The Relationship Between Oxidative Stress And Reproductive Investment,Extra-Pair Paternity In Varied Tit(Sittiparus Varius)

Reproductive investment has always been a hot topic in the study of bird behavioral ecology.The life history trade-off theory holds that the reproductive investment of parents is balanced with their own survival investment,and increasing reproductive investment is at the expense of maintaining their own survival investment.Oxidative stress is considered to be the key physiological mechanism to maintain the life history trade-off theory.However,despite a large number of studies,there are significant differences or even complete opposition among the research results.Further experimental exploration is still needed on the effect of oxidative stress on the reproductive investment of birds.Extra-pair copulations is an important part of the complex reproductive strategy of birds.The causes of its occurrence have attracted much attention.There are few reports on the effects of oxidative stress on the extra-pair copulations behavior of birds.Therefore,in this study,the varied tit（Sittiparus varius）,a social monogamous bird with a high incidence of extra-pair paternity,was selected as the research object to analyze the changing trend of plasma oxidative stress level of parent birds of the varied tit during breeding period.The relationship between plasma oxidative stress level in early breeding period and individual reproductive investment and the relationship between plasma oxidative stress level and extra-pair paternity of breeding nest was also discussed.The main results are as follows:1.At the population level,compared with the early breeding period,the plasma reactive oxygen species(female:t_（38,36）=10.619,P<0.001;male:t_（41,38）=11.118,P<0.001)and superoxide dismutase activity(female:t_（35,33）=11.563,P<0.001;male:t_（39,35）=13.438,P<0.001)were significantly lower at brooding period.At the individual level,the variation trend of oxidative stress level was consistent with that of population level,and it was significantly decreased at brooding period(ROS:t_（25,25）=9.084,P<0.001;SOD:t_（25,25）=10.223,P<0.001).There was a significant positive correlation between the plasma reactive oxygen species（ROS）level in the same individual at the early breeding period and the brooding period（R=0.436,P=0.030,n=25）.Reactive oxygen species（ROS）levels between social mates of the breeding nest of varied tit（R=0.678,P<0.001,n=35）and superoxide dismutase activity（R=0.911,P<0.001,n=29）had a very significant positive relationship during brooding period.2.The relationship between plasma reactive oxygen species concentration and the date of birth of the first egg（t=2.934,P=0.007）,brood number（t=3.064,P=0.005）,number of flights（t=2.127,P=0.042）,reproductive effort（t=2.919,P=0.007）and the total body mass of offspring in the breeding nest（t=2.901,P=0.007）.It was positively correlated with clutch number（t=1.915,P=0.065）,but was positively correlated with incubation days,brooding rate,brooding days,flight rate,reproductive success rate,average body mass,average tarsus length and average body condition index of offspring in the breeding nest were not significantly correlated（P>0.05）.There was no significant correlation between the plasma oxidative stress level and Hissing call behavior of female varied tit in early breeding period（P>0.05）.3.There were no significant differences in plasma oxidative stress levels between male and female parental birds with extra-pair paternity nests and those without（P>0.05）;There was no significant difference in the level of oxidative stress between female social and extra-pair mate（P>0.05）.However,in the breeding nests with extra-pair paternity,there was a significant positive correlation between the plasma reactive oxygen species level of female varied tit and extra-pair offspring number（β=0.940,P=0.002）and extra-pair offspring rate（β=0.838,P=0.019）.There was no significant correlation between males（P>0.05）.In conclusion,the plasma oxidative stress level of parent birds of varied tit decreased significantly with the advance of reproductive process,and the plasma oxidative stress level of parent birds in the early breeding period has a regulatory effect on reproductive investment.The higher the level of plasma reactive oxygen in the early breeding period,the later the first egg delivery,the more offspring to feed and the more reproductive effort,the larger number of flights.In addition,the higher the plasma reactive oxygen level of female birds in the breeding nest with extra-pair paternity,the higher the extra-pair offspring number and extra-pair offspring rate.