Biomedical subjects

Jean-Pierre Maelfait

Publications and source records attributed to Jean-Pierre Maelfait.

8 recordsLinked to original sources

PubMed2004

The importance of biological factors affecting trace metal concentration as revealed from accumulation patterns in co-occurring terrestrial invertebrates.

As physicochemical properties of the soil highly influence the bioavailable fraction of a particular trace metal, measured metal body burdens in a particular species are often assumed to be more reliable estimators of the contamination of the biota. To test this we compared the Cd, Cu and Zn content of three spiders (generalist predators) and two amphipods (detritivores), co-occurring in seven tidal marshes along the river Schelde, between each other and with the total metal concentrations and the concentrations of four sequential extractions of the soils. Correlations were significant in only one case and significant site x species interactions for all metals demonstrate that factors affecting metal concentration were species and site specific and not solely determined by site specific characteristics. These results emphasize that site and species specific biological factors might be of the utmost importance in determining the contamination of the biota, at least for higher trophic levels. A hypothetical example clarifies these findings.

Animals↗

PubMed2003

Low propensity for aerial dispersal in specialist spiders from fragmented landscapes.

Aerial dispersal by ballooning is a passive flight, by which wind drag generates an upward lift on a silk thread. It is likely to reflect an aerial lottery, in which the absence of flight direction control is a serious cost for long-distance dispersal in a fragmented landscape. For species occurring in one patchily distributed habitat type, dispersal should evolve in a different way from morphological traits, directly linked to active dispersal. Therefore, we expect that if the risk of landing in an unsuitable habitat is lower than the probability of reaching a suitable habitat, selection should benefit a well-developed ballooning behaviour. We investigated interspecific variation in the ballooning-initiating tiptoe behaviour as it is linked to spider dispersal performance. Our results indeed indicate that ballooning performance is negatively related to habitat specialization in spiders from patchy grey dunes, so habitat specialists are characterized by poorly developed dispersal behaviour. These findings are concordant with recent insights that dispersal is selected as risk spreading in generalists, while it is selected against in specialist species.

Animals↗

PubMed2003

Patch quality and connectivity influence spatial dynamics in a dune wolfspider.

The spatial population dynamics of the wolfspider Pardosa monticola, inhabiting patchily distributed grasslands in the Flemish coastal dunes of Belgium and Northern France were investigated with incidence function models using field survey data from 1998 and 2000. Vegetation height and patch size were related to habitat quality. Mark-recapture experiments revealed maximum cursorial dispersal distances of 280 m for moss dunes and 185 m for higher dune grassland. Higher shrub vegetation appeared to be dispersal barriers. These habitat-dependant cursorial distances and the theoretically estimated ballooning distance were included with patch distances into a connectivity index for both dispersal modes. Forward multiple regression indicated that patch occurrence was influenced by habitat quality and ballooning connectivity. Habitat quality and cursorial connectivity explained patterns in short-term colonisation. Extinction appeared to be stochastic and not related to habitat quality and connectivity. Genetic differentiation and variability was low. The discrepancy between the estimated low dispersal capacity and the indirect estimate of gene flow ( F(ST)) indicates that historical population dynamics and/or historical ballooning dispersal influence the genetic structure in this species.

Animals↗

PubMed2003

Absence of cadmium excretion and high assimilation result in cadmium biomagnification in a wolf spider.

Cd biomagnification in the terrestrial food chain appears to be dependent on the physiological properties of the organisms rather than on their trophic level. Although high Cd body burdens in spiders from the field have been reported many times, experimental verification of the key factors that determine the rate of cadmium accumulation is lacking. We investigated the cadmium assimilation rate in the common wolf spider Pirata piraticus fed with contaminated fruit flies. Spiders were fed for 42 days with contaminated flies, followed by a detoxicification period of 28 days. Every 14 days, a subsample of spiders and flies was taken for Cd determination. It was demonstrated that a high cadmium assimilation (69.5%) and an excretion rate approaching zero resulted in high Cd concentration factors. The results indicate the importance of spiders in cadmium biomagnification along critical pathways.

Animals↗

PubMed2003

Storage mediums affect metal concentration in woodlice (Isopoda).

Terrestrial invertebrates are becoming widely established as tools to assess heavy metal pollution at contaminated sites. A practical and time saving method to sample terrestrial invertebrates consist of pitfall traps, often filled with a 4% formaldehyde solution and some detergent. The reliability of metal concentrations based on organisms captured and stored in this solution might however be questioned and we therefore tested the effect of formaldehyde on Zn, Cu, Cd and Pb concentration experimentally in three isopod species. Our results showed that in many cases, significant decreases in Cu concentrations compared to animals stored in a freezer were observed that could be as high as 40%, while Zn, Cd and Pb concentrations increased. A regression analysis of individual dry weight on individual size revealed that formaldehyde decreases the dry weight substantially and in that way causes increased measurements of Zn, Cd and Pb concentrations. We conclude that pitfall traps with formaldehyde should better not be used to collect animals in which concentrations of heavy metals or other toxic substances will be determined.

Animals↗

PubMed2003

Contrasting allozyme and RAPD variation in spider populations from patchy forest habitats.

During the last 1000 years, massive deforestation events have occurred in Flanders (the northern part of Belgium) and the remaining forests have become very isolated patches. It is expected that organisms bound to these patchy forest habitats and with limited dispersal capacities will likely experience strong effects of genetic drift. One such organism is the spider Coelotes terrestris. Allozyme data suggested that 10 Flemish populations of this spider showed little genetic variation, as only one out of 20 loci was polymorphic (phosphoglucose isomerase). In view of this result, we used random amplified polymorphic DNA (RAPD) markers to test whether this lack of allozyme diversity is an inherent feature of the populations and/or species studied or whether it rather reflects a characteristic of the markers and/or methods used. Since the RAPD data revealed a substantial amount of genetic diversity in the same 10 populations, our results suggest that the latter is true. Furthermore, the RAPD data agree with the expectations for an organism with low dispersal capacities that has lived in isolated forest patches for at least 200 generations. Supplemented with the results of other techniques and studies, these findings might be of importance for the future conservation of this spider species in Flanders.

Animals↗

PubMed2002

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.

Adaptation, Physiological↗

PubMed2002

Heavy metal concentrations in the spiders Pirata piraticus (Clerck, 1757) and Clubiona phragmitis (C.L. Koch, 1843) along the Scheldt Estuary (Belgium).

Wetland ecosystems may be affected by deposition and accumulation of heavy metals. Metal concentrations in the spiders Pirata piraticus and Clubiona phragmitis living in marshes along the river Scheldt (Flanders, Belgium) were analyzed. The organisms were sampled on seven sites along a gradient from freshwater to brackish marshes. Except for lead, P. piraticus contained higher metal concentrations than C. phragmitis. This is related to physiological and ecological differences between species. No correlation was found between metal concentration in the organisms and soil total concentration.

Animals↗