Plasticity matches phenotype to local conditions despite genetic homogeneity across 13 snake populations
Résumé
In a widespread species, a matching of phenotypic traits to local environ-mental optima is generally attributed to site-specific adaptation. However,the same matching can occur via adaptive plasticity, without requiring gen-etic differences among populations. Adult sea kraits (Laticauda saintgironsi)are highly philopatric to small islands, but the entire population withinthe Neo-Caledonian Lagoon is genetically homogeneous because femalesmigrate to the mainland to lay their eggs at communal sites; recruits dispersebefore settling, mixing up alleles. Consequently, any matching between localenvironments (e.g. prey sizes) and snake phenotypes (e.g. body sizes andrelative jaw sizes (RJSs)) must be achieved via phenotypic plasticity ratherthan spatial heterogeneity in gene frequencies. We sampled 13 snake colo-nies spread along an approximately 200 km northwest–southeast gradient(n> 4500 individuals) to measure two morphological features that affectmaximum ingestible prey size in gape-limited predators: body size andRJS. As proxies of habitat quality (HQ), we used protection status, fishingpressure and lagoon characteristics (lagoon width and distance of islandsto the barrier reef). In both sexes, spatial variation in body sizes and RJSswas linked to HQ; albeit in different ways, consistent with sex-based diver-gences in foraging ecology. Strong spatial divergence in morphology amongsnake colonies, despite genetic homogeneity, supports the idea that phenoty-pic plasticity can facilitate speciation by creating multiple phenotypicallydistinct subpopulations shaped by their environment.