Search publications of the members of the Royal Belgian institute of natural Sciences
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5de Vlaams-Nederlandse Natuursteendag 15-16.5.2014, Brussel Betekenisvol gebruik van natuursteen - Excursie natuursteen Brussel
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Belgisch Marmer
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Petrografisch onderzoek van natuurstenen in knooppunt Schuman: Yellow Rock en Sunny Yellow
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Allozyme variation in two forest populations of Platynothrus peltifer (Acari, Oribatida)
- Samples of tritonymph individuals of Platynothrus peltifer were collected from two forest populations showing clear ecological and temporal divergences, and subjected to electrophoretic analysis of three enzymes, superoxide-dismutase, malate-dehydrogenase and esterases. Electrophoretic patterns were quite similar in both populations. This suggests that, after more than 40 generations, heterochronic differentiations do not seem to be related to allozyme alterations. Yet, a study of clonal diversity and its temporal modifications in both populations is required to confirm this hypothesis. © 1990.
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Horizontal and vertical distribution of Dolichopodidae (Diptera) in a woodland ecosystem
- Analysis revealed four distinct species groups, which also proved to be clearly different on a broader ecological basis. The horizontal distributions in many species could be explained by different environmental conditions. Although nearly all species were unequally distributed over the traps, their stratification patterns generally showed no significant correlation with recorded biotic and abiotic features. The observed vertical distributions may therefore be results of a combination of specific and environmental characteristics. -from Authors
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Temperature dependence of the Mössbauer parameters of the Fe-Ni phases in the Santa Catharina meteorite
- The temperature variation in the range 8-760K of the hyperfine parameters of the Fe-Ni phases in the Santa Catharina meteorite has been determined. It is suggested that the disordered 50-50 Fe-Ni phase actually consists of two distinct fractions, i.e. a completely disordered phase and one with intermediate long-range ordering parameter. The single-line subspectrum of the 28\%-Ni phase was found to display magnetic ordering below approximately 25K. © 1992 J.C. Baltzer A.G., Scientific Publishing Company.
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Cladistic Analysis of Metazoan Relationships: A Reappraisal
- Abstract-A recently published cladistic analysis of metazoan relationships based on 77 embryological and morphological characters is shown to be defective with respect to both methodological issues and the interpretation of certain characters. Consequently, many conclusions of this analysis are not supported by the data. Alternative phylogenetic hypotheses are therefore proposed, based on a re-evaluation of an adapted data set. © 1993 The Willi Hennig Society.
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Rediscovery of Astenocypris papyracea (Sars, 1903) (Crustacea, Ostracoda) in Kerala, India
- Astenocypris papyracea (Sars, 1903) has been found in paddyfields in Kerala, India. This is the first rediscovery of this enigmatic species since its original description from an unknown locality in Sumatra, almost 90 years ago. Astenocypris (the new name for Leptocypris) is a monospecific genus and, as the original description was incomplete, its exact taxonomic position has long been uncertain. Relying on the present redescription, we can confirm its allocation to the subfamily Cypricercinae, although a number of features hint at a relationship with the Isocypridinae. © 1993 The Linnean Society of London.
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Morphological and ecological characterization of Hercostomus (Hercostomus) plagiatus and a sibling species, H. verbekei sp.n. (Diptera: Dolichopodidae)
- Although two forms of Hercostomus plagiatus are separated in identification keys, both were considered to belong to one single species. My investigations, however, revealed that two distinct species were included. In this respect, H. plagiatus is redescribed, whereas H. verbekei sp.n. is described as new. Both species occur mainly in central and southern Europe; H. plagiatus is more common than its congener at nearly all sites investigated. Aspects of macro- and microhabitat preference, phenology and sex ratios in H. plagiatus are discussed. It is suggested that these two species are closely related. © 1993.
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Microtektite-like impact glass associated with the Frasnian-Famennian boundary mass extinction
- Glass spherules of probable impact origin occur in the Late Devonian Hony section in Belgium. They are found at the stratigraphic level of the Frasnian-Famennian boundary, which is marked by one of the largest mass extinctions in the Phanerozoic. The Hony glass spherules are chemically identical to those previously described from the stratigraphically equivalent Senzeille section located 90 km to the west-southwest. In contrast to the Senzeille layer, the age of the Hony spherule layer is well constrained by conodont biostratigraphy. The spherules have morphological and chemical characteristics similar to tektites and microtektites. They have a broad range of chemical composition with generally high [ K2O Na2O] and [ Al2O3 (Na2O + K2O)]. Their water content is in the range measured for tektites and impact glasses. Small inclusions of lechatelierite may be present in the spherules. These glass spherules are likely to be the product of an impact event that occurred at or very near the Frasnian-Famennian boundary. The target rock was probably a clay-rich pelitic sediment intermixed with carbonates. The 368 ± 1 Ma Siljan Ring crater (Sweden) is the most likely impact-site candidate. The Hony and Senzeille glass spherules represent the first substantial evidence that an impact event may be linked to the Frasnian-Famennian mass extinction. © 1994.
