Does gene flow balance the effect of habitat fragmentation in a population of the hermit beetle Osmoderma barnabita?

A fine-scale spatial genetic structure is rarely analysed within insect populations, although such a structure influences the level of inbreeding and kin dynamics and can have implications for long-term population persistence. A high level of genetic structure is expected in a divided population of the hermit beetle Osmoderma barnabita due to its philopatry and habitat loss/fragmentation. To assess the variability and population genetic structure, sex contributions to genetic variation, and gene flow, the beetles were collected in a fragmented forest (2920 ha) employing sex pheromone-baited traps, georeferenced, and morphologically identified to species and sex; 187 sampled specimens were then evaluated using 10 microsatellite loci. Based on our data, the population as a whole is characterised by low genetic diversity (He = 0.34) and a high level of inbreeding (Fi(Avg). = 0.31). Nevertheless, the level of differentiation between field subpopulations is low, indicating a high level of gene flow (a patchy model). This was evidenced by small pairwise F-ST estimates and slight differences in Ho, He, and allelic richness, a lack of well-defined boundaries between subpopulations, and relatively low relatedness among neighbouring female and male dyads. Sex-biased gene flow was evidenced from the analysis of isolation by distance (regression relatedness) but not from assignment tests. Mating between close kin and recent colonisation from a small source are presented as a possible explanation for high inbreeding, low genetic diversity, and minimal population structure. Still, additional evidence is required to support this hypothesis. The results suggest that the population can be treated as a single management unit.