No association between plant mating system and geographic range overlap

Premise of the Study Automatic self-fertilization may influence the geography of speciation, promote reproductive isolation between incipient species, and lead to ecological differentiation. As such, selfing taxa are predicted to co-occur more often with their closest relatives than are outcrossing taxa. Despite suggestions that this pattern may be general, the extent to which mating system influences range overlap in close relatives has not been tested formally across a diverse group of plant species pairs. Methods We test for a difference in range overlap between species pairs where zero, one, or both species are selfers, using data from 98 sister species pairs in 20 genera across 15 flowering plant families. We also use divergence time estimates from time-calibrated phylogenies to ask how range overlap changes with divergence time and whether this effect depends on mating system. Key Results We find no evidence that automatic self-fertilization influences range overlap of closely related plant species. Sister pairs with more recent divergence times had modestly greater range overlap, but this effect did not depend on mating system. Conclusions The absence of a strong influence of mating system on range overlap suggests that mating system plays a minor or inconsistent role compared to many other mechanisms potentially influencing the co-occurrence of close relatives.