Cooperative Fish and Wildlife Research Units Program: all
Education, Research and Technical Assistance for Managing Our Natural Resources

Genetic admixture is a biological event inherent to genetic rescue programs aimed at the long-term conservation of endangered wildlife. Although the success of such programs can be measured by the increase in genetic diversity and fitness of subsequent admixed individuals, little is known about the fine-scale costs of admixture at the molecular level. In this study, we analyzed nonsynonymous variation from conserved genes to quantify and compare mutation load levels (i.e., proportion of deleterious alleles and genotypes carrying these alleles) among endangered Florida panthers with different genetic backgrounds and non-endangered Texas pumas. Specifically, we used canonical (i.e., non-admixed) Florida panthers, Texas pumas, and F₁ (canonical Florida x Texas) panthers dating from a genetic rescue program, including Florida panthers with Central American ancestry resulting from an earlier admixture event. We found genetic drift had no significant effect in reducing overall proportions of deleterious alleles in the severely bottlenecked canonical Florida panthers. Furthermore, these deleterious alleles were distributed into a disproportionately high number of homozygous genotypes due to close inbreeding and inefficient purifying selection in this group. Conversely, admixed Florida panthers (either with Texas or Central American ancestry) presented reduced levels of homozygous genotypes carrying deleterious alleles but increased levels of heterozygous genotypes carrying these variants. Although admixture is likely to alleviate the load of standing deleterious variation present in homozygous genotypes, our results highlight concerns that introduced novel deleterious alleles (temporarily present in heterozygous state) could potentially be expressed in subsequent generations of rescued populations if their effective sizes remain small.