Diversification and hybridization in a treefrog endemic to the Brazilian Cerrado: genetics, morphology and behavior

Author(s)

Renato Christensen Nali

• Document type: Doctoral Thesis
• Press: Rio Claro. 2016-11-18.
• Institution: Universidade Estadual Paulista (Unesp). Instituto de Biociências. Rio Claro
• Defense date: 2016-10-04
• Advisor: Cynthia Peralta de Almeida Prado

Abstract

Landscape configuration and phenotypic characteristics linked with mating recognition may influence population genetic structure and diversification processes. Moreover, reproductive interactions among different species may alter the evolutionary history of lineages with the formation of viable hybrids. To investigate these complex interactions we studied the treefrog Bokermannohyla ibitiguara, a species with prolonged reproduction, complex calls, elaborate courtship, choosy females and territorial/aggressive males. It is endemic to the threatened Brazilian Cerrado and breeds in streams associated with riparian forests within and outside the Serra da Canastra National Park (SCNP), a contact zone with the congener B. sazimai. We sampled many streams and developed microsatellite markers to analyze the roles of topography and land cover on genetic differentiation. We then compared morphology and calls throughout the range and examined the roles of sexual selection, genetic drift, and acoustic adaptation to forested habitats (Acoustic Adaptation Hypothesis; AAH) on call differentiation. We also tested the hypothesis that B. ibitiguara and B. sazimai may hybridize due to phenotypic similarities. Individuals of B. ibitiguara showed significant genetic differentiation among streams, except those within the Park, which had higher levels of allelic richness and heterozygosity. Genetic differentiation was best explained by topographic complexity, as were some within-population genetic measures. Calls varied more than morphology, suggesting stronger selective pressures on this behavioral phenotype. Acoustic traits associated with individual discrimination and/or female attraction showed significant population differences. Neither genetic differentiation nor riparian forest cover (the AAH) explained population acoustic differences, but call traits that varied in contrast with AAH indicated a role of male competition associated with increased density. Ten percent of individuals within the SCNP were hybrids, showing overlapping but intermediate values of genetic dissimilarities compared to parental B. ibitiguara and B. sazimai. Morphology and calls were not intermediate, but a mosaic of phenotypes, including a distinct call type in two hybrids. We underscore that topography is a strong driver of genetic structure in amphibians, and differences observed within and outside the Park may rely on the degree of topographic relief. Conservation strategies should incorporate not only habitat disturbance, but also topographic complexity, especially in threatened regions such as the Cerrado. Our phenotypic analyses suggest that sexual selection shapes call differentiation in this species in the forms of individual recognition, female preferences and intermale competition. A multi-trait and multi-mechanism approach was nevertheless crucial to explain these intricate processes. Also, records of hybridization in frogs with elaborate behavior and/or long reproductive period are underrepresented, but may also occur likely due to similarities in mating recognition systems and alternative mating tactics, such as satellite males. The multi-faceted diversification of B. ibitiguara enhances our knowledge on conservation, evolution and behavioral ecology. We believe that our results can be applied to different animals and biomes, given the widespread associations observed among individuals with the landscape, with conspecifics (within and between the sexes) and with other sympatric species. (AU)

• FAPESP's process: 12/06228-0 - Genetic, morphological and acoustic diversification in populations of an anuran endemic to the Serra da Canastra, Brazil
• Grantee: Renato Christensen Nali
• Support Opportunities: Scholarships in Brazil - Doctorate