Search publications of the members of the Royal Belgian institute of natural Sciences
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Adaptive reproductive variation along a pollution gradient in a wolf spider
- When populations are exposed to environmental pollutants, growth and reproduction might be strongly reduced due to an increased detoxification effort. Sublethal metal pollution is therefore to be expected to cause the same selection pressure as a low resource habitat and might alter the reproductive strategy. Optimality models of life history theory predict that when resource availability is reduced, growth and reproductive output are reduced and that the release of fewer but larger propagules will be favoured. This was tested by applying a life history model to reproductive trait measurements in six populations of the wolf spider Pirata piraticus in which the assumptions of the model are satisfied. Internal Cd, Cu and Zn body burden were strongly correlated with each other, and differed strongly between the populations, indicating consistently differing metal exposure at the different sites. Pb levels were extremely variable within each population and did not differ between the populations. Females from populations with high concentrations of the first three heavy metals showed a strongly reduced reproductive output and fecundity, indicating a high reduction in resource availability due to detoxification processes. Egg size in contrast was negatively correlated with fecundity and reproductive output and as a consequence positively related with internal metal burden. Our results are thus in strong agreement with the predictions of the optimality models and confirm the benefits of a larger propagule size when resource availability is reduced.
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Allozyme characterization of Hogna species (Araneae, Lycosidae) of the Galapagos Archipelago
- The colonization of species on remote islands may result in phenotypic diversification and ultimately speciation. On the Galapagos Archipelago. seven very closely related morpho-species of the wolf spiders genus Hogna are distinguishable based on small somatic and genital differences. Based on habitat preference, these species can broadly be categorized into (i) "high elevation species" occurring on the volcanic highlands, (ii) three "coastal dry" species occurring in dune habitats along the coast, and (iii) one generalist species which is chiefly found in wet coastal habitats such as salt marshes but also in wet habitats at higher altitudes. To determine the degree of reproductive isolation among these morpho-species. we investigated gene flow among populations and species based on nine allozyme loci. Genetic analysis by means of genetic distance estimates and cluster agglomerative analyses confirmed the status of the defined morpho-species. Allele frequencies were highly similar among populations within a species but differed profoundly among species. Genetic differentiation within the generalist species was generally very low. There were no constant differences between high elevation and coastal populations for this species. Neutral genetic divergence between species appeared to correspond more to geographic distribution rather than to a clear separation of the two different ecological groups within an island. This suggests that a parallel parapatric divergence between high elevation and coastal dry species may have taken place on the oldest islands of San Cristobal and Santa Cruz.
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Anthelmintic tolerance in free-living and facultative parasitic isolates of Halicephalobus (Panagrolaimidae)
- Studies on anthelmintic resistance in equine parasites do not include facultative parasites. Halicephalobus gingivalis is a free-living bacterivorous nematode and a known facultative parasite of horses with a strong indication of some form of tolerance to common anthelmintic drugs. This research presents the results of an in vitro study on the anthelmintic tolerance of several isolates of Halicephalobus to thiabendazole and ivermectin using an adaptation of the Micro-Agar Larval Development Test hereby focusing on egg hatching and larval development. Panagrellus redivivus and Panagrolaimus superbus were included as a positive control. The results generally show that the anthelmintic tolerance of Halicephalobus to both thiabendazole and ivermectin was considerably higher than that of the closely related Panagrolaimidae and, compared to other studies, than that of obligatory equine parasites. Our results further reveal a remarkable trend of increasing tolerance from fully free-living isolates towards horse-associated isolates. In vitro anthelmintic testing with free-living and facultative parasitic nematodes offers the advantage of observing drug effect on the complete life cycle as opposed to obligatory parasites that can only be followed until the third larval stage. We therefore propose Halicephalobus gingivalis as an experimental tool to deepen our understanding of the biology of anthelmintic tolerance.
