The genetics of polymorphism in the goose anser caerulescens.

TLDR: This paper is an attempt to analyze the genetic basis for the polymorphism in this dimorphic species, by investigating a sample of the large colony at Boas River, Southampton Island, North West Territories, Canada.

Abstract: Although the most recent A.O.U. checklist of North American Birds (1957) records the Blue Goose and the Lesser Snow Goose as distinct species (Chen caerulescens [= Anser caerulescens] and C. hyperborea [= A. hyperborea] respectively), many ornithologists today agree with the conclusion of Cooch (1961) that the smaller subspecies of the Snow Goose Anser caerulescens caerulescens is polymorphic and has two clearly defined color phases, a blue phase and a white phase. Some authors, e.g. Manning et al. (1956) prefer to regard the Blue Goose and the Lesser Snow Goose as conspecific but consisting of two subspecies. Polymorphism is well known in birds and has been well documented by Mayr (1942) and Huxley (1955). In only a few cases, however, has it been possible to infer the genetic basis of the polymorphism. O'Donald and Davis (1959) have studied the genetics of the color phases of the Parasitic Jaeger (Stercorarius parasiticus) . Meyerriecks ( 1957) has some observations on genetics of polymorphism in the Great Blue-Great White Heron complex. Williamson (1957) reported on the genetic basis for the dimorphism found in the goslings of the Ross's Goose, and Ryder (1967) extended these observations. Lowther (1961) recorded an interesting case of polymorphism in the White-throated Sparrow and Thorneycroft (1966) presented cytological evidence for the genetic basis of this polymorphism. Most observers, however, have had either to ignore the genetic basis or to suggest a genetic basis with no genetic evidence on which to base their speculations. Genetic data of this nature are not easy to obtain in non-domesticated birds. Many birds will not breed in captivity. In the wild it is possible to gain meaningful genetic evidence only if a large number of families is studied and if the polymorphism is detectable in nestling stage, or alternatively if the nestling can be kept in captivity, or can be marked for individual recognition until the adult plumage appears. The polymorphism of Anser caerulescens is in many ways ideal for study. Large colonies, where the different morphs interbreed, can be found. The polymorphism is detectable in both adult and gosling plumages and is observable in both sexes. Most species of birds produce too few offspring in anyone season for a genetic study based on individual families to be feasible, but when a large population can be examined, some pooling of data allows conclusions about the genetic basis to be drawn. This paper is an attempt to analyze the genetic basis for the polymorphism in this dimorphic species, by investigating a sample of the large colony at Boas River, Southampton Island, North West Territories, Canada. Although there are indications that color differences lead to differences in choice of nest sites and time of breeding, these attributes of the polymorphism have been ignored in the present study. In the course of this analysis, observations on the assortative mating behavior were made. These observations, which are described in detail below, led to the conclusion that some form of imprinting, as suggested by Huxley (1955), was operating. This in turn suggested that such imprinting, if complete, could lead in a few generations