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Mesocyclops thermocyclopoides species-group: redefinition and content
- Within the genus Mesocyclops the thermocyclopoides species-group is defined on the basis of the presence of spiniform armature on the maxillar coxa. Examination of nineteen, mainly Palaeotropical species of Mesocyclops and nine representatives of the closely related genus Thermocyclops revealed, that the coxal part of the maxillar syncoxa of the species recently unified in the thermocyclopoides group is adorned with distinct rows of big spinules on its frontal surface. This character, with only one known exception in South Indian M. cf. papuensis, is absent in other species of Mesocyclops and all the Thermocyclops studied here. These species have no spinules on the maxillar coxa at all or very tiny scattered ones. © 1994 Kluwer Academic Publishers.
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Depth distribution of oligochaetes in Lake Baikal (Siberia - Russia)
- In the course of a preliminary sampling program, oligochaetes were collected along two transects in soft sediments in Lake Baikal. The number of oligochaetes present in the samples was counted, without distinguishing between species. The results suggest an exponential decrease in number of individuals (N) relative to depth (11,165 N m-2 at 21 m, 265 N m-2 at 1200 m). Most oligochaetes were found in the top 7 cm of sediment. The orange colour of the sediments suggests a high oxygen availability, even at the greatest water depths.
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Random amplified polymorphic DNA (RAPD) and parsimony methods
- Random amplified polymorphic DNA (RAPD) data possess a number of undesirable features for parsimony analysis. These features include their non-codominant inheritance, their anonymous nature, their different (a)symmetrical transformation probabilities, and their possible GC priming bias. As a consequence, no single parsimony method seems appropriate for RAPD data. Moreover, the presence/absence coding of RAPDs is equivalent to the invalid independent allele model for allozymes. These issues are discussed and the way in which parsimony analysis of RAPDs can be misleading is illustrated. © 1995.
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A new branchipodid genus and species (Crustacea: Branchiopoda: Anostraca) from South Africa
- Rhinobranchipus martensigen. et sp. nov.(Anostraca: Branchipodidae) was collected from a shallow temporary pool in the surroundings of Grahamstown (Cape Province, South Africa) (33ring operator18′S, 26ring operator32′E).Rhinobranchipusshares partial fusion of the chitinized basal parts of the male antennae, the so-called clypeus, with other Branchipodidae. The new genus is distinguished from confamilial genera by the morphology of the basal part of the penes. The new species, known from its type locality only, should be considered endangered, if it has not already become extinct as a result of recent modifications of its habitat. © 1995 The Linnean Society of London.
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Evidence for sex-related differences in phototactic bahaviour of Streptocephalus proboscideus (Crustacea: Anostraca)
- The phototactic behaviour of adults of the Sudanese fairy shrimp Streptocephalus probiscideus was studied under laboratory conditions. Males were less negatively phototactic than females. This was also evident when colour filters were used. females only became little less negatively phototactic under yellow light, whereas males showed a strong positively phototactic response. The response to the positioning of a yellow filter was stronger than to the use of a red or blue filter for both sexes. The laboratory findings were compared with casual field observations on Streptocaphalus torvicornis that indicate differential vertical distribution between the sexes and a nocturnal vertical migration. Migratory behaviour with ascent starting at dusk is also predicted for S. proboscideus. This behaviour may reduce common stress factors in desert pools such as photodamage, visual predation pressure, and high surface temperatures. © 1995 Kluwer Academic Publishers.
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Collagen Extraction from Recent and Fossil Bones: Quantitative and Qualitative Aspects
- Type I collagen is the major protein in bones. The mineral matrix protects collagen from denaturation, thus permitting the recovery of large collagen peptides from fossil bones thousands or millions of years old. Collagen peptides are more or less denatured in fossil bones, with diagenetic alteration being the major cause of such denaturation. Classical extraction methods alter the remaining large collagen peptides by extensive solubilization. A method is described here that used shorter collagen solubilization times. Resulting collagen yields are favourably compared with classical methods. The size of the large peptide (10 kDa) fraction improves considerably. Combined with a particular concentration step, the use of this shorter solubilization technique should be useful for collagen analyses that necessitate large peptides, as in the case of palaeoimmunology. © 1995 Academic Press. All rights reserved.
