USEFULNESS OF MOLECULAR MARKERS FOR DETECTING POPULATION BOTTLENECKS VIA MONITORING GENETIC CHANGE

It is important to detect population bottlenecks in threatened and man aged species because bottlenecks can increase the risk of population e xtinction. Early detection is critical and can be facilitated by stati stically powerful monitoring programs for detecting bottleneck-induced genetic change. We used Monte Carlo computer simulations to evaluate the power of the following tests for detecting genetic changes caused by a severe reduction in a population's effective size (N-e): a test f or loss of heterozygosity, two tests for loss of alleles, two tests fo r change in the distribution of allele frequencies, and a test for sma ll N-e based on variance in allele frequencies (the 'variance test'). The variance test was most powerful; it provided an 85% probability of detecting a bottleneck of size N-e = 10 when monitoring five microsat ellite loci and sampling 30 individuals both before and one generation after the bottleneck. The variance test was almost 10-times more powe rful than a commonly used test for loss of heterozygosity, and it allo wed for detection of bottlenecks before 5% of a population's heterozyg osity had been lost. The second most powerful tests were generally the tests for loss of alleles. However, these tests had reduced power for detecting genetic bottlenecks caused by skewed sex ratios. We provide guidelines for the number of loci and individuals needed to achieve h igh-power tests when monitoring via the variance test. We also illustr ate how the variance test performs when monitoring loci that have wide ly different allele frequency distributions as observed in five wild p opulations of mountain sheep (Ovis canadensis).