Lead impact on nutrition, energy reserves, respiration and stress protein (hsp 70) level in Porcellio scaber (Isopoda) populations differently preconditioned in their habitats

Terrestrial isopods as model organisms in soil ecotoxicology: a review

Isopods play an important role in the decomposition of leaf litter and therefore are making a significant contribution to nutrient cycling and soil ecosystem services. As a consequence, isopods are relevant models in soil ecotoxicology, both in laboratory toxicity tests and in field monitoring and bioindication studies. This paper aims at reviewing the use of isopods as test organisms in soil ecotoxicology. It provides an overview of the use of isopods in laboratory toxicity tests, with special focus on comparing different exposure methods, test durations, and ecotoxicological endpoints. A brief overview of toxicity data suggests that chemicals are more toxic to isopods when exposed through soil compared to food. The potential of isopods to be used in bioindication and biomonitoring is discussed. Based on the overview of toxicity data and test methods, recommendations are given for the use of isopods in standardized laboratory toxicity tests as well as in situ monitoring studies.

Cross tolerance in beet armyworm: long-term selection by cadmium broadens tolerance to other stressors

Long lasting exposure of animals to stressing factor may lead to the selection of population able to cope with the stressor at lower cost than unexposed individuals. The aim of this study was to assess whether 130-generational selection of a beet armyworm to cadmium in food might have induced tolerance also to other stressors. The potential tolerance was assessed by means of unspecific stress markers: HSP70 concentration, DNA damage level, and energy budget indices in L5 larval instars of beet armyworm. The animals originated from Cd-exposed and control strains exposed additionally in a short-term experiment to high/low temperature or pesticide-spinosad. The application of the additional stressors caused, in general, an increase in the levels of studied parameters, in a strain-dependent manner. The most significant increase was found in HSP70 level in the individuals from the Cd-strain exposed to various spinosad concentration. Therefore, multigenerational contact with cadmium caused several changes that enable the insect to survive under a chronic stress, preparing the organism to the contact with an additional, new stressor. This relationship may be described as a sort of cross tolerance. This may, possibly, increase the probability of population survivorship and, at the same time, decrease the efficiency of pesticide-based plant protection efforts.

Metallothioneins and heat shock proteins 70 in Armadillidium vulgare (Isopoda, Oniscidea) exposed to cadmium and lead

The heavy metals bioaccumulation capability in Armadillidium vulgare feeded with chestnut leaves contaminated with various sublethal concentrations of Cd and Pb, was evaluated under laboratory conditions. The metal concentration found in the hepatopancreas of treated animals, as measured by Inductively Coupled Plasma Mass Spectrometry (ICP-MS), affected the expression and localization of MT and HSP70 as shown by immunohistochemical and western blotting analysis. The Cd content of the animals treated with the various concentrations of the metal has been always higher than that of chestnut leaves contaminated. The accumulation of Pb was, instead, always modest compared to the content of the chestnut leaves. The immunohistochemical investigation in hepatopancreas tissue of animals treated with increasing concentrations of Cd and Pb, by using the anti-MT and anti-HSP70 antibodies, has provided a response clearly positive even if differentiated in relation to the metal and concentration tested. In particular, a positive response to anti-MT antibody was detected in B and S cells nuclei and S cells cytoplasm; the localization of HSP70 was particularly intense at the cell surface. Western blotting analysis showed significant up-regulation of the expression (about 2.6 fold) of HSP70 proteins in the hepatopancreas of animals exposed to highest Pb concentrations respect to control. Moreover, samples exposed to higher Cd and Pb concentrations showed a higher expression of MT (3.2 fold and 4 fold respectively) compared to control. In summary, our data beyond to clearly demonstrate for the first time the expression of MT in terrestrial isopods, suggest that A. vulgare would be a suitable organism for assessing Cd and Pb exposure in environments threatened by metal pollution as suggested by the modulation of the biomarkers MT and HSP70.

