Responses Of The Diamondback Moth,Plutella Xylostella,to Oxygen Stress

The diamondback moth,Plutella xylostella,is one of the most devastating pests of the global Brassica industry.Brassica vegetables,an important part of the Tibetan plateau vegetable industry,accounts for more than 70%of the vegetable planting area and influences animal development,economic development and the lives of the Tibetan people.Extreme environments(such as low pressure,low oxygen,low temperature and strong radiation)provide an ideal natural laboratory for studies on adaptive evolution.P.xylostella is highly adaptive to extreme ecological environments and provides an ideal model to study fast adaptation.The Qinghai-Tibet Plateau,with an average elevation of more than 4000 metres,has approximately 60%oxygen of that observed at sea level.Due to long-term habitation in a hypoxic environment,the Qinghai-Tibet Plateau diamondback moth may better adapt to a hypoxic environment than the plain diamondback moth.Research on molecular adaptation to hypoxic environments in the diamondback moth is currently lacking.Here,I conducted a pilot study by combining high-throughput sequencing technology with an age-stage two sex life table to reveal the molecular mechanisms underlying the hypoxic adaptation of P.xylostella.The age-stage two sex life tables were set up for both the Fuzhou and Tibetan colonies.Compared with the Tibetan DBM,the results showed that the hypoxic environment had a great influence on the developmental periods of all instars(egg,larva,pupa and adult),which were significantly shorter in the hypoxic environment.Significant reductions in duration in the first generation was observed,whereas the difference decreased along with the time.The fecundity and survival rates did not change significantly.There were significant differences in the population dynamics of the Fuzhou colony in the hypoxic environment.The intrinsic rate of increase(r),finite rate of increase(?),net reproductive rate(R0),and mean generation time(T)were significantly lower.Our results indicated that the diamondback moth individuals from Tibet had higher fitness and were superior in the hypoxic environment than those from the Fuzhou colony,which may be a result of local adaptation.Genes with expression differences(DEGs)between treatments(partial oxygen pressure was 21 kPa and 1.8 kPa)were enriched using gene ontology(GO)and the Kyoto Encyclopedia of Genes and Genomes(KEGG)databases.DEGs were enriched in functions related to biological processes,including fatty acid biosynthesis,propionic acid metabolism,amino acid metabolism(proline,methionine and arginine),citrate cycle,glycolysis/gluconeogenesis and ubiquitin-hydrolysis.Down-regulation of genes in the ubiquitin-hydrolysis pathway promotes binding of hypoxia-inducible factor alpha and beta dimer,which contributes to hypoxic adaptation.In addition,some DEGs are enriched in pathways associated with DNA replication,such as DNA repair,nucleotide excision repair,base excision repair,mismatch repair and homologous recombination.Specifically,pathways with significant changes are associated with energy metabolism.Thus,we assumed that insects could adapt to different environments by regulating their metabolism.Our findings indicated that although adaptive mechanisms to hypoxia in different DBM strains could be similar,DBM individuals from Tibet had superior tolerance to hypoxia compared with those of the Fuzhou strain.Local adaptation of the Tibetan colony was assumed to be responsible for this difference.