Among-population pollen movement and skewed male fitness in a dioecious weed

Abstract

Dioecious plant species are presented with the challenge of needing both males and females to be present to ensure seed production and self-sustaining populations. In this situation the contribution of pollen from outside sources to mating events may become reproductively important. Salix cinerea (willow) is used as an ecological model for investigating the importance of inter-population pollen movement for the local reproductive dynamics of a dioecious environmental weed using microsatellite-based paternity analysis. Nearly 40 % of seeds produced are sired by fathers from outside the local site (500 m) indicating that invasive S. cinerea populations are linked through pollen movement. Thus in the absence of males at a site up to 40 % of seed production would be maintained by immigrant pollen. Observed patterns of within-site mating dynamics revealed a highly skewed male fitness distribution with a small number of fathers being responsible for a large proportion of successful fertilisation events. High inter-population pollen flow for this dioecious weed suggests that between population reproductive dynamics may increase the likelihood of colonisation success of dioecious weeds. Control strategies that take into account inter-population pollen dispersal need to be developed for effective management.