Topography, more than land cover, explains genetic diversity in a Neotropical savanna tree frog

Abstract

Aim: Effective conservation policies rely on information about population genetic structure and the connectivity of remnants of suitable habitats. The interaction between natural and anthropogenic discontinuities across landscapes can uncover the relative contributions of different barriers to gene flow, with direct consequences for decision-making in conservation. We aimed to quantify the relative roles of land cover and topographic variables on the population genetic differentiation and diversity of a stream-breeding savanna tree frog (Bokermannohyla ibitiguara) across its range. Location: Serra da Canastra mountain range, Cerrado of Minas Gerais State, Brazil. Methods: We collected samples and extracted DNA samples from 12 populations within and outside a strictly protected park, and used 17 microsatellite markers to assess genetic structure, among-population differentiation and within-population diversity measures. We incorporated landscape data derived from digital models and satellite images to create connectivity matrices to correlate with genetic differentiation using Mantel tests. We used generalized linear models and path analyses to assess the roles of each landscape variable in shaping genetic diversity in this species. Results: Populations within and outside the park boundaries belonged to four genetic clusters. Most populations showed evidence of limited gene flow, with significant genetic differentiation, except for those within the park, which also had higher levels of allelic richness and heterozygosity. However, genetic differentiation among populations in this landscape was primarily explained by topographic complexity. Likewise, within-population measures of genetic diversity were best explained by models including elevation and topographic complexity, and not the amount of natural habitat or gallery forests. Main conclusions: Our results underscore that topography may be a strong historical factor shaping genetic structure among amphibian populations. Therefore, effective conservation strategies for endangered amphibians should avoid focusing exclusively on habitat suitability, and incorporate topographic complexity, which seems to be a key factor for the fauna of the extremely threatened Brazilian savanna.