Genetic analysis of the population structure of socially organized oystercatchers (Haematopus ostralegus) using microsatellites

On the island of Schiermonnikoog (The Netherlands), the breeding population of oystercatchers can be divided into two groups: 'residents' and 'leapfro gs', based on their distinct social characteristics and limited probabiliti es of status change between breeding seasons. In order to investigate wheth er this social organization has caused local genetic differentiation, leapf rogs and residents were compared at eight polymorphic microsatellite loci. No significant genetic subdivision between residents and leapfrogs was obse rved (Theta = 0.0000; 95% confidence interval (CI), -0.0027-0.0033), indica ting that the oystercatcher population on the island of Schiermonnikoog has to be considered as one panmictic unit. Investigation of three additional locations in the northern part of The Netherlands did not reveal significan t genetic population subdivision either (Theta = - 0.0005; 95% CI, - 0.0045 -0.0037), despite the fact that adult oystercatchers show extreme fidelity to their breeding localities. These results indicate panmixis and considera ble levels of gene flow within the northern part of The Netherlands. Thus, the results from genetical analyses do not seem to be in agreement with obs ervational data on the dispersal behaviour of breeding individuals. It is a rgued that the lack of population structure, locally on Schiermonnikoog as well as across larger geographical distances, is to be attributed to high l evels of gene flow through dispersal of juvenile birds.