In some species, the high costs of parental care are shared by both parents during biparental care, which typically evolves if the male stays instead of seeking alternative mating opportunities. Biparental cooperation is only possible if sexual conflict over the often opposing evolutionary interests of each parent is resolved. This dynamic is well studied in evolutionarily derived family systems like altricial birds, but why and how it occurs in species with facultative care, where neither parent must remain with the young (a state likely to prevail during the evolution of parental care), is poorly understood. We investigated this phenomenon by examining the resolution of sexual conflict over care behaviours in Nicrophorus vespilloides . These carrion-breeding beetles exhibit facultative biparental care comprising multiple components exhibited by both sexes, with high variation in male efforts. This variation may be explained by a negotiation ‘tug-of-war’ over investments, where one partner adjusts their efforts to the other, but may also depend on repeatable individual differences in males, selected for by environmental gradients or different pace-of-life strategies. Here, we aimed to disentangle these mechanisms by testing repeatability of male care efforts over multiple reproductive bouts. By conducting these bouts with either the same or different female partners, and taking female care contributions into account, we determined to what degree male care efforts depend on the accompanying female, or on the male itself. We found that male larval feeding was negatively correlated with female contributions and only repeatable in monogamous males, indicating that this behaviour is largely driven by the female partner. Conversely, maintenance of the carcass nursery was repeatable across males regardless of their partner, indicating little flexibility in this niche-constructing behaviour. Overall, our findings show that male care repeatability and sexual conflict resolutions differ between care components, probably depending on different selective pressures shaping each behaviour in either sex. • Males show repeatable differences in effort put into biparental care. • Repeatability and sexual conflict resolution vary between care behaviours. • Repeatable differences may indicate diverging strategies among males. • Resolution differences likely depend on different selective pressures in either sex. • First study assessing Nicrophorus male care variation across reproductive bouts.
Körner et al. (Mon,) studied this question.