Study Of The Applicability Of The "Genetic Compatibility" Hypothesis In The Cause Of Extra-Pair Paternity In Varied Tit (Parus Varius)

Birds may form a mating system when they are in breeding season,while the mating system varies in different avian species.Avian mating systems generally fall into four categories:monogamy,polygony,polyandry,and promiscuity.Monogamy is one of the most common form of mating system,with about 92%of bird species are monogamous.The application of molecular techniques has revolutionized our view of avian mating systems.The phenomenon that copulation occurring outside of the pair-bond and resulting in extra-pair offspring is common,This phenomenon challenges traditional views of sexual selection and mating system,and has become one of the hot-spots in the avian behavior ecology.The field observations show that Varied Tit(Parus varius)has been described as monogamy,but it lacks of supporting of molecular data.We have taken bloods from Varied Tit to perform paternity identification and found that the mating system of Varied Tits was not the strict monogamy in genetically.Hypotheses explaining the benefits include fertility assurance,good genes,genetic compatibility,and genetic diversity.The main purpose of our study is preliminary to test and verify the applicability of "genetic compatibility" hypothesis in explaining the reason of EPP in Varied Tit.During the breeding season from March to July in 2011 and 2012,we collected 300 individual samples from 39 broods.3 of 39 broods were second broods,and in 6 of 39 broods,sample is not complete,but in 2 of 6 broods,offspring were sibling relationship,therefore we obtain the result of paternity identification for 191 offspring from 32 broods.We also calculated the genetic similarity of parental birds,the standard individual heterozygosity between within-pair offspring(WPO)and extra-pair offspring(EPO)and other breeding parameters about offspring.Results show that:(1)totally,14.13%of offspring were not the genetic offspring of their social fathers and at least one EPO occurred in 46.88%(15/32)of the broods.(2)genetic similarity of pair mates did not significantly differ for pairs without EPP and pairs with EPP in their broods(P=0.504),namely,we found no evidence for a positive association between the genetic similarity of social pair mates and the occurrence of extra-pair paternity,therefore,we could not support the"genetic compatibility" hypothesis from the perspective of parents.(3)we analyzed the offspring heterozygosity from two years data,results show that there was no significant difference not only between offspring from purely within pair broods and the WPY from mixed-paternity broods(P=0.118),but also between EPO and WPO within mixed-paternity(Paired t tests:t=-1.300,two tailed P=0.206),that is to say,Varied Tit did not obtain heterozygous benefit from the extra-pair copulation(EPC),therefore,we could not support the "genetic compatibility" hypothesis from the perspective of offspring heterozygosity.(4)Comparisons of physical indicators between WPO and EPO were performed when they were 12-days old and the results showed that there was not a significant difference(p>0.05),this suggests that EPO is not higher than WPO in the offspring survival,thus we also reject the "genetic compatibility" hypothesis from the perspective of survival of offspring.In summary,we test the "genetic compatibility" hypothesis about the cause of EPP in Varied Tit from the viewpoint of parents and offspring,both results show that we will not support the "genetic compatibility" explanation of cause of EPP in Varied Tit.