Fragmentation and patch size shape genetic structure of brook trout populations

Abstract

We tested the relative influence of habitat patch size and connectivity on genetic structure and effective population size in eight brook trout (Salvelinus fontinalis) habitat patches in a watershed in Virginia, USA. Variation at eight microsatellite loci in 2229 young-of-the-year brook trout for two successive cohorts (2010 and 2011) was examined. Genetic differentiation across all populations was pronounced. Overall [Formula: see text] was 0.397 (95% CI: 0.322–0.525) and overall FST was 0.124 (95% CI: 0.096–0.159). Above-barrier patch size had a strong positive relationship with genetic diversity, [Formula: see text], and genetic differentiation. Our analysis is consistent with greater extinction risk in smaller above-barrier patches. Larger above-barrier patches contained greater genetic diversity but reduced [Formula: see text] relative to adjacent below-barrier patches. The primary effect of barriers may be to reduce available above-barrier spawning habitat, even for larger above-barrier patches. Below-barrier patches also showed evidence of reduced genetic diversity and lack of connectivity. Genetic monitoring focused at gaining a broader understanding of the relationships here will be necessary to fully evaluate local extinction risks.

River mainstem thermal regimes influence population structuring within an appalachian brook trout population

“…Finally, Bayesian and maximum likelihood clustering methods found little evidence of population substructure within Shavers Fork. In contrast to recent studies documenting strong population structuring in systems with barriers to dispersal (e.g., Whiteley et al (2013)), our results show that in the absence of barriers, brook trout may exhibit low levels of differentiation among tributaries.…”

“…The causes of these continuing declines include overharvest, acid precipitation, habitat degradation, competition with non-native species, and climate change (Petty and Thorne 2005;Flebbe et al 2006;McClurg et al 2007;Hudy et al 2008). An important consequence of habitat loss and/or degradation for stream dwelling fishes like brook trout is isolation, which may lead to reduced gene flow among populations making them more susceptible to stochastic environmental events and elevated genetic drift, potentially leading to the loss of unique adaptive variability (Fagan 2002;Allendorf and Luikart 2007;Whiteley et al 2013). Consequently, there is considerable demand for implementation of restoration programs that will maximize population recovery and resilience of brook trout (EBTJV 2013;Petty and Merriam 2012).…”

“…This information is used to make decisions about whether management should focus on protection and restoration of isolated habitats and populations or whether it should focus on restoring connectivity of habitats and metapopulations at the scale of whole watersheds (Fausch et al 2002). Genetic studies of contemporary brook trout populations in the central and southern Appalachians show that they persist primarily as fragmented and genetically isolated units (Richards et al 2008;Hudy et al 2010;Kanno et al 2011;Whiteley et al 2013). Typical explanations for the observed population structuring include natural and artificial barriers to dispersal (e.g., waterfalls, dams, reduced flow), dependence of brook trout on cold water, competition with exotic fishes such as rainbow trout (Oncorhynchus mykiss) and brown trout (Salmo trutta), and habitat degradation and warming in larger river main stems that historically served as dispersal corridors.…”

Effective number of breeders, effective population size and their relationship with census size in an iteroparous species,Salvelinus fontinalis

“…These results suggest that published estimates of effective population size obtained with random samples of individuals of mixed ages for iteroparous species with overlapping generations and even those based on unadjustedN b can be biased, and should thus be considered with caution. As seen in other studies [15][16][17], we also found thatN eðadj2Þ /N c ratios were variable across populations in the same geographical area, ranging from a high of 0.29 (CY) to a low of around 0.01 (e.g. CV, TB).…”

“…Resident salmonid populations inhabiting small streams generally exhibit relatively short generation times, facilitating the study of the relationship between effective and census population sizes. Recent studies have produced variable estimates of N b /N c for stream brook trout populations, with large differences among studies as well as among populations within studies in these ratios [15][16][17]. The differences have been linked to differences in habitat variability and habitat quality, which in turn result in differences in census population size and potentially also in life-history traits such as age and size at maturation, and age-specific survival or reproductive lifespan [15,17].…”