By Kai Kolodziej
Evolution is thought to be random, but new evidence suggests that it is in fact quite predictable and deterministic. The research group of Mahler and Ingram studied Caribbean Anolis and found some amazing results.
So first what are Anolis? These are rather small, mostly green or brown, mostly arboreal lizards, and there are several species living on the various Caribbean Islands. Each Caribbean Island, like Puerto Rico, Jamaica or Hispaniola, has its own set of Anolis, and they aren’t particularly closely related to each other. But if you aren’t an expert and you visit some of these islands, you would guess that you always see the same species of lizards, they almost look totally identical.
On each island you have the same set of Anolis:
– High up in the canopy are the tree specialists, those are robust and rather big green species, which have long and strong legs.
– On small twigs the twig specialists are moving in their slow way, showing a lichen-like pattern, short legs and prehensile tails.
– Along the tree trunks and ground Anolis are living their life, they are brown in colour, medium in size and have strong and long legs.
– In the grass on the ground you find grass-dwelling Anolis, rather small and fragile species, brown in colour and often with longitudinal stripes on their back or sides.
We all know convergent evolution like it happened in the green tree python (Morelia viridis) and the Emerald tree boa (Corallus caninus) but why is convergent evolution in these small Anolis species so important? The reason why this discovery is so important to science is that there is an ongoing debate: If life would start all over again, would the outcome be the same of today or something totally different? Stephen Jay Gould, an evolutionary biologist argued, that the outcome would be very different as you can’t predict evolution. Convergent evolution, like whether it is displayed in green tree pythons and emerald tree boas or in various Anolis species suggest that the result of such an experiment may be rather the same, as our world now.
The unique thing about Anolis is that they played out this experiment on the Caribbean Islands. So, the researcher team examined almost all Anolis species of the Caribbean Islands and took measurements of their body and tail length, leg length and many more characteristics. With statistical tests they showed that the degree of convergence was much higher than possible just by coincidence and proved that given the almost identical source material and same landscape, evolution can indeed be much more predictable than most researchers thought. Naturally there are always exceptions, like a leaf litter anole on one of the islands, where no counterpart is found on any other island. But these little lizards showed the world that evolution can be much more repeatable and predictable than we once thought and changed the look of science on this particular topic.
Literature:
Mahler, Ingram, Revell & Losos (2013): Exceptional Convergence on the Macroevolutionary Landscape in Island Lizard Radiations. Science 341(6143).
