Observations on zelleriella-antilliensis (protozoa: Opalinata) from the Cane Toad Bufo-Marinus in Australia

Zelleriella antilliensis (Metcalf, 1914) was found in Australia in the cloaca of the introduced American cane toad, Bufo marinus (Linnaeus, 1758). Drawings and measurements (length, width) were made with the help of a camera lucida. Other measurements were performed with the help of a digitiser. The presence of some native anuran Protoopalina spp. was noticed. 657 native Anura in 61 species and 4 families checked for Z. antilliensis were negative. Experimental infections of various anuran tadpoles of the genus Limnodynastes, Litoria and Xenopus, show that the opalinid can only survive for a limited time in these unnatural hosts. Cyst viability seems not to exceed three weeks in water. Gamonts and gametes were not observed during experimental infections. It is suggested that a protrophont (mononucleate) excysts and within 24 hours after infection of the host becomes a young trophont (binucleate). Mononucleate forms observed in the adults are recognised as Z. antilliensis and not as a species of Hegneriella

Simulated winter browsing may lead to induced susceptibility of willows to beavers in spring

Browsing may lead to an induced resistance or susceptibility of the plant to the herbivore. We tested the effect of winter browsing by Eurasian beavers (Castor fiber L., 1758) on food quality of holme willows (Salix dasyclados Wimm.) in and after the following growth season. Shrubs were pruned in February, and new shoots from these (cut) shrubs were compared with those of untreated (uncut) ones in May and November. The shoots were analysed for dry matter, nitrogen, acid detergent fibre, and total phenolics. In May, the leaves from the cut treatment had a better food quality (more water, more nitrogen, and less phenolics) than those from the uncut one. There was in part also a systemic response, with lower total phenolics in both the cut and untreated parts of pruned shrubs (uncut–cut) than in the uncut shrubs. In November, we did not find significant differences in biochemistry of bark among cut, uncut, or uncut–cut treatments. These results are in accordance with a cafeteria experiment in the field: in May the beavers preferred shoots from the cut treatment, but in November they showed no preference. The results suggest that willows invest in compensatory growth rather than a defence response early in the regrowing phase.

Group living and investment in immune defence : an inter-specific analysis.

1. Since parasite transmission is often density-dependent, group living is normally thought to lead to an increased exposure to parasitism. As a consequence, it is predicted that animals living in groups will invest more resources (energy, time, risk, etc.) in parasite defence than those living solitarily. 2. We tested this prediction by measuring basal immune parameters in the larvae of 12 species of Lepidoptera, grouped into six phylogenetically matched species-pairs, each comprising one solitary feeding and one gregariously feeding species. 3. Contrary to expectation, the solitary species in all six species-pairs had higher total haemocyte counts than the gregarious species, and in five out of six species-pairs the solitary species also exhibited higher phenoloxidase activity. Both measurements were positively correlated with each other and with the magnitude of the cellular encapsulation response. 4. The relationship between infection risk and group living was investigated with a dynamic, spatially explicit, host–pathogen model. This shows that when individuals aggregate in groups, the per capita risk of infection can be reduced if the lower between-group transmission more than compensates for the higher within-group transmission. 5. We conclude that the expectation that group living always leads to increased exposure to pathogens and parasites is overly simplistic, and that the specific details of the social system in question will determine if there is increased or decreased exposure to infection