Genetic and reproductive evidence of incomplete isolations barriers between Pterodon emarginatus and P. pubescens (Leguminosae, Papilionoideae)

Abstract

Pterodon emarginatus Vogel and P. pubescens (Benth.) Benth. are phylogenetically related trees that compose a clade of sister species abundant in the Brazilian Savanna. Despite their morphological differences, some individuals with intermediate morphological characteristics have been reported, indicating the formation of interspecific hybrids. This study proposed to evaluate the genetic structure and controlled pollination of individuals of P. pubescens and P. emarginatus in areas of sympatry with the presence of putative hybrids. For this purpose, we genotyped seven microsatellite loci from 61 individuals collected from four apparent contact zones between P. pubescens and P. emarginatus. Controlled pollination experiments were performed on 4,133 flowers from six trees of P. emarginatus and five of P. pubescens. We observed two genetic clusters (k= 2) that corroborate the divergence between P. pubescens and P. emarginatus. The individual genetic assignment showed evidence of natural hybridization between P. pubescens and P. emarginatus. The genetic assignment did not fully support the visual description of the diagnoses of individual morphological characteristics. Controlled interspecific pollination generated fruit and seed production, possibly indicating the absence of a reproductive barrier at the pollination and ovule fertilization levels between these species. Our results enlarge the understanding of the diversification process of Pterodon species.

Keywords:
Controlled pollination; Microsatellite markers; Neotropical tree; Speciation; sucupira-branca