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Terry Burke - One of the best experts on this subject based on the ideXlab platform.
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male age is associated with Extra Pair Paternity but not with Extra Pair mating behaviour
bioRxiv, 2017Co-Authors: Antje Girndt, Terry Burke, Charlotte W T Chng, Julia SchroederAbstract:Extra-Pair Paternity is the result of copulation between a female and a male other than her social partner. In socially monogamous birds, old males are most likely to sire Extra-Pair offspring. The male manipulation and female choice hypotheses predict that age-specific male mating behaviour could explain this old-over-young male advantage. These hypotheses have been difficult to test because copulations and the individuals involved are hard to observe. Here, we studied the mating behaviour and Pairing contexts of captive house sparrows, Passer domesticus. Our set-up mimicked the complex social environment experienced by wild house sparrows. We found that middle-aged males, that would be considered old in natural populations, gained most Extra-Pair Paternity. However, both female solicitation behaviour and subsequent Extra-Pair matings were unrelated to male age. Further, copulations were more likely when solicited by females than those initiated by males (i.e. unsolicited copulations), and unsolicited within-Pair copulations were more common than unsolicited Extra-Pair copulations. To conclude, our results did not support either hypotheses regarding age-specific male mating behaviour. Instead, female choice, independent of male age, governed copulation success, especially in an Extra-Pair context and post-copulatory mechanisms might determine why older males sire more Extra-Pair offspring.
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Age-dependent trajectories differ between within-Pair and Extra-Pair Paternity success.
Journal of Evolutionary Biology, 2017Co-Authors: Yu Hsun Hsu, Terry Burke, Antje Girndt, Julia Schroeder, Mirre J. P. Simons, Isabel S. Winney, Shinichi NakagawaAbstract:Reproductive success is associated with age in many taxa, increasing in early life followed by reproductive senescence. In socially monogamous, but genetically polygamous species, this generates the interesting possibility of differential trajectories of within-Pair and Extra-Pair siring success with age in males. We investigate these relationships simultaneously using within-individual analyses with 13 years of data from an insular house sparrow (Passer domesticus) population. As expected, we found that both within- and Extra-Pair Paternity success increased with age, followed by a senescence-like decline. However, the age trajectories of within- and Extra-Pair Paternity successes differed significantly, with the Extra-Pair Paternity success increasing faster, albeit non-significantly so, in early life, and showing a delayed decline by 1.5 years on average later in life compared to within-Pair Paternity success. These different trajectories indicate that the two alternative mating tactics should have age-dependent payoffs. Males may partition their reproductive effort between within- and Extra-Pair matings depending on their current age in order to reap the maximal combined benefit from both strategies. The interplay between these mating strategies and age-specific mortality may explain the variation in rates of Extra-Pair Paternity observed within and between-species. This article is protected by copyright. All rights reserved.
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Levels of Extra‐Pair Paternity are associated with parental care in penduline tits (Remizidae)
Ibis, 2017Co-Authors: Alexander Ball, Terry Burke, Deborah A Dawson, René E. Van Dijk, Penn Lloyd, Ákos Pogány, Stephen Dorus, Rauri C. K. Bowie, Tamás SzékelyAbstract:In most passerine birds, individuals attempt to maximize their fitness by providing parental care while also mating outside their Pair bond. A sex-specific trade-off between these two behaviours is predicted to occur, as the fitness benefits of Extra-Pair mating differ between the sexes. We use nest observations and parentage analysis to reveal a negative association between male care and the incidence of Extra-Pair Paternity across three species of penduline tit (Remizidae). This provides evidence of a trade-off between these two behaviours, possibly due to the devaluing of paternal care by Extra-Pair offspring.
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The colour of Paternity: Extra-Pair Paternity in the wild Gouldian finch does not appear to be driven by genetic incompatibility between morphs.
