Friday, September 9, 2016

How many giraffes are there, anyway?

New research co-sponsored by the Giraffe Conservation Foundation has revealed at least four different species of giraffe!  Yes, you read that right.  Four different species of giraffe!  I was previously aware of the giraffe subspecies, but this new study from Fennessey et al. indicate that four of the subspecies are very divergent and different and therefore should be recognized as different species.  How different are they?  These giraffes are roughly as different from each other as the various species of donkeys, zebras, and horses differ amongst themselves.  That's pretty different.

What makes this so delightful to me is how unexpected it was.  As I said, different subspecies of giraffe had been known for a while, nine in all.  Giraffes range across a wide area of Africa, and there are noticeable differences in their coloration and spotting.  Until now, though, researchers hadn't done a really thorough job of examining the genetics of different giraffe populations.  When they did, they got a surprise!  There were four genetically distinct groups of giraffes:

  • The southern giraffe (Giraffa giraffa) includes giraffes from South Africa and Namibia.
  • The Masai giraffe (Giraffa tippelskirchi) is found in Zambia, Tanzania, and Kenya.
  • The reticulated giraffe (Giraffa reticulata) mostly lives in Kenya and into Somalia and Ethiopia.
  • The northern giraffe (Giraffa camelopardalis) consists of a number of isolated populations along the northern-most part of sub-Saharan Africa, primarily in the countries of South Sudan, the Central African Republic, Chad, Cameroon, and Niger.

This research reminds me of one of the central mysteries of biology: How do species become different?  On the one hand, you have zebras and horses that look different and have quite noticeable differences in their genes.  On the other, you have giraffes, which look pretty much like giraffes but are genetically distinct.  Why do some species diverge genetically and in appearance, while other species diverge only genetically?  How is it that some groups like camels and llamas have very similar chromosome structures, while others like the horses and zebras have very different chromosome structures?  Camels and llamas look very different, but their chromosomes are all organized very similarly.  Horses and zebras, even though they look similar and can readily interbreed, have very different chromosome organizations.  Why does this happen?  What does genetic divergence have to do with the way species look?

I don't have an answer to these questions, but now I have wonderful new things to wonder about when I see a giraffe.

Fennessey et al. 2016. Multi-locus Analyses Reveal Four Giraffe Species Instead of One.  Current Biology DOI 10.1016/j.cub.2016.07.036.

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