Sunday, 18 December 2016

New Mammal Species 2016

Reticulated giraffes
2016 has, on the whole, been a bit of a rubbish year. Or so the common wisdom has it; one suspects that, for instance, the deaths of some particularly prominent celebrities at the beginning of the year has heightened our perception of those that died later on (relative to any other given year). And it's probably been quite a good year for you if happen to be a Trump supporter, or a fan of Nigel Farage.

But that debate doesn't belong here, instead, as the year draws to a close, it's time to take a survey of the species of mammal that have been newly discovered this year. Or, more accurately, newly named, since what we generally do these days is find some population of a previously known species that turns out not to belong to it, and to be something else instead. There have, as always, been a fair number of them this year, and there's no guarantee that they'll all stand the test of time, and still be considered valid species in, say, 2026.

My survey is, therefore, inevitably biased, with a just a semi-random sample of some of the species announcements I happen to have come across. Most of them are going to be small animals, since they're easier to overlook in the first place, but there are a couple of quite large ones. And, by "large", I don't mean just "wolf-sized", either.

Oh, and in keeping with the general tone of 2016, I'll also be mentioning a few species that didn't make the cut, by being demoted or banished to taxonomic oblivion. Because there are some species that we knew about this time last year that actually don't exist. Species, like celebrities, don't live forever...

A Plethora of Rodents

Apart from bats, rodents offer one of the best fields for the discovery of new mammalian species. There are a huge number of them already, and, especially when it comes to the more mouse-like rodents, a lot of them look extremely similar to one another. There are, in fact, depending on how mouse-like you want to get, at least two families of rodent that can reasonably be described as "mice". The actual mouse family itself (Muridae) is the one that includes things like house mice and brown rats, and is the largest of all mammalian families, with over 700 species. The second, which, from its Latin name, is technically the "hamster family" (Cricetidae), also includes, not only voles, but a large number of American species that look, to all intents and purposes, exactly like the "real" mice of the Old World.

With around 600 species, this second family is nearly as large as the mouse family proper, and we have added a number of new species to it this year. Perhaps the best known of these mice, at least to Americans, are the deer-mice (Peromyscus spp.), which are found through across both northern and southern continents in great numbers. There are a lot of species of deer-mice, many of them restricted to quite small areas. One such is the Chiapan deer-mouse (P. zarhynchus), usually said to live only in the state of Chiapas, in southern Mexico. But there had for a while been unconfirmed reports that they also lived across the border in Guatemala. A recent review of the evidence for these Guatemalan specimens revealed that, while they were undeniably real, they actually weren't the Chiapan species at all, but were different enough to be listed as a new species, named Gardner's deer-mouse (P. gardneri) in honour of a local expert on the subject.

According to the study, the DNA of Gardner's deer mouse differs from that of the previously known Chiapan species by about 4%. Which, you will note, is higher than that usually quoted for the difference between humans and chimpanzees - although a lot, of course, depends on exactly how you measure it, and the two figures aren't entirely comparable. At any rate, many other species of rodent named this year have rather larger differences from those they were previously included with.

Back in 2001, the white-throated woodrat (Neotoma albigula) was split into two species, with the new one being named the "white-toothed woodrat" (N. leucodon) . The two species, the existence of which have been confirmed by more recent studies, live in the southwestern US and northwestern Mexico, and are broadly separated by the Rio Grande. However, the exact boundary between the two in Mexico was unclear, so a new study aimed to find which of the two it was that lived in the general area of the states of Sonora and Chihuahua. It turned out that, while the animals there were clearly closer to the white-throated species, they differed genetically by over 7%, which is about the same sort of difference seen between other woodrats that are already regarded as separate species. Minor physical differences, such as a slightly darker fur colour, had been enough to recognise these animals as a subspecies, but the genetic data was enough, at least in the opinion of the authors to promote this to a full species as the black-tailed woodrat (N. melanura).

Similar genetic work during a survey of bolo mice in Argentina discovered some specimens that differed by as much as 11% from every known species - quite a bit more than any of the known species differed from each other. Examining them more closely also found notable physical differences, and they were announced as Lillo's bolo mouse (Necromys lilloi) this year, in honour of an Argentinian naturalist and collector from the early 20th century. An even larger genetic difference allowed the identification of a sort of tree-climbing mouse in the Atlantic Forest of south-eastern Brazil, which turns out not to even have the same number of chromosomes as its previously known relative, the lesser Wilfred's mouse, and so presumably would have significant difficulty breeding with it, even if it wanted to. This is now named the Aracuaria Forest tree mouse (Juliomys ximenezi).

