Genetic analysis of a documented population bottleneck: introduced Bennett's wallabies (Macropus rufogriseus rufogriseus) in New Zealand

Few bottlenecks of wild populations are sufficiently well-documented to con stitute models for testing theories about the impact of bottlenecks on gene tic variation, and subsequent population persistence. Relevant details of t he Bennett's wallaby (Macropus rufogriseus rufogriseus) introduction into N ew Zealand were recorded (founder number, source and approximate bottleneck duration) and suggest this may provide a rare opportunity to examine the e fficacy of tests designed to detect recent bottlenecks in wild populations. We first assessed the accuracy of historic accounts of the introduction us ing genetic diversity detected in mitochondrial DNA (mtDNA) and at five mic rosatellite loci. Phylogenetic analyses of mtDNA D-loop sequence haplotypes were consistent with the reported origin of the founders as Tasmania, rath er than one of the Bass Strait islands in which Bennett's wallabies are als o found. Microsatellite allele frequencies from the Tasmanian source popula tion were then used to seed bottleneck simulations encompassing varying siz es and numbers of generations, in order to assess the severity of bottlenec k consistent with diversity observed in the New Zealand population. The res ults suggested that the founder number was unlikely to have been as small a s the three animals suggested by the account of the introduction. Nonethele ss, the bottleneck was probably severe; in the range of three to five pairs of wallabies for one to three generations. It resulted in significantly re duced levels of allelic diversity and heterozygosity relative to the source population. This bottleneck is only detectable under the infinite allele m odel (IAM) and not under the stepwise mutation model (SMM) or the two-phase model (TPM), and possible explanations for this are discussed.