CARR, DAVID E.1*, MICKY D. EUBANKS2, and CHRISTOPHER T. IVEY1. 1Blandy Experimental Farm, University of Virginia, 400 Blandy Farm Lane, Boyce, VA, 22620; 2Department of Entomology and Plant Pathology, 301 Funchess Hall, Auburn University, Auburn, AL, 36849. - Inbreeding and its effects on plant-herbivore interactions.
Studies of the genus Mimulus have made important contributions
to our understanding of the effects of inbreeding on plant fitness.
The genetic and phenotypic changes produced by inbreeding may have
effects beyond the boundary of the inbreeding population, however, by
altering ecological interactions with other species. Genetic studies
of ecological interactions have focused primarily on adaptive
evolutionary change, but few studies have considered the nonadaptive
loss of genetic variation produced by inbreeding. Mimulus
guttatus has proven to be an excellent system in which to study
the interspecific effects of inbreeding. In greenhouse studies we have
demonstrated that inbreeding in M. guttatus can reduce
tolerance to attack by spittlebugs (Philaenus spumarius).
Spittlebugs have almost no impact on outbred plants but can reduce
biomass by as much as 30% in inbred plants. Herbivory greatly
increases inbreeding depression and could therefore affect
mating-system evolution, but the interaction between inbreeding and
herbivory is two-sided. Spittlebugs can take 10% longer to develop on
inbred plants and even display a preference for less inbred host
plants, suggesting that inbreeding reduces host plant quality.
Recently we have produced self and outcross progeny from four M.
guttatus populations by controlled hand-pollinations in the
greenhouse and transplanted these seedlings back into their home sites
in Napa County, California. These ongoing studies are examining the
natural colonization of inbred and outbred M. guttatus by a
range of herbivores and will document the impact of herbivory in the
Key words: herbivory, host plant quality, inbreeding, mating system, Mimulus guttatus, tolerance