Some parasites with complex life-cycles are able to manipulate the behaviour of their intermediate hosts in a way that increases their transmission to the next host. Gammarids infected by the tapeworm Cyathocephalus truncatus (Cestoda: Spathebothriidea) are known to be more predated by fish than uninfected ones, but potential behavioural manipulation by the parasite has never been investigated. In this study, we tested the hypothesis that C. truncatus is able to manipulate the behaviour of one of its intermediate hosts, Gammarus pulex (Crustacea: Amphipoda). To assess if any behavioural change was linked to other phenotypic alterations, we also measured the immunity of infected and uninfected individuals and investigated the pathogenic effects of the parasite. Infected gammarids were significantly less photophobic than uninfected ones, but no effect of infection on the level of immune defence was found. The results on survival, swimming activity and oxygen consumption suggest that the parasite also has various pathogenic effects. However, the alteration in host phototaxis was not correlated to some of these pathogenic effects. Therefore, we propose that the modification in host reaction to light is a behavioural manipulation, explaining the previously observed increase of gammarid predation rate.

The freshwater scud Echinogammarus stammeri is a very abundant benthic crustacean in riverine systems of northern Italy.The molecular physiology of L-[3H]leucine transport across cell membranes of E. stammeri was investigated. At pH 7.4, thepresence of a NaCl gradient stimulated the leucine transport rate, when compared with KCl gradient. By contrast, alkaline pHstrongly inhibited transport activity. In NaCl medium at acidic pH, leucine uptake displayed a specific activity 2.1-fold lowerthan that measured at neutral pH. Analysis of the uptake as a function of external leucine concentration revealed saturation kinetics.Leucine uptake appeared broadly unspecific and it was much strongly inhibited by the non-polar amino acids phenylalanine,methionine, and BCH, as well as by hydrophobic hydroxyacids. These results revealed important differences with respect toamino acid transport systems described in marine crustaceans. Their relevance in the feeding adaptation of the scud is brieflydiscussed.

Ce travail présente la répartition de 5 espèces de Gammaridae (Echinogammarus berilloni, E. spinulicornis, Gammarusfossarum, G. p. pulex, G. roeseli) dans la Région Centre qui correspond approximativement au bassin de la Loiremoyenne et au sud du bassin de la Seine moyenne. Environ 300 stations ont été échantillonnées entre 1980 et 1990.G. fossarum n'est présente que dans l'Allier. L'espèce la plus répandue est G. p. pulex ; elle apparaît souvent en sympatrieavec E. berilloni. E. spinulicornis et G. roeseli sont deux espèces en extension dans la région. E. spinulicornis estnettement dominante à l'ouest, mais uniquement dans le bassin de la Loire, tandis que G. roeseli est plus abondanteà l'est aussi bien dans le bassin de la Loire que dans celui de la Seine.