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Assemblage structure and conservation value of spiders and carabid beetles from restored lowland river banks
- We assessed the composition of spider and carabid beetle assemblages along river banks from the Common Meuse (Belgium) to determine their relationships with local topographical and landscape-related characteristics. Data were gathered with pitfall traps in 1998 and explored by ordination and grouping methods. Our analysis revealed that the presence of xerothermic spider species was limited to scarcely covered, less dynamic gravel banks. Riparian spider species were found on frequently flooded as well as on rather elevated and high gravel banks, while riparian carabid beetles were dominant on all sampled banks. The level of flooding disturbance, the vegetation density and the presence of silt appeared to be the most important environmental determinants of spider and carabid beetle assemblage structure. Consequently, local environmental factors influence species occurrence patterns in a similar way for the two investigated arthropod groups. Nevertheless, distinct ecological groups are differently ordered along the prime environmental gradients. Nature management should therefore consider the conservation, restoration and connectivity of both dynamic and more elevated banks in order to obtain a high degree of local and regional heterogeneity throughout the river system.
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Can multiple mating compensate for slower development and shorter adult life in a male dimorphic dwarf spider?
- Oedothorax gibbosus (Blackwall, 1841) is a dwarf spider characterized by the occurrence of a male dimorphism: the tuberosus male does not show any remarkable differentiation at the dorsal side of the carapace; the gibbosus morph on the contrary has a hunch behind the eye region, with a transversal groove densely clothed with hairs. These structures play an important function in the gustatorial courtship, being the uptake of secretions by the female from a body part of the male during courtship. Based on standardized survival experiments we show that tuberosus has a greater overall survival strength for different humidity levels than gibbosus. The two male morphs of O. gibbosus also have a different mating strategy: tuberosus as well as gibbosus copulate with virgin females, but gibbosus copulates significantly more with already inseminated females. Because of this strategy gibbosus secures its offspring notwithstanding the faster development, the longer adult life and the greater overall survival strength of tuberosus. (C) 2004 The Linnean Society of London
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Changes in the distribution area of vascular plants in Flanders (northern Belgium): eutrophication as a major driving force
- In large parts of Western Europe agricultural intensification after World War II has led to an increased use of fertilisers. The resulting nutrient enrichment (=eutrophication) has a huge impact on the occurrence and distribution of plant species and is one of the main pressures on native plant communities. We used the distribution maps (grid size: 16 km(2)) of individual plant species, obtained through two consecutive survey projects (1939-1971 and 1972-2004) in Flanders (northern Belgium), to estimate the relative change in their distribution area. The comparison of changes in range size among groups of taxa classified according to habitat preference and Ellenberg indicator values, demonstrated a marked decline in distribution area in species that are characteristic for nutrient-poor habitats. To assess geographic patterns in the change of species assemblages, we calculated the mean Ellenberg N- and R-values for every grid cell during each of both survey periods. Differences between these values were analysed in relation to soil type and estimates of atmospheric nitrogen deposition. The largest shifts in Ellenberg N-values, reflecting a decline of species from nutrient-poor conditions and/or an increase of nitrophilous plants, were observed in areas with nutrient-poor, acid sandy soils and high nitrogen deposition rates. Hence, shifts in species composition were modulated by geographic variation in soil type and levels of nitrogen deposition. As the levels of atmospheric nitrogen deposition are still very high in Flanders, it is likely that species from nutrient-poor habitats such as heathlands, will further decline in the near future.
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Complementarity effects drive positive diversity effects on biomass production in experimental benthic diatom biofilms
- P1. Positive effects of species diversity on ecosystem functioning have often been demonstrated in 'macrobial' communities. This relation and the responsible mechanisms are far less clear for microbial communities. Most experimental studies on microorganisms have used randomly assembled communities that do not resemble natural communities. It is therefore difficult to predict the consequences of realistic, non-random diversity loss. 2. In this study, we used naturally co-occurring diatom species from intertidal mudflats to assemble communities with realistically decreasing diversity and analysed the effect of non-random species loss on biomass production. 3. Our results demonstrate a highly positive biodiversity effect on production, with mixtures outperforming the most productive component species in more than half of the combinations. These strong positive diversity effects could largely be attributed to positive complementarity effects (including both niche complementarity and facilitation), despite the occurrence of negative selection effects which partly counteracted the positive complementarity effects at higher diversities. 4. Facilitative interactions were, at least in part, responsible for the higher biomass production. For one of the species, Cylindrotheca closterium, we show its ability to significantly increase its biomass production in response to substances leaked into the culture medium by other diatom species. In these conditions, the species drastically reduced its pigment concentration, which is typical for mixotrophic growth. 5. Synthesis. We show that both species richness and identity have strong effects on the biomass production of benthic diatom biofilms and that transgressive overyielding is common in these communities. In addition, we show mechanistic evidence for facilitation which is partly responsible for enhanced production. Understanding the mechanisms by which diversity enhances the performance of ecosystems is crucial for predicting the consequences of species loss for ecosystem functioning.
