Reproductive Skew Of The Azure-winged Magpie In The Occurrence Of Extra-pair Copulation

In the researches of animal behaviors,the concept of reproductive skew(Rs)was originally termed to address the question of how an individual allocates its reproductive sharing along multiple mating partners.Although it has always been used in cooperatively-breeding systems,in which it is treated as an important way adopted by the dominant to calm down the within-group conflicts,the reproductive skew may have broader usage,such as in explaining the evolution of extra-pair copulation(EPC)that had been widely uncovered in avian species.As individuals that engage in EPC also encounter how to allocate reproductive sharing between their social and extra-pair mates,they need to take into consideration how to reduce the cost of multi-mating.On the contrary,for those individuals whose social mates have more EPC chances,how to cope with the risk of being cuckolded.To address these questions plays a key role in realizing individual fitness,either for the cuckolding or for the cuckolded individuals.In this study,I propose that to introduce the concept of reproductive skew into the studies of avian EPC may be helpful to illustrate how does this behavior evolve,particularly in bi-parental nests.Based on the inclusive fitness theory,I propose a new hypothesis that concerns the reproductive skew in the occurrence of EPC.As the fitness of female breeders relies largely on the amount of parental care for their offspring,a female breeder may determine the number of her offspring according to the quality of her social mate.The lower the quality of her social mate,the more likely that the female do not produce the largest clutch.In another word,she may reserve a part of fecundity when pairing with a low-quality male.This reserved fecundity of female can by explored by extra-pair mates.Consequently,when a female obtains EPC chances,she will adopt the multimating strategy,in which she can influence the tradeoff of her social mate via the reproductive skew.Under the condition that his social mate is more likely to engage in EPC,a social male may have two coping strategies.The first is called ‘hindsight compensation' strategy,that is,to increase parental care for the mixed brood to ensure the survival of their own offspring if the reproductive skew is biased towards himself.The other is call ‘foresight prevention' strategy,that is,to prompt his social mate to engage in EPC with his relatives,so that the cuckolded male can obtain indirect fitness from the reproduction of his relatives.In this study,I tested this hypothesis in the azurewinged magpie(Cyanopica cyanus).In an azure-winged magpie population that breeds on the Tibetan Plateau,we collected data about the life history and parental provisioning behaviors,as well as blood samples in bi-parental nests,based on which parental analysis was carried out to examine the frequency of EPC that social female and male engaged in.In this premise,I examined potential factors that might influence the reproductive skew of females and males that engaged in EPC.Moreover,the fitness consequences of reproductive skew to the cuckolding or cuckolded individuals were also explored.The major findings of this study are listed below.1)Both the female and male had engaged in high frequency of EPC.Both sexes produced more genetic offspring via EPC;and simultaneously their cuckolded social mate did not reduce parental care for the mixed brood.This finding implies that cuckolding individuals have realized higher ratio of benefits to costs of EPC in the azure-winged magpie.2)The reproductive skew values of females and males are significantly related to their social mates' beak gape and body mass,respectively.It indicates that the higher the quality of their social mates,the larger the reproductive sharing that cuckolding individuals allocate to their social mates.By contrast,neither the heterozygosity of their social mate nor the genetic relatedness between a social pair was significantly related to the reproductive skew of cuckolding individuals.3)For those males that their social mates engaged in EPC,their inclusive fitness was significantly influenced by their relatedness to the extra-pair male,implying that when cuckolding females allocate more paternity to their extra-pair mates,cuckolded males can obtain indirect fitness from the EPC of their close relatives and social mates.4)The within-and extra-pair young of neither cuckolding females nor cuckolding males exhibited significantly differences in their body parameters and heterozygosity,indicating that azure-winged magpies that engage in EPC did not obtain genetic benefits for their offspring.In conclusion,this study proves in the azure-winged magpie that the risk of engaging EPC of an individual breeder can bring both the pressure,by paternity loss,and the impetus,by higher reproductive skew,to its social mate.For those individuals that encounter higher risk of being cuckolded,they can make responses by either the‘hindsight compensation' strategy or the ‘foresight prevention' strategy.Therefore,this study provides a new explain for the evolution of avian EPC behaviors.