title: Host manipulation by an ichneumonid spider ectoparasitoid that takes advantage of preprogrammed web-building behaviour for its cocoon protection.
abstract: Host manipulation by parasites and parasitoids is a fascinating phenomenon within evolutionary ecology, representing an example of extended phenotypes. To elucidate the mechanism of host manipulation, revealing the origin and function of the invoked actions is essential. Our study focused on the ichneumonid spider ectoparasitoid Reclinervellus nielseni, which turns its host spider (Cyclosa argenteoalba) into a drugged navvy, to modify the web structure into a more persistent cocoon web so that the wasp can pupate safely on this web after the spider's death. We focused on whether the cocoon web originated from the resting web that an unparasitized spider builds before moulting, by comparing web structures, building behaviour and silk spectral/tensile properties. We found that both resting and cocoon webs have reduced numbers of radii decorated by numerous fibrous threads and specific decorating behaviour was identical, suggesting that the cocoon web in this system has roots in the innate resting web and ecdysteroid-related components may be responsible for the manipulation. We also show that these decorations reflect UV light, possibly to prevent damage by flying web-destroyers such as birds or large insects. Furthermore, the tensile test revealed that the spider is induced to repeat certain behavioural steps in addition to resting web construction so that many more threads are laid down for web reinforcement.
authors.affiliation: Laboratory of Insect Biodiversity and Ecosystem Science, Graduate School of Agricultural Science, Kobe University, Hyogo 657-8501, Japan keizaf@gmail.com.
authors.forename: Keizo
authors.initials: K
authors.lastname: Takasuka
authors.affiliation: Department of Chemical Science and Engineering, Graduate School of Engineering, Kobe University, Hyogo 657-8501, Japan.
authors.forename: Tomoki
authors.initials: T
authors.lastname: Yasui
authors.affiliation: Department of Chemical Science and Engineering, Graduate School of Engineering, Kobe University, Hyogo 657-8501, Japan.
authors.forename: Toru
authors.initials: T
authors.lastname: Ishigami
authors.affiliation: Faculty for the Study of Contemporary Society, Kyoto Women's University, Kyoto 605-8501, Japan.
authors.forename: Kensuke
authors.initials: K
authors.lastname: Nakata
authors.affiliation: Osaka Museum of Natural History, Osaka 546-0034, Japan.
authors.forename: Rikio
authors.initials: R
authors.lastname: Matsumoto
authors.affiliation: Laboratory of Stress Cytology, Graduate School of Agricultural Science, Kobe University, Hyogo 657-8501, Japan.
authors.forename: Kenichi
authors.initials: K
authors.lastname: Ikeda
authors.affiliation: Laboratory of Insect Biodiversity and Ecosystem Science, Graduate School of Agricultural Science, Kobe University, Hyogo 657-8501, Japan.
authors.forename: Kaoru
authors.initials: K
authors.lastname: Maeto
mesh_terms: D000818:Animals; D001522:Behavior, Animal / Q000502:physiology; D006790:Host-Parasite Interactions; D047011:Silk / Q000502:physiology*; D013112:Spiders / Q000469:parasitology* / Q000502:physiology*; D014466:Ultraviolet Rays; D014863:Wasps / Q000254:growth & development*
chemical_list: D047011:Silk
keywords: Cocoon web; Cyclosa argenteoalba; Fibrous thread decoration (FTD); Reclinervellus nielseni; Resting web; Tensile test