Is there any kid who does not love giraffes? They are just so amazing: tall, leggy, fast and graceful, with prehensile tongues and a need to go through complex calistehnics in order to drink. The favourites at zoos, in natural history museums and on TV nature shows.
Giraffes were also important players in the history of evolutionary thought and I bet you have all seen, and heard the criticisms of, the iconic comparison between Lamarck’s and Darwin’s notions of evolution using a comic strip featuring giraffes and how they got their long necks.
Giraffes sleep very little and mostly standing on their feet. They give birth while standing, with no apparent ill consequences to the newborn which, after falling from such a great height, gets up on its feet and is ready to walk and run with the herd within minutes.
Like almost any other mammalian species, a giraffe can sometimes be born albino, but in this case only the yellow background is white, while the brown splotches remain (similar to the “tuxedo” mutation in quail) suggesting that just one of the multiple “color” genes is malfunctioning.
The behavioral (sexual selection) hypothesis that the length of the giraffes’ necks has something to do with male-male fighting, co-called “necking”, is apparently going out of favor, while more ecological hypotheses are gaining in acceptance (again – this appears to be cyclical).
But, one thing that you think when you think of giraffes is the giraffe, i.e., one thing, one species. There have been inklings recently that this thinking may change, finally culminating in a very interesting paper published yesterday in Journal of Biology (free pdf of the paper is available):
A central question in the evolutionary diversification of large, widespread, mobile mammals is how substantial differentiation can arise, particularly in the absence of topographic or habitat barriers to dispersal. All extant giraffes (Giraffa camelopardalis) are currently considered to represent a single species classified into multiple subspecies. However, geographic variation in traits such as pelage pattern is clearly evident across the range in sub-Saharan Africa and abrupt transition zones
between different pelage types are typically not associated with extrinsic barriers to gene flow, suggesting reproductive isolation.
By analyzing mitochondrial DNA sequences and nuclear microsatellite loci, we show that there are at least six genealogically distinct lineages of giraffe in Africa, with little evidence of interbreeding between them. Some of these lineages appear to be maintained in the absence of contemporary barriers to gene flow, possibly by differences in reproductive timing or pelage-based assortative mating, suggesting that populations usually recognized as subspecies have a long history of reproductive isolation. Further, five of the six putative lineages also contain genetically discrete populations, yielding at least 11 genetically distinct populations.
Such extreme genetic subdivision within a large vertebrate with high dispersal capabilities is unprecedented and exceeds that of any other large African mammal. Our results have significant implications for giraffe conservation, and imply separate in situ and ex situ management, not only of pelage morphs, but also of local populations.
In other words, there appear to be more than one species of giraffes currently living in Africa – probably six species, and perhaps as many as eleven. And while the individuals of different giraffe species readily mate in captivity, it seems not to happen out in the wild.
Furthermore, two of those six new species belong to very small and shrinking populations. If the finding of this paper is accepted by the scientific community and the six populations receive official recognition as six species, this will turn the two smallest populations into endangered species, worthy of our protection.
An anonymous commenter on Grrrl’s blog has a great idea and I think we should start a contest: make a picture of Noah’s Ark with SIX pairs of giraffes towering over all the other pairs of animals instead of just one pair. Feel free to make it a LOLgiraffe picture. Post the links in the comments here or on Grrrl’s post and we’ll highlight them and pronounce the winners after the holidays.
* Apologies to A.A.Milne