Biogeography of shell morphology in over-exploited shellfish reveals adaptive tradeoffs on human-inhabited islands and incipient selectively driven lineage bifurcation

Aim: To identify potentially human-mediated biogeographic patterns in selection and adaptive tradeoffs affecting the evolution an over-exploited shellfish.

Location: Hawaiian Archipelago

Taxon: Mollusca, Gastropoda, Patellagastropoda, Nacellidae, Cellana exarata, ‘Opihi makaiauli

Methods: We surveyed phenotypic characters associated with temperature and predation avoidance across the entire species range and tested for differences in the relationship between these characters and latitude, on islands with and without humans.

Results: Among all limpets surveyed, there was a bimodal distribution in shell color (light, dark) and a parapatric pattern of shell coloration across the archipelago with lighter shells being prevalent on the uninhabited islands and darker, more camouflaged shells being prevalent on the inhabited islands.  On the cooler, uninhabited islands, all morphometric characters associated with thermal avoidance (surface area, height, and doming) increased with de...