PARENT SESSION
Oral Session 6: Herbivory I: Dynamics, Communities, and Photosynthesis.
Presiding: C Ivey
Monday, August 2, 8:00 AM to 11:30 AM, Meeting Room B 114.

Pollinators, herbivores, and plant sex: The community genetics of plant mating systems.

Ivey, Christopher^{*,1, 2}, Carr, David², ¹ Illinois Natural History Survey, Champaign, IL² University of Virginia, Boyce, VA

ABSTRACT- Mating systems, and in particular selfing rates, are one of the strongest predictors of genetic diversity in plant populations. Identifying factors that contribute to variation in selfing rates can therefore highlight mechanisms maintaining diversity in plants. Selfing rates vary widely among plant populations, and prior work has established that some of this variation can be traced to the behavior of mutualistic pollinators. In contrast, the role of antagonistic interactions for selfing rate variation has been largely unexplored, despite evidence that antagonists can alter pollinator behavior and other factors likely to influence selfing. Moreover, recent studies have found inbreeding to alter the impact of antagonists on plants, which may in turn affect selfing rate variation. These previous observations motivated a 2 x 2 factorial experiment that explored the influences of inbreeding and spittlebug (Philaenus spumarius) herbivore attack on pollinator behavior and selfing rates in Mimulus guttatus. Pairs of self-fertilized and randomly outcrossed plants from multiple plant families were placed in arrays in the field, and one member of each pair received a single spittlebug nymph. We measured floral characters, pollinator behavior, and examined allozyme variation in the seeds at the end of the season to estimate selfing rates of plants. Self-fertilized plants had 24% fewer flowers, 15% smaller flowers, and as a consequence, received one-third fewer visits from pollinators. Pollinators also spent an average of five seconds longer while visiting inbred flowers, which may have improved transfer of outcross pollen. Spittlebug herbivores reduced flower size by 7%, but had no significant effect on pollinator behavior. Inbreeding reduced selfing rates by about one-half, which may have been a consequence of altered pollinator behavior or early-acting inbreeding depression. In contrast, spittlebugs increased selfing rates twofold, which may indicate that spittlebugs trigger post-pollination resource shifts in Mimulus. To our knowledge, this is the first evidence identifying herbivores, a ubiquitous natural enemy of plants, as an ecological force contributing to mating system variation in plants.

Key words: pollination, herbivory, inbreeding, mating systems