Date of Award

Summer 8-18-2023

Level of Access Assigned by Author

Open-Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Ecology and Environmental Sciences

Advisor

Michael Kinnison

Second Committee Member

Wesley Larson

Third Committee Member

Joseph Zydlewski

Additional Committee Members

David Hiebeler

Kristina Cammen

Abstract

Artificial propagation has been utilized for over a century to offset anthropogenic declines of abundance for many fishes. Complex and poorly documented histories of habitat degradation and stockings have resulted in considerable uncertainty regarding whether contemporary populations are of native, hatchery, or mixed origins. This uncertainty is problematic as it precludes prioritizing the conservation of native populations that are postulated to possess local adaptations and greater evolutionary potential. Population genetics can assess the relative reproductive contributions of previous stocking events and in this dissertation I apply these methods to four empirical studies of native charr (genus Salvelinus) that have been extensively stocked and undergone varying degrees of historical habitat degradation. Results from relatively undisturbed populations in Maine suggest that hatchery contributions have been relatively modest, native populations have not been unintentionally supplanted, and these populations may be able to purge hatchery ancestry. This purging hypothesis is further supported by individual-based simulations intended to mimic the supplemental stocking of maladapted trout into a preexisting native metapopulation. Results from more disturbed regions in the Midwestern United States suggest that historical habitat degradation may have extirpated many native populations as natural (i.e., hydrologically based) population structure is largely absent. These populations do remain significantly differentiated from hatchery strains and similar evidence of hatchery ancestry purging is observed. However, we show that the relatively small effective population sizes of these populations, and limited gene flow between them, allows for rapid genetic drift that can lead to chronic underestimation of hatchery ancestry that is exacerbated with the amount of time since stocking cessation. In contrast, populations of Arctic charr (Salvelinus alpinus oquassa) founded by known stocking events in Maine exhibit slow rates of divergence and largely retain the diversity of their source populations, which afforded the opportunity to determine the genetic origins of historically supplemented populations. Collectively, these results provide information relevant to the conservation and management of local populations, broader insights into evolutionary processes affecting the introgression and purging of hatchery ancestry, and potential pitfalls of commonly used methods to quantify hatchery introgression for species that are prone to rapid genetic drift.

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