Factors and processes shaping the population structure and distribution of genetic variation across the species range of the freshwater snail radix balthica (Pulmonata, Basommatophora).

Markus Pfenninger,Moritz Salinger,Barbara Feldmeyer,Timm Haun

doi:10.1186/1471-2148-11-135

Abstract

BackgroundFactors and processes shaping the population structure and spatial distribution of genetic diversity across a species' distribution range are important in determining the range limits. We comprehensively analysed the influence of recurrent and historic factors and processes on the population genetic structure, mating system and the distribution of genetic variability of the pulmonate freshwater snail Radix balthica. This analysis was based on microsatellite variation and mitochondrial haplotypes using Generalised Linear Statistical Modelling in a Model Selection framework.ResultsPopulations of R. balthica were found throughout North-Western Europe with range margins marked either by dispersal barriers or the presence of other Radix taxa. Overall, the population structure was characterised by distance independent passive dispersal mainly along a Southwest-Northeast axis, the absence of isolation-by-distance together with rather isolated and genetically depauperated populations compared to the variation present in the entire species due to strong local drift. A recent, climate driven range expansion explained most of the variance in genetic variation, reducing at least temporarily the genetic variability in this area. Other factors such as geographic marginality and dispersal barriers play only a minor role.ConclusionsTo our knowledge, such a population structure has rarely been reported before. It might nevertheless be typical for passively dispersed, patchily distributed taxa (e.g. freshwater invertebrates). The strong local drift implied in such a structure is expected to erode genetic variation at both neutral and coding loci and thus probably diminish evolutionary potential. This study shows that the analysis of multiple factors is crucial for the inference of the processes shaping the distribution of genetic variation throughout species ranges.

Highlights

Factors and processes shaping the population structure and spatial distribution of genetic diversity across a species’ distribution range are important in determining the range limits
Sampling We identified 1084 individuals sampled from 64 sites as R. balthica with DNA barcoding
Apart from the expected effects of a recent range expansion, other processes or factors suggested in the literature had only a minor effect on the geographic distribution of genetic variability

Summary

Introduction

Factors and processes shaping the population structure and spatial distribution of genetic diversity across a species’ distribution range are important in determining the range limits. We comprehensively analysed the influence of recurrent and historic factors and processes on the population genetic structure, mating system and the distribution of genetic variability of the pulmonate freshwater snail Radix balthica. This analysis was based on microsatellite variation and mitochondrial haplotypes using Generalised Linear Statistical Modelling in a Model Selection framework. One of the most influential framework on the distribution of genetic variation across species’ ranges is the Abundant-Centre Hypothesis (ACH) [7] It states that individuals of a species should become most abundant in areas where the conditions for reproduction and population growth are most favourable. Geographically marginal populations are expected to harbour less genetic variation and to be more strongly isolated from one another [11], because the population size and its recurrent fluctuations determine the loss rate of genetic variation due to genetic drift

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Discussion

Conclusion