DOI: 10.5061/dryad.p2ngf1vxw
title: Temperature variability is associated with the occurrence of extra-pair paternity in blue tits

description: In birds, extra-pair paternity (EPP) constitutes an alternative mating
 strategy, with potentially important fitness consequences for both males
 and females and their offspring. Several factors have been identified that
 can influence the occurrence of EPP, but the role of environmental
 variability has so far received relatively little attention. Using
 long-term data set from a wild population of blue tit (Cyanistes
 cearuleus) we assess the importance of ambient temperature in modulating
 the levels of extra-pair paternity. Here, we show that variability of
 local thermal conditions affects the occurrence of EPP. Specifically, we
 found that the probability of EPP increased with increasing variability in
 ambient temperature experienced by females prior to egg laying. This
 pattern is consistent with the idea of plastic female responses to
 unpredictable environmental conditions. Our results suggest that
 extra-pair mating may represent an adaptive behavioural strategy to
 compensate for possible negative effects of unpredictable environmental
 conditions. 
description: Study area Our research spans the years
 2008–2016 and is part of a long-term study conducted in a nest-box
 breeding population of the blue tits on the island of Gotland, Sweden
 (57°03′ N, 18°17′ E). In our population, females lay a single clutch per
 season and each year almost all breeding attempts are recorded and as many
 reproducing individuals as possible are captured, for a more detailed
 description of the study site and general field procedure (for details see
 Drobniak et al., 2022). Genetic and paternity
 analyses We took a blood sample (ca. 20µL) from
 nestlings on the second day after hatching and from adults when they were
 caught by mist-nets or inside the nest boxes while feeding 14-day-old
 nestlings, DNA was extracted from blood samples with Chelex following the
 procedure described in Griffiths et al. (1998). In the following EPP
 analyses, the number of microsatellite loci used to determine parentage
 varied between years. In 2009–2010 and 2012–2015, the paternity was
 identified using five microsatellite loci (Arct et al., 2013). In 2011, we
 used 15 microsatellite loci (Arct et al., 2022), for a more detailed
 description of parentage assignment in blue tits see also Arct et al
 (2017). In our population, each year on average 30% of nests contain at
 least one EPY (range 14 to 45%). In our population a relatively high
 proportion of females seek extra-pair paternity; however, we have a small
 proportion of extra-pair young in the nests – 7.09%. For this reason, we
 treated EPP as a binary response, as we did in other previous
 studies. Temperature data We
 acquired temperature data using the website of the Swedish Meteorological
 and Hydrological Institute (http://opendata-download-metobs.smhi.se/explore/?parameter=3). We obtained data from the meteorological station located in Hemse (56.92°N, 18.15°E; approximately 10 km north from the study area). Raw climate data were used to compute the following descriptive measures of the local variation in ambient temperature for a period of 14 days prior to the laying of the first egg for each clutch: 1.     mean ambient temperature (°C) calculated within those 14 days; 2.     temperature variability (i.e., variance of average daily temperatures across those 14 days, expressed in °C<sup>2</sup>). References Arct A, Drobniak SM, Podmokła E, Gustafson L, Cichoń M 2013 Benefits of extra-pair mating may depend on environmental conditions—an experimental study in the blue tit (<em>Cyanistes caeruleus</em>). Behav. Ecol. Sociobiol, 67, 1809-1815. Arct A, Sudyka J, Podmokła E, Drobniak SM, Gustafsson L, Cichoń M. 2017 Heterozygosity–fitness correlations in blue tit nestlings (<em>Cyanistis caeruleus</em>) under contrasting rearing conditions. Evol. Ecol., 31, 803-814. Arct A, Drobniak SM, Mellinger S, Martyka R, Gustafsson L, Cichoń M 2022 Extra‐pair paternity in Blue Tits (<em>Cyanistes</em> <em>caeruleus</em>) depends on the combination of social partners' age. Ibis, 164(2), 388-395. Drobniak SM, Cichoń M, Janas K, Barczyk J, Gustafsson L, Zagalska‐Neubauer M 2022 Habitat shapes diversity of gut microbiomes in a wild population of blue tits <em>Cyanistes</em> <em>caeruleus</em>. J. Avian Biol., e02829. (https://doi.org/10.1111/jav.02829)] Griffiths R, Double MC, Orr K, Dawson RJ 1998 A DNA test to sex most birds. Mol Ecol. 7(8):1071-5
description: # Temperature variability is associated with the occurrence of extra-pair
 paternity in blue tits 
 Here, we showed that variability of local thermal conditions affects the
 occurrence of extra-pair paternity (EPP) in blue tits. Specifically, we
 found that the probability of EPP increased with rising variability in
 ambient temperature experienced by females prior to egg laying. ##
 Description of the data and file structure YEAR = year of study
 RINGM/FRING = unique identifier of the social male/female MAGE/ FAGE=
 social male’s/female’s age (YEARLING/OLDER) LD=laying date CS =clutch size
 EPC = absence/presence of extra-pair offspring (0/1) in the nest
 TEMP_BROOD14_mea = mean ambient temperature (°C) calculated within 14 days
 prior to the laying of the first egg for each clutch; TEMP_BROOD14_var =
 temperature variability (i.e., variance of average daily temperatures
 across those 14 days, expressed in °C2). PRCP_BROOD14\_ = average daily
 sum of precipitation (mm) calculated within 14 days prior to the laying of
 the first egg for each clutch PRCP_BROOD14_var  = precipitation
 variability (i.e., variance of average daily sum of precipitation across
 those 14 days, expressed in mm).  missing data codes = NA Please contact
 dr Aneta Arct for more details (). ##
 Sharing/Access information Daily temperature and precipitation records
 were obtained from the meteorological station at Hoburgen (56.92°N,
 18.15°E; approximately 10 km from the main study areas). The data were
 accessed via the website of the Swedish Meteorological and Hydrological
 Institute
 (). ##
 Code/Software