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Condition-dependent mate choice and its implications for population differentiation in the wolf spider Pirata piraticus
- When populations face different environmental conditions, both local adaptation and phenotypic plasticity may cause interpopulation divergence of behavioral or phenotypic properties on which mate choice is based. If sustained, this may result in genetic differentiation even in the presence of extant gene flow. Condition dependence of mate choice is one of the main mechanisms explaining these environmental effects. We tested whether experimental food stress affects mate choice in male and female Pirata piraticus spiders from one heavily polluted and one unpolluted reference population. Compared with control females, food-stressed females from the reference population showed a decreased probability of copulation and preferred smaller mates. Females from the polluted population, in contrast, did not show a significant response to food stress and showed size-assortative mating, most strongly under food stress. We explain these results in 2 complementary ways. First, spiders from populations that are not adapted to cope with stress may be less willing to mate when eggs are not fully matured. Second, food-deprived females may show a larger responsiveness toward smaller males because the latter resemble prey more and hungry females tend to attack moving objects more often. Results from this study support the prediction that variation in body condition, driven by local ecological factors, may affect mating behavior and may ultimately lead to population divergence in important life-history traits such as body size.
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De novo Transcriptome Assembly and SNP Discovery in the Wing Polymorphic Salt Marsh Beetle Pogonus chalceus (Coleoptera, Carabidae)
- Background: The salt marsh beetle Pogonus chalceus represents a unique opportunity to understand and study the origin and evolution of dispersal polymorphisms as remarkable inter-population divergence in dispersal related traits (e. g. wing development, body size and metabolism) has been shown to persist in face of strong homogenizing gene flow. Sequencing and assembling the transcriptome of P. chalceus is a first step in developing large scale genetic information that will allow us to further study the recurrent phenotypic evolution in dispersal traits in these natural populations. Methodology/Results: We used the Illumina HiSeq2000 to sequence 37 Gbases of the transcriptome and performed de novo transcriptome assembly with the Trinity short read assembler. This resulted in 65,766 contigs, clustering into 39,393 unique transcripts (unigenes). A subset of 12,987 show similarity (BLAST) to known proteins in the NCBI database and 7,589 are assigned Gene Ontology (GO). Using homology searches we identified all reported genes involved in wing development, juvenile- and ecdysteroid hormone pathways in Tribolium castaneum. About half (56.7\%) of the unique assembled genes are shared among three life stages (third-instar larva, pupa, and imago). We identified 38,141 single nucleotide polymorphisms (SNPs) in these unigenes. Of these SNPs, 26,823 (70.3\%) were found in a predicted open reading frame (ORF) and 6,998 (18.3\%) were nonsynonymous. Conclusions: The assembled transcriptome and SNP data are essential genomic resources for further study of the developmental pathways, genetic mechanisms and metabolic consequences of adaptive divergence in dispersal power in natural populations.
