High levels of gene flow among partially isolated populations can overwhelm selection and limit local adaptation. This process, known as "gene swamping," can homogenize genetic diversity among populations and reduce the capacity of a species to withstand rapid environmental change. We studied brown anole lizards (Anolis sagrei) distributed across seven islands in The Bahamas. We used microsatellite markers to estimate gene flow among islands and then examined the correlation between thermal performance and island temperature. The thermal optimum for sprint performance was correlated with both mean and maximum island temperature, whereas performance breadth was not correlated with any measure of temperature variation. Gene flow between islands decreased as the difference between mean island temperatures increased, even when those islands were adjacent to one another. These data suggest that phenotypic variation is the result of either (1) local genetic adaptation with selection against immigrants maintaining variation in the thermal optimum, (2) irreversible forms of adaptive plasticity such that immigrants have reduced fitness, or (3) an interaction between fixed genetic differences and plasticity. In general, the patterns of gene flow we observed suggest that local thermal environments represent important ecological filters that can mediate gene flow on relatively fine geographic scales.

Animal signals experience selection for detectability, which is determined in large part by the signal transmission properties of the habitat. Understanding the ecological context in which communication takes place is therefore critical to understanding selection on the form of communication signals. In order to determine the influence of environmental heterogeneity on signal transmission, we focus on a wolf spider species native to central Florida, Schizocosa floridana, in which males court females using a substrate-borne vibratory song. We test the hypothesis that S. floridana is a substrate specialist by 1) assessing substrate use by females and males in the field, 2) quantifying substrate-specific vibratory signal transmission in the laboratory, and 3) determining substrate-specific mating success in the laboratory. We predict a priori that 1) S. floridana restricts its signaling to oak litter, 2) oak litter best transmits their vibratory signal, and 3) S. floridana mates most readily on oak litter. We find that S. floridana is almost exclusively found on oak litter, which was found to attenuate vibratory courtship signals the least. Spiders mated with equal frequency on oak and pine, but did not mate at all on sand. Additionally, we describe how S. floridana song contains a novel component, chirps, which attenuate more strongly than its other display components on pine and sand, but not on oak, suggesting that the ways in which the environment relaxes restrictions on signal form may be as important as the ways in which it imposes them.