Strong gene flow across an urbanised coastal landscape in a dune specialist digger wasp

Abstract

ContextGenetic connectivity is often disrupted by anthropogenic habitat fragmentation, and therefore often a focus in landscape-scale conservation. Landscape genetics methods allow for studying functional connectivity in heterogenous landscapes in detail and have the potential to inform conservation measures for a species regional persistence. Yet, for insects, functional connectivity through landscape genetics remains largely unexplored. ObjectivesWe aimed to assess the functional connectivity in the dune-specialist digger wasp Bembix rostrata, in a human-altered 15 km section along the Belgian coast, based on landscape genetics methods. MethodsWe optimised landscape resistance distances according to individual genetic distances with the package ResistanceGA. We combined this with a multi-model inference approach to deduce relative conductance or resistance of gene flow to natural and anthropogenic landscape types. ResultsOverall, the populations of this dune-specialist insect are genetically well-connected. We detected-- on top of the prominent background process of isolation-by-distance--a weak but consistent signal of urban features facilitating gene flow. ConclusionsUrban areas are not a barrier to genetic connectivity of the dune-specialist insect B. rostrata in the focal human-altered landscape. However, because urbanisation leads to larger scale fragmentation, its impact on the distribution of populations in the landscape and related effective regional gene flow remains substantial. As this species depends on early-succession dune vegetations, restoring and increasing sand dynamics at the local and landscape scale should be the focus of conservation aimed at the regional species persistence, rather than trying to increase habitat connectivity in this human-altered dune ecosystem.