While genetic data is useful, it's by no means the only way of identifying new species. The exact shape of the skull and teeth are often important, especially with fossil species, and can help to clarify the physical differences between new species once you've found them by other methods. Another method used this year, however, was closely examining the shape of the penis. This could be significant, since there's a fair chance that females won't want to mate with males with funny-shaped penises, explaining how the two species remain separate once they have evolved. In 2016, admittedly together with genetic data, this method was used to identify two new species of birch mice (Sicista spp.) in eastern Europe, raising them from subspecific status. The same study, however, also demoted Severtzov's birch mouse (S. severtzovi) from the Ukraine and Russia back down to a mere subspecies of the southern birch mouse (S. subtilis).

But there was also at least one rodent discovered this year that really was new, and not previously classified as something else.

In my year-end post for 2014, I mentioned the discovery of a carnivorous rat from Sulawesi in Indonesia that was not very closely related to anything previously known. Carnivorous (or, more precisely, insectivorous) rodents are a rare thing. Rodents are ideally suited to gnawing, and that generally means that they eat plant matter. The newly identified species turns out to be the closest known relative of the one discovered in 2014. However, it's still not very close, and one of the differences is that it's really an omnivore, since a fair proportion of its stomach contents turned out to be plant roots. Since all of its other relatives only eat flesh, it presumably evolved back to a more omnivorous state from a carnivorous ancestor. Together with a number of significant physical differences, that's enough to consider it, not just a new species, but an entirely new genus, giving it the name Gracilimus radix.

Things That Aren't Rodents

Not every new mammal that has been discovered this year is a rodent. In the realm of "looks a bit like a rodent at first glance but actually isn't" we do have some new shrews. Two of these, Crocidura yaldeni and C. afeworkbekelei, belong to the already massive genus of the white-toothed shrews, and are found only in Ethiopia. A third was found in the Venezuelan Andes; a close relative of the Merida small-eared shrew (Cryptotis meridensis) that lives elsewhere in the mountain range, it was distinguished largely on the basis of having teeth with a notably different shape.

Rather more dramatic, though, is the case of the monito del monte. This is a rather strange animal, which I have previously posted about. It's a marsupial, native to South America, yet not closely related to any of the South American opossums. Instead, it's related to Australian marsupials, and quite what it's doing in South America is unclear - it's either a survivor of the early marsupials that headed to the other continent, but somehow got left behind, or it's actually headed back from Australia after originally having evolved there.

At any rate, it's been known since 2008 that there is a large genetic diversity within the species, which can be divided into three genetic groups, spaced roughly north to south through central Chile and neighbouring parts of Argentina. While the 2008 study stopped short of naming these groups as even subspecies, a new analysis concludes, on the basis of clear physical and genetic differences, that all three should be regarded as separate species. The original is the most southerly of the three, and perhaps surprisingly, also lives on a large island off the Chilean coast (one might expect that, if any population would diverge from the others, it would be the one on the island... but apparently not). The two new species are named as Pancho's monito del monte (Dromiciops boziniovici) and Mondaca's monito del monte (D. mondaca).

But, as I noted at the beginning, it isn't all new species. If genetic studies can show that, say, a 7% difference between two groups of animals is enough to warrant them being described as different species, then the opposite can also occur. That happened this year to the San Jose brush rabbit, a critically endangered animal found on only one small desert island off the coast of Baja California in Mexico. A new analysis showed that, while they were distinct, the rabbits on the island differed genetically from their mainland kin by only 1.3%, about as much as those rabbits differ from each other across their range. Accordingly, it has been proposed that the island animals be demoted to a subspecies of the western brush rabbit (Sylvilagus bachmani), a very common animal across the western coasts of both Mexico and the US. They consequently lose their "endangered species" status, on the grounds of not being a species, although, of course, that doesn't absolutely prevent efforts to conserve the few that still survive.

Another species that bit the dust was the Singapore whiskered bat (Myotis oreias). Very little was known about this bat, which supposedly only lived on Singapore, an almost implausibly small locality for something that can fly. The reason so little was known was that only example of the animal had ever been seen, and that was in 1840. The specimen in question had been preserved, and was the only reason we ever considered the animal a species in the first place, with the general consensus being that, Singapore not exactly being a remote wilderness, it must surely have gone extinct in the meantime.

