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

Abstract Perhaps the most intriguing example of insular radiations in crabs is the invasion of montane habitats by Sesarma Say, 1817 on Jamaica, an ecologically unusual island in the Greater Antilles that lost its continental biota through submergence. Jamaican sesarmids lost their marine larvae which in turn provided the means for these crabs to diversify in montane ecosystems, a remarkably rare phenomenon. We herein report a yet undescribed species of montane Sesarma from Hispaniola, challenging the uniqueness of the Jamaican radiation. The geological histories of these islands are dramatically different, and Hispaniola had a relatively inhospitable continental incumbent biota. To assess the history of colonization in these taxa, we created a phylogeny of Sesarma and show that the new Hispaniolan species is sister to the Jamaican clade and split from it ca. 3.9 mya. Based on these results, we discuss the influence of islands’ ecosystems on the invasion of land by crabs. Our study also 1) uncovered an additional undescribed species of Sesarma, 2) casts doubt on the validity of the sesarmid genus Metopaulias Rathbun, 1896, and 3) sheds light on transisthmian and basinal speciation in the American tropics.