Too attractive to self: How pollinators can interfere with the evolution of selfing.

Pollinators are widely invoked to explain the evolution of selfing despite genetic conditions favoring outcrossing. But their role in maintaining outcrossing despite genetic conditions favoring selfing remains unexplored. We use consumer-resource models to explicitly consider the how the plant-pollinator mutualism can constrain the evolution of selfing. We model outcrossing as a function of attractiveness and account for the cost of attractiveness as a saturating, linear, or exponential function alongside the costs of selfing: inbreeding depression and pollen discounting. We show specific, clear combinations of ecological and genetic conditions where pure selfing can invade a resident population of partial selfers. Complete selfing can evolve in the face of pollen discounting so long as there is a cost to pollinator attraction and reward. However, we also predict conditions under which mixed mating is maintained even when inbreeding depression is low. Our model highlights how under some scenarios mixed mating represents the worst of both worlds, leaving plants to pay the costs of both inbreeding depression and attraction and even leading to extinction. By linking pollinator attraction to the selfing rate, our models provide a likely common mechanism to explain pollen discounting and an alternative evolutionary pathway to the selfing syndrome.