Molecular Genetic (RAPD) Analysis of Breeding Magpie Geese

Abstract

-Magpie Geese (Anseranus semipalmata) typically form nesting trios consisting of two females and one male, an uncommon breeding arrangement for waterfowl. To study aspects of their reproductive biology, 20 reproductively active adults representing seven reproductive groupings (broods) were scored for 106 polymorphic primer-specific RAPD bands. Genetic distances between all possible adult pairs were calculated, and these values were analyzed using the Mantel test. In the pairwise comparison of genetic distances, those between males were significantly less than those for other adult combinations (P < 0.05). Using the same analytical approach, we found that females that shared a nest were more like one another than were females that did not share a nest (P < 0.05). We suggest that a plausible hypothesis to account for the relative genetic homogeneity of the male population is that males seeking to enter the breeding population do so at their natal site. The females they recruit are more closely related to one another than are females in general. Received 5 April 1995, accepted 29 June 1995. LARGE NUMBERS of Magpie Geese (Anseranus semipalmata) congregate at seasonal wetlands in tropical northern Australia. The bird's unique morphology (including partially webbed, heavily clawed feet with an opposable fourth toe) led to its taxonomic placement in its own family. This uniqueness also is evident at the molecular level, and recent taxonomies derived from mitochondrial DNA sequences support the view that this species should be assigned to a family of its own (Sraml et al. 1996). Although abundant in parts of northern Australia, the current distribution of the Magpie Goose is only a remnant of its former range, which has been severely restricted over the past 200 years by the introduction of European-style agricultural practices. Situations that threaten this species could arise again as the result of conflicts between the bird's habitat requirements and changing human activities. Proposed changes associated with tropical agriculture could threaten the conservation status of these birds (Whitehead 1991). In attempting to sustain adequate numbers of a species, it is important to understand the species' reproductive biology. Unlike most water4E-mail: horn@science.canberra.edu.au fowl, Magpie Geese commonly form breeding trios consisting of two females and one male (Frith and Davies 1961). In situations where females share a nest, all three attendants typically have a direct reproductive (genetic) interest in the clutch, and they are involved in many aspects of care and defense of the eggs and young. Chicks remain with their parents for their first year of life, possibly learning about seasonal resource distribution (Whitehead and Tschirner 1990). The stability of these polygynous groups from year to year distinguishes Magpie Geese from other communal breeders (Brown 1987). When joined in a reproductive trio, individual females seem to decrease their potential reproductive output as measured by numbers of eggs laid. Egg counts (x = 8.6) in nests with only one female and one male are not much smaller than those (x = 9.4) from nests with two females and one male (Frith and Davies 1961). In addition, behavioral observations of trios suggest that males mate with both females and that both females contribute eggs approximately equally to these joint nests. Assignments of young to specific females have been done using restriction-fragment-length-polymorphism (RFLP) analysis of DNA. In making those assignments, conspecific nest parasitism was