Aim

Accelerating environmental changes caused by human activities result in habitat loss and fragmentation, profoundly affecting wildlife population genetic structure and evolution. Urbanised and geographically marginal areas are often characterized by unfavourable environments, reducing the connectivity among populations and resulting in an increase in population genetic differentiation and a decrease in intra-population genetic diversity. In this context, we examined the effect of geographic marginality and anthropogenic pressures on population genetic features in the protected southern damselfly (Coenagrion mercuriale, Odonata), which has low dispersal capabilities and specific habitat requirements and whose populations are declining.

Location

Two contrasting areas were studied: one located in semi-natural habitats at the northern limit of the species geographic range (northern France) and the second one located within the species’ range core, in an urbanised area surrounding the city of Strasbourg (Alsace, eastern France).

Methods

We genotyped 2743 individuals from 128 populations using microsatellite loci, and analysed the spatial distribution of neutral genetic diversity and the levels of genetic differentiation within the two areas. We also examined fine-scale patterns of genetic structure and migration rate in the urbanised area of Alsace.

Results

Northern peripheral populations showed lower levels of genetic diversity and higher levels of genetic differentiation compared to central Alsacian populations. Although located in anthropized habitats, geographically central Alsacian populations exhibited substantial levels of gene flow, with dispersal events mainly occurring overland and not restricted to watercourses. However, the highly urbanised city of Strasbourg negatively impacted the neighbouring populations by decreasing levels of genetic diversity and migration rates, thereby magnifying the extent of genetic differentiation.

Main conclusions

Altogether, these results suggested the need for management action by restoring breeding sites and creating migratory corridors for marginal southern damselfly populations. However, our results also highlighted the resilience of southern damselfly in central range populations even facing strong urbanisation pressures.

Genotyping of individuals using microsatellite loci.