Lynn M. Brodsky

Bio: Lynn M. Brodsky is an academic researcher from Carleton University. The author has contributed to research in topics: Anas & Population. The author has an hindex of 2, co-authored 2 publications receiving 105 citations.

Behavioral and ecological factors contributing to American black duck-mallard hybridization

Abstract: Investigation of courtship and pair formation of a wintering population of American black ducks (Anas rubripes) and mallards (A. platyrhynchos) near Ottawa, Ontario, indicated that initially drakes of both species exclusively courted and paired intraspecifically. After all female mallards had paired, the remaining mallard drakes joined black duck courtship groups. Of the 33 unpaired black duck females remaining at this time, only 27% formed intraspecific pairs, whereas 73% selected mallard drakes as mates, despite there being an excess of black duck drakes. Based on these results, a scenario for black duck-mallard hybridization is proposed. It involves ecological factors including the male-biased sex ratio in northern wintering populations, artificial feeding, and roost-site limitation. Other behavioral aspects, such as the earlier pair formation in mallards and the superiority exhibited by mallard drakes when competing for black duck females are discussed. J. WILDL. MANAGE. 48(3):846-852 One factor essential to a species' genetic integrity is its continued reproductive isolation from congenerics through geographic, habitat, or behavioral means (Lack 1971). Two species of dabbling duck, the American black duck and the mallard, are similar both morphologically and behaviorally, and their hybrids appear to be as viable and as fertile as the parental species (Johnsgard 1961). However, geographic range and evolved habitat differences have until recently deterred hybridization between these two species. Prior to 1900, the black duck and mallard were geographically isolated. Heusmann (1974) examined the evolutionary history of the black duck and hypothesized that it evolved during the Pleistocene glacial period when a population along the eastern coast of North America became isolated from western mallard populations. Habitat differences further segregated these populations as the black duck began breeding in the forested regions of the east and the mallard nested in grassland habitats of the west. In the present century, however, land use changes, including the deforestation of the eastern region, have caused a decline in the available breeding habitat of black ducks while simultaneously providing favorable habitat for nesting mallards. Johnsgard (1967) concluded that these environmental modifications were facilitating the colonization, by mallards, of extensive eastern areas formerly occupied by the black duck. The invasion of the mallard into black duck breeding territory has also resulted in the convergence of these two species on wintering grounds. Since the majority of pair bonding in both species occurs throughout the winter (Stotts and Davis 1960, Lebret 1961) and the courtship displays that lead to pair formation are similar (Johnsgard 1960), interspecific pairing can readily occur where these two species winter together. As a result of black duck hybridization with the much larger mallard gene pool and the constant reduction of its nesting habitat, it is believed by many that the black duck as a "pure" species will eventually disappear. The objectives of this study were to examine courtship activity and pair formation in 846 J. Wildl. Manage. 48(3):1984 This content downloaded from 157.55.39.110 on Sat, 24 Sep 2016 06:00:00 UTC All use subject to http://about.jstor.org/terms BLACK DUCK-MALLARD HYBRIDIZATION * Brodsky and Weatherhead 847 black ducks and mallards wintering together at the northern limit of their range and to determine the factors contributing to interspecific pairing between these two species. We thank H. G. Merriam for suggesting the suitability of the Manotick waterfowl population for this study, C. A. Barlow for comments on an earlier draft of this manuscript, and J. Sharkey-Thomas for feeding the ducks. Financial support was provided by the Nat. Sci. and Eng. Counc. of Can. and Carleton Univ.

Behavioural thermoregulation in wintering black ducks: roosting and resting

Abstract: Black ducks (Anas rubripes) wintering near Ottawa, Canada, used a variety of behaviours to reduce their energy costs. The roost site that they occupied provided greater protection from wind than th...

Mitochondrial gene trees and the evolutionary relationship of mallard and black ducks.

Abstract: We assayed restriction site differences in mitochondrial DNA (mtDNA) within and among allopatric populations of the Mallard (Anas platyrhynchos) and the American Black Duck (A. rubripes). The observed mtDNA clones grouped into two phylogenetically distinct arrays that we estimate differ by about 0.8% in nucleotide sequence. Genotypes in one clonal array were present in both species, while genotypes in the other array were seen only in Mallards. In terms of the mtDNA "gene tree," the assayed Mallards exhibit a paraphyletic relationship with respect to Black Ducks, meaning that genealogical separations among some extant haplotypes in the Mallard predate the species separation. Evidence is advanced that this pattern probably resulted from demographically based processes of lineage sorting, rather than recent, secondary introgressive hybridization. However, haplotype frequencies were most similar among conspecific populations, so the Mallard and Black Ducks cluster separately in terms of a population phenogram. The results provide a clear example of the distinction between a gene tree and a population tree, and of the distinction between data analyses that view individuals versus populations as operational taxonomic units (OTUs). Overall, the mtDNA data indicate an extremely close evolutionary relationship between Mallards and Black Ducks, and in conjunction with the geographic distributions suggest that the Black Duck is a recent evolutionary derivative of a more broadly distributed Mallard-Black ancestor.

