Geographical variation in osmoregulatory abilities among populations of ten species of fiddler crabs from the Atlantic coast of Brazil: A macrophysiological analysis

Author(s)

Thurman, Carl L. ^[1] ; Faria, Samuel C. ^{[2, 3]} ; McNamara, John C. ^{[2, 4]}

Affiliation

^[1] Univ Northern Iowa, Dept Biol, 144 McCollum Sci Hall, Cedar Falls, IA 50614 - USA

^[2] Univ Sao Paulo, FFCLRP, Dept Biol, BR-14040901 Ribeirao Preto, SP - Brazil

^[3] Univ Fed Rio Grande, Inst Ciencias Biol, BR-96203900 Rio Grande, RS - Brazil

^[4] Univ Sao Paulo, Ctr Biol Marinha, BR-11600000 Sao Sebastiao, SP - Brazil

• Document type: Journal article
• Source: Journal of Experimental Marine Biology and Ecology; v. 497, p. 243-253, DEC 2017.
• Web of Science Citations: 4

Abstract

Geographical variation is often the earliest stage leading to divergence and speciation. Osmoregulatory ability was assessed in 64 populations of 10 species of semi-terrestrial fiddler crabs along the Atlantic coast of Brazil between Amapa and Santa Catarina. In the laboratory, crabs were exposed for 5 days to media ranging in osmolality from 15 to 3550 mOsm/kg H2O. Hemolymph osmolality was measured in 10-mu L aliquots using a Wescor 5520 osmometer. Survivorship, lower- (LLC50) and upper (ULC50) lethal osmolalities, and isosmotic concentrations {[}ISO] were estimated in populations for which habitat osmolality was also measured. All fiddler crab species were excellent hypo-/hyper-osmoregulators. Mean {[}ISO] was < 600 mOsm/kg H2O in the lone oligo-saline species, between 650 and 770 mOsm/kg H2O in the seven mesosaline species, and > 800 mOsm/kg H2O in the two eusaline species. Intraspecific variation in {[}ISO] was significant only in Minuca rapax, emphasizing the importance of this parameter as a physiological set-point. Although ULC50 varied intraspecifically in six species, habitat osmolality varied significantly for M. rapax and M. victoriana alone. Thus, intraspecific variation in ULC50 likely results from local osmotic acclimatization. Since genetic variation appears to be minor and unstructured across populations in most fiddler crab species, the consistency of {[}ISO] reflects its importance as a physiological property. In contrast, intraspecific differences in ULC50 among populations indicate that this character is ecophenotypic. Unquestionably, physiological studies on fiddler crab populations distributed over a wide geographical range can provide insight into the biological basis of adaptation and the evolution of species in this semi-terrestrial genus. (AU)

• FAPESP's process: 09/50799-0 - Carl Leo Thurman II | University of Northern Iowa - United States
• Grantee: John Campbell McNamara
• Support Opportunities: Research Grants - Visiting Researcher Grant - International