MITOCHONDRIAL-DNA SEQUENCE PATTERNS OF HARBOR PORPOISES (PHOCOENA-PHOCOENA) FROM THE NORTH AND THE BALTIC SEA

To investigate genetic differentiation between harbour porpoises (Phoc oena phocoena) of the North and the Baltic Sea, a total of 39 individu als were screened for sequence polymorphisms at a highly polymorphic p art of the mitochondrial DNA control region. DNA was extracted from li ver or skin samples of stranded animals. After PCR amplification and d irect sequencing, 420 bp were scored. Nine haplotypes were found, diff ering from one another by one to four transitions. Haplotypes separate d out into two clusters A and B by a specific nucleotide substitution. All Baltic harbour porpoises showed type A haplotypes, which was foun d only in 45% of the North Sea specimens. Genetic variation in terms o f nucleotide and haplotype diversities was much lower in the Baltic Se a than in the North Sea population. Haplotype composition and nucleoti de divergence suggest a colonization of the Baltic Sea several thousan d years ago and a limited genetic exchange since then. The genetic dif ferentiation between Baltic and North Sea populations of harbour porpo ises is corroborated by published data both on skull character differe nces and enzyme polymorphisms.