Study On Extra-Pair Paternity In Chinese Blackbird (Turdus Mandarinus)

Monogamy is a common mating system in birds.In many social monogamous birds,the loss of paternity is a comparatively phenomenon.Among Passeriformes,86%of the studied species had extra-pair paternity.Because the extra-pair copulation of birds is secretive and difficult to observe,it is common to use molecular technology to study the generation of extra-pair paternity.In the past two decades,many studies have focused on testing evolutionary and ecological hypotheses.However,the empirical data supporting these hypotheses are incomplete in many aspects,and the reasons why females seek extra-pair copulation are still unclear.Therefore,this study took the Chinese Blackbird(Turdus mandarinus)as the research object to explore the mechanism of extra-pair paternity of monogamous birds in the context of emerging cities and its relationship with environment factors.From 2017 to 2020,224 newly built Chinese Blackbird nests were investigated during the breeding season,including 176 in Nanchang City(Qianhu Campus of Nanchang University)and Yugan County of Shangrao City(Dashandi village,Chaijiashan village,Dongjiadian village,etc.),Jiangxi Province.Nine nest site factors and five nest factors of 224 nests were measured.A total of 74 infrared cameras and 92RC-4 temperature recorders were used to monitor the behaviors,the environment and nest temperatures of Chinese Blackbird during the breeding season.We counted the reproductive parameters of 136 breeding nests(clutch size ? 1),and measured the egg parameters of 286 eggs and the physical parameters of 272 nestlings.Due to the influence of natural conditions,predation and human disturbance,we collected a total of 285 Chinese Blackbird samples from 78 breeding nests for molecular experiments,including 268 nestlings and 17 adult birds.Through the field experiments and molecular experiments,we concluded the following results:(1)Using Cervus 3.0 to identify paternity and Kingroup v2 to calculate the genetic degree of offspring,the results showed that 34 nests had extra-pair paternity in 78 sampling nests and 37 were extra-pair offspring in 268 nestlings.In this study,13.8%of Chinese Blackbird were found to have extra-pair copulation,but the proportion of extra-pair copulation was not significantly higher than that of other Passeriformes.(2)The mechanism of extra-pair copulation in Chinese Blackbird was consistent with the hypothesis of ensuring fertilization,excellent gene and non-matriarchal effects.The results showed that the hatching rate(z =-2.39,df = 56,P = 0.027)and the brood size(z =-2.18,df = 56,P = 0.028)of the birds with extra-pair copulation were significantly higher than those with faithful mate.The comparison of egg parameters showed that the egg quality of extra-pair fertilization was better,including egg weight,short diameter and egg volume were significantly higher than those fertilized with faithful mate,respectively.From the perspective of individual fitness,our results support that the individual fitness between out of extra-pair offspring is stronger than that of within-pair offspring in terms of egg weight,egg size,hatching rate,growth curve of chicks and other reproductive parameters.(3)The nest site selection of Chinese Blackbird was mainly affected by the distance to road.The Logistic regression results show that the key factor affecting the nest site selection of Chinese Blackbird belonged to the distance to road.The farther from the road is,the more hidden the nest,and the less human interference,the more likely the females is to have extra-pair copulation.Minimum nest spacing was less than100 m,the number of nests with extra-pair copulation is the most,and with the increase of the minimum nest spacing,the number of nests with extra-pair copulation decreases significantly.The reproductive synchronization of Chinese Blackbird was the largest in the early stage of the breeding season,and the probability of mating is the largest when the reproductive synchrony reaches the peak.In the peak of female breeding,extra-pair copulation will be affected by the ambient temperature when bird lays eggs,too high or too low temperature is not conducive to the female seeking mating.The breeding failure caused by nest predation may be related to the female's seeking for extra-pair copulation.