Meeting Abstract

23.2  Saturday, Jan. 4 13:45  Symbionts are couch potatoes: rounded bodies and loss of swimming in symbiotic “swimming” crabs. EVANS, N*; PAULAY, G; Univ. of Florida evansnat@ufl.edu

Most members of the brachyuran family Portunidae swim with an efficiency unmatched by any other clade of crabs. This has been attributed to a number of morphological adaptations typical of the group including having a broader, more laterally streamlined carapace and highly modified posterior legs shaped like paddles. Yet some portunids exhibit a divergent ecology and morphology that suggests they have abandoned a natatory lifestyle. Among these, members of the subfamily Caphyrinae (28 spp.) have evolved commensal associations with a number of organisms including algae, sea cucumbers and soft corals. Relative to most portunids, these crabs are smaller, less streamlined and many have nearly or completely lost the paddle shape of their posterior legs. Phylogenetic analyses presented here reveal significant phylogenetic support for Caphyrinae being derived within the portunid genus Thalamita (91 spp.). This surprising result suggests that while Thalamita’s significant diversification may have involved limited morphological change in which carapace shape and allometric growth trajectories remained highly conserved, morphological diversification was significant and rapid during the ecological diversification of Caphyrinae, and resulted in the evolution of two (or more) novel allometric growth trajectories corresponding to the genera Caphyra and Lissocarcinus. To investigate these hypotheses I am using geometric morphometric methods, collecting data on shape, size, and allometric growth of the carapace. Final datasets will be analyzed using an approach that combines fossil calibrated molecular dating with phylogenetic, model-based tests capable of inferring patterns and rates of morphological evolution. Progress on this research will be discussed.