Many hermaphrodite plants (and some animals) — including many crops — have what is called a mixed mating reproductive strategy. That means they reproduce by both self- and cross-fertilization, with important consequences for the amount and structure of their genetic variation. The prevalence of mixed mating systems is surprising because inbreeding depression should work to get rid of self-fertilization, resulting in “pure strategies of either outcrossing or selfing.” Now a new study suggests that its natural enemies — pests, parasites, herbivores, etc. — may have a strong effect on the evolution of a plant’s mating systems:
For example, enemies may alter the availability of mates in a population, which may have direct consequences for victim mating system evolution. Enemies may also influence the expression of traits that are important for mating system evolution, thereby improving the evolutionary stability of mixed mating as a reproductive system.
Thus the dynamics of the interactions between a species and the biodiversity that surrounds it can counter the effects of inbreeding depression and lead to the stability of an otherwise doomed evolutionary strategy. I wonder how important this has been in the evolution of agrobiodiversity. After all, concentrating plants in dense near-monocultures like agriculture does is a boon to natural enemies.