DOI: 10.5061/dryad.8w9ghx3r0
title: Partner retention as a mechanism to reduce sexual conflict over care in a seabird

description: 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.
description: # Title of Dataset: Partner retention as a mechanism to reduce sexual
 conflict over care in a seabird Set of csv files with data used to perform
 all analyses described in the paper. ## Description of the Data and file
 structure Each file is linked to one of the 5 hypotheses described in the
 paper. These data were used for principal component analysis and data
 derived from there were used in models to test our hypotheses. Below the
 variables used in each of the 5 analyses is described in detail: **File 1:
 Courtship PCA** PairID: unique identifier for the breeding pair
 DisplayRate: courtship displays per hour JulianDateFirstCourtship: Number
 of days between the first courtship observation in the colony was observed
 and the onset of focal pair's courtship JulianLayDate: Number of days
 between 1st April and the date female laid first egg DaysCourtLay: number
 of days between first courtship of a pair and first egg lay date
 PairBondDuration: number of years focal pair had breed together as
 partners prior to current breeding attempt EstablishedPair: binary coding
 for whether or not a pair had bred together at least once before current
 breeding attempt MaleAge: age in years of breeding male FemaleAge: age in
 years of breeding female MeanAge: mean age of male and female combined
 **File 2: Synchrony PCA impute** PairID: unique identifier for the
 breeding pair PropOneInc: proportion of incubation photos where a single
 parent was incubating on the nest PropMidBoutSwitch: number of brief
 parental swapping on nest as a proportion of all incubation photos taken
 PropSyncDisplay: proportion of all within-pair courtship displays that
 were synchronous, as described in paper Prop2BirdSync: proportion of
 within-pair courtship displays where both partners actively participated
 and were also synchronous, as described in paper PairBondDuration: number
 of years focal pair had breed together as partners prior to current
 breeding attempt EstablishedPair: binary coding for whether or not a pair
 had bred together at least once before current breeding attempt MaleAge:
 age in years of breeding male FemaleAge: age in years of breeding female
 MeanAge: mean age of male and female combined **File 3: Pair investment
 PCA impute** PairID: unique identifier for the breeding pair
 WeightedMeanVol: mean egg volume of focal pair, weighted by clutch size
 (number of eggs) IncShare: Absolute deviation of male contribution to
 incubation (calculated as proportion of incubation photos where male was
 incubating eggs) from 0.5. MaleRegurgitation: Number of times a focal male
 regurgitated for partner as a proportion of all observation hours
 performed PairBondDuration: number of years focal pair had breed together
 as partners prior to current breeding attempt EstablishedPair: binary
 coding for whether or not a pair had bred together at least once before
 current breeding attempt MaleAge: age in years of breeding male FemaleAge:
 age in years of breeding female MeanAge: mean age of male and female
 combined Other variables not used in this paper **File 4: Pair investment
 PCA impute** BirdID: unique identifier for individual bird
 PropNBSweeps: number of nest-building observations as a proportion of all
 the nest-building checks performed since nesting began DefenceRate: number
 of nest defence displays/total observation hours since nesting began
 CountALLDisplaysBirdInvolvedIn: number of courtship displays observed for
 focal individual CountEPDisplay: number of courtship displays by focal
 individual directed towards individual other than breeding partner
 PropEPDisplays: proportion of all displays recorded that were directed
 towards individual other than breeding partner PropParticipatedWP:
 proportion of all within-pair displays that the focal bird actively
 participated in ObsHours: total hours a bird was observed for Sex: binary
 coding for molecular sex (1=male, 0=female PairBondDuration: number of
 years focal pair had breed together as partners prior to current breeding
 attempt EstablishedPair: binary coding for whether or not a pair had bred
 together at least once before current breeding attempt Age: age in years
 of bird Other variables not directly used in paper **File 5: Pair
 investment PCA impute** PairID: unique identifier for the breeding pair
 InvestPC1: first principal component value from PCA on partner investment
 InvestPC2: second principal component value from PCA on partner investment
 CommitPC1Mean: first principal component value from PCA on partner
 commitment CommitPC2Mean: second principal component value from PCA on
 partner commitment DisplaySync: proportion of pair's courtship
 displays that were performed synchronously, as described in paper
 MeanAge: mean age of male and female combined