Responses To Changes In Temperatures And Host Plants For Sitibion Avenae From Different Altitudes And The Underlying Genetic And Molecular Basis

The climate warming trend can cause a significant increase in the mean global surface temperature.Elevated temperatures have been shown to have variable effects on plants in terms of phenology,distribution,and abundance.These changes can be particularly disruptive for natural ecosystems and various agricultural ecosystems.However,studies on responses of aphids to climate change are rare.In order to explore potential effects of climate change on aphids,we sampled populations of the wheat aphid,Sitobion avenae,from different altitudes of the Qinling Mountains.We compared their life-history characters,phenotypic plasticities and transcriptional responses under different temperatures?i.e.,15?,22?and 29??and on different cereal and herbaceous plants?i.e.,wheat,barley,brome and rye?.We also analyzed their bacterial microbiomes using a high-throughput 16S rDNA amplicon sequencing approach,and genotyped S.avenae samples with seven microsatellite markers,in order to explore the genetic basis for varied responses of this aphid under the abovementioned conditions.The main results are as follows:1?High-altitude S.avenae presented higher mortality and proportions of alate individuals under 29?than S.avenae from low-and middle-altitudes.The plasticities in the developmental times of 1^st instar,4^th instar and entire nymphal stage for low-altitude S.avenae tended to be higher under 15?than high-or middle-altitude S.avenae,and similar results were found on plasticity of pre-reproduction duration.Under 29?,low-altitude S.avenae presented lower plasticities in 10-d fecundity,pre-reproduction duration,and the developmental time of 2^nd instar and 3^rd instar,compared to middle-or high-altitude S.avenae.These results showed that life-history trait plasticities varied significantly among S.avenae populations from different altitudes under different temperatures,and could play significant roles in this aphid?s responses to changing temperatures.Moreover,low temperature?i.e.,15??presented significant selection gradients for plasticity in developmental times of 1^stt instar,3^rd instar and entire nymphal stage for middle-altitude S.avenae.Selection gradients for plasticity in the developmental time of 1^st instar,3^rd instar and 4^th instar for high-altitude S.avenae were significantly positive under 29?.Additionally,compared with high-altitude S.avenae,low-altitude S.avenae showed shortened developmental time of nymphs and pre-reproduction duration,as well as increased fecundity under 22?,suggesting that adaptation to specific temperature conditions was variable among S.avenae populations from different altitudes.These results indicated that S.avenae from different altitudes could respond differently to changing temperatures in the context of global warming.2?Low-altitude S.avenae presented longer developmental times,longer pre-reproduction durations,higher mortalities and lower fecundities on grasses?i.e.,rye and brome?than on cereals?i.e.,wheat and barley?,suggesting that the fitness of low-altitude clones was lower on grasses?i.e.,rye and brome?than on cereals?i.e.,wheat and barley?.Compared with wheat or brome,barley and rye significantly prolonged the nymphal developmental times?i.e.,1^stt instar and entire nymphal stage?and pre-reproduction durations,and reduced survival rates and fecundities for high-altitude S.avenae;showing that the fitness for high-altitude clones was lower on barley and rye.Furthermore,compared with high-altitude clones,low-altitude clones presented shortened developmental times,shortened pre-reproduction durations and increased fecundities on wheat,barley or rye.When feeding on brome,low-altitude clones showed higher plasticities of the developmental time of 1^st and 3^rd instar in comparison to high-altitude clones,and similar results were found on plasticity of pre-reproduction duration.When S.avenae was transferred onto barley,plasticities of the pre-reproduction duration and developmental time of 4^th instar tended to be higher for low-altitude clones than those for high-altitude clones.Low-altitude S.avenae on rye presented lower plasticities in the developmental times of 3^rd instar and entire nymphal stage than high-altitude S.avenae,and similar results were obtained on plasticity of pre-reproduction duration and 10-d fecundity.These results showed S.avenae from different altitudes could respond to changing host plants with varied plasticities.Moreover,barley showed significantly negative selection gradients for plasticities in 10-d fecundity and the developmental time of 4^th instar of low-altitude clones.When low-altitude clones were fed on rye,significantly positive selection gradients were found for plasticities in the developmental time of 4^th instar,but the selection gradients for plasticities in the developmental time of 1^st instar were significantly negative.In most cases,tested host plants did not show significant selection gradients for life-history trait plasticities of high-altitude clones,and the