Isolation by distance and non-identical patterns of gene flow within two river populations of the freshwater fish Rutilus rutilus (L. 1758).

S Crookes,P W Shaw

doi:10.1007/s10592-016-0828-3

Abstract

The spatial distribution of organisms is maintained by a combination of in situ reproduction and dispersal of conspecifics from elsewhere within its habitable range. The determination of dispersal origin and sub-population connectivity has a vital role to play in forming effective management policies. The common roach (Rutilus rutilus) is an important component of the economically and socially valuable recreational fishery and represents a well-studied member of the Cyprinidae. Microsatellite allele data were used to investigate hypothetically variant levels of microevolutionary structuring and isolation-by-distance (IBD) in in the Rivers Stour and Thames. A strong signal of IBD was found in the Stour, probably due to the limited capacity for unrestricted bidirectional dispersal in this river compared with the Thames. A weak inference of IBD in the Thames is likely erroneous and effected by a strong localised genetic signal from a recent stocking event. Whilst we found significantly genetically divergent upstream areas in the River Stour, a strong signal of IBD remained when the headwater sub-population was removed, suggesting that that the signal is not biased by non-equilibrium conditions in upstream reaches. We discuss these results with reference to the management of aquatic bioresources and emphasise the idiosyncrasy that aquatic biota and hydrological complexity may imprint upon patterns of biodiversity within any given system.Electronic supplementary materialThe online version of this article (doi:10.1007/s10592-016-0828-3) contains supplementary material, which is available to authorized users.

Highlights

The ability to determine the extent to which sub-populations are connected is vital to understanding, conserving and managing populations (Hughes et al 2009)
Of the 129 locus-by-location comparisons in the Thames (Table S1), ten were found to violate the assumptions of Hardy–Weinberg equilibrium (HWE), close to the 6.45 expected by chance. This number was greater in the Stour, where 20 out of 88 locus-by-location comparisons all showed a deficit of heterozygotes (Table S2)
Overall levels of microsatellite diversity were similar for both river populations (Fig. 2) and are consonant with estimates observed in this species in the UK, exhibiting significant overlap between mean and variances in heterozygosity and allelic richness across all surveyed Thames sub-populations (Hamilton et al 2014)

Summary

Introduction

The ability to determine the extent to which sub-populations are connected is vital to understanding, conserving and managing populations (Hughes et al 2009). Migration provides a means other than direct recruitment for an organism to maintain temporal and spatial persistence. Most species display some degree of population substructuring, dependent upon physical limitations of habitats and the capability for dispersal. Rivers channel the movements of aquatic organisms along physically delimited pathways resulting in a directional bias to passive dispersal (Fagan 2002). Riverine ecosystems consist of a patchwork of habitat (Matthews 1998), the distribution of which may vary due to the effects of periodic droughts or floods. Such events may facilitate or impede the ability of individuals to commute. Anthropogenic modification may drastically alter the natural state of riverine ecosystems (e.g., Bravard et al 1986) potentially

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Conclusion