Response by two species of crabs to a rhizocephalan extract

Parasitic castration of Pseudaletia separata by Cotesia kariyai and its association with polydnavirus gene expression

Parasitization by the endoparasitoid Cotesia kariyai caused the inhibition of spermatogenesis of Pseudaletia separata. This phenomenon is called parasitic castration. The degree of castration was dependent on the host stage parasitized. Host parasitized on day 1 of the 4th stadium (the time of primary spermatocyte accumulation), had testicular cells with abnormal chromosomes appearing two days after parasitization, and spermiogenesis was completely inhibited. However, when hosts were parasitized on day 0 of the 6th (final) stadium, the degree of castration was less severe, and elongated cells appeared similar to those found in nonparasitized larvae. Results of this study involving injection of C. kariyai polydnavirus (CkPV) and venom suggested that these wasp components caused the appearance of abnormal chromosomes in specific germ cells, which were in mitotic or meiotic prophases. The amount of CkPV gene expression in host testes increased immediately after parasitization and reached a maximum 12h later. The early-expressed CkPV gene(s) may be related to the parasitic castration phenomenon.

The neuropeptide schistosomin and haemolymph from parasitized snails induce similar changes in excitability in neuroendocrine cells controlling reproduction and growth in a freshwater snail

Infection of the snail Lymnaea stagnalis with the schistosome parasite Trichobilharzia ocellata results in inhibition of reproduction and in giant growth. Parasite-related effects on the neuroendocrine centres that control these processes were studied electrophysiologically. Haemolymph from infected snails reduced the excitability of the caudodorsal cells, which control egg laying. In contrast, the excitability of the growth-controlling Light Green Cells was increased under these conditions. The endogenous anti-gonadotropic neuropeptide schistosomin, the presence of which is strongly enhanced in parasitized snails, induced similar effects. Schistosomin apparently plays an important role in the balance between reproduction and growth in Lymnaea. This balance is severely disturbed during parasitic infection, probably as a result of the release of the peptide.