Hit the road Jane! Roads decrease the relatedness for females lesser horseshoe bats

Abstract

The understanding of how human-induced habitat disturbance shapes the contemporary population structure and gene flow at a fine-spatial scale is key for adequate management of species with small and fragmented populations and with limited dispersal abilities. To date, there are few studies focusing on how barriers (e.g. roads, habitat fragmentation) might influence gene flow at fine scales. Roads are known for causing millions of roadkill every year and for causing movement disruptions mainly for species with low dispersal abilities, thus changing the genetic structure of these populations. Some bat species, despite the high potential for dispersal, may show low dispersal movements due to high flight costs, which combined with a high vulnerability to roadkills, can have a strong effect on population structure. Moreover, differential sex-specific dispersal, often biased towards males is commonly observed on bat populations. Thus, we expect that females will possess strong local affinities, whereas males may act as genetic mediators among colonies. In this study, we investigated how landscape features drive the gene flow and sex-specific relatedness structure on a lesser horseshoe bat (Rhinolophus hipposideros) population. We combined multiple regressions on genetic distance matrices and spatially explicit analysis to fit models of genetic individuals- relatedness to landscape resistance surfaces. Genotyping involved 2,837 SNPs and 327 bat samples collected across a Mediterranean agroforestry system of southern Portugal. Our analysis based on relatedness structure supported the male-biased dispersal hypothesis. Females are thought to be philopatric, whereas males display uniform levels of relatedness throughout the landscape. Furthermore, we demonstrated that the effect of the landscape features could also be sex-specific. The relatedness analyses showed that the female´ colonies bisected by roads were less related between themselves than to those where no roads were present. In fact, relatedness among females’ colonies was negatively correlated with proximity of roads, unlike males. However, the long-generation time for lesser of horseshoe bat, jointly with time lag since the road construction may not be sufficient to detect a clear genetic signal of isolation. Thus, main finding of presented study is that the roads reduced but did not halt the gene flow, although they may be major drivers of contemporary genetic population structure with medium to long-term consequences on the local bat populations. Furthermore, our results yield evidence that unsuitable habitat, such as the presence of agricultural areas, is an important factor in mediating population connectivity between colonies. This study underscores the potential of conducting sex-specific analysis by identifying landscape elements that differentially promote or impede functional connectivity between sexes, particularly when studying species with different sex-dispersal abilities, as may uncover processes that may otherwise remain cryptic. Our findings are important for lesser horseshoe bat conservation, road planning schemes and habitat management, due to the threatened conservation status and species-specific traits (e.g. low flying, highroad mortality), that increase the risk of road barrier effect. The strong effect of roads at fine scale on the contemporary genetic structure shows that effective management measures are required to increase across-road connectivity allowing to preserve high survival rates of breeding females and maintaining continuous exchange of individuals between colonies.