Tuesday, August 28, 2012

Bucking the Trend


Convergent evolution has become the trademark of West Indian anoles. Species occupying distinct structural niches exhibit high levels of convergence in morphology (e.g., similar body proportions and general shape), ecology (e.g., habitat selection) and behavior (e.g., foraging and movement patterns) -- what are referred to as ecomorphs.  Decades ago E.E. Williams & colleagues began their studies of ecomorphology and convergence in anoles across the Majar Antilles, and this topic continues to be an active area of significant research. At the present, with the exception of aquatic anoles, convergent evolution has been found across many traits from morphology to physiology… but the run seems to have come to an end.
     To make a long story short, I was able to convince Brian a while back that a study of brain evolution in anoles was an easy, low-hanging fruit. In other words, it was ripe for the picking. Initially Brian seemed more interested in the evolution of "play" behavior in lizards, but I was finally able to persuade him that I was ignorant about that subject so he should wait to "work play" for his postdoctoral research. Well, a few years and hundreds of hours of tedious work later, Brian has completed the first study addressing brain evolution in anoles (and one of only a handful of studies of brain evolution in reptiles). Needless to say, the fruit was not hanging that low ... it was much closer to the canopy!!!
What appears to be a low hanging "pana" but look closely and there are many more near the canopy
There are a few shelves like this one, packed with brain sections
   Brian's findings are reported in a paper recently published in Brain, Behavior, and Evolution (pdf here). The results show an absence of convergence in brain size between members of the same ecomorph class. In fact, there were no differences between ecomorphs in either overall brain size or in the size of major brain structures after correcting for body size and phylogeny. This is a surprising finding because the brain is often considered to be the substrate upon which selection might act to shape differences in behavioral traits that are commonly reported between ecomorphs. This raises the question, why does the brain buck the trend and fail to exhibit convergence? One possibility is that convergence is present at a finer scale, such as neuron density or connections. Alternatively, we are only beginning to scratch the surface of that big black box called the brain, and it is highly likely that once we learn more about the complexity of the box, we will realize how na├»ve we were with our early predictions.

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