Alternative tactics and individual reproductive success in natural associations of the burying beetle, Nicrophorus vespilloides

Alternative reproductive tactics can be maintained through different evolutionary avenues. They can be genetically or stochastically determined, in which case they must yield equal fitness, or their use can be conditional, in which case the fitness payoff of alternatives may differ. We attempted to assess the reproductive success of alternative reproductive tactics employed by wild male and female burying beetles in natural associations on carcasses placed in the field. A beetle's reproductive tactic was defined by its potential involvement in care of larvae, and parentage was assessed using oligolocus DNA fingerprinting of offspring and potential parents. Both in males and in females, alternative tactics yielded significantly different reproductive benefits: subordinate females (brood parasites) and males (satellite males) had considerably lower reproductive success than dominant or uncontested individuals. Joint breeding was too infrequent for statistical inferences, generating intermediate offspring numbers. About 15% of offspring were sired by males not present on the carcass, suggesting that mating away from reproductive resources can produce reproductive benefits to males. Our results, in concert with the observation that beetles using one tactic can be manipulated into employing the alternative, support the notion that Nicrophorus vespilloides uses alternatives conditionally, opportunistically employing lower-benefit tactics when more profitable tactics are not available, or as additional on-the-side tactics to bolster reproductive success.