The Effects of Population Density on Growth and Reproduction of Biomphalaria glabrata (Say) (Gasteropoda: Pulmonata)

Thomas, J. D.; Benjamin, Marcus

doi:10.2307/3156

Cited by 49 publications

(34 citation statements)

References 29 publications

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“…Each treatment was replicated 10 times for fed and deprived snails in both size groups. Each snail was weighed on days 0, 3, 6 and 12 (Thomas & Benjamin 1974) and specific growth rates calculated as [1/ t × ln( w t / w 0 )] × 100, where t = time in days and w t and w 0 are the weights on day t and day 0, respectively. Snails were killed individually by immersion in water at 69 °C for 10–15 seconds, the alimentary canal dissected and the stomach and the remainder of the gut (intestine + rectum) placed in separate Petri dishes.…”

Section: Methodsmentioning

confidence: 99%

Particle selection by snail hosts of human schistosomes in relation to their survival strategies and possible control by ‘environmental antibodies’

Thomas

2001

Journal of Applied Ecology

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Summary1. Experiments were undertaken with Biomphalaria glabrata to (i) elucidate the mechanisms used for selecting, regulating and utilizing sand particles and (ii) evaluate particulate controlled-release formulations (CRF), or 'environmental antibodies', to control target snails. 2. The snails selected sand particles by size, mass and density. The numbers and mass of sand particles in the guts increased with snail size, and fed snails had significantly more sand particles in their guts than deprived snails. 3. Snails benefited from ingesting sand particles. Increasing the weights of 63-125-µ m sand particles from 8·5 mg to 150-170 mg resulted in progressive, significant, increases in the numbers of sand particles in the various gut compartments and also enhanced snail growth. 4. Snails did not discriminate between sand and glass particles of the same size. When offered unwashed acidic sand there was a lag of 5-6 h before ingestion, but this could be reduced by preconditioning in media rich in base cations or chemical factors of snail origin. Under equilibrium conditions ingested sand constituted approximately 2·5% of the total snail weight but this amount was exceeded when snails were presented with large quantities of sand. 5. The parts of the gut involved in sorting and regulating the turnover of sand particles and food were described. The gizzard, caecal and digestive gland strings traversed the gut as far as the rectum in approximately 2·8 h, 6-8 h and 8 h, respectively. 6. Coprophagy by the snails facilitated the recycling of sand and its retention in the gut. 7. Optimally sized, 63-250-µ m, protein microcapsules containing butanoate and maltose were ingested by snails in significantly greater amounts than untreated control microcapsules. The addition of copper caused the capsules to become repellent. 8. These results will advance the design of effective, ecologically acceptable, environmental antibodies in the form of controlled-release microcapsules to control schistosome snails. This work illustrates how a combination of detailed study of snail anatomy, feeding experiments and ecological understanding can contribute to the control of the intermediate hosts of a major human parasite.

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Section: Methodsmentioning

confidence: 99%

Particle selection by snail hosts of human schistosomes in relation to their survival strategies and possible control by ‘environmental antibodies’

Thomas

2001

Journal of Applied Ecology

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“…The effects of grazing on the density and community structure of epiphyton (a) Previously grazed epiphyton. The treatments consisted of placing four adult L. peregra (II mm :t:SE 1 mm in shell length) or four adult P. planorbis (10 mm -tSE 2 mm in shell diameter) together with one growing shoot of Ceratophyllum (length 14 cm, eighleen leaf nodes, one growing tip) in 1.2 litres of chalk aquifer water (Thomas & Benjamin. 1974) contained in a 1.5 litre plastic beaker covered with perforated clingfilm.…”

