Year of Award

2022

Document Type

Dissertation

Degree Type

Doctor of Philosophy (PhD)

Degree Name

Fish and Wildlife Biology

Department or School/College

Wildlife Biology Program

Committee Chair

Andrew Whiteley

Commitee Members

Lisa Eby, Winsor Lowe, Paul Lukacs, Gordon Luikart

Keywords

Brook trout, Conservation genomics, Effective number of breeders, Fisheries, Genetic monitoring, Genetic rescue

Abstract

Brook trout (Salvelinus fontinalis) populations have experienced dramatic declines throughout their native range, in part, due to anthropogenic land use and habitat fragmentation. In the mid-Atlantic region, brook trout populations often occupy small, headwater habitat fragments in demographic and genetic isolation, making them vulnerable to inbreeding and genetic drift. My dissertation evaluates different methods for genetic assessment, monitoring, and management of small, isolated brook trout populations. First, I examined the potential value of effective number of breeders (Nb) estimates for genetic monitoring by determining whether Nb estimates were sensitive to habitat characteristics known to affect brook trout populations. Using genetic data from 71 brook trout habitat patches, I found significant evidence that Nb estimates were positively related to habitat size and base flow index, and negatively related to temperature. These results provide further support for the use of Nb in genetic assessments and monitoring of isolated salmonid populations. Human-mediated gene flow is a promising approach to reduce extinction risk and alleviate negative fitness effects associated with small effective population size (i.e., genetic rescue). However, there had not been an assessment of the statistical power of commonly used approaches to determine fitness effects of gene flow, despite calls for more widespread use of human-mediated gene flow. I addressed this need by using individual-based simulations of gene flow and found that these monitoring approaches frequently suffered from low statistical power but also identified strategies to improve inference. Finally, I examined the multigenerational effects of genetic rescue in a small, isolated population of brook trout and found consistent evidence of elevated fitness in F1 hybrids as compared to resident individuals. In contrast, I found a negative relationship between proportion migrant ancestry and lifetime reproductive success in backcrosses (F2 and later generations). Still, backcrosses with less than 0.48 migrant ancestry had lifetime reproductive success greater than residents, on average. These results highlight that gene flow often introduces beneficial and deleterious variation with the net-effect depending on the efficacy of natural selection, which suggests that ecological conditions affecting demography can play an outsized role in determining the outcome of genetic rescue attempts.

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© Copyright 2022 Zachary Lorn Robinson