Well, now the specimen that defines the species has been re-examined. The conclusion was that the specimen was actually bits of two different animals kept together, and that not enough remained of either to identify exactly what sort of bat they had originally come from. The most likely explanation is that it never existed in the first place, and the specimen only looked unique because, Piltdown Man-style, it consisted of two different things that didn't belong together.

But, on the plus side, if it didn't exist, it can't be extinct...

Absolutely, Definitely, Not Rodents

Undoubtedly the biggest "new species" story of the year, and one that I suspect few regaulr readers of this blog will have missed, was the discovery of new kinds of giraffe. Giraffes are, of course, amongst the very largest land animals that there are - especially if you consider height more important than weight. And they aren't exactly obscure, so you might well think that we'd know them quite thoroughly. So how exactly, did we miss this one until now?

Well, the reality is that we didn't. There has been debate over how many species of giraffe there really are for quite some time, and those who follow this sort of thing were well aware of it. (It had, for example, been mentioned back in 2006 in the blog Tetrapod Zoology, which I'm confident gets a lot more readers than this one does). Nonetheless, the consensus had been that there was only one living species, Giraffa camelopardalis, first named in 1758 in the first ever catalogue of what we'd now consider to be scientific animal names. If you'd asked me, I'd probably have said that that would have been my guess, too. Giraffes are pretty variable in physical appearance and coat colour, and they all seem able to breed with one another,so I'd likely have settled with the "they're just subspecies" consensus.

The study that changed all of this didn't look directly at the genetic difference between the various subspecies. In fact, that was already known to be quite low, and part of the reason why the "one species" hypothesis had stuck since the early 20th century, when numerous previously identified species were agreed to all really be the same thing. The study instead used a series of analyses to estimate that, while they can interbreed if they have to, some populations of giraffe had not done so to any noticeable extent for well over a million years. Their DNA - in particular, the mitochondrial DNA that is passed down only from mother to offspring - was distinct and unmixed, and presented a clear pattern of different kinds of giraffe living in different parts of Africa. Over a million years of separation, the authors argued, was surely enough, and there now seems to be at least a reasonable amount of agreement that that's right.

Now, we had known of nine giraffe subspecies, and by no means all of them were promoted as a result of this study. Indeed, two of the subspecies were scrapped altogether, showing that this wasn't just an exercise in "upgrading" populations to a higher status. The end result, though, is that we can now identify four species of giraffe - which is actually one more than most of those proposing multiple species would have guessed.

Firstly, we have the northern giraffe, which, since it appears to be the one that Linnaeus was referring to back in 1758, is the "original" species, and gets to keep the existing name. It has three subspecies, and is found in a patchy band of territory just south of the Sahara. At the opposite end of the continent, from Nambia to Mozambique and South Africa, is the southern giraffe (G. giraffa), which has two subspecies.

Over in Kenya, we have the reticulated giraffe (G. reticulata), so named because of the net-like pattern of fine lines between the blotches on its coat. Those who had argued for three species had thought that at least all the giraffes in Kenya had to be one species, but the new study showed that those in the south, and down into Tanzania and Zambia, were a fourth species, the Masai giraffe (G. tippelskirchi), distinguished by a much more jagged shape to the coloured blotches.

Funnily enough, though, the giraffe was not the largest species of mammal to be divided this way in 2016. Big though giraffes undeniably are, they are not quite as big as giant beaked whales (Berardius spp.) There are two species of this animal, both about twice as long as a giraffe is high, and weighing over ten times as much as a giraffe does. One lives only in the Antarctic Ocean, and the other only in the North Pacific, so they don't exactly mix much.

Yet there had long been reports that the northern species, Baird's beaked whale (B. bairdii) existed in two different forms, one grey, and one black. Of itself, that might not mean anything; all sorts of animals exist in more than one colour form, often within the same litter. But a genetic analysis comparing the two types showed that the difference was more than skin-deep, and that the black form was, if anything, less closely related to the grey one than it was to Arnoux's beaked whale down in the Antarctic.

This new species has not, as yet, been given a name, but it's surely standing in line in the queue.

Synapsida will return in the New Year. Merry Christmas!

[Photo credited to "a relative of Brandt Luke Zorn", from Wikimedia Commons.]

No comments:

Post a Comment