The winner of this year’s Division of Ecology and Evolution Huey Award, Matt McElroy, gave an interesting presentation on gene flow and the Bogert Effect in Anolis cristatellus in Puerto Rico. Roughly, the Bogert effect says that thermoregulatory behaviors may shield a species from selection pressures on physiological processes experienced in different thermal environments. Therefore, divergent selection is expected to be weak in thermoregulating species, which can adjust their behavior to maintain a consistent body temperature in a range of thermal habitats. Alternatively, thermoconformers’ body temperatures match that of the environment, and so face strong divergent selection when exposed to new thermal habitats. Gene flow is expected to be high across thermal gradients for the thermoregulators and low for the thermoconformers.
Matt investigated the phylogeographic population structure and gene flow in A. cristatellus on the island of Puerto Rico, discovering three distinct populations. The southwestern population, in the arid rain shadow, was most divergent from the other two. He also conducted trasects up the mountain (a decreasing temperature gradient), finding that genes were moving out of the arid zones, but not the other way. If the Bogert effect held true, we would expect gene flow in both directions in this thermoregulating species; perhaps there is strong selection on cool adapted genotypes in warm habitats, but not vice versa. Matt suggested that higher population densities in lower elevations may influence the uni-directional flow, or that habitat destruction (e.g. hurricanes, agriculture) creates open, sunny patches, allowing the low-elevation populations (warm-adapted) to exploit elevations that they would not have been able to otherwise.