Date of Award

Spring 5-1-2025

Document Type

Thesis

Degree Name

Master of Science in Coastal Marine and Wetland Studies

Department

Coastal and Marine Systems Science

College

College of Science

First Advisor

Derek Crane

Second Advisor

John J. Hutchens

Third Advisor

Megan Cevasco

Additional Advisors

Tanya Darden; Mark Scott

Abstract

Habitat loss, fragmentation, and land use changes in river networks are common globally. The resulting fragmentation of landscapes and riverscapes threatens biodiversity and can affect dispersal and subsequently, gene flow and genetic health of species. Headwater streams are an integral part of river networks and contribute to biodiversity by providing habitat for temporary and permanent residents, yet they are easily altered and fragmented. The sandhills chub (Semotilus lumbee) is an endemic headwater leuciscid that lives in highly fragmented streams of the sandhills ecoregion in North and South Carolina, USA. New knowledge on the population genetics of the sandhills chub is available, and anthropogenic dams that may limit gene flow, reduce genetic diversity, and threaten their long-term species viability are pervasive throughout their geographic distribution. Therefore, I used a newly-generated genetic dataset utilizing 23 microsatellite loci to investigate the relationships between dam distributions and sandhills chub genetic differentiation, genetic diversity, and inbreeding rates. Genetic samples were collected from 887 sandhills chubs across 30 sites, spanning the geographic distribution of the species. I used spatial analyses to quantify distances between sites, the number of dams between sites, upstream drainage areas (km2), cumulative free-flowing stream length connected to a site (km), and the number of dams upstream and downstream of sites. Bayesian linear models were used to investigate the relationship between pairwise FST, distance between sites, and the number of dams between sites. Additionally, I used Bayesian linear mixed models to investigate relationships between metrics of genetic health (i.e., HE, NA, G-W, and FIS), with upstream drainage area, length of free-flowing stream connected to a site, and the number of dams upstream and downstream from a site. Pairwise FST values ranged from 0.014 to 0.425 and unrelated to the number of dams between sites. Instead, genetic differentiation was related to whether sites were within the same sub-watershed. Genetic diversity was moderate at most sites (mean HE = 0.446), and unrelated to dams or site attributes. There was evidence of a distribution-wide bottleneck observed across all sites which likely reflects geological events (stream capture/isolation) rather than anthropogenic fragmentation of streams over the last 150 years. This study provides a framework for assessing relationships between genetic differentiation, genetic diversity, and fragmentation across riverscapes. Although fragmentation can have deleterious genetic effects on populations through reduction of effective population sizes, gene flow, and genetic variation, barriers may be irrelevant to the ecology of species that evolved in isolated habitats.

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