Microsatellite variation in the yellowhammer Emberiza citrinella: population structure of a declining farmland bird

In recent years, there has been much concern in the UK about population dec lines of widespread species in agricultural habitats. Conservation-orientat ed research on declining birds has focused on vital rates of survival and p roductivity. However the environmental factors which may influence movement s between populations of widespread species is poorly understood. Populatio n genetic structure is an indirect description of dispersal between groups of individuals. To attempt to develop an understanding of genetic structuri ng in a widespread, but declining, farmland bird, we therefore investigated the yellowhammer, Emberiza citrinella, population in England and Wales usi ng microsatellite data. Our first aim was to investigate whether there was genetic substructuring in the population. A second aim was to investigate i f there was a relationship between genetic distances and various environmen tal variables. Finally, we analysed the microsatellite data for evidence of loss of genetic variation due to population decline. Our data showed a sli ght but significant structure within the yellowhammer population. This ther efore cannot be considered a panmictic population. Our example from South C umbria implies that high-altitude barriers may have a slight influence on p opulation structure. However, on the whole, genetic distances between sampl e sites were not significantly correlated with geographical distances, degr ees of population connectivity, high altitudes, or differences in precipita tion between sites. Finally, we detected departures from mutation-drift equ ilibrium (excess heterozygosity), which is indicative of a loss of genetic variation through recent decline.