percidae probably divide from the others reasonably basally. Ten genera of living Percidae are currently recognised, with more than two hundred species. Phylogenetic analysis of the family by Sloss et al. (2004) recognised three main clades of unresolved relationships - the Holarctic genus Perca, the mostly Eurasian clade of Gymnocephalus plus Luciopercinae (genera Romanichthys, Sander and Zingel, with three species of Sander in North America), and the North American clade of Etheostomatinae (Ammocrypta, Crystallaria, Etheostoma and Percina). [The tenth genus includes the single uncommon species Percarina demidoffi of rivers running into the Black Sea, and was not analysed by Sloss et al. due to lack of material. Percarina was previously classified in the possibly non-monophyletic Percinae* with Perca and Gymnocephalus and differs from most other Percinae in spawning in brackish waters, so establishing its relationships would be very interesting.] While the greater phylogenetic disparity of Percidae is concentrated in the western Palaearctic and the family is believed to have originated in that area, the greater diversity of species is definitely found in North America. Well over two-thirds of percid species belong to the Etheostomatinae, with the greater part of those in the genus Etheostoma (which, however, may not be monophyletic).

*Though the non-monophyly of Percinae found by Sloss et al. is in contrast to their breeding behaviour - Percinae differ from other percids in laying their eggs encased in long gelatinous strands, while Luciopercinae and (ancestrally) Etheostomatinae are broadcast spawners.


The European perch, Perca fluviatilis. A very similar species, Perca flavescens, is found in North America. Photo from here.

Human interest in the Percidae (as with most matters, really) has usually been related to one of two things - eating or sex. The larger percids of the "Percinae" and Luciopercinae are widely caught for food, and the European perch Perca fluviatilis has been introduced to many localities outside its native range such as New Zealand for the amusement of anglers. Some percids, such as the walleye Sander vitreus, have been recorded reaching lengths of over a metre (though such sizes are, of course, exceptional - a more average walleye would be about twenty centimetres). Species of the Etheostomatinae, known as darters, are not targets of fishing - members of this subfamily (as well as some species of Luciopercinae) are smaller than other percids, less than ten centimetres in length*, and wouldn't offer much in the way of eating. Still, darters more than make up their interest in the other regard of sex. They show a wide diversity of breeding behaviour, from broadcast spawners to some that bury their eggs in sediment or gravel to species that lay their eggs safely hidden on the underside of rocks. Other species may glue their eggs to vegetation (Winn, 1958a, b). During the breeding season, most (but not all) darters move from deeper to shallower waters (many species favour riffle areas) where the males usually establish a breeding territory (as reported by Winn, 1958b, the presence of other males seems to be required to incite the successful establishment of a territory - solitary males tended to lose interest in a potential territory and wander off). Some darter species are fairly relaxed about their territories and only fend off males of their own species, but other darters may be decidedly pugnacious and attack just about anything that moves. Challenging males approach each other with fins held high, and their colours will often become brighter. They may circle each other and butt or bite at each other's tail regions. After a male has mated with a female and she has laid her eggs, he may or may not remain in the area to guard them. Experiments have shown that if the eggs are removed or replaced, the male continues to guard the same spot, so it is the territory that induces guarding behaviour rather than the presence of eggs. Hybrids have been recorded between a number of darter species and seem to be not uncommon, especially where species have been spread outside their native range (Stauffer et al., 1995).

*As a corollary of their smaller size, it is worth noting that darters (and the smaller Luciopercinae) also lack swim bladders.


Percarina demidoffi as illustrated by N. Kondakov in a 1957 Russian textbook. For some reason, I find a certain whimsy in this illustration of what is perhaps one of the more mysterious percids. Image via NOAA Photo Library.

REFERENCES

Reeves, C. D. 1907. The breeding habits of the rainbow darter (Etheostoma cœruleum Storer), a study in sexual selection. Biological Bulletin 14 (1): 35-59.

Sloss, B. L., N. Billington & B. M. Burr. 2004. A molecular phylogeny of the Percidae (Teleostei, Perciformes) based on mitochondrial DNA sequence. Molecular Phylogenetics and Evolution 32 (2): 545-562.

Stauffer, J. R., Jr, J. M. Boltz & L. R. White. 1995. The fishes of West Virginia. Proceedings of the Academy of Natural Sciences of Philadelphia 146: 1-389.

Winn, H. E. 1958a. Observation on the reproductive babits of darters (Pisces-Percidae). American Midland Naturalist 59 (1): 190-212.

Winn, H. E. 1958b. Comparative reproductive behavior and ecology of fourteen species of darters (Pisces-
Percidae). Ecological Monographs 28 (2): 155-191.

(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.