Crayfish populations genetically fragmented in streams impounded for 36–104 years

Abstract

Dams and their associated impoundments may restrict dispersal and gene flow among populations of numerous freshwater species within stream networks, leading to genetic isolation. This can reduce effective population sizes and genetic diversity, increasing the risk of local extinction. We studied crayfishes from multiple up‐ and downstream sites in three impounded and two unimpounded streams in the Bear Creek and Cahaba River drainages, Alabama, U.S.A. Using mitochondrial DNA (cytochrome oxidase subunit I gene) sequence data generated from population‐level sampling of two abundant native crayfishes, Faxonius validus and Faxonius erichsonianus (Decapoda: Cambaridae), we assessed species’ spatial genetic structure and genetic diversity, estimated the magnitude and directionality of gene flow, and compared results between the species. For both species, levels of genetic diversity (number of haplotypes, and haplotypic and nucleotide diversity) were the same or higher in impounded compared to unimpounded streams. Conversely, crayfish populations in up‐ and downstream sections of unimpounded streams displayed high genetic similarity and bidirectional gene flow, whereas in impounded streams, crayfish populations typically had greater up‐ and downstream genetic differentiation and predominantly unidirectional, downstream gene flow. Although impoundments were associated with lower connectivity between up‐ and downstream sections for F. validus and F. erichsonianus, the magnitude of genetic effects was species‐specific, with greater differentiation between F. validus populations up‐ and downstream of impoundments. In an ecologically short timeframe, impoundments appear to have fragmented stream crayfish populations, and even species with relatively high abundances and large ranges had lower gene flow among populations in impounded streams compared to unimpounded streams. In addition, feedbacks between genetic and demographic effects on fragmented populations may decrease the probability of long‐term persistence.

Assessing Genomic Diversity, Connectivity, and Riverscape Genetics Hypotheses in the Endangered Rough Hornsnail,Pleurocera Foremani, Following Habitat Disruption

“…IBD influences genetic diversity across the riverscape, which is likely a phenomenon that predates dam construction as IBD is common in freshwater taxa from non-modified habitats ( Blanchet et al 2010 ; Meffe and Vrijenhoek 1988 ). Higher levels of genetic diversity in Lake Mitchell and the Coosa River at Wetumpka compared with sites in the Coosa River tributary Yellowleaf Creek are also likely a result of historical genetic diversity, and fragmentation does not appear to be causing decreases in genetic diversity of remaining P. foremani populations compared to other freshwater species ( Dehais et al 2010 ; Faulks et al 2011 ; Fluker et al 2014 ; Sotola et al 2017 ; Yamamoto et al 2019 ; Barnett et al 2020 ; Rougemont et al 2020 ). For example, Barnett et al (2020) observed a decrease in genetic diversity of crayfish across impoundments in as little as 36 years, about 36 generations, while P. foremani has been impounded for almost 100 years, around 100 generations.…”

“…Higher levels of genetic diversity in Lake Mitchell and the Coosa River at Wetumpka compared with sites in the Coosa River tributary Yellowleaf Creek are also likely a result of historical genetic diversity, and fragmentation does not appear to be causing decreases in genetic diversity of remaining P. foremani populations compared to other freshwater species ( Dehais et al 2010 ; Faulks et al 2011 ; Fluker et al 2014 ; Sotola et al 2017 ; Yamamoto et al 2019 ; Barnett et al 2020 ; Rougemont et al 2020 ). For example, Barnett et al (2020) observed a decrease in genetic diversity of crayfish across impoundments in as little as 36 years, about 36 generations, while P. foremani has been impounded for almost 100 years, around 100 generations. Similarly, Faulks et al (2011) demonstrated that in as little as 10 years, or 3 generations, the Macquarie perch ( Macquaria australasica ) experienced significant bottlenecks and population diversity declines.…”

“…For example, Fluker et al (2014) showed that a single hydropower impoundment on the Tallapoosa River resulted in decreased gene flow among populations of the fishes Etheostoma tallapoosae and Cyprinella gibbsi. Similarly, Barnett et al (2020) recently established that within timeframes as short as 36 years after impoundment, crayfish experienced significant genetic fragmentation in the Bear Creek and Cahaba River drainages in Alabama and Mississippi. Outside of the southeastern United States, fragmentation has been shown to hinder gene flow and decrease genetic diversity of fish ( Blanchet et al 2010 ; Dehais et al 2010 ; Faulks et al 2011 ; Gouskov et al 2015 ; Sotola et al 2017 ; Yamamoto et al 2019 ) and mussels ( Liu et al 2019 ).…”

“…Furthermore, determining genetic responses to anthropogenic activities is central to conservation genetics ( Khan et al 2016 ; Allendorf 2017 ). Despite well-documented declines of freshwater fauna in the southeastern United States ( Williams et al 1993 ; Lydeard and Mayden 1995 ; Neves et al 1997 ; Johnson et al 2013 ), little or no data exist about riverscape genetics of most species (but see Fluker et al 2014 ; Whelan et al 2019 ; Barnett et al 2020 ; Wright et al 2020 ). This hinders broad understanding of how genetic patterns in a global biodiversity hotspot are influenced by human activity.…”

The Use of Barriers to Limit the Spread of Aquatic Invasive Animal Species: A Global Review

“…However, river-resident fish also need to undertake longitudinal movements to forage, spawn, seek refugia, and recolonise vacant habitat patches (Meyers et al, 1992;Lucas and Baras, 2008), and multiple lines of evidence suggest even small barriers can have negative impacts on potamodromous fish (Junker et al, 2012;Branco et al, 2017;Coleman et al, 2018). Nor are barrier effects restricted to fish, with documented impacts on crustaceans (Barnett et al, 2020), amphibians (Murphy et al, 2018), reptiles (Bennett et al, 2010), and molluscs (Watters, 1996). Indeed, all biota need to disperse; such movement is essential to the maintenance of metapopulations, enables recolonisation following natural disturbances, and contributes to the maintenance of biodiversity (Fullerton et al, 2010).…”