Search publications of the members of the Royal Belgian institute of natural Sciences
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A new scincomorph lizard from the Paleocene of Belgium and the origin of the Scincoidea in Europe
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Dental and tarsal morphology of the European Paleocene/Eocene "condylarth" mammal Microhyus
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Early Eocene (Ypresian) continental vertebrate assemblage from India, with description of a new anthracobunid (Mammalia, Tethytheria)
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Asian gliriform origin for arctostilopid mammals
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Rapid Asia–Europe–North America geographic dispersal of earliest Eocene primate Teilhardina during the Paleocene–Eocene Thermal Maximum
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The acme of the micromammal Paschatherium across the Paleocene-Eocene boundary in continental Europe
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Woodland in a f luvio-lacustrine environment on the dry Mongolian Plateau during the late Paleocene: Evidence from the mammal bearing Subeng section (Inner Mongolia, P.R. China)
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Paleocene-Eocene land mammals from three new latest Clarkforkian and earliest Wasatchian wash sites at Polecat Bench in the Northern Basin, Wyoming
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Temporal constraints and depositional palaeoenvironments of the Vastan Lignite Sequence, Gujarat: Analogy for the Cambay shale hydrocarbon source rock
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High-resolution carbon isotope stratigraphy and mammalian faunal change at the Paleocene-Eocene boundary in the Honeycombs area of the Southern Bighorn Basin, Wyoming.
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Oldest fossil avian remains from the Indian subcontinental plate
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A first analysis on the relationship between forest soil quality and spider (Araneae) communities of Flemish forest stands
- A project aiming at the development of a practical bio-indication system for evaluating forest soil duality was recently started up. The project is funded by the Flemish Forestry Administration responsible for the protected Flemish forests and is managed by the Institute for Forestry and Game Management (IBW). In the project the arthropod fauna of fifty forest stands distributed all over the Flemish Region was sampled by traps operative from spring 1997 till spring 1998. All these plots were also investigated in relation to the physical and chemical properties of their soil and litter layers. The variation of the composition of the spider communities of these stands is unclear when we compare it with the most important litter and soil parameters, but future investigations with more (structural) parameters will hopefully give a good explanation. On a subregional scale, in forests on the same soil type (loam), spider community composition seems to be determined by humidity and density of tree coverage. Spider species for which abundance correlates with these major environmental factors are candidate bio-indicators to monitor forest soil quality.
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A land snail's view of a fragmented landscape
- Habitat fragmentation may influence the genetic structure of populations, especially of species with low mobility. So far, these effects have been mainly studied by surveying neutral markers, and much less by looking at ecologically relevant characters. Therefore, we aimed to explore eventual patterns of covariation between population structuring in neutral markers and variation in shell morphometrics in the forest-associated snail Discus rotundatus in relation to habitat fragment characteristics. To this end, we screened shell morphometric variability and sequence variation in a fragment of the mitochondrial 16S rDNA gene in D. rotundatus from the fragmented landscape of the Lower Rhine Embayment, Germany. The 16S rDNA of D. rotundatus was highly variable, with a total of 118 haplotypes (384 individuals) forming four clades and one unresolved group. There was a geographic pattern in the distribution of the clades with the river Rhine apparently separating two groups. Yet, at the geographic scale considered, there was no obvious effect of fragmentation on shell morphometrics and 16S rDNA variation because G(ST) often was as high within, as between forests. Instead, the age of the habitat and (re-)afforestation events appeared to affect shell shape and 16S rDNA in terms of the number of clades per site. The ecologically relevant characters thus supported the presumably neutral mitochondrial DNA markers by indicating that populations of not strictly stenecious species may be (relatively) stable in fragments. However, afforestation after large clearcuts and habitat gain after the amendment of deforestation are accompanied by several, seemingly persistent peculiarities, such as altered genetic composition and shell characters (e.g. aperture size). (C) 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 98, 839-850.
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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. (C) 2003 Elsevier Science (USA). All rights reserved.
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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.
