Characterization of the migratory phenotype in lake sturgeon
In Lake St. Clair of the Great Lakes system, lake sturgeon (Acipenser fulvescens) are partial migrants, with some individuals out-migrating to lakes and others residing in the river year-round. This population has been previously reported to be panmictic with gene flow occurring between populations. To characterize the migratory phenotype, we analyzed morphometrics, epigenetics, and genetic differentiation using neutral markers. To assess genetic differentiation microsatellites were used to determine if there was gene flow between the river residents and the lake migrators. Lake sturgeon (n=153) were analyzed at 12 microsatellite loci and Bayesian analysis was performed to determine population differentiation. Blood samples and photographs were collected from 150 telemetered fish. We used photographs to analyze 17 morphometric characters for 60 telemetered fish (35 residents, and 25 out-migrators). Morphometric data was analyzed with the principal component analysis (PCA). For the epigenetic analysis, differential methylation was measured using the methylation sensitive (MS)-AFLP protocol on 14 individuals (7 migrants and 7 residents). Two additional years of data will be added to increase the power of this analysis.
Based on the microsatellite loci, it appeared that there is only one population in the St. Clair River system, indicating gene flow among river residents and out-migrators. The results of the PCA on the morphometric data did not support morphologic differences between migratory phenotypes. An AMOVA performed for individual loci detected two restriction sites that were nearly statistically different (ɸ=0.05, P=0.063). Locus 118 and 153 were methylated in four of seven individuals of the migrant phenotype, but were unmethylated in all resident individuals. To increase the power of this analysis, MS-AFLPs will be performed on all telemetered fish. These preliminary results indicate that epigenetic changes are the only differences between the two phenotypes and may be the most useful tool for evaluating rapid adaptation in the presence of substantial gene flow.