Population genetic structure and direct observations reveal sex-reversed patterns of dispersal in a cooperative bird.
Bottom Line: Direct observations revealed that (i) natal philopatry was rare, with both sexes typically dispersing locally to breed, and (ii), unusually for birds, males bred at significantly greater distances from their natal group than females.Examining the spatial scale of extra-group mating highlighted that the resulting 'sperm dispersal' could have acted in concert with individual dispersal to generate these genetic patterns, but gamete dispersal alone cannot account entirely for the sex differences in genetic structure observed.We highlight the potential importance of sex differences in the distances over which dispersal opportunities can be detected.
Affiliation: Zoological Society of London, Regent's Park, London, NW1 4RY, UK; Centre for Ecology & Conservation, University of Exeter, Cornwall Campus, Penryn, TR10 9FE, UK.Show MeSH
Related in: MedlinePlus
Mentions: Dominant breeding positions were rarely inherited by birds within their natal groups (8 of 54 dominance turnover events, 14.8%), and there was no clear sex difference in the incidence of doing so (3 of 25 (12.0%) female dominance turnovers; 5 of 29 males (17.2%); binomial test: = 0.03, P = 0.88). Of the 46 dominance turnovers that did not involve inheritance within the natal group, 33 of the new dominants were known natal dispersers (i.e. they were known to be securing their first dominant position), two were known breeding dispersal events (i.e. the bird was previously dominant in another group), and for the remaining 11, the birds originated outside the study population and so could have been undertaking either natal or breeding dispersal. For the 33 known natal dispersal events, the natal dispersal distances (from the birds’ natal site to their first attainment of dominance) of males were significantly larger than those of females (mean ± SE males: 440.13 m ± 94.7; females: 223.28 ± 36.57; randomized P = 0.04, 95% CI = 0.037–0.046, Fig.1). As the mean distance between the centres of neighbouring territories in our population was 117 m (Harrison et al. 2013a), these translate into mean (± SE) detected natal dispersal distances of 3.78 (± 0.85) territories for males and 1.92 (0.34) territories for females. Simulations confirmed local dispersal by both sexes: the observed natal dispersal distances were significantly shorter than would be expected by chance if individuals were dispersing randomly with respect to distance within our study site (males: P = 0.003; females: P < 0.001). It seems unlikely that females frequently engage in a second long-distance dispersal strategy that has gone undetected due to the scale of our study site, as dominance positions within our study population were rarely secured by females originating outside it (just 4 of 25 dominance turnovers; 16.0%); the same was true for males (7 of 29; 24.1%).
Affiliation: Zoological Society of London, Regent's Park, London, NW1 4RY, UK; Centre for Ecology & Conservation, University of Exeter, Cornwall Campus, Penryn, TR10 9FE, UK.