Date of Award


Publication Type

Doctoral Thesis

Degree Name



Biological Sciences


Biology, General.



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Creative Commons Attribution-Noncommercial-No Derivative Works 4.0 License
This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 4.0 License.


A large scale survey of natural populations of Daphnia pulex was undertaken in the spring of 1985. Seventy seven populations were sampled from southwestern Ontario and central Michigan. Clones were also collected from Churchill, Manitoba. Clonal characteristics were determined by protein electrophoresis and restriction fragment pattern analysis of mitochondrial DNA. A large amount of genetic variability was revealed by both the electrophoretic and mitochondrial data sets. A total of 104 genetically distinct clones were discovered. Comparison of the two data sets revealed that the obligate asexuals must have arisen polyphyletically from cyclic parthenogenetic ancestors. Contagious spread of a dominant sex-limited meiosis suppressor is the most probable mechanism by which such a process could have occurred. Asexuality apparently arose in the north and is presently spreading southward at the expense of sexual populations. These results have important implications for the evaluation of the ecological and evolutionary potential of asexuals. The observed distribution of asexuals may reflect intrinsic genetic constraints rather than an optimization of breeding strategy by natural selection.Dept. of Biological Sciences. Paper copy at Leddy Library: Theses & Major Papers - Basement, West Bldg. / Call Number: Thesis1988 .S735. Source: Dissertation Abstracts International, Volume: 49-04, Section: B, page: 0986. Thesis (Ph.D.)--University of Windsor (Canada), 1988.