Gene Flow Disruption and Population Declines in a Soil Arthropod in Fragmented Habitats

Abstract

Intensification of land use over past millennia has magnified loss and fragmentation of natural habitats. This causes reductions in population sizes and restricts gene flow, processes that amplify genetic drift with pro-found negative impact on species and populations. However, we have lim-ited data on effects of habitat fragmentation on population genetic compo-sitions, especially for species presumed to be widespread and abundant such as insects and other arthropods. Reports on significant declines in abun-dances of arthropods are accumulating, and their short generation times and low dispersal capacity make them particularly vulnerable to habitat fragmentation. This study analyses whole-genome re-sequencing data in the collembola Entomobrya nicoleti from Danish grasslands with the aim to evaluate effects of habitat fragmentation on demographic history, ge-netic diversity, gene flow, and genetic structure. Abundances of E. nicoleti suggest that cultivation reduces habitat suitability and fragments popula-tions. Demographic modelling supports the hypothesis that intensification of land use is associated with declines in effective population sizes. It is likely that these declines have yet to reach their full effect on current lev-els of genetic diversity because of the ’drift debt’, where genetic diversity of recently declined populations will erode over future generations. Gene flow estimates reveal sharp declines which coincide with the intensification of agricultural land use. Our findings highlight that seemingly abundant species in fragmented landscapes may experience severe reductions in effec-tive population size and gene flow. These demographic shifts predict future genetic erosion and emphasize the delayed yet inevitable consequences of habitat fragmentation for population persistence.