Limited pollen flow and high selfing rates toward geographic range limit in an Atlantic forest bromeliad

Abstract

Bromeliaceae is a Neotropical family that evolved ecological key innovations in association with extensive adaptive radiation. Its species present a variety of different mating system strategies varying within and among species, within genera and subfamilies. Also, species with a wide geographical range can display large variation in mating system, reproductive success and genetic diversity. Here we combined data from hand pollinations and genetic analysis to assess outcomes of contemporary gene flow and mating system variation at the range edge of Vriesea gigantea. Results from pollen germination rates showed that this species is cryptically self-incompatible. Hand-pollination experiments and genetic analysis of progeny arrays revealed that V. gigantea has a mixed mating system, with high selfing rates (s=0.612), and high inbreeding coefficient (F=0.372). Inbreeding in V. gigantea at southern edge of its distribution range was caused by high levels of selfing rather than by mating among relatives. Moreover, strong pollen pool genetic structure was observed (Φ'FT=0.671), with an increase from north to south. The parameters observed help us to understand historical and ecological conditions under which V. gigantea has experienced moderate to high levels of selfing in the face of reduced pollen flow from central to peripheral populations due to recent southward range expansion.