# No Evidence for Male Retaliation in a Population With High Level of Extra‐Pair Paternity

## TL;DR

This study found no evidence that male collared flycatchers retaliate against unfaithful mates by reducing parental care, even in a population with high infidelity.

## Contribution

The study provides new empirical evidence contradicting the certainty of paternity hypothesis in a high infidelity bird population.

## Key findings

- Males did not reduce feeding rates in response to the presence or proportion of extra-pair young.
- Feeding rates were only correlated with brood size, not paternity certainty.
- Results contradict earlier findings in the same species, suggesting population-specific factors.

## Abstract

Extra‐pair paternity (EPP) is a widespread phenomenon, as EPP has been observed in 76% of the socially monogamous bird species. Many hypotheses try to explain the evolution of infidelity. While females may participate in extra‐pair copulations, for instance, to ensure the fertilisation of their eggs or to obtain potential genetic benefits for their offspring, unfaithful females face many potential costs too. As nestling provisioning is one of, if not the most energetically costly forms of parental care, the certainty of paternity hypothesis predicts that males with an unfaithful partner reduce their parental investment to avoid the fitness loss arising from rearing unrelated nestlings. We investigated the relationship between the presence and proportion of extra‐pair young (EPY) and the feeding rate of the social male to reveal whether males recognise and penalise unfaithfulness. We conducted the study in a Hungarian population of collared flycatchers (
Ficedula albicollis
) where the EPP rate had been reported to be high. We cross‐fostered nestlings so that each parent reared offspring from two foreign broods and none from their own. Thus, any relationship between paternal investment and paternity in the original brood of the male should be the direct consequence of the female's mating behaviour (as perceived by the male) and not the result of early maternal effects or different behaviour of extra‐ and within‐pair offspring. We found that 63.6% of the broods contained EPY, and 23% of the nestlings were sired by extra‐pair fathers. The only relationship we found was that males with larger broods fed their offspring more frequently. Neither the prevalence nor the proportion of EPY was related to the male feeding rate; thus, our results do not support the certainty of paternity hypothesis. This might be explained by the inability of the males to track their females' behaviour in a population with a high EPP rate.

In an experimental study, we investigated the relationship between within‐pair paternity of the males and their feeding rates in a monogamous passerine with a high rate of infidelity to reveal whether males recognise and penalise the unfaithfulness of their social partners. Our results contradict those previously found in another population of the same species. We argue that the contradictory findings may be explained by the dissimilar rate of extra‐pair copulations in the two populations and the trade‐off between males' extra‐pair mating activity and ability to assess their within‐pair paternity reliably.