Abstract
We employ mitochondrial (mt) DNA markers to examine the matrilineal component of population genetic structure in the snow goose Chen caerulescens. From banding returns, it is known that females typically nest at their natal or prior nest site, whereas males pair with females on mixed wintering grounds and mediate considerable nuclear gene flow between geographically separate breeding colonies. Despite site philopatry documented for females, mtDNA markers show no clear distinctions between nesting populations across the species' range from Wrangel Island, USSR to Baffin Island in the eastern Canadian Arctic. Two major mtDNA clades (as well as rare haplotypes) are distributed widely and provide one of the few available examples of a phylogeographic pattern in which phylogenetic discontinuity in a gene tree exists without obvious geographic localization within a species' range. The major mtDNA clades may have differentiated in Pleistocene refugia, and colonized current nesting sites through recent range expansion via pulsed or continual low-level dispersal by females. The contrast between results of banding returns and mtDNA distributions in the snow goose raises general issues regarding population structure: direct contemporary observations on dispersal and gene flow can in some cases convey a misleading impression of phylogeographic population structure, because they fail to access the evolutionary component of population connectedness; conversely, geographic distributions of genetic markers can provide a misleading impression of contemporary dispersal and gene flow because they retain a record of evolutionary events and past demographic parameters that may differ from those of the present. An understanding of population structure requires integration of both evolutionary (genetic) and contemporary (direct observational) perspectives.
Highlights
The degree of faithfulness to natal site or to social group is often sex-biased
According to Greenwood (1980; p. 1144), among all bird species "The lesser snow goose is the best documented example of male biased natal and breeding dispersal. ..." For example, among 223 banded goslings of snow geese that returned to breed at their natal colony, only eight (3.6%) were males; whereas among 55 banded goslings recovered from a breeding colony other than their natal site, only four (7.3%) were females (Cooke et al, 1975)
We assess the matrilineal component of population structure within and among geographic samples of lesser and greater snow geese (Chen caerulescens caerulescens and C. c. atlantica, respectively) representing distinct nesting colonies, and their close relative the Ross' goose (c. rossi), through analyses of restriction site variation in mitochondrial DNA
Summary
MATRIARCHAL POPULATION GENETIC STRUCTURE IN AN AVIAN SPECIES WITH FEMALE NATAL PHILOPATRY. Despite the evidence for philopatry by female snow geese, it is not a foregone conclusion that significant mtDNA differences will exist among colonies, for at least two reasons: (a) females occasionally do breed at non-natal locales (Geramita and Cooke, 1982; Hanson et al, 1972), and even a low level ofintercolony exchange of breeding individuals may override the effects of genetic drift of neutral alleles under an equilibrium model of population structure (Slatkin, 1985, 1987); and (b) most of the current breeding range of the snow goose, which extends from Wrangel Island, USSR across the Canadian Arctic to Baffin Island, was no doubt uninhabitable during the last ice age, and must have been colonized within the last several thousand years. An absence of significant mtDNA differentiation among snow geese colonies would indicate that contemporary observations on dispersal behavior can be inadequate or even misleading predictors of evolutionary components of population genetic structure of this (or other) species
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