title: Quantitative evaluation of hybridization and the impact on biodiversity conservation.
abstract: Anthropogenic hybridization is an increasing conservation threat worldwide. In South Africa, recent hybridization is threatening numerous ungulate taxa. For example, the genetic integrity of the near-threatened bontebok (Damaliscus pygargus pygargus) is threatened by hybridization with the more common blesbok (D. p. phillipsi). Identifying nonadmixed parental and admixed individuals is challenging based on the morphological traits alone; however, molecular analyses may allow for accurate detection. Once hybrids are identified, population simulation software may assist in determining the optimal conservation management strategy, although quantitative evaluation of hybrid management is rarely performed. In this study, our objectives were to describe species-wide and localized rates of hybridization in nearly 3,000 individuals based on 12 microsatellite loci, quantify the accuracy of hybrid assignment software (STRUCTURE and NEWHYBRIDS), and determine an optimal threshold of bontebok ancestry for management purposes. According to multiple methods, we identified 2,051 bontebok, 657 hybrids, and 29 blesbok. More than two-thirds of locations contained at least some hybrid individuals, with populations varying in the degree of introgression. HYBRIDLAB was used to simulate four generations of coexistence between bontebok and blesbok, and to optimize a threshold of ancestry, where most hybrids will be detected and removed, and the fewest nonadmixed bontebok individuals misclassified as hybrids. Overall, a thresholdQ-value (admixture coefficient) of 0.90 would remove 94% of hybrid animals, while a threshold of 0.95 would remove 98% of hybrid animals but also 8% of nonadmixed bontebok. To this end, a threshold of 0.90 was identified as optimal and has since been implemented in formal policy by a provincial nature conservation agency. Due to widespread hybridization, effective conservation plans should be established and enforced to conserve native populations that are genetically unique.
authors.affiliation: National Zoological Gardens of South Africa Pretoria South Africa; Genetics Department University of the Free State Bloemfontein South Africa.
authors.forename: Anna M
authors.initials: AM
authors.lastname: van Wyk
authors.affiliation: National Zoological Gardens of South Africa Pretoria South Africa; Genetics Department University of the Free State Bloemfontein South Africa.
authors.forename: Desiré L
authors.initials: DL
authors.lastname: Dalton
authors.affiliation: Department of Life Sciences and Biotechnology University of Ferrara Ferrara Italy; The Morton Arboretum Lisle IL USA; National Institute for Mathematical and Biological Synthesis (NIMBioS) University of Tennessee Knoxville TN USA.
authors.forename: Sean
authors.initials: S
authors.lastname: Hoban
authors.affiliation: Cardiff School of Biosciences Cardiff University Cardiff UK.
authors.forename: Michael W
authors.initials: MW
authors.lastname: Bruford
authors.affiliation: Cardiff School of Biosciences Cardiff University Cardiff UK.
authors.forename: Isa-Rita M
authors.initials: IM
authors.lastname: Russo
authors.affiliation: CapeNature Stellenbosch South Africa.
authors.forename: Coral
authors.initials: C
authors.lastname: Birss
authors.affiliation: Genetics Department University of the Free State Bloemfontein South Africa.
authors.forename: Paul
authors.initials: P
authors.lastname: Grobler
authors.affiliation: Molecular Zoology Laboratory Department of Zoology University of Johannesburg Auckland Park South Africa.
authors.forename: Bettine Janse
authors.initials: BJ
authors.lastname: van Vuuren
authors.affiliation: National Zoological Gardens of South Africa Pretoria South Africa; Genetics Department University of the Free State Bloemfontein South Africa.
authors.forename: Antoinette
authors.initials: A
authors.lastname: Kotzé
keywords: HYBRIDLAB; NEWHYBRIDS; STRUCTURE; blesbok; bontebok; hybridization