Hybridization and mechanisms of reproductive isolation of Atlantic Forest lizards

Abstract

Elucidating the mechanisms that generate and maintain biodiversity are one of the main goals of evolution and biogeography (e.g. Mayr 1963). In this context, species formation and lineage divergence are key processes, especially in mega-diverse tropical areas. The Atlantic Forest central corridor is such a place. It is considered a hotspot (central corridor) within a hotspot (the Atlantic Forest) (Carnaval et al. 2009), because it is species rich and highly threatened (Mittermeier et al. 1999). Regardless of the high number of endemics and extremely divergent intra-specific (phylogeographic) lineages in this region, mechanisms that generate and maintain biodiversity are still far from being understood (Moritz et al. 2000, Carnaval et al. submitted).Areas of secondary contact and hybridization between phylogeographic lineages or sister species are natural laboratories for the study of species formation and mechanisms that maintain them (Harrison 1993). Put simply, the outcomes of secondary contact include unrestricted gene flow between lineages/species (e.g. Grant e Grant 2002, Taylor et al. 2006) or restricted hybridization, limited, for example, by genetic incompatibilities or selection against hybrids (Coyne e Orr 1989). On the other hand, instances where complete reproductive isolation evolved, closely related lineages do not exchange genes, but secondary contact might result in intense ecological interactions, motivated by their parapatric distribution and ecological similarity (Anderson 1948). The outcomes of secondary contact depend on the conditions, extension, and time of divergence, as well as time since secondary contact (Schluter 2000). Assessment of hybrid composition and patterns of phenotypic variation can help elucidate mechanisms and conditions of divergence. With this proposal, we are going to address such mechanisms by studying contact zones between phylogeographic lineages and sister species in one of the most diverse areas in the world, the Brazilian Atlantic Forest. The biological system includes lizard species that are ideal for such questions. Species of the genera Leposoma (Gymnophthalmidae) and Enyalius (Leiosauridae) show (1) deep phylogeographic structure and phylogeographic lineages with parapatric distribution, (2) instances of biogeographic mito-nuclear discordance, and (3) extremely divergent populations both genetically and morphologically that are geographically isolated at Serra do Espinhaço (in Bahia) and at the Jequitinhonha River (in Minas Gerais (Damasceno 2013). Moreover, one introgressed population with color pattern and mitochondrial genome of Enyalius catenatus and nuclear genome of E. pictus was discovered at the margins of the Jequitinhonha river, at the boundary of the distribution of both species (Damasceno 2013).This proposal is going to generate new knowledge about one of the most endangered Brazilian biomes, the Atlantic Forest. The future results have the potential to be applicable to a much broader context, going beyond these two lizard genera. The results are going to be relevant regionally, especially to other taxa with similar biogeographic and phylogeographic patterns, as well as to contact zones with in the area. More broadly, our results are going to contribute to a better understanding of mechanisms of species formation and hybridization in mega-diverse areas worldwide. (AU)