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Date of Award

1979

Document Type

Thesis - Pacific Access Restricted

Degree Name

Master of Science (M.S.)

Department

Graduate School

First Advisor

Steven Obrebski

First Committee Member

Joel W. Hedgpeth

Second Committee Member

Edmund H. Smith

Abstract

Genetic variation at twelve loci which code for enzymes and non-enzymatic protein has been studied by means of starch gel electrophoresis in two apparent species of the pelecypod genus Transennella, Variable allozymes include esterase, leucine aminopeptidase, malate dehydrogenase, phosphoglucose isomerase, tetrazolium oxidase, and nonenzymatic protein, Observed allele frequencies for these systems are in close agreement with Hardy-Weinberg expectations indicating that these protandric hermaphrodites are outbreeding. The genus is characterized by two distinct morphotypes which differ in shell shape and pigmentation. Genetic similarity (I) and genetic distance (D) statistics were computed for the two morphotypes and for two populations of each morphotype. The I and D values derived from intraspecific comparisons of Transennella tantilla populations are 0.99 and 0,004; for Transennella sp., the I value is also 0.99 and D is 0,002. The I and D values obtained from interspecific comparisons (T. tantilla versus T, sp.) are 0,521 and 0,650 respectively. An extensive survey of the phosphoglucose isomerase system was conducted to evaluate microgeographic variation and age-dependent frequency selection at this locus. Differences in allele frequencies were found to be non-significant, suggesting that this locus is without selective import, or that selection for a particular genotype is too slight to be detected with the sample sizes employed, The amount of genetic divergence found between the morphotypes is comparable to interspecific estimates made for a variety of invertebrate species. The results indicate that the morphological divergence apparent in the two morphotypes has been accompanied by substantial genetic differentiation.

Pages

71

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