Hybridization

Abstract Hybridization occurs between species or populations, and can arise from either natural or anthropogenic causes. Hybridization is important in natural evolutionary processes, but can be a harmful force reducing species identity and reproductive success. Hybridization can increase fitness through heterosis, or reduce fitness through outbreeding depression. Genetic analysis can effectively identify hybridization and has frequently used diagnostic loci that have different allele frequencies in the parents. Hybrid indices or admixture analyses use proportions of parental ancestry in individuals to identify hybrids. Hybridization contributes to decline and extinction of species through loss of reproductive potential and reduced population growth, or through genetic mixing and loss of genetically distinct populations. Determining whether hybridization is natural or anthropogenic is crucial for conservation. Protection of hybrids is often based on whether they are genetically distinct through long-term isolation or speciation, or whether they represent recent, ongoing, or anthropogenic hybridization.