CARAPACE RELATIVE GROWTH OF TRAPEZIA LATREILLE, 1828 (DECAPODA, BRACHYURA), CRABS THAT ARE SYMBIONTS OF HARD CORALS, FROM CLIPPERTON ATOLL AND THE REVILLAGIGEDO ISLANDS: ECOLOGICAL AND ZOOGEOGRAPHICAL IMPLICATIONS BY LAURA SANVICENTE-AÑORVE 1,3 ), MARGARITA HERMOSO-SALAZAR 1 ), VIVIANNE SOLÍS-WEISS 1 ) and ISAÍAS H. SALGADO-UGARTE 2 ) 1 ) Universidad Nacional Autónoma de México, Instituto de Ciencias del Mar y Limnología, Apdo. Postal 70-305, 04510 Mexico, D.F., Mexico 2 ) Universidad Nacional Autónoma de México, Facultad de Estudios Superiores Zaragoza, Batalla 5 de mayo esquina Fuerte de Loreto, 09230 Mexico, D.F., Mexico ABSTRACT Decapod metapopulation dynamics are better understood by confronting theoretical studies with empirical data. In this study, our goal was to analyse the morphometric characteristics and relative growth of the carapace of Trapezia bidentata (Forskål, 1775) and T. digitalis Latreille, 1828, crabs from the islands Clipperton and Revillagigedo, in order to assess the degree of inter- and intraspecific similarity of the four insular populations. We examined 325 specimens and identified four species: T. bidentata (72.9% of total abundance), T. digitalis (23.1%), T. formosa Smith, 1869 (3.4%), and T. corallina Gerstaecker, 1857 (0.6%). Three carapace measurements were taken for each specimen: carapace width (CW), carapace length (CL), and interocular distance (ID). The variables CL and ID were fit to a power equation taking CW as the reference dimension. As in other brachyurans, growth pattern analyses indicated an isometric type in all CW vs CL and CW vs ID relationships examined. Interspecific differences included a larger body size for T. bidentata and larger ID/CW for T. digitalis. Significant intraspecific differences in the two insular populations of T. digitalis were evidenced in the ID/CW ratio. In contrast, populations of T. bidentata were morphometrically closer. These results indicate a higher degree of connectedness of the parts of the T. bidentata metapopulation than of that of T. digitalis, probably due to differences in the duration of their larval stages. We think that the larger body size in T. bidentata might account for competitive advantages in food gathering and habitat selection over the remaining species. In turn, as a counteracting trait for its smaller size, the larger ID might allow T. digitalis a better ability to perceive 3D and to judge relative distances between objects, thus avoiding competitive combats and improving antipredatory or escape responses. 3 ) Corresponding author; e-mail: lesa@servidor.unam.mx or: sanvi@cmarl.unam.mx © Koninklijke Brill NV, Leiden, 2010 Crustaceana 83 (11): 1371-1383 Also available online: www.brill.nl/cr DOI:10.1163/001121610X533520