Abstract
Although roads are widely seen as dispersal barriers, their genetic consequences for animals that experience large fluctuations in population density are poorly documented. We developed a spatially paired experimental design to assess the genetic impacts of roads on cyclic voles (Microtus arvalis) during a high-density phase in North-Western Spain. We compared genetic patterns from 15 paired plots bisected by three different barrier types, using linear mixed models and computing effect sizes to assess the importance of each type, and the influence of road features like width or the age of the infrastructure. Evidence of effects by roads on genetic diversity and differentiation were lacking. We speculate that the recurrent (each 3–5 generations) episodes of massive dispersal associated with population density peaks can homogenize populations and mitigate the possible genetic impact of landscape fragmentation by roads. This study highlights the importance of developing spatially replicated experimental designs that allow us to consider the large natural spatial variation in genetic parameters. More generally, these results contribute to our understanding of the not well explored effects of habitat fragmentation on dispersal in species showing “boom-bust” dynamics.
Highlights
Verges, and structural passages beneath or above the paved surface influences road permeability for terrestrial species[29]
We further discuss other possible explanations to this pattern based on the characteristics of the study species, such as that the large population size reached during peak phases was marginally affected by genetic drift and there is no spatial variation in genetic structure independently of gene flow
Since all locus showed no departure from Hardy Weinberg equilibrium (HWE) and no evidence for null alleles across all sites (Supplementary Tables S1, S2), all of them were kept for further analysis
Summary
Verges, and structural passages beneath or above the paved surface influences road permeability for terrestrial species[29]. Common vole populations reach high local abundances and may experience extreme fluctuations in density (1–2000 individuals per hectare)[46] through 3–5 years population cycles with well-known phases This cyclic variation in population size make this species interesting to investigate the potential vulnerability to road barriers, compared to what has been described for other sympatric small mammals with more stable p opulations[8,48,49]. The alternative scenario (road barrier effect) would generate—given enough generations—observable differences in the distribution of genetic variation within plots bisected by roads but not in plots without roads
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