Studies on the chemical ecology of Biomphalaria glabrata: The effects of chemical conditioning by the snails kept at various densities on their growth and metabolism

Abstract

It has been shown that heterotypically conditioned media (Het. C.M.) produced by lettuce fed snails maintained at various densities can influence the allometric growth and the rates of specific growth, ingestion, egestion, assimilation and heart beat of isolated assay snails. The growth rate of the assay snails was enhanced by increasing the density of snails producing the Het. C.M. to an optimum threshold of one snail per 100 ml. Further increases in density were followed by a decline in their growth rate. The higher growth achieved by the assay snails in the optimum treatment can be attributed to the fact that their specific growth rates over the first three weeks of the experiment were higher than those of snails in other treatments. Ingestion and assimilation correlated well with specific growth rates. Percentage assimilation values are high, ranging from 78.4 to 89.6%. The onset of reproductive activity is followed by a dramatic decline from approximately 26 % to 5 % in the gross efficiency of utilization of food for somatic growth. Snails not receiving Het. C.M. from the outer tanks have a relatively higher ratio of specific growth rate in weight to length than was the case with snails in the other treatments. The heart beat rates of snails in the Het. C.M. produced by snails at densities of 80 to 160 snails per 41 are significantly lower than those of snails at other densities. The possible causation and adaptive significance of these effects are discussed.

Effects of mating, breeding system and parasites on reproduction in hermaphrodites: pulmonate gastropods (Mollusca)

“…In the same species trade-offs between the allocation of resources to growth versus reproduction (Ritchie et al, 1966;Thomas et al, 1975;Vernon, 1993) have been reported.…”

“…Vernon (1995) suggested that an absence of social facilitation, caused by deprivation of social communication as a result of isolation, may play a role in reducing reproductive output of isolated B. glabrata although the substance(s) that are responsible for this observation are not known. Basommatophoran freshwater snails may release communication substances in the water that may influence feeding, growth, metabolism and reproduction in conspecifics (Ritchie et al, 1966;Thomas et al, 1974Thomas et al, , 1975. Individuals of B. glabrata are thought to be receptive to even very low concentrations of chemicals that are released by nearby conspecifics but the exact nature of these communication substances is not yet known.…”

The ecophysiology of apple snails in rice: implications for crop management and policy

“…Growth rates decline after egg laying and are inversely proportional to oviposition rates ( P. canaliculata ; Albrecht et al ., ). Apart from direct competition for limited food resources, lower growth rates under crowded conditions may also be due to chemical suppressants, including growth suppressive chemicals such as occur in slime trails of other aquatic snails (Berrie & Visser, ; Thomas et al ., , ). The possibility that suppressive chemicals may determine apple snail growth and development in paddy fields has received little research attention.…”

Influence de la densité animale sur la croissance et la reproduction de l’escargot Limicolaria flammea (Müller) en conditions d’elevage

“…Les effets de la densité englobent, d'une part, les facteurs de stimulation de la croissance tels que les polypeptides, les glycoprotéines, les lipoprotéines, les acides aminés et les ionophores qui sont probablement produits par l'escargot luimême à travers les micro organismes de ses voies digestives (Thomas et al 1975). D'autre part, les effets de la densité englobent également des facteurs inhibiteurs de croissance comme l'ammoniaque, les métabolites provenant des aliments ou des fèces.…”