The Study On The Influence Of Extra-pair Mating To Offspring's Fitness Of Varied Tit(Parus Varius)

The avian mating system includes monogamy,polygyny,polyandry and polynandry,while the monogamy is the most common mating system,with 92%of birds belonging to monogamy.Recent studies have found that the extra-pair phenomenon is very common in social monogamous birds,especially in small passerine birds.Varied Tit(Parus varius)is a social monogamy small forest cavity-nesting bird.Our previous studies have shown that the Parus varius has a high degree of extra-pair paternity(EPP).Although there are many papers related to the the extra-pair behavior in birds,the exact reasons for birds to participating in the extra-pair copulation(EPC)are still unclear.Several hypotheses have been proposed to explain the EPP in the respect of genetical benefits including "good genes"hypothesis,"fertility insurance" hypothesis,"genetic compatibility" hypothesis and"genetic diversity" hypothesis.There were many experiments to test the four related hypotheses,however,no consistent conclusion has obtained.Although there significant different in the base of the four hypotheses,the clear benefit of all these hypotheses will result in the increase of offspring fitness.In this study,we will compare the fitness of offspring between extra-pair(EP)and within-pair(WP)to test whether Parus varius engaging in the EPC was on the consideration of genetic benefit.Three indicators from the level of genetic,physiological and morphological were chose to reflect the overall fitness of young chicks.In this study,breeding season is from March to July of 2011 and 2012.Samples was collected which including blood samples,blood smear samples and physical indicators.After the end of the breeding season,molecule experiments were started,blood samples were used to insure the paternity and to get genetic diversity data,individual immunity strength was get through the blood smear samples,physical indicators were used to obtain by comparing the relevant signs parameters offspring body size,and other parameters,and combined with paternity test results to compare the the three indicators difference between the offspring marital and extramarital offspring.33 nests Parus varius was attracted and all 198 offspring was paternited through micro-satellite.Our results showed that:(1)In the 33 nests,17 nests(48.5%)with extra-pair offspring,30 extra-pair mating offspring out of 198,which accounting for 15.2%of all the offspring;(2)Genetic diversity was no significant between 168 offspring in-pair and 30 offspring extra-pair;(3)The weight,body length,wing length,tail length,long mouth,mouth wide,tarsus length,after toe long and long toe were compared with no significant difference;(4)The immunity do not have significant difference.In summary,Parus varius nests which lost paternity were as high as 48.5%,and 15.2%of the offspring were created by extra-pair copulations.The differences of genetic diversity,immunity and physical indicators of offspring between in and out extra-pair copulations were not notable.Therefore we concluded that the extra-pair copulations of Parus varius could not increase the fitness of the offspring.