Journal of Evolutionary Biology, 2016Co-Authors: Peri E. Bolton, Terry Burke, Lee A. Rollins, James Brazill-boast, Kang-wook Kim, Simon C. GriffithAbstract:In socially monogamous species, individuals can use Extra-Pair Paternity and offspring sex allocation as adaptive strategies to ameliorate costs of genetic incompatibility with their partner. Previous studies on domesticated Gouldian finches (Erythrura gouldiae) demonstrated a genetic incompatibility between head colour morphs, the effects of which are more severe in female offspring. Domesticated females use differential sex allocation, and Extra-Pair Paternity with males of compatible head colour, to reduce fitness costs associated with incompatibility in mixed-morph Pairings. However, laboratory studies are an oversimplification of the complex ecological factors experienced in the wild and may only reflect the biology of a domesticated species. This study aimed to examine the patterns of parentage and sex ratio bias with respect to colour Pairing combinations in a wild population of the Gouldian finch. We utilized a novel PCR assay that allowed us to genotype the morph of offspring before the morph phenotype develops and to explore bias in morph Paternity and selection at the nest. Contrary to previous findings in the laboratory, we found no effect of Pairing combinations on patterns of Extra-Pair Paternity, offspring sex ratio or selection on morphs in nestlings. In the wild, the effect of morph incompatibility is likely much smaller, or absent, than was observed in the domesticated birds. Furthermore, the previously studied domesticated population is genetically differentiated from the wild population, consistent with the effects of domestication. It is possible that the domestication process fostered the emergence (or enhancement) of incompatibility between colour morphs previously demonstrated in the laboratory.
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Tests of Ecological, Phenotypic, and Genetic Correlates of Extra-Pair Paternity in the House Sparrow
The Condor, 2006Co-Authors: Ian R K Stewart, Terry Burke, Richard D. Hanschu, David F. WestneatAbstract:Abstract We performed a two-year study of Extra-Pair Paternity in the House Sparrow (Passer domesticus) to test a suite of hypotheses relating to ecological factors associated with breeding conditions and parental phenotypes and genotypes. Extra-Pair fertilizations (EPFs) accounted for 45 of 419 (11%) nestlings and occurred in 33 of 126 (26%) broods. EPFs were not correlated with breeding synchrony or breeding density, although they were significantly more common toward the end of each breeding season. Body size and the size of the bib, a secondary sexual character, were no different between males that were cuckolded and those that achieved full Paternity in their nests. Older males were cuckolded as frequently as yearlings, and there was no difference between males that were cuckolded and those that were not with regard to two measures of individual genetic diversity. There was no evidence that females sought EPFs to avoid inbreeding, since EPFs were equally likely to be present among Pairs that were closely related and those that were only distantly related, and females were equally related to their Extra-Pair mates as they were to their within-Pair mates. Furthermore, Extra-Pair sires did not possess alleles that were rare in the population. In sum, despite a substantial sample size, we found few correlates of Extra-Pair Paternity in House Sparrows.
Bart Kempenaers - One of the best experts on this subject based on the ideXlab platform.
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exposure to predator models during the fertile period leads to higher levels of Extra Pair Paternity in blue tits
Journal of Animal Ecology, 2020Co-Authors: Peter Santema, Mihai Valcu, Bart KempenaersAbstract:: The perceived risk of predation can affect breeding behaviour and reduce reproductive success in prey species. Individuals exposed to predators may also adopt different mating tactics with potential consequences for the distribution of Paternity in socially monogamous species that engage in Extra-Pair copulations. We experimentally increased perceived predation risk during the fertile period in blue tits Cyanistes caeruleus. Every morning between nest completion and the onset of egg laying, we presented a model of either a predator or a non-predator (control) near active nestboxes. Broods from Pairs exposed to predators had higher levels of Extra-Pair Paternity than control broods. This mainly resulted from a higher proportion of Extra-Pair offspring in broods with at least one Extra-Pair young. Females exposed to predators first emerged from the nestbox later in the morning, stayed away from the nestbox for longer and were less likely to be visited at the nest by their social mate, but we detected no behavioural differences once the model was removed. Our results suggest that the higher rates of Extra-Pair Paternity resulted from the disruption of morning routines, which may have inhibited within-Pair copulations or increased opportunities for females to engage in Extra-Pair copulations. We conclude that the perceived risk of predation can have substantial effects on levels of Extra-Pair Paternity.
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Exposure to predator models during the fertile period leads to higher levels of Extra-Pair Paternity in blue tits.
