The Effect of Diet and Reproductive Maturity on the Growth and Reproduction of Helisoma anceps (Pulmonata) Infected by Halipegus occidualis (Trematoda)

Abstract

Inhibition of snail reproductive activity by larval trematodes often results in increased growth of the snail, termed gigantism, during which the snail is hypothesized to allocate excess energy normally used for reproduction to somatic growth. Using the planorbid snail Helisoma anceps and the hemiurid trematode Halipegus occidualis, this hypothesis was examined by raising snails on low and high quality diets under 3 infection conditions: uninfected (UNI) and infected prior to (IPR) and after (IAR) reproductive maturity. Snails exhibited gigantism as an increase in wet mass only in the IPR condition on a high quality diet; snails in the IAR condition were not significantly different in size from UNI controls. Throughout the experiment, snails raised on a high quality diet were larger than those on the low quality diet, regardless of infection status, primarily because of increased growth rates prior to the onset of reproduction. Egg production by UNI snails on the high quality diet was 20 times higher than snails on the low diet, even though diet quality only differed by a factor of 4, and infected snails (both IPR and IAR) showed significantly reduced reproductive activity compared to UNI controls. The number of cercariae shed by each snail on a daily basis was not significantly different between IPR and IAR conditions when each diet quality was examined separately; more cercariae were produced by snails raised on the high quality diet. The prevalence of infection at the end of the experiment was lowest among snails raised on the low quality diet, suggesting the diet, i.e., energy intake, influences the loss of infections. Snail mortality did not differ among the various treatment conditions. These data suggest that gigantism is dependent upon snail reproductive maturity at the time of infection and food quality, and comparison to growth rates and fecundity data from previous field studies indicates that H. anceps in the field are probably protein deprived. Gigantism does not appear to be adaptive for the snail because survival was not increased, or for the parasite because cercariae production was the same for snails exhibiting gigantism or not. These results also stress the need for caution when examining the fecundity and growth rates of both uninfected and infected snails in the laboratory, especially when comparing these data to other laboratory or field studies.

Variability in the prevalence of infection and cercarial production in Galba truncatula raised on a high-quality diet

“…Indeed, in the system Bulinus truncatus -Schistosoma haematobium, the raising of snails on a mixture of foods resulted in a better fitness in terms of snail survival and prevalence of infections (Ismail and Haroun 2001). In contrast, in two other snail-parasite models, snail mortality (Keas and Esch 1997;Rondelaud et al 2002) and the prevalence of infections (Rondelaud et al 2002) did not significantly differ among snail groups raised on a low-or a highquality diet. In contrast, little information is available on the lengths of the prepatent and patent periods in infected and well-fed snails, whatever the model studied by authors.…”

“…Kendall 1949;Boray 1969;Lee et al 1995;Keas and Esch 1997;Ismail and Haroun 2001;Rondelaud et al 2002) when snails were raised on a high-quality diet. However, in the present study, there was a variability in the intensity of cercarial shedding, as cercarial production from snails raised on lettuce+Tetraphyll was 1.9-11.3 times higher than that noted in groups raised on lettuce.…”

Aquatic eutrophication promotes pathogenic infection in amphibians

“…3C). This likely occurred because of enhanced snail survival and growth under high-resource conditions (older and larger snails generally produce more parasites) or because of an increased capacity to translate snail resources into parasite secondary production (12,15,(23)(24)(25). Importantly, although nutrient-mediated increases in infected host size contributed strongly to the observed increase in cer- Fig.…”

“…First, higher resource availability will increase the population growth of susceptible snail hosts (22), leading to enhanced parasite transmission and a higher density of infected snails (12). Second, higher resource levels will reduce infected snail mortality, increase snail body size, and enhance host vigor (15,(23)(24)(25), promoting parasite secondary production within infected individuals. Thus, a higher density of infected snails and a greater per-snail production of parasites should jointly drive an increase in amphibian infection and disease risk.…”

Infestation of Lymnaea stagnalis by digenean flukes in the Jeziorak Lake

“…In laboratory experiments, gigantism of infested snails (Probst and Kube 1999;McCarthy et al 2004) and their shell hypercalcification were studied (McClelland and Bourns 1969;Malek and Cheng 1974;Sluiters et al 1980;Pinheiro and Amato 1995). Stimulation of growth of the parasitized snails and the increase of calcium content in their shells are often regarded as a consequence of the parasitic castration (Joose and van Elk 1986;Lafferty 1993a;Keas and Esch 1997;Żbikowska 2003). In castrated snails, energy, which would otherwise be partitioned to reproduction, is used by parasites, and the remaining resources are spent for increased growth Hurd 2001).…”