Artificial barriers prevent genetic recovery of small isolated populations of a low-mobility freshwater fish

Abstract

Habitat loss and fragmentation often result in small, isolated populations vulnerable to environmental disturbance and loss of genetic diversity. Low genetic diversity can increase extinction risk of small populations by elevating inbreeding and inbreeding depression, and reducing adaptive potential. Due to their linear nature and extensive use by humans, freshwater ecosystems are especially vulnerable to habitat loss and fragmentation. Although the effects of fragmentation on genetic structure have been extensively studied in migratory fishes, they are less understood in low-mobility species. We estimated impacts of instream barriers on genetic structure and diversity of the low-mobility river blackfish (Gadopsis marmoratus) within five streams separated by weirs or dams constructed 45–120 years ago. We found evidence of small-scale (<13 km) genetic structure within reaches unimpeded by barriers, as expected for a fish with low mobility. Genetic diversity was lower above barriers in small streams only, regardless of barrier age. In particular, one isolated population showed evidence of a recent bottleneck and inbreeding. Differentiation above and below the barrier (FST = 0.13) was greatest in this stream, but in other streams did not differ from background levels. Spatially explicit simulations suggest that short-term barrier effects would not be detected with our data set unless effective population sizes were very small (<100). Our study highlights that, in structured populations, the ability to detect short-term genetic effects from barriers is reduced and requires more genetic markers compared to panmictic populations. We also demonstrate the importance of accounting for natural population genetic structure in fragmentation studies.

Riverscape genetics in brook lamprey: genetic diversity is less influenced by river fragmentation than by gene flow with the anadromous ecotype

“…Despite the strong asymmetric gene flow toward downstream populations (probably due to passive drift of larvae), restoring the possibility for upstream active migration from downstream populations could increase genetic diversity and evolutionary potential in the most upstream populations (Brauer et al, 2016;Pavlova et al, 2017;Coleman et al, 2018). In addition, our comparative analyses among sympatric, parapatric and allopatric areas support the hypothesis that sympatric populations display higher levels of genetic diversity due to introgression from L. fluviatilis (Rougemont et al, 2015(Rougemont et al, , 2016(Rougemont et al, , 2017.…”

Simulation of over‐exploitation of ornamental fish and its consequences for the functional structure of assemblages of Amazonian streams

“…However, rapidly declining populations may increase the risk of local extinction due to the occurrence of new disturbances and even as a result of stochastic processes (Jackson et al, 2001). This potential deleterious effect can be strengthened in headwater streams as these habitats are naturally less connected to the rest of the drainage network (Brown & Swan, 2010), where colonisation from downstream sections may be limited by natural and anthropogenic barriers (Coleman et al, 2018).…”

Evaluating the Effects of Barriers on Slimy Sculpin Movement and Population Connectivity Using Novel Sibship‐based and Traditional Genetic Metrics

“…For example, barriers have the potential to create small, isolated populations with decreased genetic diversity that may be at risk of inbreeding and that lack resilience to environmental changes (Coleman et al. ). Despite these speculations, few studies have documented the effects of barriers on sculpin movement.…”

“…This characteristic limited movement combined with an annual mean female fecundity of approximately 70 eggs (Grossman et al 2002) is believed to make sculpins vulnerable to the effects of in-stream barriers (Natsumeda 2007). For example, barriers have the potential to create small, isolated populations with decreased genetic diversity that may be at risk of inbreeding and that lack resilience to environmental changes (Coleman et al 2018). Despite these speculations, few studies have documented the effects of barriers on sculpin movement.…”