title: Collapse of Insect Gut Symbiosis under Simulated Climate Change.
abstract: Global warming impacts diverse organisms not only directly but also indirectly via other organisms with which they interact. Recently, the possibility that elevated temperatures resulting from global warming may substantially affect biodiversity through disrupting mutualistic/parasitic associations has been highlighted. Here we report an experimental demonstration that global warming can affect a pest insect via suppression of its obligate bacterial symbiont. The southern green stinkbug Nezara viridula depends on a specific gut bacterium for its normal growth and survival. When the insects were reared inside or outside a simulated warming incubator wherein temperature was controlled at 2.5°C higher than outside, the insects reared in the incubator exhibited severe fitness defects (i.e., retarded growth, reduced size, yellowish body color, etc.) and significant reduction of symbiont population, particularly in the midsummer season, whereas the insects reared outside did not. Rearing at 30°C or 32.5°C resulted in similar defective phenotypes of the insects, whereas no adult insects emerged at 35°C. Notably, experimental symbiont suppression by an antibiotic treatment also induced similar defective phenotypes of the insects, indicating that the host's defective phenotypes are attributable not to the heat stress itself but to the suppression of the symbiont population induced by elevated temperature. These results strongly suggest that high temperature in the midsummer season negatively affects the insects not directly but indirectly via the heat-vulnerable obligate bacterial symbiont, which highlights the practical relevance of mutualism collapse in this warming world.
  
  
  
  Climate change is among the biggest environmental issues in the contemporary world, and its impact on the biodiversity and ecosystem is not only of scientific interest but also of practical concern for the general public. On the basis of our laboratory data obtained under strictly controlled environmental conditions and our simulated warming data obtained in seminatural settings (elevated 2.5°C above the normal temperature), we demonstrate here that Nezara viridula, the notorious stinkbug pest, suffers serious fitness defects in the summer season under the simulated warming conditions, wherein high temperature acts on the insect not directly but indirectly via suppression of its obligate gut bacterium. Our finding highlights that heat-susceptible symbionts can be the "Achilles' heel" of symbiont-dependent organisms under climate change conditions.
authors.affiliation: National Institute of Advanced Industrial Science and Technology (AIST) Hokkaido, Sapporo, Japan.
authors.forename: Yoshitomo
authors.initials: Y
authors.lastname: Kikuchi
authors.affiliation: Graduate School of Agriculture, Kyoto University, Kyoto, Japan.
authors.forename: Akiyo
authors.initials: A
authors.lastname: Tada
authors.affiliation: Saint Petersburg State Forest Technical University, Saint Petersburg, Russia.
authors.forename: Dmitry L
authors.initials: DL
authors.lastname: Musolin
authors.affiliation: Graduate School of Agriculture, Kyoto University, Kyoto, Japan.
authors.forename: Nobuhiro
authors.initials: N
authors.lastname: Hari
authors.affiliation: Faculty of Science, Kyushu University, Fukuoka, Japan.
authors.forename: Takahiro
authors.initials: T
authors.lastname: Hosokawa
authors.affiliation: Graduate School of Agriculture, Kyoto University, Kyoto, Japan.
authors.forename: Kenji
authors.initials: K
authors.lastname: Fujisaki
authors.affiliation: National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Japan t-fukatsu@aist.go.jp.
authors.forename: Takema
authors.initials: T
authors.lastname: Fukatsu
mesh_terms: D000818:Animals; D057231:Climate Change; D000069196:Gastrointestinal Microbiome / Q000528:radiation effects*; D020062:Heteroptera / Q000254:growth & development / Q000382:microbiology* / Q000528:radiation effects*; D008962:Models, Theoretical; D013559:Symbiosis / Q000528:radiation effects*; D013696:Temperature