Journal of Animal Ecology, 2019Co-Authors: Peter Santema, Mihai Valcu, Bart KempenaersAbstract:The perceived risk of predation can affect breeding behaviour and reduce reproductive success in prey species. Individuals exposed to predators may also adopt different mating tactics with potential consequences for the distribution of Paternity in socially monogamous species that engage in Extra-Pair copulations. We experimentally increased perceived predation risk during the fertile period in blue tits Cyanistes caeruleus. Every morning between nest completion and the onset of egg laying, we presented a model of either a predator or a non-predator (control) near active nestboxes. Broods from Pairs exposed to predators had higher levels of Extra-Pair Paternity than control broods. This mainly resulted from a higher proportion of Extra-Pair offspring in broods with at least one Extra-Pair young. Females exposed to predators first emerged from the nestbox later in the morning, stayed away from the nestbox for longer and were less likely to be visited at the nest by their social mate, but we detected no behavioural differences once the model was removed. Our results suggest that the higher rates of Extra-Pair Paternity resulted from the disruption of morning routines, which may have inhibited within-Pair copulations or increased opportunities for females to engage in Extra-Pair copulations. We conclude that the perceived risk of predation can have substantial effects on levels of Extra-Pair Paternity.
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Extra-Pair Paternity and Sexual Selection
From Genes to Animal Behavior, 2011Co-Authors: Emmi Schlicht, Bart KempenaersAbstract:Parentage analyses can reveal hidden reproductive interactions between individuals that are not social partners. Extra-Pair mating is a special case of promiscuity where social Pair bonds exist and persist despite copulations with multiple partners by one or both Pair members. The relevance of Extra-Pair interactions in reshaping social mating systems varies among species. In some species or populations, Extra-Pair matings are no more than exceptional events (e.g., Dearborn et al. 2001; Egger et al.2006), whereas in others Extra-Pair Paternity (EPP) is a phenomenon that cannot be ignored when describing mating patterns because of a substantial discrepancy between the observable apparent mating system and the actually realized mating system (e.g., Double and Cockburn 2003; Sefc et al. 2008). Extra-Pair copulations (EPCs) are of special interest in socially monogamous species where promiscuity is otherwise absent. Pair bonding and social monogamy are relatively rare – except in birds (Lack 1968, p. 148) – yet occur in a wide range of animal taxa (e.g., Caldwell 1997; Kvarnemo et al. 2000; Baeza 2008; Steinauer 2009). However, social monogamy frequently goes hand in hand with multiple mating (e.g., Griffith et al. 2002; Chapple 2003; Lode and Lesbarreres 2004; Cohas and Allaine2009).
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a novel song parameter correlates with Extra Pair Paternity and reflects male longevity
Proceedings of The Royal Society B: Biological Sciences, 2002Co-Authors: Wolfgang Forstmeier, Bart Kempenaers, Axel Meyer, Bernd LeislerAbstract:Although elaborate bird song provides one of the prime examples of a trait that evolved under sexual selection, it is still unclear whether females judge the quality of males by attributes of their song and whether these song features honestly signal a male's genetic quality. We measured the ability of male dusky warblers Phylloscopus fuscatus to maintain a high sound amplitude during singing, which probably reflects an individual's physiological limitations. This new measure of singing performance was correlated with male longevity and with Extra-Pair Paternity, indicating that females who copulated with better singers obtained 'good genes' for their offspring. Our findings are consistent with the idea that females assess male quality by subtle differences in their performance during the production of notes, rather than by the quantity or versatility of song. In addition, observations on territorial conflicts indicate that attractive males invest less in competition over territories because they can reproduce via Extra-Pair Paternity.
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Extra Pair Paternity in birds explaining variation between species and populations
Trends in Ecology and Evolution, 1998Co-Authors: Marion Petrie, Bart KempenaersAbstract:Molecular techniques used to assign Paternity have revealed previously unknown incidences of Extra-Pair Paternity in socially monogamous bird species. DNA fingerprinting has now been used sufficiently often for mating-system biologists to appreciate the natural variation in the frequency of broods showing Extra-Pair young. The variation between species and between populations of the same species is surprisingly marked. Explaining this variation may help us to understand the factors promoting sexual selection. Recent comparative studies and detailed behavioural studies suggest that factors such as breeding density, genetic variation in the population and the intensity of sexual conflicts determine the costs and benefits to males and females of engaging in Extra-Pair copulations, and therefore contribute to the variation among populations.
Jan T. Lifjeld - One of the best experts on this subject based on the ideXlab platform.
