Differentiation across a common Neotropical landscape: contrasting molecules, calls, and morphology in two closely related gladiator frogs

Previous studies have supported the notion that the Cordillera de Mérida (CM), the easternmost branch of the Northern Andes, as well as the Orinoco River (OR), represent important geographic barriers for terrestrial vertebrates. The gladiator frogs, Boana pugnax and B. xerophylla (Anura: Hylidae) are distributed on either side of the CM, while the latter also occurs on either side of the OR. Herein, we assessed the genetic, acoustic, and morphological differentiation within both species across the CM and within B. xerophylla across the OR. We sequenced two mitochondrial and one nuclear marker, recorded advertisement calls, and measured adult male morphology. We assessed geographical differentiation for each type of data, tested for a correlation between genetic and geographic distance, and carried out a molecular phylogenetic analysis. Genetic and morphometric analyses of populations from opposite sides of the CM revealed differentiation in B. pugnax but not in B. xerophylla. Within the latter species, we found molecular, acoustic, and morphometric differentiation among samples of B. xerophylla from western Venezuela versus the Guiana Shield. Genetic variation within both species was not explained by geographic distance. Thus, our data show conspecific population structure across the CM in B. pugnax, plus the possible existence of two species within what today is considered B. xerophylla, yet the CM was not involved in this divergence. These results suggest that even for closely related species with shared ecology and distribution, genetic and phenotypic differentiation respond differently to common ecological or historical factors.