Date of Award

5-2005

Level of Access Assigned by Author

Campus-Only Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Marine Biology

Advisor

Philip O. Yund

Second Committee Member

Susan H. Brawley

Third Committee Member

C. Sarah Cohen

Additional Committee Members

Kevin J. Eckelbarger

Paul D. Rawson

Abstract

A survey of published data on self-fertilization in animals reveals that self- fertility is widely distributed among invertebrate species. However, data to completely evaluate the role of self-fertilization in overall reproductive strategies is lacking for most self-compatible species. For the few better studied species, self-fertilization appears to be associated with dispersal distance.

Although most interest in self-fertilization concerns detrimental effects on individuals and populations, benefits may occur under some circumstances. Self- fertilization can ensure reproductive success when mates are unavailable or maintain gene combinations that have been successful. These circumstances should be more common to individuals with limited dispersal. To investigate the potential correlation between dispersal and self-fertility, I evaluated three ascidian species with contrasting dispersal patterns for the ability to self-fertilize, likelihood that they self-fertilize under natural conditions, and consequences of self-fertilization for progeny fitness.

In sessile ascidians dispersal is primarily results from gamete and larval movement. Molgula provisional, a direct developing species with limited dispersal potential, readily self-fertilized even in flowing water and did not exhibit inbreeding depression, suggesting that M. provisionalis utilizes self-fertilization as a component of its reproductive strategy. Botryllus schlosseri has limited larval dispersal but may realize greater gene flow through long-lived sperm. Colonies of this species exhibited high levels of self-fertilization when self-sperm were available. However, temporal separation of male and female phases appears to effectively prevent self-fertilization under natural conditions. Self-fertilized progeny of B. schlosseri suffered severe inbreeding depression, suggesting that self-fertilization plays a limited role in its reproductive biology. Ciona intestinalis, the most dispersive species, exhibited intra-specific variation in self-fertility. Self-compatible individuals were unable to self-fertilize in limited water flow, and self-fertilized C. intestinalis progeny exhibited reduced fitness at all life stages examined. These results suggest that C. intestinalis is not naturally self-fertilizing. Because intra-specific variability exists for self-fertility in C. intestinalis, potential genetic and environmental influences on the trait of self-fertility were investigated, but results were inconclusive. Similar to the patterns evident among the reviewed species, the ascidian species used in this study with the most limited dispersal is the most likely to use self-fertilization as part of its life history strategy.

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