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!!!
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| What appears to be a low hanging "pana" but look closely and there are many more near the canopy |
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| 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 naïve we were with our early predictions.
