Explore the vast range of titles available.

Functional explanations for forced copulation, an extreme manifestation of intersexual conflict, remain underexplored. We investigated the adaptive significance of forced extra-pair copulation (FEPC) in European blackbirds. Our results contradict the prevailing hypothesis that the primary function of FEPC is fertilization. FEPC frequency peaked at the beginning of the breeding season and declined thereafter, despite the continued presence of fertile females. Furthermore, we found no evidence that males selectively target fertile females; within the reproductive cycle, females were equally susceptible to FEPC during the pre-fertile and fertile periods. We propose that sexual aggression in blackbirds reflects competition. As predicted, the incidence of FEPC was highest early in the season, and females attempting to settle between established pairs were at higher risk of becoming victims. Females were not passive in the conflict and could significantly reduce the risk of FEPC by shifting home ranges. We conclude that FEPC is an instrument of aggression rather than an expression of sexual interest. Neighboring males attempt to deter new competitors by targeting the weaker member of a pair. For females, FEPC is part of the landscape of fear.

Extra-pair copulation (EPC) occurred in most socially monogamous bird species. The mechanisms leading to the frequent occurrence of extra-pair offspring (EPO, EPY) in socially monogamous couples, as well as the ‘function’ of EPC, are the subjects of strong debates and raise many unanswered questions. We studied the relationship between extra-pair paternity (EPP) and the different characteristics of males and females in the European pied flycatcher in Western Siberia (Russia). The analysis was based on the genotyping of 232 males, 250 females, 1485 nestlings (250 nests). The European pied flycatchers were predominantly socially and genetically monogamous, but about 20% of birds could be involved in EPP. Loss of paternity tended to be more frequent in one-year-old males. EPCs could be multiple: one individual may have up to three extra-pair partners. The EPP rate was independent of the breeding time. The extra-pair mates of an individual were mainly its near neighbours. The EPC status of an individual was unrelated to most of its morpho-physiological traits. The occurrence of EPP was almost twice as high in females nesting in good quality territories. The fitness of within-pair offspring, EPO, paternal half-sibs of EPO and maternal half-sibs of EPO did not differ statistically significantly. Assuming very low heritability of extra-pair mating, we argued that EPCs could be incidental side effects (by-product) of selection. We believe that the evolution and maintenance of extra-pair mating are the episelective processes in the case of the European pied flycatcher.

An increasing number of empirical studies in animals have demonstrated male mate choice. However, little is known about the evolution of postpairing male choice, specifically which occurs by differential allocation of male parental care in response to female signals. We use a population genetic model to examine whether such postpairing male mate choice can evolve when males face a trade-off between parental care and extra-pair copulations (EPCs). Specifically, we assume that males allocate more effort to providing parental care when mated to preferred (signaling) females, but they are then unable to allocate additional effort to seek EPCs. We find that both male preference and female signaling can evolve in this situation, under certain conditions. First, this evolution requires a relatively large difference in parental investment between males mated to preferred versus nonpreferred females. Second, whether male choice and female signaling alleles become fixed in a population versus cycle in their frequencies depends on the additional fecundity benefits from EPCs that are gained by choosy males. Third, less costly female signals enable both signaling and choice alleles to evolve under more relaxed conditions. Our results also provide a new insight into the evolution of sexual conflict over parental care.

Quantitative genetic analysis is often fundamental for understanding evolutionary processes in wild populations. Avian populations provide a model system due to the relative ease of inferring relatedness among individuals through observation. However, extra-pair paternity (EPP) creates erroneous links within the social pedigree. Previous work has suggested this causes minor underestimation of heritability if paternal misassignment is random and hence not influenced by the trait being studied. Nevertheless, much literature suggests numerous traits are associated with EPP and the accuracy of heritability estimates for such traits remains unexplored. We show analytically how nonrandom pedigree errors can influence heritability estimates. Then, combining empirical data from a large great tit (Parus major) pedigree with simulations, we assess how heritability estimates derived from social pedigrees change depending on the mode of the relationship between EPP and the focal trait. We show that the magnitude of the underestimation is typically small (<15%). Hence, our analyses suggest that quantitative genetic inference from pedigrees derived from observations of social relationships is relatively robust; our approach also provides a widely applicable method for assessing the consequences of nonrandom EPP.

The ecology and behaviour of the endangered Carnaby’s Cockatoo Calyptorhynchuslatirostris have been studied in detail at Coomallo Creek in the northern wheatbelt of Western Australia from 1969 until the present. Results of research on this breeding population conducted on individually marked birds from 1970 to 1990 were compared with results from analyses of DNA taken from nestlings in the study area from 2003, 2005, and each year from 2009 to 2013. Analyses of DNA confirmed earlier findings about the stability of adult breeding pairs, and that females used the same breeding hollow they used previously, provided the hollow was not occupied when they returned to breed. When moving to another hollow, they chose a hollow in the same vicinity of the previous hollow. Analyses in 22 cases where DNA was obtained from both nestlings of a breeding attempt revealed that in six (27.3%) cases, the second egg was fertilised by a male not paired with the female. These extra-pair copulations were not suspected during the earlier study based on observations of individually marked birds.

