Adaptation to local temperature environments in zebra mussel, Dreissena polymorpha, populations along the latitudinal gradient formed by the Mississippi River

For chapter 1, we sampled seven populations of zebra mussels along a latitudinal gradient in the Mississippi River. We scored 6 allozyme loci for all individuals using cellulose acetate gel electrophoresis. We analyzed the genetic data for F_is, F_it, and theta to estimate heterozygosity and genetic variation among populations.; In chapter 2 we determined that zebra mussels in southern locations may be more heat-tolerant than those from northern locations, and these population differences may have a genetic basis. Previously we found allozyme differences among populations along the latitudinal gradient formed by the Mississippi River. These populations live under different local conditions including different local average temperatures. This study examined whether populations along the latitudinal gradient formed by the Mississippi River differ in their response to high temperatures. In a common garden experiment we exposed 160 individuals from each of 3 populations along the Mississippi River to 32°C until all individuals expired. Both shell length (P = 0.0015) and a condition index (P < 0.0001) affected survival time, and were therefore included as covariates in the analysis for inter-population differences in heat tolerance. In chapter 3, we continued our genetic research on Zebra mussels, Dreissena polymorpha , which are an aquatic nuisance species originally from the Caspian Sea. We employed amplified fragment length polymorphism (AFLP) analysis on the tissue of the same organisms used in the allozyme study in order to repeat a genetic analysis on the same individuals using a neutral molecular marker. We used analysis of molecular variance (AMOVA) on six population from the Mississippi River and found significant (p < 0.001) genetic variation among populations (F_st = 0.15). Using a Mantel test we tested the correlation of the pair-wise genetic distances to the geographic distances among populations. We found no significant geographic trend in relatedness of individuals using AFLP. We also tested for correlations between genetic distance calculated using allozymes and AFLP's, and found no significant relationship between the two. Also, using unweighted pair group method with arithmetic means (UPGMA) we found no relatedness among individuals by sampling site using AFLP. We had previously found similar results at the five allozyme loci other than Lap. This supports our previous hypothesis that deterministic processes, such as selection maybe acting at the Lap or an adjacent locus. (Abstract shortened by UMI.)...