Effects of heavy metal accumulation on some reproductive characters in Armadillidium granulatum Brandt (Crustacea, Isopoda, Oniscidea)

The impact of heavy metal bioaccumulation on reproduction of the isopod Armadillidium granulatum was studied by exposing the animals to food contaminated with various sub-lethal concentrations of cadmium, lead and zinc salts over a period of three weeks. The analysis carried out by atomic absorption spectrometry on whole body and on isolated female and male genital systems highlighted that, although metal's bioaccumulation was always concentration-dependent, it varies considerably depending on the metal (Cd>Zn>Pb) as pointed out by the respective values of the concentration factor. The heavy metals bioaccumulation has influenced in different ways the reproductive characters observed; while no significant difference was found with regard to the length of the incubation period and the number of broods--A. granulatum has an iteroparous reproductive strategy--the onset and the length of the reproductive season were negatively affected by the increase in concentration of the tested metals, in particular of Cd. The rate of gravid females, instead, was negatively affected by the bioaccumulation of Cd and Zn while in the groups treated with the highest concentrations of Pb all females produced at least one brood. The number of juveniles released from the brood pouch at the end of incubation resulted considerably higher and it was always positively correlated to the increase of the concentration of each metal, except for the highest Pb concentration. The explanation of this result, apparently anomalous, could be the object of a future research.

Antioxidative responses in females and males of the spider Xerolycosa nemoralis (Lycosidae) exposed to natural and anthropogenic stressors

The aim of this study was to assess the intensity of enzymatic antioxidative parameters [i.e., superoxide dismutase (SOD), catalase (CAT), and the glutathione peroxidases each selene dependent, GPOX or selene independent, including GSTPx, glutathione S-transferase, and GST] and non-enzymatic antioxidative parameters [i.e., glutathione total (GSH-t), the heat shock proteins of Hsp70, and metallothioneins (Mt)] in the midgut glands of female and male wolf spiders Xerolycosa nemoralis (Lycosidae) exposed to natural stressors (i.e., heat shock and starvation) and anthropogenic stressors (i.e., the organophosphorous pesticide dimethoate) under laboratory conditions. The spiders were collected from two differentially polluted sites both localized in southern Poland: Olkusz, which is heavily polluted with metals, and Pilica, the reference site. In response to the stressing factors, increases in Hsp70 levels, in the concentrations of total glutathione and in the activity levels of glutathione-dependent enzymes (GPOX, GSTPx, and GST) were found in the midgut glands of males. In the females, high levels of activity of CAT and SOD were revealed, as well as an increased percentage of Mt-positive cells. Preexposed females, in comparison to the individuals from the reference site, responded with increased SOD activity, irrespective of the stressing factor. In contrast, the changes in the antioxidative parameters in the midgut glands of male X. nemoralis seem to reflect a short-term reaction to the applied stressors and do not confirm the effects of long-term selection in a polluted environment.

Energy reserves and accumulation of metals in the ground beetle Pterostichus oblongopunctatus from two metal-polluted gradients

Living in an area chronically polluted with metals is usually associated with changes in the energy distribution in organisms due to increased energy expenses associated with detoxification and excretion processes. These expenses may be reflected in the available energy resources, such as lipids, carbohydrates, and proteins. In this context, the energy status of Pterostichus oblongopunctatus (Coleoptera: Carabidae) was studied in two metal pollution gradients near Olkusz and Miateczko Śląskie in southern Poland. Both regions are rich in metal ores, and the two largest Polish zinc smelters have been operating there since the 1970s. Beetles were collected from five sites at each gradient. Zinc and cadmium concentrations were measured in both the soil and the beetles. The possible reduction in energy reserves as a cost of detoxifying assimilated metals was evaluated biochemically by determining the total lipid, carbohydrates, and protein contents. At the most polluted sites, the Zn concentration in the soil organic layer reached 2,906 mg/kg, and the Cd concentration reached 55 mg/kg. Body Zn and Cd concentrations increased with increasing soil Zn and Cd concentrations (p = 0.003 and p = 0.0001, respectively). However, no relationship between pollution level and energetic reserves was found. The results suggest that populations of P. oblongopunctatus inhabiting highly metal-polluted sites are able to survive without any serious impact on their energy reserves, though they obviously have to cope with elevated body metal concentrations.