Extra-pair copulations (EPCs) are the poorly known antecedents of extra-pair fertilizations (EPFs) in birds. EPFs occur in most bird species that have been examined, but sexual conflict will generally reward females hiding their EPCs from males attempting to protect their paternity. EPCs will be difficult for researchers to document, and necessarily underestimated, in that case. We measured EPC behaviors and EPF frequency in a colonial seabird, the Nazca booby Sula granti , in which all copulations occur in a visually open setting with numerous possible copulatory partners readily available. Females are larger and more physically powerful than males, and are the numerically limiting sex, perhaps limiting options for males to control females. We found that all copulations were voluntary, and females’ sexual activities were wholly unconstrained by male coercion. Most females had multiple copulatory partners in the weeks preceding egg-laying. Despite the commonness of EPC, EPFs did not occur. The different schedules of EPC and within-pair copulation (WPC) provided a sufficient explanation for this outcome: during the ovulation window days before laying, WPC rate increased and EPC rate approached zero. To our knowledge, this is the first robust evidence of complete sexual agency in a female bird aside from lek-mating species, contributing a valuable exemplar to the literature on sexual conflict over reproduction.

Red-winged Blackbirds (RWBL; Agelaius phoeniceus) have a polygynous mating system and, because territorial males commonly have harems of two to five females, some second-year (SY) and after-second-year (ASY) males do not establish nesting territories, but become floaters. Previous studies have revealed high rates of extra-pair copulations in this species and that sexually mature male floaters and territory owners do not differ in size, testosterone levels, or reproductive capability, suggesting that floaters may occasionally gain paternity. During May and June 2008, we observed the behavioral responses of floater males to taxidermic mounts (models) of female RWBL placed in a precopulatory position. Floaters intruded into territories during 46% of model presentations, with 20% of intrusions by ASY floaters and 80% by SY floaters. During intrusions, ASY floaters attempted to copulate with models 93% of the time compared to 80% for SY floaters. Copulations were successful during 30% of attempts by ASY males and 25% of attempts by SY floaters. The frequency of intrusions by ASY and SY floaters, attempted copulations by SY floaters, and successful copulations by ASY floaters increased as territorial males spent more time off their territories. Responses of floater males toward models in our study suggest that floater male RWBL attempt to exploit available breeding opportunities. The lack of evidence for extrapair young (EPY) fathered by floater male RWBL in previous studies, combined with our results indicating that the presence of territorial males limits floater intrusions, copulation attempts, and successful copulations, suggests that the reproductive success of floater males is limited in part by the aggressive behavior of territorial males. La poliginia es el sistema de apareamiento de la especie Agelaius phoeniceus y, debido a que los machos territoriales suelen tener harenes de dos a cinco hembras, algunos machos en su segundo año (SY) y de mas de dos años de edad (ASY) no establecen territorios, pero algunos se vuelven flotantes. Estudios previos revelaron que existen altas tasas de cópulas extra-pareja en esta especie y que los machos flotantes sexualmente maduros y los machos dueños de territorios no difieren en tamaño, niveles de testosterona, o capacidad reproductiva, lo que sugiere que los machos flotantes en algunas ocasiones pueden adquirir paternidad. Durante mayo y junio de 2008, observamos el comportamiento de machos flotantes que respondieron a modelos de hembras de A. phoeniceus colocados en una posición precópula. Los machos flotantes invadieron los territorios en 46% de las presentaciones de modelos, con 20% de las intrusiones por flotantes ASY y 80% por flotantes SY. Durante las intrusiones, los flotantes ASY intentaron copular con el modelo en 93% de los casos, en comparación con 80% para los flotantes SY. Las copulaciones fueron exitosos en 30% de los intentos por machos ASY y en 25% de los intentos por flotantes SY. La frecuencia de las intrusiones por flotantes ASY, y SY, las cópulas intentadas por flotantes SY, y las copulaciones exitosas de flotantes ASY aumentaron a menudo que los machos territoriales pasaban más tiempo fuera de sus territorios. Las respuestas de machos flotantes hacia los modelos en nuestro estudio sugieren que los machos flotantes de A. phoeniceus intentan explotar las oportunidades disponibles para reproducir. La falta de pruebas de la existencia de pichones extra-pareja engendrados por machos flotantes en estudios anteriores de esta especie, junto con nuestros resultados que indican que la presencia de machos territoriales limitan las intrusiones en territorios por machos flotantes y sus intentos de cópula y cópulas exitosas, sugieren que el éxito reproductivo de los machos flotantes es limitado en parte por el comportamiento agresivo de los machos territoriales.

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. Perceived predation risk can have many behavioural consequences, but how it affects mating behaviour has rarely been tested. The authors exposed blue tits to predator models during the peak fertile period and found that levels of extra‐pair paternity were substantially increased, possibly because early morning behaviour was disrupted.

The theoretical literature predicts that parentage differences between the sexes, due to females mating with multiple males, select males to provide less parental care and females to care more for the offspring. We formulate simple evolutionary games to question the generality of this prediction. We find that the relationship between paternal care and fitness gained from extrapair matings is important. A trade-off between these two quantities is required for partial paternity and complete maternity to bias the evolutionary stable strategy (ESS) toward more female care. We argue that this trade-off has been implicitly or explicitly assumed in most previous theories. However, if there is no trade-off between paternal care and extra-pair matings, parentage differences do not influence the ESS sex roles. Moreover, it is also possible for these two quantities to have a positive relationship, in which case we predict selection for male care is possible. We support these predictions using agent-based simulations. We also consider the possibility that caring males have greater opportunities to guard their paternity, and find that this mechanism can also select for male-biased care. Hence, we derive the conditions under which male care may be selected despite partial paternity and complete maternity.