Section: Methodsmentioning

confidence: 99%

Grazing interactions between pulmonate snails and epiphytic algae and bacteria

Underwood

Thomas

1990

Freshwater Biology

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1. The effects of grazing by Lymnaea peregra and Planorbis planorbis on Ceralophyllum demersum epiphyton were investigated under simulated natural conditions.2. Grazing resulted in significant reductions in algal cell densities, number of algal taxa and in diversity. Grazing did not influence equitability values.3. The use of Ivlev's Electivity index demonstrated positive and negative selection by feeding snails for large, pedunculate, and small, adnate algae, respectively. 4. Inoculation of artificial surfaces revealed that 61.1% and 62..**% of the algal taxa present in the diet of L. peregra and P. planorbis., respectively (mainly the smaller species), were able to survive passage through the gut, resettle and grow.5. The results are discussed with particular reference to the survival strategies available to the epiphytes, and the possible mutual benefits which algae and snails may derive from coexistence.

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“…Animals which can reproduce asexually may nevertheless have higher reproductive output in the presence of other individuals (Thomas and Benjamin 1973). In selffertile snails, Biomphalaria glabrata, and parthenogenetic female lizards, Cnemidophorus uniparens, individuals housed in isolation produce fewer offspring than individuals housed in groups, apparently because of exposure to courtship behaviour, although they do not actually mate (Crews et al 1986;Vernon 1995).…”

Section: Physiological Stimulationmentioning

confidence: 99%

Dangerously few liaisons: a review of mate‐finding Allee effects

et al. 2009

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In this paper, we review mate-finding Allee effects from ecological and evolutionary points of view. We define 'mate-finding' as mate searching in mobile animals, and also as the meeting of gametes for sessile animals and plants (pollination). We consider related issues such as mate quality and choice, sperm limitation and physiological stimulation of reproduction by conspecifics, as well as discussing the role of demographic stochasticity in generating mate-finding Allee effects. We consider the role of component Allee effects due to mate-finding in generating demographic Allee effects (at the population level). Compelling evidence for demographic Allee effects due to matefinding (as well as via other mechanisms) is still limited, due to difficulties in censusing rare populations or a failure to identify underlying mechanisms, but also because of fitness trade-offs, population spatial structure and metapopulation dynamics, and because the strength of component Allee effects may vary in time and space. Mate-finding Allee effects act on individual fitness and are thus susceptible to change via natural selection. We believe it is useful to distinguish two routes by which evolution can act to mitigate mate-finding Allee effects. The first is evolution of characteristics such as calls, pheromones, hermaphroditism, etc.which make mate-finding more efficient at low density, thus eliminating the Allee effect. Such adaptations are very abundant in the natural world, and may have arisen to avoid Allee effects, although other hypotheses are also possible. The second route is to avoid low density via adaptations such as permanent or periodic aggregation. In this case, the Allee effect is still present, but its effects are avoided. These two strategies may have different consequences in a world where many populations are being artificially reduced to low density: in the first case, population growth rate can be maintained, while in the second case, the mechanism to avoid Allee effects has been destroyed. It is therefore in these latter populations that we predict the greatest evidence for mate-finding Allee effects and associated demographic consequences. This idea is supported by the existing empirical evidence for demographic Allee effects. Given a strong effect that mate-finding appears to have on individual fitness, we support the continuing quest to find connections between component mate-finding Allee effects (individual reproductive fitness) and the demographic consequences. There are many reasons why such studies are difficult, but it is important, particularly given the increasing number of populations and species of conservation concern, that the ecological community understands more about how widespread demographic Allee effects really are, and why.

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The Effects of Population Density on Growth and Reproduction of Biomphalaria glabrata (Say) (Gasteropoda: Pulmonata)

Cited by 49 publications

References 29 publications

Particle selection by snail hosts of human schistosomes in relation to their survival strategies and possible control by ‘environmental antibodies’

Particle selection by snail hosts of human schistosomes in relation to their survival strategies and possible control by ‘environmental antibodies’

Grazing interactions between pulmonate snails and epiphytic algae and bacteria

Dangerously few liaisons: a review of mate‐finding Allee effects

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