Brook Trout Population Genetic Tools for Natural Barriers in Fragmented Subwatersheds

Barriers to fish movement can cause aquatic habitat fragmentation by reducing the amount of available habitat. The primary goal of my research was to investigate applications of population genetic analysis tools as indicators of barrier effects on brook trout populations in fragmented subwatersheds.

In chapter1, I tested the hypothesis that brook trout population genetic differentiation (FST) above and below barriers will differ in relation to barrier height and gradient. I also tested the hypothesis that average gene diversity per locus (H) and the numbers of alleles (A) differed between samples below and above each barrier. There was no significant difference in average number of alleles (A) or average gene diversity per locus (H) between the above- and below-barrier samples, but linear regression identified a statistically significant relationship between barrier height and FST values. Unrooted neighbor-joining consensus trees of Cavalli-Sforza and Edwards (1967) chord distances provided evidence of genetic differentiation between samples of resident brook trout above and below natural barriers. Additionally, average total allelic diversity (A), average gene diversity per locus (H), average number of private alleles per locus per sample, and total alleles per sample differed between Level III Ecoregions.

In chapter 2 I tested the hypothesis that the presence of a barrier, total habitat potentially isolated above a barrier (km), road density, and percent forest cover within a subwatershed (USGS 6th-level Hydrologic Units) were significant habitat fragmentation factors affecting the effective population size (Ne) of brook trout in the Blue Ridge Level III Ecoregion. Multivariable linear regression indicated that total habitat above the barrier (km) and road density were significant variables retained in the model to predict Ne.

In chapter 3, the objective of the study was to infer relationships between barriers and family structure in brook trout populations. Maximum likelihood analysis of pairwise kinship relationships between above- and below-barrier individuals indicated the presence of parent-offspring relationships between above- and below-barrier individuals at six sites in the Blue Ridge Level III Ecoregion and five sites in the Northern Lakes and Forests Level III Ecoregion, which indicated movement of individuals between the above- and below-barrier locations.