Olfactory-based Mechanism Of Male-male Mating Behavior In Bactrocera Dorsalis

The variety and ubiquity of same-sex courtship,pair bonding and copulation has been observed in a wide range of species,yet the evolutionary maintenance of such behaviors remains enigmatic as they do not directly increase reproductive success by generating progeny.Many hypotheses have been suggested to explain the persistence of male-male mating behavior,however,due to the specificities of species evolution,the causes of same-sex sexual behavior vary greatly from species to species.Therefore,the evolutionary mechanism of homosexual behavior in insects,especially the male-male mating mechanism,still needs to be further explored.Based on the observed typical male-male mating behavior in Bactrocera dorsalis,the causes and influencing conditions were explored in this study.I found that the olfactory system could influence gene expression of fruitless and thus participated in the regulation of male-male mating behavior.And our results also showed that dopamine could be involved in regulating of male-male mating behavior.Therefore,it would be interesting and helpful to better understand the evolutionary implications of same-sex sexual behavior,and bring novel insight into the ethology and causes of homosexual behavior in oriental fruit fly.The main results are as follows:(1)Occurrence of male-male mating behavior has the following characteristicsCompared with other feeding conditions with different male-female ratios,male-male mating behaviors were more likely to be induced under the feeding conditions with a shortage of females(the male-female ratio was more than 1:1).The male-male mating frequency could reach to be as high as 43.33 %-50.00 %,and it was not dependent on the female density.The number of female flies had no significant effect on male-male mating behavior.To empirically test ’practice for future heterosexual encounters’ hypotheses for the maintenance of such behaviours: I found no evidence that the males use homosexual copulations to practice behaviours that increase their subsequent heterosexual reproductive performance.It was further verified that the male-male mating was caused by mistaken identity of individuals or inaccurate pheromone detection,and the results showed that the ratio of male-male mating behavior was significantly different under the condition of different sex pheromone treatments,therefore,the sex pheromones could affect the male-male mating to some extent.(2)It also found that under red light in which they are virtually blind,or removing antennae,maxillary palps,propodeum,or wing to cut off their perception of volatile pheromones and non-volatile pheromones,the flies failed to mate successfully.Therefore,olfaction,gustation and visual sense have important influences on male-male mating behavior,also suggesting involvement of olfactory receptor on the male–male mating behavior.In this study,the functions of olfactory receptors genes on homosexual copulations in B.dorsalis were studied by using RNAi technology and RT-q PCR.It was demonstrated that behavioral assay analyzes showed that the ratio of homosexual copulations after silencing the expression of ORco,OR13 a,OR13b,OR13 c,OR7,OR4,OR22,OR20,OR10,OR18,OR2 a,OR2c,OR2 d,or OR2 e,increased significantly compared to control groups of injected DEPC and ds GFP by 57.70 %,37.7 %,55.79 %,55.79 %,50.25 %,50.10 %,45.97 %,33.79 %,52.15 %,31.90 %,59.40 %,28.70 %,54.21 %,58.36 %,respectively.However,after interfered with the expressions of OR2 g and OR24,the ratio of male-male mating behaviors was reduced by 58.91 % and 63.66 %.Then those identified effective 14 ORs were used to examine their roles in perception pheromones.After RNA interference,these RNAi flies were subjected toc VA treatment,and the results found that the mating ratio has no significant change in the group of OR2 d,OR2e,OR7 and OR13 b RNAi samples compare with the group without adding c VA.Therefore,OR2 d,OR2e,OR7 and OR13 b might have roles in perception signal from c VA,and thus involved in male-male mating behavior.I also used the same method to verify that OR2 a and OR10 are important as being recognition receptors of 7-T.(3)fru gene is important in male-male mating behaviorThe copulation behavior is important for insects,as they are key factors for the development of population.In this study,I cloned the full length of fru gene in B.dorsalis and analyzed its role in male-male mating behavior through RNA interference.The results indicated that the full length offru was 2 865 bp,encoding 954 amino acids.fru locus generates a complex set of transcripts,which encoded BTB domain-containing and zinc finger proteins.At 72 h after injection of ds RNA targeting at fru,the rate of male-male mating was increased(21.09 %)relative to the group of DEPC water and group of ds GFP injection,indicated that fru plays important roles in regulating homosexual behavior of B.dorsalis.In the samples that interfered with the olfactory gene,the expression of fru gene was also affected,indicating that the olfactory gene could participate in the mating behavior by affecting the expression of fru gene.(4)The participation of dopamine on the mating behavior of males in B.dorsalisI used genetic and pharmacological approaches to manipulate the dopamine level in B.dorsalis and investigated the consequence of this manipulation on male-male mating behavior.Males with increased dopamine level showed enhanced propensity to mate other males.So increased dopamine level enhances male-male mating behavior in B.dorsalisIn conclusion,the olfactory system could influence fru gene expression and thus have role in regulation of male-male mating behavior.Then I also found that increased dopamine level enhanced male-male mating behavior in B.dorsalis.Therefore,the results in this study would be helpful to better understand the evolutionary implications and causes of male-male mating behavior,which could be applied to control pest populations by its influences on the social dynamics of wild populations.