Mitochondrial phylogeography of Rhinella stanlaii (Anura: Bufonidae) in the transition zone of dry forests in central South America

Abstract

Organisms are genetically structured by geographical, climatic, and topographical factors throughout their evolutionary history. In central South America, seasonally dry forests and savannas form heterogeneous landscapes shaped by distinct ecoregions, climates, and topography. These environments act as barriers or corridors for biodiversity, influencing genetic diversity patterns. Within this ecological framework, we investigated the phylogeography of the Neotropical toad Rhinella stanlaii, a species restricted to forested areas within a dry, heterogeneous landscape across Bolivia, the Brazilian states of Mato Grosso and Mato Grosso do Sul, and Paraguay. Using mitochondrial 16s sequences (n=44), we examined the time of diversification, the delimitation of its lineages, population structure and diversity, the factors that delimit it, demographic history, and habitat stability. Phylogenetic analyses revealed initial diversification in the Early Pleistocene ~1.2 Million years ago (Mya) with two major clades diverging ~0.8 Mya. FastBAPS identified three structured populations, population 1 distributed further north, population 2 in the south-central region, and population 3 overlapping with population 2 in the north. Haplotype networks highlighted strong genetic structuring, while Bayesian Skyline Plots indicated recent long-term stability with slight current expansions. Distance-based redundancy analyses showed geographic isolation as the primary driver of structure, with additional effects from climate and topography. Species distribution models indicated climatically suitable areas contraction during the Last Glacial Maximum followed by expansion in the Holocene and present. Our findings emphasize the role of climate and topography in environmental and geographic heterogeneity in the structuring of R. stanlaii diversification and highlight dry forest corridors as dynamic landscapes influencing evolutionary trajectories in central South America.