Effects Of High Temperature On Two Predatory Mirid Species And The Genome Analysis Of Cyrtorhinus Lividipennis

Cyrtorhinus lividipennis and Tytthus chinensis are two predatory natural enemies with similar habits,distribution and body size in the rice fields,mainly feeding on the eggs of planthoppers,leafhoppers and other hemipteran pests,both of which are important biological control factors in the rice ecosystem.With climate change,the average temperatures and the frequency of extreme weather events have been increasing in recent years,which will not only affect the growth and development of individual organisms,but also break the balance of interspecific relationships such as competition,predation and parasitism,thus causing unexpected consequences for biodiversity and ecosystem functioning.In this study,we studied the development,body weight,longevity,reproduction and other biological parameters of the two mirid predators at different temperatures,observed the changes in predation ability and populations under different temperature conditions,and conducted a preliminary comparative study on the molecular response mechanisms of the two species under heat stress.These works are of great significance for further understanding the effects of global warming on natural enemy biology,interspecific relationships and biological control.In addition,we also sequenced,assembled,annotated and conducted comparative genomic analysis on the genome of C.lividipennis,providing important molecular biological resources for the study of natural enemies and the Miridae family.The main results are as follows:1.The heat tolerance of two mirids and their prey,the brown planthopper,were compared,and the fitness of two predators at different temperatures was also measured.The results showed that the LTim₅₀(half lethal time at 44?)and LTem₅₀(half lethal temperature in 1 h)of T.chinensis were 18.59 h and 46.31?,respectively,exhibiting the strongest heat tolerance among the three species.The LTim₅₀ and LTem₅₀ of their prey N.lugens were 5.27 h and 45.74?,respectively.C.lividipennis exhibited the lowest LTim₅₀(1.59 h)and LTem₅₀(44.35?),suggesting the weakest heat tolerance compared to its competitor T.chinensis and prey N.lugens.The results of Briere's regression model showed that the optimum and upper threshold developmental temperatures of T.chinensis were 34.57?and 40.28?,respectively,while those of C.lividipennis were 32.83?and 36.11?,respectively.Compared with C.lividipennis,T.chinensis nymphs completed their development in a much wider temperature range and grew faster at high temperatures.The results of each biological parameter showed that the body weight,longevity,fecundity and hatchability of both mirids were significantly affected by the increasing temperature.From the interspecific comparison,the body weight of C.lividipennis was significantly higher than that of T.chinensis at 26°C,and the longevity and fecundity were also better than those of T.chinensis(not significant).However,as the temperature increased,the fitness advantage of C.lividipennis decreased gradually compared with that of T.chinensis,its fecundity and hatchability were almost lost at 38?,and the body weight was also significantly lower than that of T.chinensis.2.The predation abilities of the two predators at different temperatures were studied and their population changes under different fluctuating temperature conditions were also observed and compared.The fitting results showed that the type of functional response of the two species did not change with the increase of temperature,and the functional responses of both mirids to the eggs of N.lugens could be well fitted by the Holling II equation under different conditions.However,the effects of temperature increase on the intensity of the functional response of C.lividipennis and T.chinensis were different.The maximum predation of C.lividipennis decreased from 36.63eggs/day at 26°C to 29.85 eggs/day at 38°C,but the maximum predation of T.chinensis increased from 34.25 eggs/day(26°C)to 40.49 eggs/day(38°C).Between the two species,the predation ability of C.lividipennis was slightly stronger than that of T.chinensis at 26°C,but the difference between the two predators was not significant;the predation ability of T.chinensis was significantly stronger than that of C.lividipennis at 38°C with significantly higher attack rate and shorter handling time.In addition,high temperature also negatively affected the prey-locating ability of C.lividipennis,but had no significant effect on that of T.chinensis.To get closer to the actual situation in the field,we observed the population changes of the two species under different fluctuating temperature conditions.When there was no interspecific competition,the population of the T.chinensis increased with temperature increasing,while that of C.lividipennis increased and then significantly decreased,and populations of the two species differed significantly at the high temperature but not at other temperature regimes.When the interspecific competition existed,the population of C.lividipennis was significantly higher than that of T.chinensis at the low temperature condition,while the proportion of the T.chinensis gradually increased with the temperature increasing,and the dominant species eventually changed to T.chinensis at the high temperature condition.3.We sequenced the transcriptomes of the two mirids under different temperature treatments,and analyzed their HSP gene families based on the transcript sequence information and the results of differential expression analysis.The transcriptome differential expression analysis showed that the expression levels of multiple HSP genes were significantly increased under high temperature treatment with high significance and fold change,indicating that HSP genes were highly correlated with heat stress in both mirid species.A total of 19 and 17 HSP genes were identified in T.chinensis and C.lividipennis,respectively.In both species,2 HSP70s and 3 s HSPs were highly upregulated at all stages.The expression patterns of the upregulated HSP genes were further analyzed under different treatments.The q RT-PCR results showed that when the treatment time was 1 h,the expression patterns of HSP genes in both species exhibited a trend of increasing and then decreasing with the increase of temperature,with the highest values reached at 44?(T.chinensis)and 42?(C.lividipennis),respectively.It indicated that the maximal induction temperature of HSP genes was higher in species with better thermal tolerance,which was consistent with previous studies.When the treatment temperature was 38?,the relative expression levels of all HSP genes in T.chinensis peaked within 3 h,and then gradually decreased and remained stable,while the induction rate and intensity of HSP genes in C.lividipennis were relatively lower than that of T.chinensis.4.The genome of C.lividipennis was sequenced,assembled,annotated and comparatively analyzed with other species.By using the Illumina,Pac Bio and Hi-C platforms,we sequenced and assembled the genome of C.lividipennis,which is an important predatory natural enemy in the rice ecosystem.The final chromosome-level genome size was 345.75 Mb,the scaffold N50 length was 27.58 Mb,and the repetitive rate was 31.10%.Approximately 97.78%of the genome bases successfully anchored to13 chromosomes.The sex-determining mechanism of C.lividipennis was XY,and the karyotype was determined to be 2n=24(22+XY).By staining the gonads with Giemsa reagent,the male meiosis was observed to be achiasmatic and showed typical post-reduction of sex chromosomes,as observed in most mirid species.Comparative genomic analysis of 17 arthropod species showed that C.lividipennis diverged from Apolygus lucorum about 67 million years ago.Compared with other hemipteran species,no significant contraction or expansion of the gene families associated with detoxification and digestion were found in the genome of C.lividipennis.While these gene families appeared to be more related to the host range and food diversity of the species and were found relatively expanded in the genome of the omnivorous species A.lucorum.The number of HSP genes identified from the genome was much higher than that from the transcriptome,and the sequences were more complete.These HSPs showed different expression patterns and their functions deserve further investigation.