POPULATION INTROGRESSION AND DIFFERENTIATION IN THE GREAT CORMORANT PHALACROCORAX-CARBO IN EUROPE

Seven hypervariable microsatellite markers were used to genotype indiv iduals from 21 European populations of great cormorant (Phalacrocorax carbo) with the aim of: (i) evaluating levels of pan-European populati on structuring; and (ii) determining the genetic provenance of birds p resent in newly formed colonies in southeast England. Significant popu lation differentiation was detected overall, with populations of the ' North Atlantic' cormorant subspecies (P.c. carbo) showing greater leve ls of divergence than populations of the 'Eurasian' subspecies (P.c. s inensis). The populations from southeast England, which are of unknown racial origin but within the geographical distribution of the P.c. ca rbo subspecies, clustered with P.c. sinensis populations in phylogenet ic topologies, highlighting the fact that P.c. sinensis individuals we re present at these sites. Multivariate analyses (principal component analysis, principal coordinate analysis and discriminant function anal ysis) indicated that these inland colonies were not comprised solely o f P.c. sinensis, but that both subspecies were living sympatrically an d were probably hybridizing. The implications for cormorant management and conservation of P.c. sinensis breeding in the UK and of populatio n introgression with P.c. carbo are considerable, and are discussed.