Toru Ishigami

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 spiders 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. Highlighted Article: Ichneumonid spider ectoparasitoids manipulate the web-building behaviour of host spiders to make the original web into an alternative ‘cocoon web’ by exploiting preprogrammed resting web construction to add specific thread decoration.

Solidification Behavior of Polymer Solution during Membrane Preparation by Thermally Induced Phase Separation

The solidification behavior of poly(vinylidene fluoride) (PVDF) solution during membrane preparation by thermally induced phase separation (TIPS) was investigated. Apparatus newly developed in our laboratory was used to quantitatively measure membrane stiffness during phase separation. In this apparatus, a cooling polymer solution, placed on a stage, is moved upwards and the surface of the polymer solution contacts a sphere attached to the tip of a needle. The displacement of a blade spring attached to the needle is then measured by a laser displacement sensor. Different phase separation modes, such as liquid-liquid (L-L) phase separation and solid-liquid (S-L) phase separation (polymer crystallization) were investigated. In the case of S-L phase separation, the stiffness of the solution surface began to increase significantly just before termination of crystallization. In contrast, L-L phase separation delayed solidification of the solution. This was because mutual contact of the spherulites was obstructed by droplets of polymer-lean phase formed during L-L phase separation. Thus, the solidification rate was slower for the L-L phase separation system than for the S-L phase separation system.

Preparation of a PVDF hollow fiber blend membrane via thermally induced phase separation (TIPS) method using new synthesized zwitterionic copolymer

Antifouling properties of PVDF hollow fiber membrane were improved by the addition of a new synthesized zwitterionic copolymer. This copolymer was synthesized using methyl methacrylate and the zwitterionic monomer 3-(methacryloylamino)propyl-dimethyl(3-sulfopropyl) ammonium hydroxide) (MPDSAH). The copolymer was used as additive in the preparation of a poly(vinylidene fluoride) (PVDF) hollow fiber membrane via thermally induced phase separation. With addition of the copolymer, the crystallization temperature and spherulite growth rate of the polymeric solution decreased sharply. Quartz crystal microbalance with dissipation monitoring results showed that bovine serum albumin (BSA) interactions with the prepared PVDF/copolymer film sharply decreased with addition of the synthesized copolymer. BSA filtration results showed that the membrane had higher antifouling resistance than a membrane without the copolymer additive.