Meeting Abstract

51.2  Saturday, Jan. 5  Using fiddler crabs to investigate the relationship between morphological variation and geographic range HOPKINS, M.J.*; THURMAN, C.L.; University of Chicago; University of Northern Iowa mjh@uchicago.edu

Studies documenting geographic variation in the morphology of numerous taxa suggest that species with greater geographic range should show more species-level morphological variation. We test this quantitatively using fiddler crabs (Crustacea: Uca) from the Atlantic and Gulf coasts of North America. Because fiddler crabs are intertidal, they are easy to study and their biology and ecology is well known. Collections made by the authors comprise several populations across each of nine species� geographic range. Geographic ranges vary between species and may be quantified using coastline length. Morphological variation is measured using geometric morphometric shape analysis of the female crab carapace and quantified using disparity metrics developed for morphometric data. Principal components analysis shows concurrence between morphological similarity and taxonomy. Contrary to expectations, results show no relationship between morphological disparity and geographic range. In addition, disparity does not correspond with substrate affinity, number of biotic provinces occupied, or salinity tolerance. Because species with planktotrophic larvae have high dispersal potential, low disparity may be due to high gene flow between populations, obscuring local adaptation and implying minimal ecophenotypy. In fact, Uca species that show higher overall disparity also show some divergence among populations in morphospace. Finally, a negative relationship between disparity and geographic range is found with the inclusion of a species with nonplanktotrophic larvae (low dispersal potential). This suggests that the degree of morphological variation across a species is due to patterns of gene flow but cannot be estimated from geographic range size per se.