Conflict and cooperation in male-male partnerships alter paternal care behavior in the ocellated wrasse

Parental care is a critical determinant of offspring fitness. Female presence and male competition affect paternal care, but male-male cooperation during mating may also be an important, yet underappreciated, driver of paternal care. In many systems, males work together to court females or defend territories against male competitors. This male-male cooperation can alter actual or perceived paternity of the parenting male and could, therefore, influence how males invest in care during the postmating period. Here, we measured how reproductive and social dynamics between nesting and satellite males during mating correlate with nesting male paternal care in the ocellated wrasse (Symphodus ocellatus). Although paternal care (fanning rates) was repeatable across days within the same nesting cycle, it was not repeatable across different nesting cycles, suggesting that males plastically alter care in response to the environment. Nesting males provided care for fewer days at nests with the most unstable relationship between the nesting and satellite male: nests with low satellite cooperation and high male-male conflict where the satellite eventually left or was evicted from the nest. Nesting males also parented more intensively, but for fewer days in the warmer year, suggesting that males may adjust care in response to temperature. Collectively, our results suggest that there is no fixed male trait that females can use to predict paternal care behavior. Instead, females may use male-male interactions as a proxy for the quality of care her offspring will receive, suggesting that sexual selection may favor the co-evolution of paternal care with male-male cooperation. © 2025 The Author(s). Published by Oxford University Press in association with International Society for Behavioral Ecology. All rights reserved. For commercial re-use, please contact reprints@oup.com for reprints and translation rights for reprints. All other permissions can be obtained through our RightsLink service via the Permissions link on the article page on our site - for further information please contact journals.permissions@oup.com.