The effect of habitat fragmentation on the population genetic structure of the Western European hedgehog (erinaceus europaeus)

Abstract

Habitat fragmentation has the potential to isolate populations from dispersal routes, and to restrict geneflow. This study investigates the genetic effects of habitat fragmentation on populations of the European Hedgehog Erinaceus europaeus. This was accomplished using mitochondrial D-loop sequence data and nuclear microsatellites. The markers included six existing microsatellite loci and five new loci developed for this project. Data on genetic mixing from analysis of mtDNA and nDNA were interpreted using information from concurrent studies by others on the dispersal behaviour of individual hedgehogs. Local-scale (<50 km)genetic effects were analysed in ihe context of the overall genetic diversity wilhin Britain. Potential barriers to dispersal, including ancient features such as estuaries and modem features such as roads, were evaluated according to their effects on population genetic structure. Previous and current local scale dispersal behaviour was inferred using molecular markers, and assessed in light of complementary radio-telemetry studies. A genetic survey, using nDNA and mtDNA, of hedgehog populations throughout Britain revealed a largely homogeneous national population, with low to moderate levels of genetic diversity. A scale effect was detected in nDNA, with the rate of increase of genetic differentiation between populations increasing significantly with geographical distance. However, analysis of molecular variance (AMOVA) of mtDNA revealed no significant component of co-variation above a regional level (approx. 50-150 km), and no evidence of national scale 'source' and 'sink' areas of genetic diversity. Preliminary analysis detected a putative nuclear insertion of mtDNA D-loop sequence. Mantel analysis of genetic distance values, based on microsatellite data, revealed an effect of isolation by distance at a local scale (<50 km) within the Southampton study area. No significant relationship was detected between the level of habitat fragmentation within 5x5-km squares and the relatedness value Rc, or inbreeding coefficient Fis, of the population inhabiting the habitat patch. Extended Mantel analysis revealed a near significant barrier effect exerted by the M3 motorway at Eastleigh. This effect became significant when related to overall road width, suggesting that barrier width may be more important than barrier frequency. No significant barrier effects were detected for any other barrier type, including minor roads and railways (relatively modem features), or the River Test and Southampton Water Estuary (ancient features). AMOVA of molecular data, from populations within the Southampton study area, yielded a significantly higher proportion of genetic variation between populations attributed to mtDNA than to nDNA. This suggests a long-standing dispersal gender bias towards male hedgehogs. In contrast assignment testing of individuals, based on microsatellite data, revealed no significant difference between male and female dispersal frequencies over the last three generations. This finding is in agreement with data collected by others on the dispersal behaviour by these same hedgehogs. It implies a recent equalisation of successful dispersals between gender. This is hypothesised to be a result of reduced probability of dispersal success in a fragmented habitat.

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