Meeting Abstract
Crabs of the family Grapsidae are common and conspicuous inhabitants of rocky shorelines and mangrove forests across the tropical and subtropical oceans. However, one lineage – three species in the genus Planes – occupies the open ocean, where crabs recruit to floating debris or pelagic animals and spend the rest for their lives rafting at the surface of the ocean. Among living substrata, Planes crabs are frequently found associated with oceanic-stage sea turtles. Currently, there are three described species of Planes: Planes minutus (N. Atlantic and Mediterranean), Planes major (worldwide, except N. Atlantic), and Planes marinus (worldwide, except N. Atlantic). While P. marinus is morphologically distinct, P. minutus and P. major show very subtle morphological differences. Genetic differentiation among Planes species and widely distributed Planes populations has never been evaluated. In this study, we performed restriction-site associated DNA-sequencing (RAD-seq) based population genomic analyses to (1) test the validity of current species designations and (2) quantify genetic connectivity of globally distributed populations. First, we found that P. marinus is distinct from P. minutus and P. major, but is not genetically distinct from Pachygrapsus laevimanus, an intertidal species. Second, we found that P. minutus and P. major are not genetically distinct and, collectively, form four intermixing populations around the world. Results of this study are not only important for understanding the ecology and evolution of Planes crabs, but also for understanding the process of speciation and population differentiation in a marine invertebrate with both planktonic and rafting dispersal.
