Invasion Without a Bottleneck: Microsatellite Variation in Natural and Invasive Populations of the Brown Mussel

Abstract: Population-level genetic diversity of the brown mussel Perna perna was investigated using nuclear microsatellite markers in 6 natural and 6 invasive populations. A total of 448 individuals from 12 populations spanning the natural and introduced ranges of the brown mussel were scored for 2 polymorphic microsatellite loci. Wright’s hierarchical F statistics (FST), Hardy-Weinberg equilibrium, Nei’s genetic distance, and other descriptive statistics were used to quantify geographic population subdivision, and to estimate the number of migrants per generation. FST values (0.007–0.042) revealed that genetic partitioning among populations was low. Microsatellite data revealed a slight difference in observed heterozygosity and no statistically significant differences in expected heterozygosity or allelic diversity between natural and introduced populations. Effective numbers of migrants (Nem) per generation ranged from 6 to 35 individuals. The potential significance of an invasive species with high genetic variation in terms of the risk of establishment and conservation implications is discussed. Key words: Perna perna, population structure, invasive species, DNA markers, microsatellites, F statistics