Degree Name

Master of Science (MS)

Semester of Degree Completion

2003

Thesis Director

Charles L. Pederson

Abstract

The exotic zooplankter Daphnia lumholtzi is believed to have been introduced into Fairfield Lake, TX in 1983. Since introduction, D. lumholtzi has spread throughout the Midwest and Southeast United States. Due to its large head and tail spines, it may be less susceptible than native species to predation and therefore pose a threat to aquatic ecosystems. Development of management practices calls for study of the dispersal and potential impact of D. lumholtzi on invaded ecosystems.

Inter-simple sequence repeat (ISSR) markers were used in an effort to determine dispersal patterns of D. lumholtzi. Previous studies have shown that ISSRs possess sufficient levels of variability to reveal relationships at the population level. My objectives were to i) examine the utility of ISSRs in defining clonal groups within and across populations of D. lumholtzi, ii) look for genetic variation that may imply alternative sources of introduction of D. lumholtzi into North America and, iii) assess dispersal patterns of D. lumholtzi across parts of North America. Analysis included populations from Illinois, Kentucky, and Tennessee, as well as the population at Fairfield Lake, Texas.

Eighteen primers were screened and two were found to be variable with respect to the D. lumholtzi populations sampled. The primers BECKY (CA)7YC and OMAR (GAG)5RC produced a total of 812 ISSR fragments of which 677 (83%) were polymorphic. Overall similarity of individuals inferred from presence/absence of bands was used to draw conclusions about D. lumholtzi populations. Cluster analysis (UPGMA) of ISSR banding patterns revealed a potential presence of two clonal lineages within the Fairfield Lake population and a large amount of genetic variation within and across all other populations sampled. Observed high levels of genetic variation in all populations except Fairfield Lake, suggests that Fairfield Lake is not the source population as is widely accepted. Furthermore, it appears that the genotypes present at Fairfield Lake are a subset of the numerous genotypes present in the other populations analyzed. If Fairfield Lake is in fact the source of introduction of D. lumholtzi into North America, my data suggest dispersal of D. lumholtzi across the U.S. resembles a "stepping stone" model of dispersal with one (or several) long distance dispersal event(s) originating at Fairfield Lake followed by several short distance dispersals.

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