Prolonged feeding of terrestrial isopod (Porcellio scaber, Isopoda, Crustacea) on TiO (2) nanoparicles. Absence of toxic effect

Nanoparticles of titanium dioxide are one of most widely used nanomaterials in different products in everyday use and in industry, but very little is known about their effects on non- target cells and tissues. Terrestrial isopods were exposed to food dosed with nano-TiO₂ to give final nominal concentration 1000 and 2000 µg TiO₂/g dry weight of food. The effects of ingested nano-TiO₂ on the model invertebrate Porcellio scaber (Isopoda, Crustacea) after short-term (3 and 7 days) and prolonged (14 and 28 days) dietary exposure was assessed by conventional toxicity measures such as feeding rate, weight change and mortality. Cell membrane destabilization was also investigated. No severe toxicity effects were observed after 3, 7, 14 or 28 days of dietary exposure to nano-TiO₂, but some animals, particularly those exposed to lower concentrations of nanoparticles, had severely destabilized digestive cell membranes. It was concluded that strong destabilization of the cell membrane was sporadic, and neither concentration- nor time-related. Further research is needed to confirm this sporadic toxic effect of nanoparticles.

Metal sensitivity of the embryonic development of the ramshorn snail Marisa cornuarietis (Prosobranchia)

We investigated the effects of metal ions on the embryonic development of the ramshorn snail, Marisa cornuarietis, by exposing embryos to varying concentrations of copper (0, 50, 100, and 250 μg Cu(2+)/L), lead (0, 5, 10, and 15 mg Pb(2+)/L), lithium (0, 1, 2.5, and 3 mg Li(+)/L), or palladium (0, 50, 100, and 500 μg Pd(2+)/L). Effects of these metals were examined by recording mortality, the rate of tentacles and eyes formation, heart rate, hatching success, and weight after hatching. Compared to the control, we found a significant delay in the formation of tentacles and eyes after treatment with 100 μg Cu(2+)/L, 15 mg Pb(2+)/L, 2.5 mg Li(+)/L or 500 μg Pd(2+)/L. The heart rate decreased significantly at 500 μg Pd(2+)/L. At 10 mg Pb(2+)/L, 2.5 mg Li(+)/L, or 500 μg Pd(2+)/L, hatching was delayed significantly; 50 μg Cu(2+)/L induced a significantly earlier hatching, and reduced body weight. The LC(50) values were calculated to be about 50 μg Cu(2+)/L, 500 μg Pd(2+)/L, 2500 μg Li(+)/L, and 10000 μg Pb(2+)/L. These results show that the embryonic development of M. cornuarietis is about as sensitive to copper and lithium, compared to the most sensitive fishes used in embryo toxicity testing. Even though the MariETT is a laboratory-based assay focusing on toxicological endpoints of a selected model species, future application is envisaged to include testing of "natural" samples such as stream water or sediment interstitial water.

Cadmium tolerance in seven Daphnia magna clones is associated with reduced hsp70 baseline levels and induction

The stress protein hsp70 is part of the intracellular alarm and repair system which enables organisms to counteract negative effects of toxicants on protein integrity. Under long-term selection pressure exerted by environmental pollution, in particular heavy metals, this system may be expected to play a major role in the course of local, microevolutionary events leading to the acquisition of toxicant resistance. Seven clones of Daphnia magna from different geographical regions were characterized regarding their sensitivity to Cd, their hsp70 expression, and Cd accumulation. In an acute immobilisation assay, the tested clones showed remarkable differences in their sensitivity to Cd. The highest EC(50) values by far were obtained for the clone displaying lowest hsp70 expression. In general, hsp70 levels reflected the order of sensitivity to Cd among the seven clones reciprocally. Clonal variations in sensitivity and hsp70 expression could not be related to differential accumulation of Cd, though. In summary, the association of stress insensitivity with low hsp70 induction which has been exemplarily reported for populations of different invertebrates under strong selection pressure could be affirmed for a largely parthenogenetic species for the first time. Furthermore, our observation has serious consequences for the interpretation of toxicological assays using a single D. magna clone solely.

Hsp70 level in progeny of aging grasshoppers from variously polluted habitats and additionally exposed to zinc during diapause

The hsp70 level in the bodies of 1st instars of grasshoppers Chorthippus brunneus from unpolluted (Pilica) and polluted (Olkusz, Szopienice) sites and additionally exposed to various doses of zinc during diapause and embryonic development prior to hatching were measured by Western blotting. The main aim of our work was to assess the relationship between the age of female grasshoppers originating from variously polluted habitat and the hsp70 level in their progeny. Possible reasons for population variation in hsp70 levels were discussed. The hsp70 level in the offspring's body depended on the place of origin. The strongest expression of hsp70 was found in the bodies of larvae hatching from the eggs laid by young females from Pilica (reference site). In contrast, a low initial level of hsp70 in larvae from polluted sites, especially in young females' progeny, was observed. The application of zinc during diapause influenced the hsp70 level in grasshopper larvae; however, the direction of the changes depended on the insects' place of origin. In larvae from the reference site, and also (but to a lesser degree) from Olkusz, the increase in the hsp70 level after zinc treatment was most pronounced. Whereas in grasshoppers from Szopienice, zinc (in 100microg g(-1) dry weight of sand) did not change the hsp70 level, or (in 500microg g(-1) dry weight of sand) caused a reduction in hsp70. The differences may result from maternal effects; however, possible adaptation also cannot be excluded. To confirm this statement further studies are needed.

