08. How many Elephants?
If you've read my very first entry, you may recall that I have a childhood fondness for elephants. I recently discovered the website Zooniverse, a crowdfunded citizen science site which features Elephant Expedition, featuring identifying animals from photos taken from hidden motion-activated cameras. Elephant Expedition, unsurprisingly, is focused primarily on elephants. So I spent the past week in my spare time scouring for those lovely beasts. There are a number of other projects on Zooniverse, so for those heathens among you who don't care for elephants can help scientists in other fun projects.
Today I was reading a little bit about Mendel and the experiments he carried out, and it lead me through the wiki wormhole to a page about microspecies (or cryptic species), species that are visually indistinguishable and frequently considered one species until genomic comparisons. And this suddenly lead me to a photo of an elephant. An African forest elephant, to be precise. Well wait, I know there are two kinds (oh boy, the word "kinds" could get me in trouble) of elephants, African and Asian, what is an African forest elephant?
Well, it's a rather interesting question. You see, there are actually three species of extant elephants; two elephants in the genus Loxodonta, and one in Elephas. The former contains our two types of African elephants, L. africana and L. cyclotis, the savanna and forest elephants; the latter contains the Asian elephant. Recent genetic and morphological evidence indicates that africana and cyclotis are in fact distinct species (more classically cyclotis was considered a subspecies of africana). L. africana are in many ways the classic African elephant, forming large matriarchal groups, with bachelor herds separate outside of mating, musthing and rampaging and bellowing.
Now, what becomes more and more interesting is that this distinction isn't new. It's not even close to recent. Rohland et al. (2010)'s paper did a wonderful nuclear DNA comparison between the three extant species, along with mammoths, and mastodons as an outgroup. What is really fascinating is that at the genetic level, the two species of Loxodonta are as divergent from one another as Elephas is from Mammuthus, which, it goes without saying, are considered entirely different genera! Examining historic ranges, what we really see is that our African elephant species have been fairly geographically isolated from one another for large spans of time, and only recently have they had much overlap at all in location. With ice ages, glaciation, and all the fun of time since the pleistocene, there's been lots of fascinating habitat fragmentation separating groups of L. cyclotis for spans of time, allowing for preservation of individual genetic lines before recombining after the thaws.
We see similar sorts of cryptospecies in other places, conveniently enough, in Africa. A recent genetic study revealed that giraffes (you know, giraffes?) are actually four distinct species instead of the one (you know, giraffes?) (Fennessy et al., 2016). And just as interesting, a combination of genetic work and references to classic historical anecdotal records indicates that the Nile crocodile (you know, Egypt?) is also multiple species, notably a species Crocodylus suchus which is especially notable because while physically nearly identical to the more commonly seen Nile crocodile, they're incredibly docile, and historically were kept as house animals and were swum among in rivers and ponds (Hekkala et al., 2011). A cursory search will reveal far more detailed discussions of either in such places as National Geographic (before the dark times).
Where this becomes particularly interesting and concerning, in all three cases, is what this means for the conservation efforts for all of these species. Suddenly, any conservation effort for the African elephant has to determine which species they're actually serving, and once that's done, is one of the species being left in the lurch? The same is true for giraffes, which have essentially fragmented into four distinct populations for the conservationists, and now watching out for one group of giraffes means you may be ignoring the other three. C. suchus is already in a rough spot, with much of its distribution now extirpated (what a fun, sad, word). So while it's certainly a good thing we're beginning to unveil these long extant microspecies, it's unfortunate as it makes the task of conservation all the more difficult.
Fennessy, J., Bidon, T., Reuss, F., Kumar, V., Elkan, P., Nilsson, M. A., … Janke, A. (2016). Multi-locus Analyses Reveal Four Giraffe Species Instead of One. Current Biology, 26(18), 2543–2549.
Hekkala, E., Shirley, M. H., Amato, G., Austin, J. D., Charter, S., Thorbjarnarson, J., … Blum, M. J. (2011). An ancient icon reveals new mysteries: Mummy DNA resurrects a cryptic species within the Nile crocodile. Molecular Ecology, 20(20), 4199–4215.
Roca, A. L., Georgiadis, N., Pecon-Slattery, J., & O’Brien, S. O. (2001). Genetic Evidence for Two Species of Elephant in Africa. Science, 293(5534), 1473–1477.
Rohland, N., Reich, D., Mallick, S., Meyer, M., Green, R. E., Georgiadis, N. J., … Hofreiter, M. (2010). Genomic DNA sequences from mastodon and woolly mammoth reveal deep speciation of forest and savanna elephants. PLoS Biology, 8(12).