Inbreeding Depression in Wild Mammals: Genomic Mechanisms and Conservation Consequences

Inbreeding depression is a widespread but highly variable threat to wild mammal populations, especially small, isolated, or fragmented ones. Genomic tools can now estimate individual inbreeding and mutation load more precisely than pedigrees or a few genetic markers. They show that similar levels of autozygosity can have very different fitness consequences. In this structured narrative review, we examine how runs of homozygosity, genomic inbreeding coefficients, and mutation load relate to inbreeding depression in wild mammals. We distinguish inbreeding (a process), autozygosity (its genomic consequence), low genetic diversity, and inbreeding depression (a fitness outcome), and we stress that high autozygosity alone does not demonstrate fitness costs. We compare land and marine case studies in which high autozygosity is associated with reduced reproduction, survival, and disease resistance, with cases in which purging or demographic history may have limited the decline in fitness. We consider how environmental stress, methodological differences, and confounding factors affect the observed inbreeding–fitness relationships. We then discuss how genomic estimates can inform conservation decisions, including the limits of genetic rescue, and we identify research priorities such as long-term studies that combine genomic, demographic, and ecological data. The review offers a framework for interpreting genomic inbreeding measures cautiously in conservation planning.