Toxic potential of municipal solid waste leachates in transgenic Drosophila melanogaster (hsp70-lacZ): hsp70 as a marker of cellular damage

Municipal solid wastes (MSWs) are one of the major sources of environmental pollution. Leachates from these wastes might contaminate the water sources and affect quality of environment. The study was carried out to determine the possible toxic effects of leachates from MSW in transgenic Drosophila melanogaster (hsp70-lacZ). Third instar larvae exposed to 1.0-3.0% of these leachates at different time intervals were examined for hsp70 expression, oxidative stress enzyme activities, proteotoxicity, tissue damage along with effect on emergence and reproduction. Maximum hsp70 expression was observed in the larvae exposed to highly acidic leachates. Overwhelming of hsp70 expression in the exposed larvae caused a concomitant decline in total protein content and a significant elevation in oxidative stress enzymes and lipid peroxidation (LPO) product. The leachates caused a significant delay in emergence of flies and affected the reproductive performance of the flies at the tested concentrations. The present study highlights the toxic potential of MSW leachates and the advantage of Drosophila as a model to evaluate the impact of leachates at organismal and cellular levels, also advocating Hsp70 as the first tier indicator of toxicity.

Effects of dinoseb on energy reserves in the soil arthropod Folsomia candida

This study evaluated the usefulness of energy reserves as an early warning system in Folsomia candida when exposed to the pesticide dinoseb. After different exposure times, survival, reproduction, growth (weight and length), lipid and protein content of the organisms were determined. After six days of exposure at 15-30microg of dinoseb/g dry soil, the weight, lipid, and protein content of the exposed organisms were higher than the controls. This stimulation seems to indicate that Collembola adopt a strategy of increasing their growth in order to improve their reproduction. This hypothesis was confirmed by the number of eggs laid which was greater in exposed organisms. After 21 days, all measured parameters decreased. The results show that after having produced an effort to increase growth and reproduction, lethality increases. The selected energy reserves are not more sensitive than the classically measured parameters such as reproduction, but can be more predictive for a pollutant stress encountered by the organisms.

Effects of dimethoate on spiders from metal pollution gradient

In this study, an attempt has been made to assess whether a chronic exposure to metals in habitats under a strong industrial pressure might have equipped spiders with biochemical defensive mechanisms enabling them to survive an additional chemical stress. To check this, non-web-building wolf spiders Pardosa lugubris (Lycosidae) and funnel web Agelena labyrinthica (Agelenidae) were collected at five variously polluted meadows and, under laboratory conditions, intoxicated with either single or multiple dose of dimethoate (OP pesticide). Then the activities of detoxifying (carboxylesterase: CarE, glutathione S-transferase: GST), antioxidative (selene-dependent and selene-independent glutathione peroxidases: GPOX and GSTPx) enzymes as well as acetylcholinesterase as a biomarker of exposure to OP pesticides were measured. In web-building A. labyrinthica, even a single application of the pesticide caused the inhibition of CarE, GSTPx and GPOX in individuals from less polluted sites and AChE and GST in specimens pre-exposed to high metal concentrations. Multiple intoxication, irrespectively of the site, caused significant, in comparison to controls, decrease in CarE, AChE and GSTPx activities. Actively hunting P. lugubris seem more resistant to acute pesticide intoxication, since the spiders from each site had a constant level of GST and AChE. In individuals of this species from heavily polluted sites, the inhibition caused by multiple intoxication with dimethoate was stated only for glutathione peroxidases.

