Are extra-pair young better than within-pair young? A comparison of survival and dominance in alpine marmot
Aurélie Cohas, Université de Lyon; Université Lyon 1; CNRS; UMR 5558, Laboratoire de Biométrie et Biologie Évolutive, 43 boulevard du 11 novembre 1918, Villeurbanne F-69622, France. Fax: +33(0)472431388. E-mail: firstname.lastname@example.org
- 1In socially monogamous species, females may seek extra-pair copulation to gain genetic benefits. In order to test this ‘genetic quality’ hypothesis, one must compare the performance of extra-pair young (EPY) and within-pair young (WPY). Such tests, however, are scarce and results published so far are inconclusive.
- 2Here, we test the ‘genetic quality’ hypothesis using multistate capture–recapture models to compare age-specific survival and access to dominance between EPY and WPY in the alpine marmot Marmota marmota, a socially monogamous mammal showing extra-pair paternities.
- 3When compared with WPY, survival of EPY was higher by 15%, 10% and 30%, for juveniles, yearlings and 2-year-old individuals, respectively. Survival at older ages did not differ.
- 4Survival corresponded to true survival for yearlings and juveniles as dispersal does not occur before 2 years of age in marmots. For older individuals, survival estimates included a mixture of survival and dispersal. The 30% increase of the 2-year-old EPY survival might reflect delayed dispersal rather than high survival of EPY as compared with WPY.
- 5WPY and EPY had the same probability (0·28) to access dominance at 2 years of age, but EPY were more successful at older ages than WPY (0·46 vs. 0·10).
- 6Both survival and reproductive performance were higher in EPY than in WPY. The fitness advantages of adopting such a mixed mating tactic are thus likely to be high for marmot females. We suggest that obtaining genetic benefits is the main evolutionary force driving extra-pair paternity in alpine marmots.