Adaptive genetic management: assessing the benefits of translocations

Declines in abundance and genetic diversity in plant and animal populations are increasingly of conservation concern. Genetic rescue, or the supplementation of declining populations with individuals from genetically different sources, may aid in demographic and genetic recovery efforts, assuming introduced individuals successfully reproduce following translocation. However, the relative reproductive contributions of resident and translocated individuals are not frequently evaluated. In the northern lower peninsula of Michigan, USA, fourteen brown trout (Salmo trutta) from each of three different tributaries were introduced into a research stream (Hunt Creek) to supplement a small, isolated resident brown trout population. Mean expected heterozygosity and mean allelic richness differed between the three translocated populations compared to residents. Additionally, inter-population variance in allele frequency (F_ST) between resident and translocated populations ranged from 0.024 to 0.098. Using genetic parentage assignments, we documented that translocated and resident brown trout did interbreed; however, intra-population mating events were more common. Simulations indicated that increases in genetic diversity among age-1 offspring were the result of reproduction by translocated adults, as genetic variation was significantly above levels expected by reproduction among residents alone (p < 0.001). To achieve management goals for genetic rescue programs, managers would be advised to conduct simulations and hypothesis testing in addition to collection of empirical genetic data to evaluate introduction outcomes.