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No evidence of Extra‐Pair Paternity in the Atlantic Puffin Fratercula arctica
Ibis, 2008Co-Authors: Tycho Anker-nilssen, Oddmund Kleven, Tomas Aarvak, Jan T. LifjeldAbstract:Paternity in Atlantic Puffins T. Anker-Nilssen et al. Short communica on No evidence of Extra-Pair Paternity in the Atlantic Puffin Fratercula arctica TYCHO ANKER-NILSSEN, 1 * ODDMUND KLEVEN, 2 TOMAS AARVAK 1 † & JAN T. LIFJELD 2 1 Norwegian Institute for Nature Research, NO-7485 Trondheim, Norway 2 Natural History Museum, Department of Zoology, University of Oslo, P.O. Box 1172 Blindern, NO-0318 Oslo, Norway
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No evidence of Extra‐Pair Paternity in the little auk Alle alle
Journal of Avian Biology, 2005Co-Authors: Jan T. Lifjeld, Ann M. A. Harding, Fridtjof Mehlum, Trond ØigardenAbstract:487.Extra-Pair Paternity is typically rather infrequent in seabirds, as in most other long-lived and socially monogamous birds. Here we report the first Paternity study of thelittle auk Alle alle, a high arctic seabird which raises only a single chick per year.Parentage was determined using three highly polymorphic microsatellite markers. Wefound that all 26 chicks in our sample were true genetic offspring of their social parents,with an upper 95% confidence limit of 10.88% for the frequency of Extra-Pair Paternity.This level of Extra-Pair Paternity is not significantly different from frequencies reportedfrom the closely related common Uria aalge and Bru¨nnich’s guillemots U. lomvia.J. T. Lifjeld (correspondence), F. Mehlum and T. Oigarden, Natural History Museum,University of Oslo, P.O. Box 1172 Blindern, NO-0318 Oslo, Norway. A. M. A. Harding,Polish Polar Station in Hornsund, Institute of Geophysics, Polish Academy of Sciences,Spitsbergen, Norway. E-mail: j.t.lifjeld@nhm.uio.no
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Extra-Pair Paternity in the Common Murre
The Condor, 2001Co-Authors: Tim R. Birkhead, Ben J. Hatchwell, Robert Lindner, Donald Blomqvist, E. Jayne Pellatt, Richard Griffiths, Jan T. LifjeldAbstract:Abstract Multi-locus DNA fingerprinting was used to estimate the frequency of Extra-Pair Paternity in the Common Murre (Uria aalge), a colonial, sexually monomorphic seabird that breeds at very high densities and in which Extra-Pair copulation is frequent. Common Murres produce a single chick. We detected 6 cases of Extra-Pair Paternity in 77 families (7.8%). This value was higher than the proportion of successful Extra-Pair copulations (1.6%) estimated from behavioral data from an earlier study of the same population.
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High frequency of Extra-Pair Paternity in a dense and synchronous population of Willow Warblers Phylloscopus trochilus
Journal of Avian Biology, 1997Co-Authors: Gro Bjørnstad, Jan T. LifjeldAbstract:Genetic parentage was studied in a Norwegian, sub-alpine population of Willow Warblers Phylloscopus trochilus by means of multilocus DNA fingerprinting. We found that 33% (36/109) of the offspring were unrelated to the putative father, and that one additional offspring was unrelated to both putative parents. Altogether 50% (10/20) of the broods contained illegitimate young. The distribution of Extra-Pair Paternity was bimodal, with several broods containing many Extra-Pair offspring. These results contrast markedly with a previous study of the same species, reporting no cases of mismatched parentage in a Swedish lowland population. Potentially, the high frequency of Extra-Pair Paternity could be attributed to a higher breeding density and/or synchrony in our study population. Cuckolded males had a lower body mass, but no shorter tarsi or wings, than non-cuckolded males. This suggests that a male's loss of Paternity is somehow related to his body condition. The data set includes five broods in which the Pair male was permanently removed on the day the first egg was laid. There was no tendency that the manipulation increased the
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Extra-Pair Paternity in monogamous tree swallows
Animal Behaviour, 1993Co-Authors: Jan T. Lifjeld, Peter O. Dunn, Raleigh J. Robertson, Peter T. BoagAbstract:Abstract Abstract. Multilocus DNA fingerprinting of offspring of monogamous Pairs of tree swallows, Tachycineta bicolor , revealed that 50% (8/16) of broods contained young sired by Extra-Pair males, totalling 38% (33/86) of all offspring analysed. No young resulted from intraspecific brood parasitism. The distribution of Extra-Pair Paternity showed a bimodal pattern; either none or many illegitimate young per brood. Thirty-three per cent of illegitimate offspring were sired by three to five nearest male neighbours. Females copulated frequently with their own mate at their own box, but they were never seen copulating with other males. Hence, there was a striking contrast between the rate of Extra-Pair copulation and the rate of Extra-Pair fertilization. There was no relationship between the Pair copulation rate and the proportion of illegitimate young in a brood, suggesting that males cannot use the number of copulations performed with their mate as a reliable cue to their share of Paternity. Males provisioned their young at nearly the same rate as did females, and males with illegitimate offspring in their nest did not reduce provisioning effort compared to males with only legitimate offspring. Hence, females did not suffer any apparent costs of promiscuity. It is argued that females control the sperm transfer success of copulations. Because females do not receive anything other than sperm from Extra-Pair copulation, the promiscuous behaviour is probably driven by some genetic factors enhancing female fitness. Although the data presented seem consistent with female choice for male genetic quality, there were no detectable phenotypic characteristics of males with high fertilization success.
