Founder effect and bottleneck signatures in an introduced, insular population of elk

The population of elk (Cervus elaphus roosevelti) inhabiting Afognak Island, Alaska, USA arose from an introduction of 8 individuals from an established population in Washington, USA in 1929, and recently peaked at approximately 1,400 individuals. We examined indices of diversity for 15 microsatellite loci in the Afognak population and compared them to levels in the parent population to determine effects of translocation and demography on genetic variation. The Afognak population differed significantly (P < 0.0001) from the source population in both allele and genotype frequencies. Allelic richness, number of private alleles and multilocus heterozygosity, but not percent loci polymorphic, were significantly lower in Afognak elk. Mean inbreeding coefficients within Afognak (f = 0.019) and source (f = -0.006) populations did not differ significantly from zero. Despite the demographic bottleneck, no evidence of a genetic bottleneck in the Afognak population was detected using a test for heterozygosity excess or mode shift of allele frequencies. Simulations indicated that rapid population growth after the translocation resulted in heterozygosity excess for only 8 years. Conversely, a statistic testing for a bottleneck signature in the ratio of allele number to allele size range (M-ratio) was significant for both the Afognak and source populations, suggesting that the Afognak population had effectively undergone serial bottlenecks. Nonetheless, Afognak failed to show a smaller M-ratio than the parent population, suggesting a failure of that statistic to detect the bottleneck associated with introduction. We show that a severe bottleneck followed by rapid population growth may be undetectable using available tests.