Genotypes of Swan Geese Anser cygnoides using 17 nuclear microsatellite loci at 14 locations.

Dispersal affects the spatial distribution and population structure of
species.Dispersal is often male-biased in mammals while female-biased in
birds, with the notable exception of the Anatidae. In this study, we
tested genetic evidence for sex-biased dispersal (SBD) in the Swan Goose
Anser cygnoides, an Asian endemic and IUCN vulnerable species, which has
been increasingly restricted to breeding on Mongolian steppe wetlands. We
analyzed the genotypes of 278 Swan Geese samples from 14 locations at 14
microsatellite loci. Results from assignment indices, analysis of
molecular variance and five other population descriptors all failed to
support significant SBD signals for the Swan Goose at the landscape level.
Although overall results showed significantly high relatedness within
colonies (suggesting high levels of philopatry in both sexes), local male
genetic structure at the 1,050 km distance indicated greater dispersal
distance for females from the eastern sector of the breeding range. Hence,
local dispersal is likely scale-dependent and female-biased within the
eastern breeding range. These findings are intriguing considering the
prevailing expectation for there to be female fidelity in most goose
species. We suggest that while behaviour-related traits may have
facilitated the local genetic structure for the Swan Goose, several
extrinsic factors, including the decreasing availability of the nesting
sites and the severe fragmentation of breeding habitats, could have
contributed to the absence of SBD at the landscape level. The
long-distance molt-migration that is typical of goose species such as the
Swan Goose may also have hampered our ability to detect SBD. Hence, we
urge further genetic sampling from other areas in summer to extend our
results, complemented by field observations to confirm our DNA analyses
conclusions about sex-specific dispersal patterns at different spatial
scales in this species.