Evolutionary history of inshore oceanic island land snails diversified in shell colour

Oceanic islands provide an excellent opportunity to study the mode and tempo of phenotypic evolution of terrestrial organisms. This study focused on land snails, which have diverse shell colours and inhabit oceanic islands within 40 km of the mainland. We aimed to reveal when they diverged and how their shell colours evolved. Double-digest restricted-site associated DNA sequencing (ddRAD-seq) was conducted using 117 individual snails Euhadra peliomphala simodae. Island land snails diversified early in the ecosystem of the Izu Islands. This suggests that proximity to the mainland, immobility and the physiological tolerance of passive dispersal in land snails were the main causes of early diversification. Moreover, our study proposes that environments covarying with elevation would determine shell colour diversity on each island through natural selection.