Reproductive Partitioning In The Cooperative Breeding System Of The Azure-winged Magpie

In the researches of animal behaviors,the concept of reproductive skew has been widely used to describe how dominant breeders in a cooperatively breeding system partitions their reproductive shares among multiple potential mates.Current models concerning reproductive skew integrate ecological conditions under which a cooperative group has been established,the relatedness among group members,relative competitive abilities between a dominant breeder and its same-sexed helpers,as well as the benefits and costs of helping,to predict the performance of reproductive skew in different cooperatively breeding species.Therefore,investigation of reproductive skew plays a key role in demonstrating the evolution of cooperation behaviors in animal societies.In this master thesis,we investigated potential factors that might influence the performance of reproductive skew of dominant females and males and its adaptive significance in a small-sized Corvidae bird,the azure-winged magpie(Cyanopica cyanus)that bred in a high-altitude habitat.The azure-winged magpie population studied in this work is located at the northeast edge of the Tibetan Plateau,which is a newly colonized population that had been dispersed from low-altitude habitats to this high-altitude habitat.Based on tenyear data about demography and behaviors,the present thesis first analyzed the temporal variation of cooperative breeding with the colonization time of this population.Then,we estimated the reproductive portioning of dominant females and males among three types of potential partners,including social mate,opposite-sexed helpers,and EPC(extra-pair copulation)mate outside the cooperative group.According to the estimated reproductive partitioning,we tested factors that might influence the value of reproductive partitioning of dominant females and males,respectively,including body conditions of a dominant breeders and that of its social mate,the relatedness between sexual partners,and the genetic heterozygosity of different types of partners.Finally,we examined the potential effects of a dominant breeder’s reproductive partitioning on its fitness and parental care of offspring.The major findings of this thesis are provided below.1)18.03% of 1004 azure-winged magpie nests were cooperative groups that contained 1-5 extra individuals as the helper,of which 61.33% contained only male helpers and the remaining contained only female helpers.Male helpers tended to be more closely related to dominant males than to dominant females.By contrast,female helpers were more closely related to dominant females than to dominant males.The proportion of cooperative groups in a colony differed significantly among years but not among colonies.Nesting saturation and colonization time were significantly related to while habitat size and nesting density unrelated to the proportion of cooperative groups in a colony.Compared with the reproductive success of bi-parental nests,cooperative groups had fledged more offspring and realized greater fledging success.2)Results of paternity analysis in all azure-winged magpie nests indicated that both dominant females and males could partition their reproductive shares to three types of partners,including the social mate,opposite-sexed helpers and EPC mates outside the group.Once a dominant breeder accessed an opportunity of EPC outside the group,the number of its genetic offspring could be increased significantly.3)By comparing the reproductive partitioning of a dominant breeder among three types of partners,I found that either the dominant female or dominant male had partitioned significantly greater reproductive share to its social mate than that to the opposite-sexed helpers and EPC mates outside the group.Results of fitting generalized linear mixed models(GLMMs),which tested potential factors that might influence the reproductive partitioning of a dominant breeder,showed that neither the dominant female nor dominant male partitioned its reproductive shares according to the body condition of its social mate;and that the reproductive partitioning of dominant females was closely related to the genetic heterozygosity of its social mate.It thus highlighted that the greater the heterozygosity of a dominant male,the larger the reproductive share that it obtained from its social mate.4)Results of fitting other two GLMMs,which tested the effects of reproductive partitioning of a dominant breeder on the number of genetic offspring of its social mates,showed that the number of a dominant female’s genetic offspring was unrelated to the reproductive partitioning of her social mate,whereas the number of a dominant male’s genetic offspring was tightly linked with the reproductive partitioning of his social mate.That means,the larger the reproductive partitioning value of a dominant female,the more offspring the dominant male sired.5)Results of fitting other GLMMs,which tested the effect of reproductive share of the dominant female,dominant male and helpers on their provisioning rate,respectively,detected no close relationship between the dependent variable and its independent variables.Regarding the effect of reproductive skew value on the provisioning rate of a dominant female and male,a significant positive relationship was detected in that of the dominant male,but not in that of the dominant female.In conclusion,the major findings in this thesis indicated that cooperative breeding of the Tibetan population of the azure-winged magpie changed with the colonization time of the population.A dominant breeder had partitioned greater reproductive shares to its social mate,even if it had opportunities to copulate with helpers or outside-group partners.Moreover,potential factors that influence a dominant breeder’s reproductive partitioning,as well as the effects of a dominant breeder’s reproductive partitioning on its fitness and parental care,exhibited apparent sexual differences.