Joint test of historical vs. contemporary biogeography supports abundant center hypothesis shaping spatial patterns of self-fertilization

Plant reproductive assurance describes the ability of a plant to successfully reproduce in an environment that is potentially devoid of conspecifics and/or pollinators. Traditionally, studies have focused on contemporary ecology-pollinator or mate availability-driving spatial patterns in reproductive assurance; however, historical processes-post-glacial range expansion-may be an understudied alternative explanation because during range expansion, selection should favor individuals with traits promoting reproductive assurance (i.e., autonomous selfing or clonal reproduction) at the range edge. While historical tests would be rooted in phylogeographic analyses, the role of contemporary ecology can be tested indirectly using the abundant center hypothesis, where it is assumed population density decreases from the range center toward marginal habitat. We used Northern pink monkeyflower-<i>Erythranthe</i> (<i>Mimulus</i>) <i>lewisii</i>-a hermaphroditic, perennial, alpine plant, to concurrently investigate the role of historical range expansion and the abundant-center hypothesis using a greenhouse survey of range-wide reproductive assurance. First, we detected significant geographic variation among populations in self-fertilization and clonal propagation. Next, using genomic data and phylogeographic analyses, we identified three distinct genetic clusters and estimated the geographic location of the most likely origins of range expansion within each cluster. We then used filtered range-wide occurrence records to identify the geographic center of the range. We used our two relative measures of population distance from the range center (historical vs. contemporary) in univariate zero-inflated models to test whether historic or contemporary biogeography better explained spatial variation in reproductive assurance. We found that the probability of autonomous selfing significantly increased, on average, with distance from the inferred contemporary range center, consistent with the abundant-center hypothesis. Models of probability of clonal propagation showed statistical support for historical range expansion, but model performance metrics favored the abundant center hypothesis model. Future work can test the support for contemporary ecology shaping range-wide reproductive assurance in <i>E. lewisii</i>, which is linked to variation in evolutionary potential, adaptability, and population persistence.