Hakan Tegelstrom - One of the best experts on this subject based on the ideXlab platform.
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Extra Pair Paternity and tail ornamentation in the barn swallow hirundo rustica
Behavioral Ecology and Sociobiology, 1997Co-Authors: Anders Pape Møller, Hakan TegelstromAbstract:Females of socially monogamous species may copulate with attractive non-mates to obtain access to the genes of such males, and a preference for attractive copulation partners may result in sexual selection. Extra-Pair copulations are common in the socially monogamous barn swallow Hirundorustica, and a 2-year study of Paternity using multi-locus DNA fingerprinting demonstrated that 33% of 63 broods and 28% of 261 offspring were sired by Extra-Pair males. The frequency of Extra-Pair offspring within broods was highly skewed with the majority of all broods having either no Extra-Pair offspring or only Extra-Pair offspring. Individual Pairs were consistent in their frequency of Extra-Pair Paternity among broods, and the repeatability of Extra-Pair Paternity of multiple broods of the same female was statistically significant. The proportion of Extra-Pair offspring was negatively related to the tail length of the male attending the nest. Behavioural observations showed that Extra-Pair fertilizations were more likely in broods raised by females that had been observed to engage in Extra-Pair copulations. The frequency of Extra-Pair offspring was unrelated to the intensity of two male Paternity guards, mate guarding and the rate of intra-Pair copulations. In an analysis of Extra-Pair Paternity and male parental care in different broods of the same male, male barn swallows fed their offspring relatively less frequently if the brood contained more Extra-Pair offspring. Therefore, female barn swallows pursue Extra-Pair copulations with attractive males, which may result in sexual selection, even though Extra-Pair Paternity is costly for females due to the reduction of paternal care by their social mates.
Anders Pape Møller - One of the best experts on this subject based on the ideXlab platform.
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Extra-Pair Paternity and antiparasitic defence
Avian Research, 2020Co-Authors: Anders Pape Møller, Jørgen Skavdal Søraker, Juan José SolerAbstract:Extra-Pair Paternity (EPP) in birds provides benefits in terms of more offspring, and characteristics for maintenance of this behaviour have been the subject of investigation. Microorganisms are known to be transmitted during mating, especially when mating with multiple partners, and factors reducing this cost of multiple mating are expected. Further, plumage brightness and colour intensity have been shown to be important traits to benefits from multiple mating as predicted by sexual selection. The aim of this study was to investigate the relationship between the rate of Extra-Pair Paternity and the relative size of the uropygial gland at the interspecific level, as the uropygial gland is an exocrine gland hypothesized to produce antiparasitic substances and further identified to affect plumage brightness. Because of the expected benefits of large uropygial gland in scenarios of sexual selection, we predicted a positive correlation with EPP. We collected information from the literature of uropygial gland size and frequency of Extra-Pair Paternity of 60 avian species of different families and explored the predicted positive correlation between them. We did so with means of comparative analyses that considered phylogenetic relationship as random factor and included body mass as covariate. We used Markov chain Monte Carlo generalized linear mixed models that were weighted by number of nests used to estimate Extra-Pair Paternity. We detected a positive relationship between level of Extra-Pair Paternity and uropygial gland size at an interspecific level. This finding is consistent with the prediction. We discuss the importance of this result in scenarios of sexual selection and argue that the detected relationship may have arisen by utilizing antiparasitic secretions through secondary sexual characters indicating parasite resistance.
