Inbreeding and Ecological Interactions |
| Inbreeding is ubiquitous in plants. Over 80% of plants have selfing rates in excess of 20%, and the evolution of selfing has been one of the most common and widespread evolutionary trends. Limited seed and pollen dispersal can also result in high levels of inbreeding because the genetic neighborhood of any given plant likely contains many close relatives. The negative effects of inbreeding on plant fitness have been well documented, but only recently have investigators focused on its effects on ecological interactions. My colleagues and I have been interested in the effects of inbreeding on the interactions between plants and both their antagonists and their mutualists. We have demonstrated that by altering host plant quality, resistance, tolerance, and rewards, the effects of inbreeding in the host plants can extend into herbivore, pathogen, and pollinator populations through these interactions. For example, inbreeding in the monkey flower, Mimulus guttatus, can reduce tolerance to herbivory by the meadow spittlebug, Philaenus spumarius (pictured right). Inbreeding in M. guttatus can have both positive and negative effects on P. spumarius, increasing adult body size but also increasing development time. This has important implications for conservation biology as well as mating-system evolution. | |
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Inbreeding alters the distribution of genetic variation. It therefore should also effect how adaptive traits evolve by changing levels of additive genetic variation, genetic correlations, and linkage disequilibrium. My colleagues and I are currently examining how mating-system evolution in Mimulus affects the evolution of host plant defenses. We have found in surveys of M. guttatus species complex that plants with smaller corollas and reduced stigma-anther separation (traits typical of Mimulus with high selfing rates) have fewer glandular trichomes on their leaves (pictured left). We are starting experiments to evaluate whether this reflects an allocation trade-off (e.g., fast development trading-off against investment into defense) or whether the evolution of selfing constrains the evolution of other potentially adaptive traits. |
| Inbreeding can also affect mutualistic interaction. Inbreeding drastically reduces male fertility in M. guttatus. Because pollen is the primary reward in this species, inbred plants may not be profitable to pollinators. My colleagues and I have documented in several studies that bumble bees and other pollinators discriminate strongly against inbred plants. Bees seem to respond to a number of cues, but we have found that pollen viability and total pollen production strongly influence the probability of visitation. Using experiments with artificial flowers provisioned with M. guttatus pollen, we are gathering evidence that suggests that bumblebees can use olfactory cues from pollen and anthers to make appropriate foraging decisions. | |