Partner retention as a mechanism to reduce sexual conflict over care in a seabird

The costs of caring for offspring are predicted to lead to an evolutionary
conflict between parents, where each parent benefits if the other provides
the majority of care. However, in many biparental species, breeding
partners remain together for multiple breeding attempts and their
respective future reproductive fitness prospects are therefore
intertwined. Since an increase in current care by a long-term partner
reduces that partner’s future investment and longevity, individuals do not
automatically only benefit when their partner provides care. We test
whether selection will favour individuals that reduce the burden of care
falling on long-term partners, thus decreasing evolutionary conflict over
parental care. Using a semi-natural, captive colony of black-headed gulls
(Chroicocephalus ridibundus), we show that benefits of long-term partner
retention can indeed reduce sexual conflict. Long-term partners have less
intense courtships and are more behaviourally compatible, and individuals
in long-term pairs spare each other’s resources by increasing their own
parental investment compared to those with new partners. Lastly, we
demonstrate that high partner compatibility in newly-formed pairs can
select for commitment to the pair bond. Our results highlight that
compatibility benefits of long-term partnerships can increase selection
for mate retention and increase parental investment.