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Determination of Cd, Cu, Pb and Zn in woodlouse (Oniscus asellus)
- The aim of this study was to assess the performance of selected destruction methods for the determination of heavy metals (Cd, Cu, Pb and Zn) in woodlouse (Oniscus asellus). A vigorous total analysis involving microwave destruction with HE HCl and HNO3 (method 1) was used as a reference method. Consistently low values for the dry ashing method may indicate incomplete dissolution of the elements and/or losses through volatilisation. Method 3 (concentrated HNO3) that frequently is used in literature, produced erroneous values for Cd, Cu and Pb. Results were consistent with the microwave digestion, provided H2O2 was used during digestion (method 4, HNO3/H2O2). Method 5 (HNO3/HClO4, one destruction step) yielded low recoveries when only one destruction step was applied. Applying two destruction steps (method 6) resulted in values consistent with the microwave method, but was at the expense of reproducibility and rendered the method more lengthy and laborious. Because of the very good performance combined with speed and simplicity, destruction with HNO3/H2O2 (method 4) emerged as the most convenient method.
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Differences in geographic distribution and habitat of some cryptic species in the Pardosa lugubris group (Lycosidae, Araneae) in Belgium
- The habitat and distribution of some closely related species of the P. lugubris s.l. group in Belgium are described to contribute to our understanding of the coexistence and speciation of these 'cryptic' species. With a few exceptions, P. lugubris has its main distribution in the lower part of Belgium where it occurs on sandy, nutrient poor soils. P. saltans occurs widely in Belgium except for in the Campine region where the species is totally absent. P. alacris was only found at three localities where limestone outcrops are present. The habitat of P. lugubris is pine and birch forests while in Fagus woodlands, only P. saltans was found. In Quercus forests, both species were found, often in mixed populations. A combination of micro- and macroclimatological features and habitat characteristics cause the differences in distribution of these species.
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Differentiation between two salt marsh beetle ecotypes: Evidence for ongoing speciation
- The plausibility of trait divergence under divergent natural selection in the presence of gene flow in natural populations is a contentious issue in evolutionary research. Its importance lies in the fact that this process is thought to be one of the key triggers in ecological speciation in which a species splits into ecologically distinct forms when separate niches are occupied. in this study we demonstrate strong genetic divergence at the IDH1 locus between pond- and canal-inhabiting individuals of the salt marsh beetle Pogonus chalceus from the Guerande salt fields. Moreover, wing size, a trait that has a heritable basis in this species, was significantly larger in the pond populations, which is in concordance with the unstable nature of this habitat. The relationship between IDH1 allele frequencies and wing size variation was consistent with patterns seen across western European populations. By means of neutral allozymes and microsatellites we detected a small but significant degree of sexual isolation between ecotypes. We conclude that speciation is ongoing and that divergence reflects a balance between selection and gene flow.
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Direct and indirect effects of metal stress on physiology and life history variation in field populations of a lycosid spider
- 1. Under stress, life history theory predicts reduced growth rates and adult sizes, reduced reproductive allocation, production of larger offspring and postponed reproduction. Both direct and indirect effects of metals can explain these trends, mainly linked to energetic constraints. Metallothionein-like proteins (MTLP's) are believed to be an important defense mechanism against the adverse effects of metals and other stressors. 2. We tested these predictions comparing six field populations of the wolf spider Pardosa saltans, three of which were on sites that are historically polluted with heavy metals. 3. As expected for life histories evolving under energetic constraints, adult size and condition correlated negatively and egg mass positively with Cd concentrations for a subset of four populations. In the population that showed the highest cadmium and zinc body burdens, reproductive output and allocation were lowest and reproduction was postponed. 4. Contrary to our expectation, for all six study populations MTLP concentrations did not increase in exposed populations, indicating that this defense mechanism cannot explain the observed variation in life histories. 5. We conclude that indirect and synergistic effects of metal pollution may be more important than physiological defense mechanisms in shaping life history traits in field populations. (C) 2011 Elsevier Inc. All rights reserved.
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Does behavioural isolation prevent interspecific mating within a parallel ecotypic wolf spider radiation from the Galapagos?
