Phylogeography and paleoclimate range dynamics explain variable outcomes to contact across a species' range

Replicability of divergence after contact are poorly characterized processes, particularly in context of phylogeography and postglacial range dynamics within species. Using contact zones located at the leading and rear edges of a species range, we examined variation in outcomes to contact between divergent lineages of Campanula americana. We investigated whether contact zones vary in quantity and directionality of gene flow, how phylogeographic structure differs between contact zones, and how historic range dynamics may affect outcomes to contact. We found that all contact zones formed at similar times via primary contact yet detected significant admixture in only the rear edge contact zone. In the northern leading edge contact zone and the mid range Virginia contact zone, gene flow was minimal and asymmetric. In the southern rear edge contact zone, gene flow was strong and symmetric. Our results emphasize the dependence of speciation processes on phylogeographic structure, demographic history, and paleoclimatic range dynamics. Our results suggest that caution need be taken when treating species as cohesive or uniform evolutionary units.