Abstracts (first author)
Decoupling population size, effective population size and pathogen prevalence in a periphery-core system in a migratory bird, the Corncrake
Inbreeding and reduced genetic diversity are known to affect the capacity of an individual to resist pathogen infection so that a negative relationship between pathogen prevalence and heterozygosity is expected. Thus, a high susceptibility to pathogens may contribute to shorten extinction time in populations with low genetic diversity. At the range scale, peripheral populations tend to be smaller and more isolated than core populations and are generally more prone to incur the costs of reduced genetic diversity. Elevated extinction risk in peripheral populations is of particular concern for species with unfavourable conservation status. However, the relationships between census size, effective size (genetic diversity) and parasite prevalence is not straightforward because gene flow from the core may maintain genetic diversity and the ability to resist pathogens at the range periphery, even in declining populations. The Corncrake Crex crex, a short live migratory bird distributed across the Palearctic has shown rapid declines in Western Europe over recent decades while Eastern populations remained large. We analysed the relationship between genetic diversity, gene flow and avian malaria prevalence across a large part of the species range. We found a very low level of population structure and no evidence of reduced diversity in peripheral populations which was likely caused by a high dispersal across the breeding range. Furthermore, contrary to expectations, the parasite prevalence was 10 times higher in core populations compared to peripheral ones, even in areas of high bird density. Our results clearly show that decouplings may occur in periphery-core systems between census and effective population size, and between genetic diversity and pathogen prevalence. Species dispersal characteristics, population densities and the ecology of pathogen community are likely to strongly affect these relationships precluding the quick and easy forecasting of a populations fate.