Corncrake conservation genetics at a European scale: the impact of biogeographical and anthropological processes

Understanding patterns of genetic structure, gene flow and diversity across a species range is required if we are to determine the genetic status and viability of small peripheral populations. This is especially crucial in species distributed across a large range where spatial heterogeneity makes it difficult to predict the distribution of genetic diversity. Although biogeographical models provide expectations of how spatially structured genetic variation may be at the range scale, human disturbance may cause strong deviations from these theoretical predictions. In this study, we investigated genetic structure and demography at a pan-European scale, in the corncrake Crex crex, a grassland bird species strongly affected by agricultural changes. We assessed population structure and genetic diversity, as well as demographic trends and direction of gene flow, in and among 15 contemporary populations of this species. Analyses revealed low genetic structure across the entire range with high levels of genetic diversity in all sites. However, we found some evidence that the westernmost populations were, to a very limited extent, differentiated from the rest of the European population. Demographic trends showed that population numbers have decreased in western Europe and remained constant across eastern Europe. Results may also suggest asymmetric gene flow from eastern to western populations. In conclusion, we suggest that the most likely scenario is that contrasting demographic regimes between eastern and western populations, driven by heterogeneous human activity, has caused asymmetric gene flow that has buffered small peripheral populations against genetic diversity loss, but also erased any genetic structure that may have existed. Our study highlight the need of coordinated actions at the European scale to preserve source populations and ensure the maintenance of reproductive productivity in the most threatened sites, in order to avoid losing any adaptive potential and too strongly relying on sink source populations whose future is uncertain.