Abstract
Salmonid fishes exhibit high levels of population differentiation. In particular, the brown trout (Salmo trutta L.) demonstrates complex within river drainage genetic structure. Increasingly, these patterns can be related to the underlying evolutionary models, of which three scenarios (member-vagrant hypothesis, metapopulation model and panmixia) facilitate testable predictions for investigations into population structure. We analysed 1225 trout collected from the River Dart, a 75 km long river located in southwest England. Specimens were collected from 22 sample sites across three consecutive summers (2001–2003) and genetic variation was examined at nine microsatellite loci. A hierarchical analysis of molecular variance revealed that negligible genetic variation was attributed among temporal samples. The highest levels of differentiation occurred among samples isolated above barriers to fish movement, and once these samples were removed, a significant effect of isolation-by-distance was observed. These results suggest that, at least in the short-term, ecological events are more important in shaping the population structure of Dart trout than stochastic extinction events, and certainly do not contradict the expectations of a member-vagrant hypothesis. Furthermore, individual-level spatial autocorrelation analyses support previous recommendations for the preservation of a number of spawning sites spaced throughout the tributary system to conserve the high levels of genetic variation identified in salmonid species.
Highlights
The discovery of microsatellites, and other hypervariable genetic markers, has enabled the study of genetic differentiation and population subdivision at small scales (e.g. Reisch and Kellermeier 2007), even down to the level of the individual (e.g. Carlsson and Carlsson 2002; Peakall et al 2003; Pemberton et al 2007)
The present study examined the variability at nine microsatellite loci in brown trout sampled from the River a 2009 The Authors Journal compilation a 2009 Blackwell Publishing Ltd 2 (2009) 537–554
Further analysis of these cases with Microchecker did not reveal any evidence of null alleles or scoring errors, the EDar case was associated with a significantly positive Fis value (Table 2), which could result from the nonrepresentative sampling of juveniles fish (‘family sampling’; Allendorf and Phelps 1981; Hansen et al 1997; Wenburg et al 1998)
Summary
The discovery of microsatellites, and other hypervariable genetic markers, has enabled the study of genetic differentiation and population subdivision at small scales (e.g. Reisch and Kellermeier 2007), even down to the level of the individual (e.g. Carlsson and Carlsson 2002; Peakall et al 2003; Pemberton et al 2007). The information gathered can have important implications for conservation work intended to preserve genetic variation The significance of this objective increased following the World Summit on Sustainable Development and the publication of the framework for action on biodiversity and a 2009 The Authors Journal compilation a 2009 Blackwell Publishing Ltd 2 (2009) 537–554 ecosystem management, which identifies genetic variation as one of the three levels of biodiversity recommended for conservation (WEHAB 2002). Studies into freshwater salmonid fishes have revealed that genetic differentiation can occur over very short distances within river catchments. This can be associated with physical barriers to movement, which can isolate populations that differentiate by genetic drift (Hindar et al 1991). Differentiation has been noted where salmonids exist without such barriers, including
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