Determinants and evolutionary consequences of effective population size in Atlantic salmon (Salmo salar).

摘要

A proper understanding of patterns and processes that determine evolutionary change in natural populations is required to effectively preserve biodiversity and develop conservation programs based on evolutionary considerations. Effective population size (Ne) is a central evolutionary concept that determines the outcome of the combined forces of natural selection, genetic drift and geneflow. Ne is therefore also relevant to understanding the importance of genetic factors affecting the persistence of populations and species. This thesis concerns Atlantic salmon (Salmo salar), a culturally and economically important species that has experienced worldwide declines, and focuses on rivers in Newfoundland and Labrador subject to former commercial exploitation. The purpose of this thesis was to quantify spatial and temporal genetic patterns over the last six decades, testing hypotheses about metapopulation dynamics and the genetic consequences of population declines. Firstly, I investigated population structure, examining the role of population size in shaping dispersal and geneflow patterns. Contemporary geneflow patterns may be underpinned by population size, though life history also affects geneflow and population structure can vary regionally. Next, a review of the literature suggested that Ne estimates may indeed indicate the importance of genetic threats to population persistence, but only after some sources of bias are accounted for. Genetic threats are most relevant for small and isolated populations, thereby emphasizing the importance of geneflow for population persistence. I then investigated effective population sizes in Newfoundland rivers in the context of demographic imbalance associated with the closure of the commercial fishery. Results indicate a lack of strong genetic erosion, possibly due to life history diversity, density-dependent factors and incoming geneflow. An examination of relative and absolute changes in contemporary geneflow suggests that abundance increases may have resulted in elevated population connectivity, hence providing one explanation for changes in Ne after the fishery closure. In conclusion, this thesis underlines the links between contemporary demography and genetic processes, and provides templates for future testing of hypotheses regarding local adaptation. An interpretation in the context of conservation suggests that Atlantic salmon management in Newfoundland may be most effective at scales larger than the individual river.