Plasticity matches phenotype to local conditions despite genetic homogeneity across 13 snake populations

In a widespread species, a matching of phenotypic traits to local environmental optima is generally attributed to site-specific adaptation. However, the same matching can occur via adaptive plasticity, without requiring genetic differences among populations. Adult sea kraits (Laticauda saintgironsi) are highly philopatric to small islands, but the entire population within the Neo-Caledonian lagoon is genetically homogenous because females migrate to the mainland to lay their eggs at communal sites; recruits disperse before settling, mixing up alleles. Consequently, any adaptive matching between local environments (e.g., prey sizes) and snake phenotypes (e.g., body sizes and relative jaw sizes) must be achieved via phenotypic plasticity rather than spatial heterogeneity in gene frequencies. We sampled 13 snake colonies spread along a ~200km northwest-southeast gradient (N>4,500 individuals) to measure two morphological features that affect maximum ingestible prey size in gape-limited ...