Lack of genetic structure in Kentish Plover Charadrius alexandrinus from the Iberian coast. What's wrong with the endangered north-western population?

Coastal wader species are sensitive to anthropogenic activity and habitat change along the coastal edge, which has been responsible for the decline in the populations of these birds. Correct management requires knowledge of the pattern and scale of genetic variation within and among populations as well as the relationships between population dynamics and genetic structure. We investigated these factors in the Kentish Plover Charadrius alexandrinus from the Iberian coast to determine the degree of vulnerability of the endangered north-western population. We analysed the genetic structure and gene flow using a 631-bp fragment of the mitochondrial (mtDNA) control region and eight microsatellite markers in 113 unrelated individuals from 31 Iberian beaches. The results do not support the recent decline hypothesis because there was no evidence of a bottleneck, but they do support a population expansion along the Atlantic coast. We found no genetic structure or isolation-by-distance, in agreement with results recently observed on a continental scale. However, explanations for high continental gene flow, such as temporary breeding habitats and high breeding dispersal, do not seem to apply to the Galician population. Galician Kentish Plovers breed solely on beaches, a suitable and more predictable habitat during the breeding period than ephemeral inland wetlands, and female movements during the breeding period are uncommon, mainly due to the extremely low hatching success. This study suggests a demographic connectivity between Portuguese and Galician populations that is referred to as source-sink population dynamics, in which individuals dispersing from Portugal support the Galician coastal population. This dispersal pattern highlights the importance of supranational management plans to protect endangered species.