Sex-specific negotiation rules in a costly conflict over parental care

Sexual conflict theory predicts a trade-off in individual parental care allocated to either current or future reproduction. The optimal amount of current parental effort is expected to differ between adult males and females, with a conflict resolution being reached by negotiation depending on multiple family cues. Currently, a debate exists on how negotiation takes place, along with its potential costs or benefits for all family members. In particular, the specific negotiation rules that male and female parents apply often remain obscure, which in part results from a shortage of empirical studies. We used captive canaries, Serinus canaria, to evaluate consequences of sexual conflict for the offspring by comparing uniparental (female cared for a half clutch) and biparental (both parents cared for a full clutch) families. Our results suggest overall less parental effort in biparental families and offspring were observed to beg harder for parental resources, weigh less as fledglings and tended to grow slower compared to uniparental families. To further increase our understanding of parental negotiation rules, we manipulated the degree of partner visibility and thus information about partner effort by temporarily splitting biparental families. Male and female provisioning strategies depended on both partner visibility and brood demand. An increase in male provisioning was observed after mate removal, whereas the opposite pattern was observed in females. Females, however, increased provisioning in response to offspring begging. We conclude that (1) sexual conflict over parental care is costly for the offspring, (2) sex-specific negotiation rules exist and probably relate to an asymmetry in gathered information and (3) changes in parental feeding strategies trigger a feedback mechanism via brood demand, highlighting the need to consider all family members in order to understand family conflicts and their potential resolution.