Apoptosis and biochemical biomarkers of stress in spiders from industrially polluted areas exposed to high temperature and dimethoate

The aim of this study was to evaluate the relations between apoptosis and the activity of antioxidant enzymes (superoxide dismutase; catalase) and quantitative changes in stress protein positive cells (Hsp70; metallothionein) in midgut glands of funnel web spiders Agelena labyrinthica (Agelenidae) and wolf spiders Pardosa lugubris (Lycosidae) exposed to high temperature and pesticide under laboratory conditions. The spiders were collected from two meadow ecosystems differently polluted with metals (Olkusz and Pilica, southern Poland). Under stress conditions, P. lugubris had fewer apoptotic cells in the midgut glands than A. labyrinthica. In P. lugubris from both sites, the observed increase in the percentage of metallothionein and Hsp70-positive cells, simultaneous with intensification of superoxide dismutase and catalase activity, suggests an anti-apoptotic function of those proteins in representatives of wandering spiders. In the midgut glands of A. labyrinthica, heat shock and dimethoate increased the number of Annexin V-positive cells as well as the amounts of mitochondria with low transmembrane potential (DeltaPsi(m)) versus the control. The changes in the percentage of MT- and Hsp70-positive cells in funnel web spiders were less than in wolf spiders. The absence of change in SOD and CAT activity in A. labyrinthica shows that the participation of those enzymes in antioxidant reactions is minimal in this species.

Energy reserves and metal-storage granules in the hepatopancreas of Oniscus asellus and Porcellio scaber (Isopoda) from a metal gradient at Avonmouth, UK

Isopods taken from populations of Onsicus asellus and Porcellio scaber from long-term polluted sites in the vicinity of metal smelting works at Avonmouth, South West England, and from a control site near Tübingen, South Germany, were examined for the frequency and size of metal-containing granules (spherites), lipid droplets and glycogen in their hepatopancreas. The number and size of spherites in the hepatopancreas of O. asellus increased with decreasing distance to the smelter, but such a trend was not found in P. scaber. A trend towards massive reduction in hepatopancreatic energy reserves (lipid, glycogen) with increasing soil metal pollution was observed for O. asellus while, in contrast, the lipid and glycogen content of P. scaber midgut gland cells was independent of the distance to the smelter. In view of previous reports on metal accumulation and biochemical responses to metal pollution, we propose that the two investigated isopod species, which form stable populations in the Avonmouth metal gradient, use different strategies to survive.

Risk assessment of heavy metal pollution for detritivores in floodplain soils in the Biesbosch, The Netherlands, taking bioavailability into account

Floodplains of the European rivers Rhine and Meuse are heavily polluted. We investigated the risk of heavy metal pollution (Cd, Cu, Pb, Zn) for detritivores living in a floodplain area, the Biesbosch, the Netherlands, affected by these rivers. Total soil, pore water and 0.01 M CaCl(2) extractable concentrations and concentrations in plant leaves, earthworms, isopods and millipedes were measured in two sites and compared with literature data to assess possible risks. Based on total metal concentrations in soil, serious effects on detritivores were expected. However, 0.01 M CaCl(2) extractable, pore water and plant leaf concentrations were similar to metal concentrations found in unpolluted areas. Concentrations of Cu and Cd in earthworms and Cu in millipedes were higher in the Biesbosch than in animals from reference areas. All other measured concentrations of heavy metals in earthworms, isopods and millipedes were similar to the ones found in reference areas. Despite high total soil concentrations, effects of Zn, Cu, Pb and Cd pollution on isopods are therefore not expected, while millipedes may only be affected by Cu. Since Cu and Cd levels in earthworms were increased compared to animals in unpolluted soils, this faunal group seems to be most at risk. Given the engineering role of earthworms in ecosystems, effects on the ecological functioning of floodplain soils therefore cannot be excluded.

The effects of heavy metal contamination on the soil arthropod community of a shooting range

Soils in clay pigeon shooting ranges can be seriously contaminated by heavy metals. The pellets contained in ammunition are composed of Pb, Sb, Ni, Zn, Mn and Cu. The total concentrations of these metals in soils, and the effects of their increasing levels on the arthropod community were investigated at seven sampling sites in a clay pigeon shooting range and compared with two controls. Research revealed that the spatial distribution of Pb and Sb contamination in the shot-fall area was strongly correlated with the flight path of the pellets. Ordination obtained through Redundance Analysis showed that Collembola, Protura and Diplura were positively correlated with major detected contaminants (Pb, Sb), while Symphyla showed a negative correlation with these pollutants. Determination of the soluble lead fraction in soil, and of its bioaccumulation in the saprophagous Armadillidium sordidum (Isopoda) and the predator Ocypus olens (Coleoptera), showed that a significant portion of metallic Pb from spent pellets is bioavailable in the soil and can be bioaccumulated by edaphic organisms, entering the soil trophic network, but without biomagnification.

