Biochemical genetic variation in populations of Larus argentatus and Larus fuscus in northwestern Europe

The techniques of biochemical population genetics were used to examine the relationships between two apparently closely related species and their component subspecies which form the Larus argentatus/fuscus species complex in northwest Europe. The systematics and taxonomy of these populations in this part of the circum-polar ring are complex and it was thought that this type of analysis might clarify the taxonomic relationships. Samples were obtained from breeding colonies along a transect from northern France (47°N), through Britain to arctic Norway (70°N), with additional samples from the Camargue on the Mediterranean coast (42°N). Twenty-one enzyme systems were examined using starch gel electrophoresis. No interspecific differences were found and only one locus (glutamate oxaloacetate transaminase) was polymorphic. There were no allelic differences within geographical groups of populations, although there were some differences between some of the subspecies. The low levels of heterozygosity ( H = 0.0081 and H = 0.0031) are considered to arise from a combination of two factors: the low levels of heterozygosity which appear to be characteristic of birds and population effects. Furthermore, no interspecific differences were detected ( I = 0.999) indicating the morphological changes rather than changes at structural gene loci may have been more important in speciation.