Aim: To test whether phylogeographical barriers in the brooding sponge Callyspongia vaginalis match breaks previously identified in the Caribbean. We also compared patterns of subdivision in the sponge to those of three of its commensals, the broadcast spawning brittle star Ophiothrix suensonii and the brooding amphipods Leucothoe ashleyae and L. kensleyi, and tested whether any shared breaks arose simultaneously. Location: Florida, Bahamas and the Caribbean. Methods: Subdivision of C. vaginalis populations was inferred from one mitochondrial (COI) and six nuclear loci using clustering analyses. We identified phylogeographical breaks in the sponge and its invertebrate commensals by determining geographical patterns of genetic variation and tested simultaneous population divergence across barriers shared among taxa using hierarchical approximate Bayesian computation. Results: Sponge populations were partitioned into western and eastern groups across the Caribbean, with hierarchical subdivision within regions. The sponge and its commensals shared barriers across their ranges despite differences in dispersal strategy: C. vaginalis, L. ashleyae and O. suensonii populations in Central America were isolated from the remainder of the Caribbean, and all four taxa shared a break between Florida and the Bahamas, although simultaneous population divergence could not be inferred with statistical certainty. Our results also suggest cryptic speciation within C. vaginalis. Main conclusions: Phylogeographical patterns in C. vaginalis largely matched barriers previously identified at the Florida Straits, Mona Passage and Bay of Honduras in other Caribbean taxa. Oceanographic features such as deep water between locations, strong currents, and eddies are likely mechanisms responsible for these breaks.

GPS_PhiST_DeBiasse_et_al_Journal_of_BiogeographyThis file contains the sampling site GPS coordinates and PhiST values for Callyspongia vaginalis, Leucothoe ashelyae, Leucothoe kensleyi, and Ophiothrix suensonii required for the Barrier analyses associated with the Journal of Biogeography manuscript "Shared phylogeographical breaks in a Caribbean coral reef sponge and its invertebrate commensals" by Melissa B. DeBiasse, Vincent P. Richards, Mahmood S. Shivji, and Michael E. Hellberg.