Lead and cadmium in soil and Isopoda woodlice in Croatia

The aim of the study was to determine lead and cadmium concentrations in Isopoda woodlice and soil and to estimate their relation in the environment and the possibility of the use of isopods as biological indicators of pollution. Samples of isopods and soil were collected at two locations in Northern Croatia and analyzed for lead and cadmium. One location was in the forest, and another in the meadow near the road. Isopods were dry- ashed and soil was extracted with nitric acid. Elements were analyzed by atomic absorption spectrometry. Results revealed that the two locations were significantly different in lead and cadmium in extracted soil and isopods. Lead concentration in extracted soil was 34.6 mg/kg dry weight in the forest and 43.3 mg/kg dry weight in the meadow near the road. Respective cadmium values were 0.147 and 0.180 mg/kg. Lead concentrations in isopods were 2.40 and 4.22 mg/kg dry weights, and cadmium 0.757 and 0.411 mg/kg dry weight, respectively. Correlation of lead or cadmium between isopods and soil irrespective of location gave significant and linear relations for both elements.

Lead reduces shell mass in juvenile garden snails (Helix aspersa)

In an earlier paper examining inherited tolerance to Pb, the shell growth of laboratory-bred offspring of Helix aspersa from contaminated sites was compared with that ofjuveniles from naive populations on dosed and undosed diets. Eight-week-old snails were fed either 500 microg g(-1) Pb or a control food in competitive trials between two populations. In the first series of trials, a parental history of exposure to Pb did not confer any advantage to either of two populations (BI and MI) competing with a naïve population (LE). whether Pb was present in the diet or not. However, in the analysis of their metal concentrations reported here, LE are found to retain higher levels of Pb in the soft tissues than either BI or MI. Compared to their siblings on the unleaded diet, dosed LE and BI juveniles had lower soft tissue concentrations of Ca and Mg. Although the growth in shell height is unaffected by diet, LE and BI juveniles build lighter shells on the Pb-dosed diet, achieving around 75% of the shell mass of their controls. In contrast, the shell weights of dosed MI juveniles are depressed by only 15% and show no change in the essential metal concentrations of their soft tissues. A second experiment using five populations fed only the dosed food show that the shell weight/soft tissue weight ratios are comparable to the dosed snails of the previous experiment. Building a lighter shell thus appears to be the common response of all Helix populations to a high Pb diet, at least amongst juveniles. The reduction in its mass means that less Ca and Mg is added to the shell and, along with the lowered soft tissue concentrations observed in some populations. may be a consequence of an increased effort to excrete Pb. The possibility that the MI population shows a genotypic adaptation. perhaps as some form of modification of its Ca metabolism, is briefly discussed.

Intraspecific competition in populations of Helix aspersa with different histories of exposure to lead

A range of invertebrates have become adapted to certain toxic metals, such that, in the presence of the contaminant, some measure of their performance, typically growth or reproduction, is superior to that of an unexposed population. Under such a toxic stress, a population with a history of exposure might outperform a naïve population in competition for limited resources. This study compared the shell growth of laboratory-bred juveniles from six populations of Helix aspersa with different histories of exposure to Pb. In 10 trials using various combinations of two populations, the snails competed for a limited supply of food that contained either no Pb or 500 micrograms/g-1 Pb, for 98 days. Each trial consisted of 10 juveniles, five from each population and was replicated four times. Nearly all of the food provided was consumed quickly after presentation. The total amount of shell growth within each replicate (the sum of the mean growth of the two populations) was highly consistent between trials so that the total amount of shell built was limited by food availability. The presence of Pb in the diet caused no measurable depression of shell growth and exposure history did not appear to confer any competitive advantage or disadvantage in any of the trials. One population consistently grew faster than its competitors in every trial of which it was a part. Shell growth tended to be greater in smaller juveniles. Snail activity is known to be inhibited at high densities and this may have contributed to the lower incremental growth in individuals kept at the higher densities. The competitive advantage enjoyed by one population may be primarily determined by their activity or perhaps their Ca metabolism.