Meeting Abstract
P3.38 Monday, Jan. 6 15:30 Variation in Osmoregulatory Ability among Ten Species of Fiddler Crabs (Crustacea, Brachyura) from the Atlantic Coast of Brazil FARIA, S.C.; THURMAN, C.L.*; MCNAMARA, J.C.; Universidade de São Paulo, Ribeirão Preto; University of Northern Iowa, Cedar Falls; Universidade de São Paulo, Ribeirão Preto thurman@uni.edu
Osmoregulatory ability was assessed in ~70 populations of 10 species of semiterrestrial crabs (genus Uca) distributed along the Atlantic coast of Brazil between Amapá and Santa Catarina. In the laboratory, crabs were exposed for 5 days to media ranging in osmolality from 15 to 3550 mOsm kg H2O-1; hemolymph osmolality was then measured in 10-μL aliquots using a Wescor 5520 osmometer. Survivorship, lower- and upper median-effective osmolality (UC50) and isosmotic concentration [ISO] were estimated in populations for which habitat osmolality was also measured. All species were excellent hypo-/ hyperosmoregulators. Mean [ISO] was <600 mOsm kg H2O-1 in the lone oligosaline species, between 650 and 770 mOsm kg H2O-1 in the seven mesosaline species, and >800 mOsm kg H2O-1 in the two eusaline species. Intraspecific variation in [ISO] was significant only in U. rapax, emphasizing its importance as a physiological set-point. Although UC50 varied intraspecifically in six species, habitat osmolality varied significantly for U. rapax and U. victoriana alone. Thus, intraspecific variation in UC50 likely results from local osmotic acclimation. Since genetic variation appears to be minor in most Uca species and unstructured across populations, the lack of physiological variation in [ISO] reflects the ecophenotypic nature of UC50. Financial support provided by Fulbright Foundation, Univ. Iowa GRERC, FAPESP, and CNPq.
