Habitat fragmentation and mating system evolution of a native wildflower

Depending on the magnitude of inbreeding depression (IBD), autonomous selfing may provide reproductive assurance (RA) for flowering plants in pollen-limited environments. Pollen limitation may result from the breakdown of once-continuous habitat into smaller, more isolated patches (habitat fragmentation) if fragmentation reduces plant and/or pollinator populations. Furthermore, theory predicts that IBD may evolve in concert with selfing rate, such that selection may reduce genetic load after multiple generations of inbreeding. Here I quantify the levels of RA and IBD among different population sizes of Collinsia parviflora, a wildflower with inter-population variation in flower size. I found that RA was greatest in small populations of small-flowered plants (where pollinator visitation was rare) and lowest in large populations of large-flowered plants (where visitation was abundant). Moreover, I found low levels of IBD in presumably selfing populations (i.e. small populations of small-flowered plants), suggesting that autonomous selfing is adaptive in fragmented habitats.