Showing papers by "Michael J. Braun published in 1994"

Mitochondrial Analysis of Gene Flow between New Zealand Mallards (Anas Platyrhynchos) and Grey Ducks (A. Superciliosa)

Abstract: ABSTP,CT.--One of the more well-known examples of hybridization in birds is the frequently documented occurrence between sexually dimorphic Mallards (Anas platyrhynchos) and several closely related nondimorphic species in the mallard complex. In New Zealand, the Grey Duck (Anas superciliosa superciliosa) is the indigenous, nondimorphic Mallardlike species, and extensive hybridization with introduced Mallards has been implicated in the population decline of Grey Ducks. Individuals from throughout the country were classified phenotypically as parentals or hybrids based on variation in plumage, bill color, and leg color. We confirmed species-specific mitochondrial DNA haplotypes by comparing restrictionenzyme fragment patterns in Grey Ducks and New Zealand Mallards to those of Pacific Black Ducks (A. superciliosa rogersi) from Australia and Mallards from North America, respectively. Our data indicate that hybridization has led not only to introgression of Grey Duck mtDNA into Mallard populations (the predicted direction of gene flow), but also to significant introgression of Mallard mtDNA into Grey Duck populations. Thus, the contention that hybridization between Mallards and nondimorphic species involves primarily Mallard males with females of the other species is not upheld for this example from New Zealand. The speciation process appears to be undergoing reversal. Received I April 1993, accepted 2 July 1993. THE INCIDENCE OF interspecific and intergeneric hybridization in the order Anseriformes is higher than in any other order of birds, reaching 30 to 40% by some estimates (Grant and Grant 1992). In addition, a substantial proportion of interspecific hybrids (20%) in this order have been reported to be fertile (Scherer and Hilsberg 1982), so there is potential for extensive gene flow and introgression between some species. Among the more well-known examples is the frequently documented incidence of hybridization between sexually dimorphic Mallards (Anas platyrhynchos) and several closely related, nondimorphic species. For instance, in North America, hybridization with Mallards has been implicated as one factor in the population decline of American Black Ducks (A. rubripes; Johnsgard 1967, Heusmann 1974, Ankney et al. 1987), Hawaiian Ducks (A. wyvilliana; Griffin et al. 1989), and Mexican Ducks (A. platyrhynchos diazi; Hubbard 1977). Increasing numbers of

Increasing proportions of uracil in DNA substrates increases inhibition of restriction enzyme digests.

Abstract: Techniques that rely upon the incorporation of uracil into DNA are being published with increasing frequency, especially in PCR protocols. We report here the efficiency of 18 type II restriction enzymes to digest PCR amplicons synthesized with varying proportions of TTP to dUTP in the PCR mixture. We find that most enzymes with A:T/U bp in their recognition site digest the amplicons less efficiently as the percentage of dUTP in the reaction mixture is increased. This effect is most dramatic when the proportion of dUTP in the nucleotide mixture exceeds 50%. All but one of the enzymes which fail to digest amplicons that are synthesized with 100% dUTP digest some amplicons which are synthesized with 90% dUTP.