Volume and Ion Regulation During Repeated Exposure to Temperature Change: Physiological Divergence in Trans‐Isthmian Cognate Pairs and Latitudinally Distant Populations of Decapod Crustacea

Abstract

When the Isthmus of Panama emerged as a land bridge, it set the stage for allopatric speciation in the marine fauna. In the present study Pacific and Atlantic populations of three cognate pairs of crabs were used to discern whether physiological divergence has occurred as a result of exposure to different thermal regimes in habitats and in the putative absence of gene flow. Additional comparison was made with Belize and Florida populations of the Atlantic Panama cognate. This was done to test the strength of correlation between physiological divergence and exposure to different thermal regimes in populations that potentially form a common genetic pool. Water temperatures decrease periodically in Pacific Panama and Florida but not in Atlantic Panama or Belize. Physiological divergence in volume and ion regulation was assessed in response to repeated exposure to either control and decreased temperature or to control and increased temperature. Results indicate that exposure to naturally occurring decreased temperatures in habitats has resulted in divergence. This divergence is demonstrated both in enhanced ability to regulate volume at decreased temperature and impaired ability to regulate volume at elevated temperature. ProblemTwo hypotheses were addressed. ( I ) Since their geologically recent separation, physiological divergence has occurred between Panamanian cognate species of crabs, relative to different habitat temperature patterns and (2) physiological divergence has occurred between geographically distant populations of the same crab species relative to exposure to different habitat temperature patterns. Change in

Ecophenotypic physiology: osmoregulation by fiddler crabs (Ucaspp.) from the northern Caribbean in relation to ecological distribution

“…vocator (Herbst, 1804). Osmotic regulation has been reported previously with certainty in only U. rapax, U. speciosa and U. thayeri (Zanders and Rojas 1996a;Ferraris and Norenberg 1997;Thurman 2002Thurman , 2003aThurman , 2003bThurman , 2005. We test the hypothesis (H o ) that the ability to osmoregulate is uniform across species of fiddler crabs inhabiting different environments.…”

“…Also the upper limits of osmotic toleration appear to vary as a result of habitat acclimation. In their study of physiological diversity in Uca, Ferraris and Norenberg (1997) assessed volume and osmoregulation in three U. rapax populations and compared this to its Pacific relative Uca herradurenesis. They found Pacific and Florida populations of the sibling species to be more similar in their patterns of regulation than Caribbean populations of U. rapax from Belize and Panama.…”

Osmoregulation in Six Sympatric Fiddler Crabs (genus Uca) from the Northwestern Gulf of Mexico

“…And from Venezuela, Zanders & Rojas (1996) have shown U. rapax to be one of the most powerful hypo‐/hyperregulating crustaceans known, exceeding the capabilities attributed to U. minax, U. pugnax and U. pugilator . In a study of the trans‐isthmian cognates U. rapax and U. g. herradurensis , Ferraris & Norenberg (1997) found Pacific and Florida populations to be more similar in their pattern of volume and ion regulation than Caribbean populations from Belize and Panama. For a related semiterrestrial genus, Sesarma , Staton & Felder (1992) have provided evidence of a physiological divergence between coastal populations in Georgia and Louisiana.…”