Runaway fathers? Limited pollen dispersal and mating system in Rhizophora racemosa populations of a disturbed mangrove estuary

Abstract

The contribution of pollen mediated gene flow in demographic stability is largely dependent on how far pollen can be dispersed, as well as how this dispersal affects the mating in breeding individuals. In this study patterns of pollen dispersal and mating systems in Rhizophora racemosa populations of the Cameroon Estuary complex (CEC) were assessed from 29 adult trees with their progeny seedlings (i.e., 483 propagules), sampled from three plots. Using progeny arrays constructed from eight microsatellite markers, we employed two-generational analyses to assess pollen pool structure, pollen dispersal distances, and mating systems. We found mean number of sires contributing to the pollen pool of a mother tree was low (2–3) and pollen dispersal distances were short (<12 m). Male gametic divergence among siblings was moderate (0.158 ≤ Φft ≤ 0.277). Low biparental inbreeding rates and moderate multi-locus outcrossing rates (0.559–0.650), suggest a mixed mating system comprising of spontaneous selfing (geitonogamy) and outcrossing. Our results show that pollen dispersal does not contribute to among patch genetic connectivity since the spatial scales of the patches far exceeds estimated pollen dispersal distances; indicating high gene flow previously reported within the CEC is predominantly mediated by propagule dispersal.