Study On The Causes Of Extra-Pair Copulations In Marsh Tit (Poecile Palustris) Based On Female Genetic Interests

Many studies have shown that there is a widespread marriage diplomacy in monogamous birds,especially in small passerines.Marsh tit Poecile palustris is a social monogamous and cavity-nesting species.The previous studies showed that there are extra-pair copulations,but the proportion of extra-pair copulations and the mechanism of extra-pair copulations behavior are still not known.This study analyzed parental relationships,clarified the proportion of extra-pair copulations,and explored the causes of extra-pair copulations about marsh tits based on female genetic interests.From 2012 to 2018,the marsh tits were caught by artificial nest boxes,in the Zhuanghe Xianrendong National Nature Reserve in Dalian.I collected a total of 286 parent-offspring blood samples from 40 broods.I identified extra-pair paternity by PCR amplification and microsatellite marker methods,and the result of molecular experiment was analyzed using Cervus 3.0,Kingroup 2.0 and SPSS 21.0.The results showed that the mating system of the marsh tits was critical monogamy and the rate of extra-pair copulations is high.Fifty percent broods had extra-pair nestlings,with 48 of 286 individuals were extra-pair fertilizations,average brood had 2.4 ± 1.57(n = 20)extra-pair nestlings,ranging from 1 to 5.Every female mates with 2 ± 1.56(n = 20)extra-pair mates,varying from 1 to 4.There were no significant differences between social spouses and extra-pair spouses(P > 0.05)in genetic heterozygosity(P = 0.082),genetic similarity(P = 0.603)and the reproductive effectiveness of with-pair offsprings and extra-pair offsprings,including clutch size,hatching rate,unfertilized rate,hatching duration,egg weight,and flight rate).There was no significant difference in the genetic similarity between the male and female of EPO or between the male and female of the non-WPO(P = 0.710);There were no significant difference the EPO and WPO in the physical signs(P > 0.05)and genetic heterozygosity(P = 0.090).No significant difference was found in heterozygosity between EPO and WPO(P = 0.655).the offspring ratio was not male-biased.Not all of females have more than 2 males.the extrapair spouse is not randomly distributed,and 4 nests females choose neighbors as extrapair spouse.There was no significant relationship between the incidence of EPC and the level of genetic diversity.In summary,the causes of EPC in marsh tits are not related to the indirect genetic interests,which do not support good genes hypothesis,genetic compatibility hypothesis or genetic diversity hypothesis,and the potential reasons need to be studied.