Discovery of new montane crab (Brachyura: Sesarmidae: Sesarma Say, 1817) in Hispaniola highlights the impact of incumbent island biotas on colonization and diversification.

This article focuses on the discovery and phylogenetic analysis of a newly identified montane species of Sesarma crabs from Hispaniola, which challenges the previously held view that the unique adaptive radiation of nonmarine larval (NML) Sesarma crabs was restricted to Jamaica. Using multi-locus molecular data, the study reveals that the Hispaniolan species is sister to the Jamaican clade, diverging approximately 3.9 million years ago, and supports a single origin of NML development facilitating colonization of montane habitats. The research highlights contrasting ecological and geological histories between Jamaica and Hispaniola that influenced the extent of Sesarma diversification, with Jamaica's lower predation and competition enabling a larger radiation. Additionally, the study questions the validity of the sesarmid genus Metopaulias and provides insights into transisthmian and basinal speciation patterns in American tropical Sesarma species.