REDUCED CUTICULAR PERMEABILITY PROMOTES INLAND HABITAT EXPANSION AND FRESHWATER SURVIVAL IN THE FIDDLER CRAB UCA MINAX BUT NOT IN ITS LESS TERRESTRIAL COUNTERPARTS U. PUGILATOR AND U. PUGNAX BY JAY A. YODER 1 ), JASON W. BOSLEY, MICHAEL J. CHAMBERS, CHLOÉ E. HART, KEVIN M. GRIBBINS and MATTHEW H. COLLIER Department of Biology, Wittenberg University, Springfield, Ohio 45501, United States of America ABSTRACT We report a two-fold suppression in activation energy for water loss in adult Uca minax males compared to co-occurring species, U. pugilator and U. pugnax, that overlap in salt marsh/estuary habitats, implying a water-tight cuticular modification that is unique to U. minax. This is further reflected by a drop in Arrhenius frequency (steric) factor A as an integrated measure of cuticular effectiveness. U. minax is also distinguished by an enlarged body size (approximately 5× as large as the other two species) and an enhanced capacity for water retention by a pronounced 4-5 fold decrease in net transpiration rate, presumably as a result of surface area to volume properties and the reduction in cuticular permeability. High net transpiration rates correspond to high activation energies in U. pugilator and U. pugnax, suggesting that they are more porous; the values for U. pugnax were the highest indicating that this species is the most prone to water stress. Features that these crab species have in common are a 67% body water content, twice the amount of water as their dry mass (size), and absence of a critical transition temperature (CTT) that safeguards them against an abrupt, lethal water loss. Lack of a CTT agrees with previous descriptions of crabs having no water-proofing epicuticular lipids and matches their rapid water loss rates and limitation to wet habitats. The ability by U. minax to conserve water by restricting water loss, however, makes them less dependent on a moisture-rich habitat, and this parallels field data that account for the differential capacity of U. minax to thrive in terrestrial inland locations by resisting desiccation and to survive in fresh water by being less porous to water entry. Results are consistent with the view that placing a priority on investigating what crabs are actually doing in the field (they operate on a smaller scale; i.e., microhabitat) is more important to application of net transpiration rate than as a general indicator of moisture-requirements for a species. RÉSUMÉ Une diminution de 2 fois de l’énergie d’activation pour la perte d’eau chez les adultes d’Uca minax comparés aux deux espèces U. pugilator et U. pugnax, qui coexistent dans les habitats 1 ) e-mail: jyoder@wittenberg.edu © Koninklijke Brill NV, Leiden, 2010 Crustaceana 83 (4): 481-492 Also available online: www.brill.nl/cr DOI:10.1163/001121610X491013