The Periodic Variation Of Testosterone And Its Influence On Reproduction In Varied Tit

The breeding behavior of birds is one of the hot topics in behavioral ecology.The breeding behavior consists of courting,choosing nest-site,nesting,laying eggs,hatching,feeding,and domain defense.Testosterone(T)is the most important sex hormone regulating the reproduction of birds.In male birds,testosterone can promote the expression of related proteins and cytokines,initiate and maintain normal male reproductive activities.In female birds,testosterone can promote the development and maturation of follicles and ovulation.Now,most of the studies work out by exogenous testosterone implantation,little has known about the effect of testosterone on the reproduction of birds in a natural state.In the study,we measured the testosterone levels during the reproductive cycle and explored the influence of testosterone on the physical parameters and reproductive activities of the Varied Tit(Sittiparus varius).The main contents of this study are as follows:(1)the periodic change of testosterone levels in Varied Tit;(2)the effects of testosterone on the reproductive behavior of the Varied Tit;(3)the relationship between the testosterone content and extra-pair paternity of the Varied Tit.The results are as follows:1.The periodic change of testosterone in the varied tits is that the testosterone content was lower in non-breeding period and it increased significantly during the whole breeding season.There was no significant difference in testosterone content between male and female birds.2.There was no significant correlation between the individual testosterone content and its physical signs of male and female birds pre-breeding period and breeding period.during the breeding periods,there was no significant correlation between the testosterone content and reproductive activities expect that the male testosterone in breeding period had significant positive correlation with the clutch size(P = 0.008).3.There was a positive correlation of testosterone levels between the social mates(P = 0.001).The results indicated that the testosterone might be involved in the process of mate selection,and it had no effect on the parental investmentand the reproduction success of the breeding nest.4.There was no significant difference of the testosterone content between parental birds with extra-pair paternity and the population levels(P = 0.401;P = 0.233),or between the male birds with or without extra-pair mating(P = 0.296),or between female birds(P = 0.505),or between the couples(P = 0.901).5.There was a significant negative correlation between the testosterone content of parental birds and their broods(P = 0.05;P = 0.002),and also between the testosterone content and the extra-pair paternity ratio(P = 0.05;P = 0.005)in the broods with extramarital offspring.In conclusion,there was no significant difference between male and female in the testosterone content of the varied tits,which showed a lower testosterone content in the non-breeding period and a significantly higher testosterone content throughout the breeding season.The testosterone content had no correlation with the physical signs and parental investment,but it could affect the mate selection of varied tits and the female with high testosterone tended to choice the one with high testosterone.The male with higher testosterone at the breeding stage usually had larger clutch size.Among the nests with extramarital offspring,the male with higher testosterone would like to have more extra-pair off springs.