Thesis Title

Evidence For Reduced Hawkmoth Pollination in Ruellia Humilis


Jessica Smith

Date of Graduation

Summer 2002


Master of Science in Biology



Committee Chair

John Heywood


Severe habitat fragmentation may be limiting visitation to native plant species by their natural pollinators, and species adapted to pollination by hawkmoths may be especially susceptible. Allozyme markers were used to estimate the historic and current outcrossing rates of four Missouri populations of self-compatible Ruellia humilis in order to assess whether there has been a recent reduction in hawkmoth-mediated outcrossing. The study sites represented both glade and prairie habitat fragments that ranged in size from approximately 10 to 4,000 acres. Historic outcrossing rates were estimated from standing levels of heterozygosity using the mixed mating model. Estimated historic outcrossing rates (th) were significantly greater than current outcrossing rates (tc) for three of the four sites, with the greatest discrepancy observed at the largest fragment (th = 0.584 compared to tc = 0.08). An alternative explanation for the data is that standing heterozygosity has been reduced by inbreeding depression, thus violating an important assumption of the mixed mating model. However, the magnitude of inbreeding depression necessary to explain the results is much greater than values reported for other primarily selfing, herbaceous species. Furthermore, contrary to theory, the population with the highest selfing rate would be required to have the greatest inbreeding depression. Therefore, the results are most consistent with a recent reduction in outcrossing in Missouri populations of R. humilis, presumably due to a reduction in hawkmoth pollination.

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© Jessica Smith