Date of Award


Degree Type


Degree Name

Doctor of Philosophy


I measured a correlation between the habitat of a freshwater mussel, Lampsilis radiata siliquoidea (Barnes 1823), and its shell morphology and growth rate. I then tried to determine the source of morphological and growth rate variation (environmental or genetic), and whether or not the phenotype/habitat correlation was due to differential adaptation.;Morphometric and annual ring analysis of mussels from Inner Long Point Bay, Lake Erie indicated that L. radiata from more exposed, sandier areas of the bay were faster growing and had thicker shells than those from less exposed, muddy areas. Variation among exposure areas in allozyme phenotypes of two gene loci (PGM and PGI) showed little evidence of genetic divergence. Statistically significant heterogeneity among exposure areas in PGM genotypes was small relative to that between mussel populations in Balsam Lake (in the Trent-Severn watershed) and the lower Great Lakes. Heritabilities of glochidia shell dimensions were low ({dollar}<{dollar}20%), providing little evidence of past or present disruptive selection of shell dimensions. Substrate preference was displayed by the mussels in experimental ponds. L. radiata preferred a finer, more heterogeneous substrate over a coarse sand, and larger mussels showed a stronger substrate preference than smaller individuals. Such habitat preference could influence the breeding structure of the population near the borders of habitat areas.;A laboratory experiment using L. radiata from Inner Long Point Bay showed that the optimal shell morphology for burrowing depended on the substrate the mussel was placed in. Less obese, thinner-shelled mussels were better burrowers in sand; the converse was true in mud. The pattern of optimal burrowing morphologies found in the laboratory experiment did not accurately predict morphological variation in the natural population. This could be because of (i) a poor fitness surrogate (burrowing), (ii) lack of important environmental variation in the experiment (e.g. turbulence), or (iii) a non-adaptive pattern of morphological variation in the natural population.



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