Host Plant-associated Population Divergence And Endogenous Mechanism Of Mating Rhythm Variation In Chilo Suppressalis

Sympatric speciation is one pattern of speciation.The reproductice isolations during speciation are the key research point in the evolutionary biology.The striped stem borer Chilo suppressalis is an important pest on rice and water-oat.C.suppressalis is suggested to diverge into rice and water-oat populations,which is under the early stage of sympatric speciation.The differences in mating time are suggested as isolation barrirers between rice and water-oat population.However,there is no unequivocal evidence for the contribution of difference in mating rhyrhm to reproductive isolation and it is still unclear what the endogenous mechanism result in mating rhythm variation in this species.Rice and water-oat popualation of C.suppressallis was used in this study.Effects of host plant shift on biology characteristics and mating rhythm of rice and water-oat population of C.suppressalis were estimated.We clarify the inheritance patterns of mating rhythm of rice and water-oat population of C.suppressalis.Contribution of difference in mating rhythm to inter-population reproductive isolation between rice and water-oat population of C.suppressalis were evaluated.We also explored the endogenous mechanism inducing the difference in mating rhythm between rice and water-oat popualtion in C.suppressalis.The main results are as follows:1.Effect of host plant shift on biology characteristics and mating rhythm of rice and water-oat population of C.suppressalisWe explore the effect of host plant on the larval survival rates,larval developmental periods,pupal weight and adult forewings of C.suppressalis by host plant shift.The results showed than host plat shift had a significant effect on the larval survival rate,larval development period,body weight of pupae,forewing length of adult,but not for the onset time of mating into scotophase.These results indicated formation of host race and gentice basis of difference in mating rhythm in C.suppressalis.2.Inheritance patterns of mating rhythm of rice and water-oat population of C.suppressalis.Populations cross and back cross were conducted to clarify inheritance patterns of mating rhythm of rice and water-oat population.When the female or male individual of F1 hybrids mated with the opposite sex individual from rice population,the mating time was the intermediate between their parents,but when F1 hybrids mated with the opposite sex individual from water-oat population,the mating time was not different from water-oat population.The parental population identity of F1 hybrids significantly affected their mating time,which indicated both the male and female adult determine the mating rhythm.The results indicated mating rhythm was mainly controlled by autosomal genes and allelic genes of water-oat population were almost dominant over that of rice population in C.suppressalis.3.Difference in mating rhythm contribute to inter-population reproductive isolation between rice and water-oat population of C.suppressalisDifferent mate choice tests were conducted to explore the contribution of difference in mating rhythm on reproductive isolation between two populations.The results showed the joint isolation index(IPSI)in no choice text,female choice test,male choice test,multiple choice test were significant different from the IPSI under random mating(IPSI=0)under the same photoperiod with difference in mating rhyrhm between two populations.However,when the photoperiod of individuals from the water-oat population was altered to more closely align their mating activity with that of the rice population,joint isolation index of different choice test was not different from that of random mating.These results indicated inter-population difference in mating time made an important contribution to the reproductive isolation.4.Endogenous mechanism inducing the difference in mating rhythm between rice and water-oat popualtion in C.suppressalisBased on the observation of female calling behavior,sex pheromone titer and biosynthesis gene expression were detected in sex pheromone gland to reveal the endogenous mechanism of difference in mating rhythm.As a main component of sex pheromone,the titer of Z11-16 Ald is higher in sex pheromone gland of rice population and the diel rhythm of titer variation was also different between two populations.However,the other two pheromone component did no show a titer rhythm due to relative low quantity in pheromone gland.Several putative sex pheromone biosynthesis genes including two lipases(Lipase1,Lipase2),two fatty-acid transport proteins(FATP1,FATP2),two desaturases(DES1?DES7),one acyl-Co A dehydrogenases(ACD1),three elongation of very long chain fatty acids(ELO1,ELO6,ELO7),two aldo-ketose reductases(ALR1,ALR2),were identified by transcriptome of sex pheromone glnad.These genes had a higher expression in the sex pheromone gland of rice population than that of water-oat population.The results of q RT-PCR validation for four of the eleven genes indicated the Lipase2,FATP2,ACD1,ELO1 had a higher expression in rice population in the three time points.These results indicated that difference in female sex pheromone titer and expression of biosynthesis genes was the endogenous factor of difference in mating rhythm between rice and water-oa population in C.suppressalis.In this study,the population-specific mating rhythm of rice and water-oat population is a phenotype resulting from long-term adaptation on different host plant in C.suppressalis.There some difference in the genetic facore controlling the mating rhythm between two populations.The inter-population differencea in mating rhythm contribute to the reproductive isolation between rice and water-oat populations.Difference in female sex pheromone biosynthesis is an endogenous reason for the difference in mating rhythm between two populations.Frstly,these results construct a data basis for further research on molecular regulation mechamism of mating rhythm variation in this speices.Then,our studies provide new evidences for the temporal isolation mechanism during the sympatric speciation.At alst,this research gives some cues for the pest management by light trap and sex pheromone trap in C.suppressalis.