FOUNDER EFFECTS AND GEOGRAPHICAL VARIATION IN THE INVADING CLADOCERAN BOSMINA (EUBOSMINA) COREGONI BAIRD 1857 IN NORTH-AMERICA

Invasions and subsequent range expansions by exotic species provide an excellent opportunity for the study of founder effects on the genetic structure of colonizing populations. Although the Great Lakes have served as the initial point of colonization for more than 100 species, few studies have examined the genetic structure of these invaders. This study shows that levels of genetic variability in North American populations of the cladoceran invader Bosmina coregoni are at least as high as those in European populations, suggesting that founding populations were large. As allelic diversity in North America is higher than in any single European population, the Great Lakes have probably been colonized repeatedly. In the past 30 years, B. coregoni has expanded its range into inland lakes within 100 km of the Great Lakes, through both long-distance dispersal and migration among neighbouring lakes. Although these secondary invasions have produced little reduction in genetic diversity, they have led to pronounced gene frequency divergence among populations from inland North American lakes.