Study On The Influence Of The Genetic Relatedness Of The Social Mates On The Frequence Of Extra-Pair Paternity In Varied Tit (Parus Varius)

In birds mating system, Monogamy is one of the most common form of mating system, with about 92% of bird species are monogamous. Birds are only very rarely sexually monogamous, with extra-pair offspring found in approximately 150 of species, including Varied Tit (Parus varius). We have taken the experiments to Varied Tit to identify the paternity and found that the mating system of Varied Tits was not the strict monogamy with a very high rate(roughly 50%) of the occurrence. Based on the researches about avian extra-pair paternity over the past decade, there are three hypothesis trying to explain the causes of extra-pair paternity:good genes, genetic compatibility and genetic diversity, "genetic compatibility" might have important fitness consequences in many populations. In particular, overall genetic similarity (i.e. genetic relatedness) between parents has been shown to have strong effects on offspring fitness Genetic similarity might also affect extrapair mate choice, particularly in populations where social mate choice is constrained in some way, as in these cases extrapair mating can provide females with a’second chance’to choose a genetically compatible mate. According to the genetic relatedness, we try to explain the reason of the extra-pair paternity in Varied Tit.We conducted our research on a population of Varied Tit during the breeding season (Match to July) of 2014. From match to April, we collected 45 samples; From May to July, we obtained the samples form 25 broods. Because of the lack of 3 broods parents’samples, we calculated 22 broods to assign fathers to all sampled offspring based on genetypes. In short, we have 85 samples of adluts and offspring. According to the paternity analysis, we make a analysis of the relationship between the occurrence of EPP and genetic relatedness of social parents, and the difference of the relatedness between the females to social males and extra-pair males. In other hand, we analysis the relationship between relatedness between the parents and the offspring.The research show that 1. In the 22 nests,11 nests (50%) with extra-pair offspring,29 extra-pair mating offspring out of 155, which accounting for 18.7% of all the offspring; 2. The broods which contain the EPO are far away from the place where we grasped the extrapair males(average distance is 2031m). the minimum distance is 757m (between brood NO.314 and extrapair male 2); The maximum is 3356 (between brood NO.135 and extrapair male 21).3. The relatedness of this population is from-0.2115 to 0.6961, the average is 0.0592±0.09.4. The relationship in line accordance with the genetic relatedness among individuals are almost unrelated. There is no difference between social mates and the extrapair males (p=0.935), which suggest that social mates genetic relatedness have no effect on the occurrence of EPP. We can conclude that social mates genetic relatedness is not the reason why EPP would happen, the occurrence of the EPP is random.5. There is a significant difference of genetic relatedness between social mates and the extrapair males (p=0.039), suggesting that genetic relatedness make a effect on the females selecting the EPP male. Moreover, females prefer to copulating to the male which are closer than their social males.6. We analysis the relationship between the genetic relatedness and the heterozygosity, quantity and gender of EPOs, and we found no difference of these.In conclusion, the occurrence of the EPP is random, females are more likely to choose the relative male to copulate the EPO, which may effect the copulate output of the relative males and the females may gain the benefits from the non-genetic value.