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Dwarf spiders (Erigoninae, Linyphiidae, Araneae): good candidates for evolutionary research
- Males of numerous erigonine dwarf spider species, including those in the genera Oedothorax and Diplocephalus, are characterised by elaborate structures on the head region. Three evolutionary hypotheses for these head structures are : lock-and-key (reproductive isolation) hypothesis, "conflict of interest hypothesis" and diverse sexual selection hypotheses. Oedothorax gibbosus (Blackwall, 184 1) is a dwarf spider characterised by male dimorphism; the gibbosus morph has a hunch on the last third of the carapace, anterior to which is a hairy groove; the tuberosus morph does not have these features. During the so-called gustatorial courtship the female inserts her chelicerae into the hairy groove of gibbosus. Species recognition experiments reveal the occurrence of interspecific homo- and heterosexual "gustatorial courtships" of the female as well as the male of the closely related species Oedothorax fuscus (Blackwall, 1834) towards the gibbosus male. These interspecific courtships can be interpreted as robbery of the nuptial gift located in the groove and the hunch of the gibbosus males. Gibbosus males can also rob the nuptial gift of each other, but this occurs only rarely. We have never observed a 'gustatorial robbery' between a tuberosus male and a gibbosus male. There are also interspecific interactions between a tuberosus male and an O. fuscus female suggesting poorly developed reproductive isolation between these sister species. These interspecific courtships are in disagreement with the lock-and-key hypothesis. Indeed, according to this hypothesis the head structures of erigonine males should function as an early prevention of hybridisation. Female chelicerae and male head structures thus do not operate as key and lock. Therefore, the head structures might have evolved under the influence of sexual selection.
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Effect of metal stress on life history divergence and quantitative genetic architecture in a wolf spider
- Effects and consequences of stress exposure on life history strategies and quantitative genetic variation in wild populations remain poorly understood. We here study whether long-term exposure to heavy metal pollution may result in alternative life history strategies and alter quantitative genetic properties in natural populations of the wolf spider Pirata piraticus. Offspring originating from a reference and a metal contaminated population and their reciprocal hybrid cross were bred in a half-sib mating scheme and subsequently reared in cadmium contaminated vs. clean environment. Results from this experiment provided evidence for a genetically based reduced growth rate and increased egg size in the contaminated population. Growth rate reduction in response to cadmium contamination was only observed for the reference population. Animal model analysis revealed that heritability for growth rate was large for the reference population under reference conditions, but much lower under metal stressed conditions, caused by a strong decrease in additive genetic variance. Heritability for growth of the metal contaminated population was very low, even under reference conditions. Initial size of the offspring was primarily determined by maternal effects, whereas egg size produced by the offspring was determined by both sire and dam effects, indicating that egg size determination is under control of the female genotype. In conclusion, these results show that metal stress can not only affect life history variation in natural populations, but also decreases the expression as well as the of the amount of genetic variation for particular life history traits.
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Effects of landscape structure and land-use intensity on similarity of plant and animal communities
- Aim Species richness in itself is not always sufficient to evaluate land management strategies for nature conservation. The exchange of species between local communities may be affected by landscape structure and land-use intensity. Thus, species turnover, and its inverse, community similarity, may be useful measures of landscape integrity from a diversity perspective. Location A European transect from France to Estonia. Methods We measured the similarity of plant, bird, wild bee, true bug, carabid beetle, hoverfly and spider communities sampled along gradients in landscape composition (e.g. total availability of semi-natural habitat), landscape configuration (e.g. fragmentation) and land-use intensity (e.g. pesticide loads). Results Total availability of semi-natural habitats had little effect on community similarity, except for bird communities, which were more homogeneous in more natural landscapes. Bee communities, in contrast, were less similar in landscapes with higher percentages of semi-natural habitats. Increased landscape fragmentation decreased similarity of true bug communities, while plant communities showed a nonlinear, U-shaped response. More intense land use, specifically increased pesticide burden, led to a homogenization of bee, bug and spider communities within sites. In these cases, habitat fragmentation interacted with pesticide load. Hoverfly and carabid beetle community similarity was differentially affected by higher pesticide levels: for carabid beetles similarity decreased, while for hoverflies we observed a U-shaped relationship. Main conclusions Our study demonstrates the effects of landscape composition, configuration and land-use intensity on the similarity of communities. It indicates reduced exchange of species between communities in landscapes dominated by agricultural activities. Taxonomic groups differed in their responses to environmental drivers and using but one group as an indicator for 'biodiversity' as such would thus not be advisable.