only significantly positive selection gradient was found for the plasticity of adult weight on rye.The abovementioned results indicated that S.avenae populations from different altitudes had diverged to a substantial degree in its adaptation to different cereal and herbaceous host plants,and their life-history trait plasticities also varied significantly on different plants.This may significantly affect their host shift and vertical distribution in the Qinling Mountains in the context of global warming.3?Through sequencing V3-V4 regions of 16S ribosomal DNA?rDNA?,Bacteroidetes and Gemmatimonadetes were only detected in low-altitude clones.Chloroflexi,Deinococcus-Thermus,Nitrospirae and Tenericutes were only found in high-altitude clones.High-altitude clones owned significantly higher abundance of Moraxellaceae than other clones,and the abundances of Rickettsia and Regiella insecticola were significantly lower in high-altitude clones in comparison to low-altitude clones.These results indicated that bacterial diversity and community composition were significantly different for S.avenae populations from different altitudes,which can be critical in genetic differentiation of these S.avenae populations.Indeed,S.avenae from different altitudes had a high level of genetic diversity,based on mean number of alleles?N_A?,mean genic diversity?Hs?and allelic richness?AR?.Observed heterozygosity?H_O?was higher than expected heterozygosity?H_e?for two low-altitude populations?i.e.,XYS and SLM?,one middle-altitude population?i.e.,YXC?and one high-altitude population?i.e.,WLP?,indicating heterozygote excess in these populations.However,the inbreeding coefficient(F_IS)values were positive for other collected populations.There was a high level of genetic differentiation(F_ST>0.15)between populations DDZ?i.e.,high-altitude?and XYS?i.e.,low-altitude?.The same pattern was also found between populations DLG?i.e.,middle-altitude?and XYS?i.e.,low-altitude?,as well as between populations DLG?i.e.,middle-altitude?and WLP?i.e.,high-altitude?.Additionally,putative migrants from low altitudes to high altitudes were more numerous than those moving in the reverse direction.The migration rate from middle altitudes to high altitudes was lower than that in the reverse direction.The unequal population connectivity identified could accelerate genetic differentiation for S.avenae populations from different altitudes.These results suggested that S.avenae populations from different altitudes had significant genetic structure and differentiation.Thus,there was a significant genetic basis for varied abilities of S.avenae populations from different altitudes responding to changing environmental conditions?e.g.,temperatures and host plants?.4?For S.avenae feeding on wheat,all differentially expressed P450?cytochrome 450monooxygenase?genes?e.g.,SavCYP6A13,SavCYP4C1 and SavCYP4G15?showed increased expression,indicating the significance of P450s in xenobiotic metabolism for this aphid on wheat.For S.avenae on barley,some genes encoding for ABC transporters?e.g.,ABCG1,ABCG4,ABCB7 and ABCA5?and UGTs?e.g.,UGT2B1 and UGT2C1?showed a dramatic increase in expression,suggesting that ABC transporters and UGTs could be critical for detoxification metabolism in S.avenae on barley.Additionally,other defense-related?e.g.,proteases,oxidases and cuticular proteins?genes showed highly inducible transcript regulation.All abovementioned genes might be directly related to host shift,host plant use,and host plant specialization in this aphid.Compared with wheat and brome,barley significantly reduced the expression of SaveCYP4C1,SaveCYP4G15 and SaveABCC4-1 for low-altitude clones,but not for high-altitude clones.For S.avenae feeding on wheat,brome,or rye,the expressions of SaveCYP6A13,SaveCYP4G15 and SaveEsterase E4 were higher in low-altitude clones than those in high-altitude clones.High-altitude clones presented lower expression of SaveEsterase E4 on barley in comparison to low-altitude clones.Multivariate analysis of variance?MANOVA?showed that detoxification genes expression was significantly different between low-altitude and high-altitude clones.Additionally,high-altitude clones presented increased SaveHSP70B2 expression and reduced expression of SaveHSC70 under 15?than under 22?,but there were no significant differences in expression of these genes for low-altitude clones.Moreover,under 29?,expression of SaveHSP60,SaveHSP70 and SaveHSC70 were significantly higher in high-altitude clones than in low-altitude clones.Compared with low-altitude clones,high-altitude clones showed significantly reduced expression of SaveHSC70 and SaveHSP83 under 15?.Thus,transcriptional responses were found to be significantly different for S.avenae from different altitudes under different temperatures,as well as on different host plants.This suggested that responses of S.avenae from different altitudes to changing environmental conditions?e.g.,temperatures and host plants?have a clear molecular basis.Our results have significant implications for understanding the molecular mechanisms underlying aphids?responses to changing environmental conditions.