A phylogenetic analysis and classification of recent dabbling ducks (Tribe anatini) based on comparative morphology

Abstract: ABSTP, Act.--Cladistic analysis of 157 characters of definitive plumages and soft parts, natal plumages, tracheae, and nontracheal skeletons of 59 Anatini (sensu Livezey 1986) provided a phylogenetic hypothesis of high consistency (C! = 0.71, excluding unique autapomorphies) and resolution (tree completely resolved except for two nested trichotomies, a trichotomy within the northern-hemisphere mallards, and the tentative placements of two poorly known species of Anas). Major phylogenetic inferences (lists of three or more taxa are in order of increasing relatedness) include the following: (1) monophyly of the tribe is weakly demonstrated; (2) the tribe comprises three subtribes--Cairineae (Cairina, Pteronetta, Aix), Nettapodeae (Chenonetta, Nettapus), and Anateae (all other genera); (3) subtribe Anateae comprises three "supergenera" (each comprising two genera)--Amazonetta (A. brasiliensis and Callonetta leucophrys), Lophonetta (L. specularioides and Speculanas specularis), and Anas (genera Mareca and Anas); (4) the genus Mareca or wigeons includes ix species--capensis, trepera, falcata, sibilatrix, penelope, and americana; nd (5) the large genus Anas comprises two weakly supported subgroups or cohorts, the first of which includes two subgenera (mallards [Anas] and blue-winged ducks [Spatula]) and the second includes four subgenera (Australasian teal [Nesonetta], pintails [Dafila], Holarctic teal [Querquedula], nd spotted teal [Punanetta]). Other findings include that a sister-relationship exists between Anas sparsa nd other mallards, that subgroups of the "true" mallards are largely congruent with biogeographic subdivisions (northern-hemispheric, African, and South Pacific), that the four species of shoveler are monophyletic, that a sister-relationship between the speckled teals (fiavirostris and andium) and brown pintails (georgica, acuta, and eatoni) exists, and that A. querquedula is the sister-group to the greenwinged teals (formosa, crecca, and carolinensis) and not closely related to the blue-winged ducks. Supplementary data and related theory indicated that (1) interspecific interfertility is a poor indicator of relationship, (2) the phylogenetic species concept provided the most practical definition of terminal taxa, (3) a majority of groups within the Anatini originated in the southern hemisphere, (4) body size, sexual size dimorphism, and egg size are strongly constrained phylogenetically, whereas sexual dichromatism and clutch size are less predictable, (5) biparental attendance of broods is primitive within Anatini, and (6) characters of definitive plumages, natal plumages, tracheae, and skeletons had similar consistencies but attained maximal utility at different levels within the phylogeny, which indicates different rates of character evolution within the tribe. Received 19 July 1990, accepted 4 December 1990.

Molecular population genetics, phylogeography, and conservation biology of the mottled duck (Anas fulvigula)

Abstract: The mottled duck (Anas fulvigula) is a year-round endemic resident of the Gulf Coast and one of two non-migratory dabbling ducks that inhabit North America. To investigate population genetic structure of allopatric mottled duck populations, we collected 5’ control region sequences (bp 78–774) from the mitochondria of 219 mottled ducks sampled at 11 widely spaced geographic localities in Texas, Louisiana, and Florida and compared them to each other and to homologous sequences from 4 Mexican ducks (A. diazi), 13 American black ducks (A. rubripes), and 10 mallards (A. platyrhynchos). We identified 57 unique haplotypes composed of 665 or 666 nucleotides in the 246 control region sequences. Of the 665 homologous positions, 8.3% (n = 55) vary among haplotypes, and 98.2% (n = 54) of these occur within the first 351 nucleotides from the 5’ end of the outgroup sequence. Neighbor-joining analysis shows a large distal clade (52.5% of mottled ducks sampled in our study) composed of two reciprocally monophyletic clades of mottled duck haplotypes, one of which is endemic to Texas and Louisiana and the other endemic to Florida. No mottled ducks sampled in Florida occur in the clade composed of mottled ducks from Texas and Louisiana or vice versa, suggesting that (1) an enduring geographic split has existed for many years between east and west, and (2) gene flow currently is non-existent (or at least undetectable) across the central Gulf Coast. The remaining 47.5% of mottled ducks sampled in our study branch basally from this derived clade, show substantially less hierarchical structure, and fall into various lineage groups of mixed species composition with no geographic or species-specific pattern. Pairwise FST values corroborate the pattern of strong differentiation observed between Texas/Louisiana and Florida. Our findings are consistent with a pattern of partial lineage sorting from a polymorphic ancestral gene pool reshuffled by hybridizing mallards. Control region data and patterns of divergence in mallard-like species worldwide, furthermore, suggest that mottled ducks are close relatives of Mexican ducks, and in turn nested within black ducks. Genetic similarities to nominate mallards are less likely to be the product of common ancestry, but the result of past hybridization with a dichromatic mallard ancestor that invaded North America from Asia many generations ago. Our findings have several important consequences for the conservation biology of mottled ducks across the Gulf Coast and our understanding of the phylogeography of mallard-like species worldwide.