Direct and indirect effects of predation on genetic variability and phenotypic divergence in yellow perch (Perca flavescens)

Yellow perch (Perca flavescens) are relatively acid- and metal-tolerant and often persist as one of the few remaining fish species in a damaged/acidified lake or are at least one of the species that first colonizes a lake once water quality improves. However, with time and increased chemical recovery in Sudbury lakes, other fish species that are potential predators of perch (e.g., walleye (Sander vitreus), smallmouth bass (Micropterus dolomieu), northern pike ( Esox lucius)) are also beginning to colonize Sudbury lakes. As these lakes recover, perch are therefore forced to cope not only with persistent stressful chemical conditions but must also adapt to changes in predation and intra/interspecific competition for food resources. Such predation or competition pressures often lead to habitat polymorphisms that involve the exploitation of two very different habitats: the littoral (or nearshore) and the pelagic (open water) zones. The addition of a predator to an established perch population generally causes the perch to abandon the pelagic zone and increase their use of the littoral habitat.;Microsatellite genotyping is an efficient and powerful tool that can provide information about the genetic structure of populations. However, it is known to be prone to errors that can affect downstream analysis. Genotyping errors in my study caused several microsatellite loci to be dropped from the analysis, which decreased the statistical significance of my results. Despite this, there are interesting trends that were revealed and recommendations for further analysis to increase the robustness of the study are suggested.;Initial analysis revealed that differences in genetic variability between perch in littoral and pelagic habitats accounted for 2% of the total variability among lakes. This evidence suggests that the increase in littoral habitat use affects, or is associated with, changes in the genetic variability of the littoral population. There was also a positive correlation between perch biomass and genetic variability in both the littoral and pelagic habitat.;The results suggest that the type of predator and its preferred location may play a role in determining the dispersal of yellow perch and consequently their levels of genetic variability. In lakes where the primary predator was smallmouth bass, a littoral zone predator, the genetic variability of perch in the littoral zone was slightly higher than in the pelagic zone. On the other hand, in lakes where the primary predator is walleye, a pelagic predator, the pattern reversed and the genetic variability of perch in the pelagic habitat was slightly higher than in the littoral zone.;In this study, genetic structure was assessed over two years in Sudbury yellow perch populations within littoral and pelagic habitats along a predation gradient in eight lakes using microsatellite genotyping. One of the study lakes (Hannah Lake) was experimentally manipulated by adding predators (smallmouth bass) to a perch population, thus creating a unique opportunity to study the immediate effects of predators on the genetic structure and morphological traits of a perch population.;Habitat polymorphisms can also lead to changes in morphological traits such as those associated with adaptation to food resources or predator avoidance. Analysis of ten morphological characteristics was conducted to allow comparisons between genetic and phenotypic differentiation. Results from this study suggest that these morphological traits are under divergent selection and represent local adaptations.;These results provide support for the link between predation pressure, phenotypic plasticity, and genetic structure of perch population. The presence of predators appears to be associated with differences in genetic variability in yellow perch populations across habitat gradients. These genetic differences occur over small spatial scales and should be taken into consideration when planning conservation efforts. Genetic variation is hypothesized to be key for long-term evolutionary change and short-term environmental adaptation and, thus, has the potential to influence restoration efforts.