A phylogeny of Antirrhinum reveals parallel evolution of alpine morphology.

Abstract

Parallel evolution of similar morphologies in closely related lineages provides insight into the repeatability and predictability of evolution. In the genus Antirrhinum (snapdragons), as in other plants, a suite of morphological characters are associated with adaptation to alpine environments. We test for parallel trait evolution in Antirrhinum by investigating phylogenetic relationships using Restriction-site associated DNA (RAD) sequencing. We then associate phenotypic information to our phylogeny to reconstruct patterns of morphological evolution and relate this to evidence for hybridization between emergent lineages. Phylogenetic analyses show that the alpine character syndrome is present in multiple groups, suggesting that Antirrhinum has repeatedly colonised alpine habitats. Dispersal to novel environments happened in the presence of intraspecific and interspecific gene flow. We find support for a model of parallel evolution in Antirrhinum. Hybridisation in natural populations, and a complex genetic architecture underlying the alpine morphology syndrome, support an important role of natural selection in maintaining species divergence in the face of gene flow.