frequency and fitness consequences of communal breeding in a natural population of burying beetles: a test of reproductive skew

1. Reproductive cooperation occurs in diverse taxa and a defining characteristic of these social systems is how reproduction is shared. Both male and female burying beetles (Nicrophorus spp.) facultatively form associations to bury a carcass and rear a single brood, making burying beetles a model system for testing skew theory. 2. In this study, 50% of 40-45 g carcasses and 75% of 55-60 g ones were buried by more than one male and/or female Nicrophorus tomentosus. 3. Females were significantly more likely to cooperate on 55-60 g carcasses than on 40-45 g ones. 4. Analysis of parentage of 13 broods using microsatellite loci as genetic markers showed that maternity analysis of only 2% of the young excluded all females captured leaving the brood chamber after burial. Males previously mated with resident females or displaced by resident males fathered 7% of the young. 5. The male and female remaining the longest were usually the parents of the most offspring, and reproductively dominant individuals also tended to be the largest. 6. Although all but two or three individuals that helped to bury the carcass produced some offspring, reproduction was often not shared equitably. Reproduction of females was significantly skewed on six of nine 40-45 g carcasses but shared fairly equitably on all three 55-60 g ones. Reproduction was skewed among males on 7 of 10 broods. 7. Both males and females relinquished a greater proportion of the brood as the days of assistance from all consexuals increased.