| Abstract: | Summary Milstein, P. Le S. 1979. The evolutionary significance of wild hybridization in South African Highveld ducks. Ostrich Suppl. 13. Wild hybrid ducks of interspecific and intergeneric origin were unexpectedly captured at Barberspan, the major waterfowl-ringing station in Africa. In addition to a single record by Shewell (1957), 24 hybrids and back-crosses between Yellowbilled Ducks Anas undulata, Red-billed Teal A. erythrorhyncha and Southern Pochard Netta erythrophthalma were captured over a three-year period. These hybrids call for a revision of current theory concerning wild hybridization with respect to monomorphic and dimorphic ducks. Frequencies are apparently only exceeded in the literature by the controversial American Black Duck Anas rubripes x Mallard A. platyrhynchos incidence. A comparative description and statistical comparison of the different phenotypes is given. Hybrid syringes and tracheae are illustrated and compared with the parent species. The apparent evolution of a biological isolating mechanism in Netta erythrophthalma is discussed on a population basis. Speculation on the origin of these hybrids seems to rule out superficially attractive solutions like rape. Genie introgression is evident in at least one species, and the contrary possibility of hybrid inviabilityMaybe present in at least one hybrid combination. To assist explanation, biological isolating mechanisms and general evolutionary tendencies in the two waterfowl tribes involved, the Anatini and Aythyini, are reviewed. Waterfowl speciation indications in the Afrotropical Region are presented, and the potential effects of climatic changes during the Pleistocene are stressed. Southern Africa's remarkable predation pressure on waterfowl is discussed. In view of its major importance in monomorphic ducks, display relevance to hybridization is discussed. Other breeding aspects of selective relevance also receive attention, including the effects of predation, pair bonds, parental care, available food and habitat. Also mentioned is the confusion surrounding the nature and homology of the so-called ?eclipse? plumage, and the puzzling tendency of the so-called ?southern? ducks to monomorphism while their equivalents in the northern hemisphere tend strongly to seasonal dimorphism. Scattered indications from the literature are developed into what appears to be a reasonable theoretical explanation for the latter phenomenon, recognizing two types of monomorphic plumage. These are incorporated into an original classification of waterfowl plumage types. The apparent secondary loss of dimorphic plumage in waterfowl isolates on islands is considered compatible with the theory. In a sequence according to the proposed plumage type allocated, and in the light of discussed indications, the likelihood of Afrotropical hybridization is considered for each of the southern African duck species.Summary Milstein, P. Le S. 1979. The evolutionary significance of wild hybridization in South African Highveld ducks. Ostrich Suppl. 13. Wild hybrid ducks of interspecific and intergeneric origin were unexpectedly captured at Barberspan, the major waterfowl-ringing station in Africa. In addition to a single record by Shewell (1957), 24 hybrids and back-crosses between Yellowbilled Ducks Anas undulata, Red-billed Teal A. erythrorhyncha and Southern Pochard Netta erythrophthalma were captured over a three-year period. These hybrids call for a revision of current theory concerning wild hybridization with respect to monomorphic and dimorphic ducks. Frequencies are apparently only exceeded in the literature by the controversial American Black Duck Anas rubripes x Mallard A. platyrhynchos incidence. A comparative description and statistical comparison of the different phenotypes is given. Hybrid syringes and tracheae are illustrated and compared with the parent species. The apparent evolution of a biological isolating mechanism in Netta erythrophthalma is discussed on a population basis. Speculation on the origin of these hybrids seems to rule out superficially attractive solutions like rape. Genie introgression is evident in at least one species, and the contrary possibility of hybrid inviabilityMaybe present in at least one hybrid combination. To assist explanation, biological isolating mechanisms and general evolutionary tendencies in the two waterfowl tribes involved, the Anatini and Aythyini, are reviewed. Waterfowl speciation indications in the Afrotropical Region are presented, and the potential effects of climatic changes during the Pleistocene are stressed. Southern Africa's remarkable predation pressure on waterfowl is discussed. In view of its major importance in monomorphic ducks, display relevance to hybridization is discussed. Other breeding aspects of selective relevance also receive attention, including the effects of predation, pair bonds, parental care, available food and habitat. Also mentioned is the confusion surrounding the nature and homology of the so-called ?eclipse? plumage, and the puzzling tendency of the so-called ?southern? ducks to monomorphism while their equivalents in the northern hemisphere tend strongly to seasonal dimorphism. Scattered indications from the literature are developed into what appears to be a reasonable theoretical explanation for the latter phenomenon, recognizing two types of monomorphic plumage. These are incorporated into an original classification of waterfowl plumage types. The apparent secondary loss of dimorphic plumage in waterfowl isolates on islands is considered compatible with the theory. In a sequence according to the proposed plumage type allocated, and in the light of discussed indications, the likelihood of Afrotropical hybridization is considered for each of the southern African duck species. |