Contrasting genetic structure in two codistributed freshwater fi sh species of highly seasonal systems

Abstract

GIVEN THE SEASONAL NATURE OF ECOSYSTEMS SUCH AS PERMANENT SINKHOLES (CENOTE´S) AND TEMPORARY WETLANDS, THEIR FISH FAUNA EXPERIENCE YEARLY LOCAL EXTINCTION AND COLONIZATION PROCESSES, WITH STRONG FLUCTUATIONS IN POPULATION SIZE. WE EVALUATED THE GENETIC DIVERSITY, POPULATION GENETIC STRUCTURE AND DEGREE OF ISOLATION OF POPULATIONS OF POECILIA ORRI AND GAMBUSIA YUCATANA AMONG AND WITHIN WETLANDS AND CENOTES. WE ALSO ASSESSED SOME ABIOTIC CHARACTERISTICS OF THE WATER BODIES AND THEIR POTENTIAL RELATIONSHIP WITH AVERAGE GENETIC DIVERSITY. BOTH SPECIES SHOWED LOW GENETIC DIVERSITY, BUT THIS WAS TWICE AS LOW IN P. ORRI. POPULATIONS OF G. YUCATANA SHOWED NO GENETIC STRUCTURE, WHEREAS THOSE OF P. ORRI DID. THE GENETIC DIVERGENCE RESULTS WERE CONSISTENT WITH ISOLATION BETWEEN CENOTES AND WETLANDS, WHERE THE DIFFERENT TYPES OF WATER BODIES HAD A DISTINCTIVE GENETIC COMPOSITION. WE SUGGEST THAT OUR GENETIC DIVERSITY AND DIFFERENTIATION RESULTS ARE ASSOCIATED WITH THE SUCCESSIVE, SEASONAL-YEARLY POPULATION SIZE SHRINKAGE AND EXPANSION EVENTS (I.E. EXTINCTION AND RECOLONIZATION) THAT OCCUR IN THESE SYSTEMS, AND ALSO WITH THE ENVIRONMENTAL TOLERANCE, BODY SIZE, AND REPRODUCTION CHARACTERISTICS OF BOTH SPECIES. OUR RESULTS SHOW HOW THESE CODISTRIBUTED SPECIES CAN HAVE MARKEDLY DIFFERENT GENETIC STRUCTURING AND DIVERSITY, MOST LIKELY DETERMINED BY THEIR PARTICULAR BIOLOGICAL AND ECOLOGICAL CHARACTERISTICS, AND PROVIDE BASELINE INFORMATION FOR FUTURE STUDIES.