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Effects of sublethal abiotic stressors on population growth and genetic diversity of Pellioditis marina (Nematoda) from the Westerschelde estuary
- Understanding the effects of anthropogenic pollutants at the ecosystem level requires a proper understanding of the toxicological effects at the population level. Species living in estuaries resist highly fluctuating conditions, and are often exposed to sublethal concentrations of pollutants coming from industrial and domestic wastes. In the Westerschelde estuary, the most upstream sampled population of the nematode Pellioditis marina is genetically less diverse than elsewhere. It experiences lower salinities and higher Cd concentrations than more downstream populations in the estuary. In the present study, we investigate whether these environmental conditions may explain the lower genetic diversity in the most upstream location. To this end we followed the development of genetically diverse P marina populations under experimental conditions during 14 days. Genetic diversity was assessed in the F1, F2 and F5 generation by screening mitochondrial cytochrome oxidase c subunit 1 variation with the single-strand conformation polymorphism method (SSCP) and nucleotide sequencing. Our results show that sublethal Cd concentrations reduce population development of P. marina at suboptimal salinities, and that low salinity conditions induce responses at the genetic level. Nevertheless, the genetic effects were not persistent over generations, which emphasize the need for longer multigenerational experiments. (c) 2007 Elsevier B.V. All rights reserved.
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Experimental beam-trawling in Lanice conchilega reefs: Impact on the associated fauna
- To study fisheries impact at the species level in temperate sandy bottom areas, a controlled field manipulation experiment was designed focusing on areas with high densities of the habitat-structuring, tube-dwelling polychaete Lanice conchilega (i.e. L. conchilega reefs). The hypothesis was that the impact on L. conchilega would be minimal, but that the fauna benefiting from the biogenically structured habitat would be impacted by beam-trawling. In this study, the impact of beam-trawl passage on intertidal L. conchilega reefs and its associated fauna was quantified. A treatment zone was exposed to a one-off experimental trawling. Subsequently, the impact on and recovery of the associated fauna was investigated for a period of 9 days post-impact. Community analysis showed a clear impact followed by a relatively quick recovery as apparent through MDS analysis (stress 0.06), a significant (p 0.001) IMS of 0.61, through ANOSIM analysis: significant (p = 0.001) dissimilarities between treatment and control and through SIMPER analysis (decreasing dissimilarities over time). This impact and subsequent recovery was largely explained by two species: Eumida sanguinea and Urothoe poseidonis. Species analysis confirmed the beam-trawl passage significantly (P = 0.001) impacted E. sanguinea for the whole period of the experiment. The experiment confirmed that closely associated species of L. conchilega reefs are impacted by beam-trawl fisheries. This small-scale intertidal study provides some pointers which indicate that the tightly associated species will be impacted significantly when beam-trawling L. conchilega reefs in subtidal areas. (C) 2007 Elsevier B.V. All rights reserved.
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Experimental exposure to cadmium affects metallothionein-like protein levels but not survival and growth in wolf spiders from polluted and reference populations
- Both local adaptation and acclimation in tolerance mechanisms may allow populations to persist under metal pollution. However, both mechanisms are presumed to incur (energetic) costs and to trade-off with other life-history traits. To test this hypothesis, we exposed Pardosa saltans (Lycosidae) spiderlings originating from metal-polluted and unpolluted sites to a controlled cadmium (Cd) treatment, and compared contents of metal-binding metallothionein-like proteins (MTLPs), internal metal concentrations, and individual survival and growth rates with a reference treatment. While increased MTLP concentrations in offspring originating from both polluted and unpolluted populations upon exposure indicates a plastic tolerance mechanism, survival and growth rates remain largely unaffected, independent of the population of origin. However, MTLP and Cd concentrations were not significantly correlated. We suggest that MTLP production may be an important mechanism enabling P. saltans populations to persist in ecosystems polluted with heavy metals above a certain level. (C) 2010 Elsevier Ltd. All rights reserved.
