Date of Award
Master of Science
The Red Queen hypothesis posits that, despite its costs, sexual reproduction is ubiquitous because it yields genotypic variation that can be adaptive in spatially or temporally heterogenous environments. Despite this, some metazoan species engage in facultative and even obligate cloning; investigation of these species can shed light on the conditions in which cloning might be an adaptive strategy. Freshwater snails are excellent study species for exploration of these questions due to their variable reproductive modes, relative ease of collection, and low vagility, leading to the ability to gather genetically distinct groups within a small geographic area. Campeloma decisum is a North American freshwater snail comprising both sexual populations, containing males and females, and parthenogenetic populations, containing only females. These two reproductive modes have been observed to be geographically grouped, with the parthenogens found in northern, formerly glaciated regions, and the sexuals living further south. The goal of this study was to obtain representatives from both sexual and parthenogenetic populations and perform phylogenetic analyses to gain insight into the origin of parthenogenesis within this group and elucidate any cryptic genetic diversity. Eleven populations of C. decisum were sampled and 46 cox1 sequences were obtained from them. These data were combined with Campeloma cox1 sequences from GenBank and maximum-likelihood trees were obtained using IQ-TREE. The resulting trees supported distinct sexual and parthenogenetic clusters, separated by relatively long internal branches. However, the outgroup branch was long, and SOWH tests 1) suggest that the position of the root of Campeloma cannot be determined with these data and 2) reject a clade comprising all C. decisum sequences. C. decisum harbors cryptic genetic diversity to the extent that it seems to comprise at least two genetically distinct lineages.
This thesis is only available for download to the SIUC community. Current SIUC affiliates may also access this paper off campus by searching Dissertations & Theses @ Southern Illinois University Carbondale from ProQuest. Others should contact the interlibrary loan department of your local library or contact ProQuest's Dissertation Express service.