Date of Graduation

Summer 2009


Master of Science in Biology



Committee Chair

John Heywood


inbreeding depression, mating systems, Ruellia humilis, selfing, prairie conservation, purging

Subject Categories



Ruellia humilis is a long-lived perennial herb found commonly in dry prairies and glades within the highly fragmented tallgrass prairie ecosystem. This species is characterized by showy chasmogamous flowers that promote outcrossing via hawkmoths and automatically self-fertilizing cleistogamous flowers which have ensured a long history of partial selfing. Previous studies have indicated a loss of hawkmoth pollination in isolated populations of Southwest Missouri resulting in significantly increased levels of self-fertilization. To examine the consequences of self-fertilization, comparisons were made in a greenhouse between selfed and outcrossed seedlings originating from seeds collected from a Southwest Missouri field population. No evidence was found for inbreeding depression in seedling establishment or survivorship. However, among 502 established seedlings, mean biomass accumulation during the first year of growth was 10% lower in selfed offspring than in outcrossed offspring. No maternal effects on the magnitude of inbreeding depression were detected, and outcrossed offspring were consistently more variable than selfed offspring, suggesting that inbreeding depression is due to many alleles of small effect. These results support earlier studies which indicate that species with an evolutionary history of selfing will typically have purged alleles responsible for early life-history inbreeding depression while maintaining alleles of small effect that cause inbreeding depression in growth and reproduction. Whether or not the loss of outcrossing presents an immediate risk to populations of R. humilis depends on the extent to which the cumulative inbreeding depression increases with age in this long-lived perennial, as well as the reproduction excess generated by the pre-fragmentation mixed mating system.


© Rick Vincent Sander

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