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Minisatellite mutation rates increase with Extra-Pair Paternity among birds
BMC Evolutionary Biology, 2009Co-Authors: Anders Pape Møller, José Javier CuervoAbstract:Background Amos [1] suggested recently that a previously reported positive relationship between minisatellite mutation rates and Extra-Pair Paternity among species of birds [2] was confounded by transcription errors and selective inclusion of studies. Here we attempted to replicate the results reported by Amos [1], but also tested for the relationship by expanding the data base by including studies published after our original paper.
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The degree of Extra-Pair Paternity increases with genetic variability
Proceedings of the National Academy of Sciences, 1998Co-Authors: Marion Petrie, Claudie Doums, Anders Pape MøllerAbstract:The amount of Extra-Pair Paternity in socially monogamous bird species varies from 0% to 76% Extra-Pair offspring. The causes of this remarkable interspecific variation are largely unknown, although intraspecific analyses suggest that females seek Extra-Pair matings to improve the genetic quality of their offspring. If this is a general explanation for the occurrence of Extra-Pair matings, then proportionally more females should seek to modify the Paternity of their clutch when there is more variation among males in their genetic quality. Here we test this prediction in birds and show that interspecific variation in the proportion of Extra-Pair offspring is positively related to the proportion of polymorphic loci as measured by protein electrophoresis, even when controlling for potentially confounding variables. Genetic variability was also assessed, for sister Pairs of species and populations differing significantly in Extra-Pair Paternity, by using random priming, which provides an estimate of genome-wide diversity. We found that genetic diversity was higher in the populations with a higher level of Extra-Pair Paternity. These results suggest that the amount of genetic variability in a population may be an important factor influencing mating patterns.
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Extra Pair Paternity and tail ornamentation in the barn swallow hirundo rustica
Behavioral Ecology and Sociobiology, 1997Co-Authors: Anders Pape Møller, Hakan TegelstromAbstract:Females of socially monogamous species may copulate with attractive non-mates to obtain access to the genes of such males, and a preference for attractive copulation partners may result in sexual selection. Extra-Pair copulations are common in the socially monogamous barn swallow Hirundorustica, and a 2-year study of Paternity using multi-locus DNA fingerprinting demonstrated that 33% of 63 broods and 28% of 261 offspring were sired by Extra-Pair males. The frequency of Extra-Pair offspring within broods was highly skewed with the majority of all broods having either no Extra-Pair offspring or only Extra-Pair offspring. Individual Pairs were consistent in their frequency of Extra-Pair Paternity among broods, and the repeatability of Extra-Pair Paternity of multiple broods of the same female was statistically significant. The proportion of Extra-Pair offspring was negatively related to the tail length of the male attending the nest. Behavioural observations showed that Extra-Pair fertilizations were more likely in broods raised by females that had been observed to engage in Extra-Pair copulations. The frequency of Extra-Pair offspring was unrelated to the intensity of two male Paternity guards, mate guarding and the rate of intra-Pair copulations. In an analysis of Extra-Pair Paternity and male parental care in different broods of the same male, male barn swallows fed their offspring relatively less frequently if the brood contained more Extra-Pair offspring. Therefore, female barn swallows pursue Extra-Pair copulations with attractive males, which may result in sexual selection, even though Extra-Pair Paternity is costly for females due to the reduction of paternal care by their social mates.
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Immune defence, Extra–Pair Paternity, and sexual selection in birds
Proceedings of the Royal Society of London. Series B: Biological Sciences, 1997Co-Authors: Anders Pape MøllerAbstract:Secondary sexual characters have been suggested to reliably reflect the ability of individuals to resist debilitating parasites, and females may gain direct or indirect fitness benefits from preferring the most Extravagantly ornamented males. Extra–Pair Paternity provides an estimate of an important component of sexual selection in birds. Species with a high frequency of Extra–Pair Paternity have a variance in realized reproductive success that is greater than the variance in apparent reproductive success, and Extra–Pair copulations and hence Extra–Pair Paternity by females are often directly associated with the expression of male secondary sexual characters. If sexually dichromatic species have experienced a long period of antagonistic coevolution with their parasites, such species should have evolved larger immune defence organs than sexually monochromatic species. Bird species with sexual dichromatism had larger spleens for their body size than monochromatic species in a comparative analysis. Furthermore, species with a high frequency of Extra–Pair Paternity were sexually dichromatic and had large spleens for their body size. These results are consistent with the hypothesis that females of dichromatic bird species seek Extra–Pair copulations to obtain indirect fitness benefits in terms of superior resistance of their offspring to virulent parasites.