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Geochemistry of the Frasnian-Famennian boundary in Belgium: Mass extinction, anoxic oceans and microtektite layer, but not much iridium?
- The Late Devonian, and in particular the Frasnian-Famennian (F/F) boundary, records one of the five largest mass extinctions in the fossil record. Glassy spherules believed to be of impact origin are associated with the F/F boundary in two Belgian sections (Senzeille and Hony). They have also been reported in sediments deposited approximately 1.5 to 2 m.y. above the boundary in south China, and in the Canning Basin (Australia) this event coincides with a 300 pg/g Ir anomaly. In this study, the F/F boundary in the Hony section was analyzed for trace and major elements to test the possibility of an Ir anomaly associated with the spherule layer. No significant positive Ir anomaly was detected in the 2 m of section investigated. Nevertheless, chalcophile elements show an increase within the dark shale bed marking the F/F boundary. This increase is interpreted to represent a reduction in oxygen concentrations in the depo-sitional environment. This level must be equivalent to the upper part of the Kellwasser anoxic event recognized throughout the paleo-Tethys in what is now western Europe. The F/F boundary seems to be marked by a succession of major events, including impact, oxygen-depleted water on the shelf, and worldwide extinction of organisms.
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The freshwater microcrustacea of Easter Island
- The 'Cladocera', Copepod and Ostracod fauna of Easter Island amounts to only five species. Three of these are wide-ranging, and four are cyclic parthenogens or at least capable of parthenogenesis. Two, the Cladoceran Alona weinecki and the Ostracod Sarscypridopsis sp., are more interesting from a biogeographic point of view, because restricted (apart from Easter Island) to the subantarctic. It is argued that this is strong evidence of their introduction by man, not by 'natural' passive dispersal.
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New hypogean cyclopoid copepods (Crustacea) from the Yucatan Peninsula, Mexico
- Four previously unknown hypogean species of cyclopoid copepods were collected in cenotes and wells of the Yucatan Peninsula, Mexico. Diacyclops chakan sp. n. and D. puuc sp. n. differ from their congeners in combining 3-segmented swimming legs, 11-segmented antennules, and legs 1-4 endopodite segment 2 all with 2 setae. Species of Diacyclops rarely occur in tropical regions, and the Diacyclops described here are only the second and third species recorded from Mexico. The benthic D. puuc was found in the large underground reservoir of a cenote. Diacyclops chakan was encountered in such large open subterranean water basins, but more frequently and abundantly in wells. The two Mesocyclops species, M. chaci sp. n. and M. yutsil sp. n., most closely resemble their epigean benthic congener M. reidae Petkovski, but are modified by loss of some body ornament and attenuation of swimming legs and mouthparts. Mesocyclops chaci sp. n. occupies crevicular spaces (wells and small caverns). The second species, M. yutsil sp. n., with more pronounced attenuation of legs, has a planktonic life in large subterranean water volumes. The extremely attenuated appendages of both species distinguish them from all other Mesocyclops, and resemble those of the hypogean Kieferiella delamarei Lescher-Moutoué. These three species are considered as a species-flock which have radiated as specialists within a highly dynamic geomorphological environment.
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Oligochaeta and Aphanoneura in ancient lakes: A review
- By their antiquity, history, rarity, great depth in many instances and the presence of highly diverse faunas with many endemics, ancient lakes constitute ecosystems of a special nature, clearly apart from the large majority of extant lakes. While the fauna of these lakes is becoming better and better known for various animals groups, the Oligochaeta are still poorly known. Tubificidae and Naididae are found in each ancient lake. On the other hand, some families are restricted to only one lake, such as Aeolosomatidae and Proppapidae in Lake Baikal or Eudrilidae and Ocnerodrilidae (megadriles) in Lake Tanganyika, but such a distribution is probably due to a lack of knowledge or sampling biases. All ancient lakes have an endemic oligochaete fauna except Lake Kinneret (Israel). The oldest, Lake Baikal (20-25 Ma), holds the most abundant and diverse oligochaete fauna, in which species flocks are even recognizable or suspected. In contrast, the oligochaete fauna of the slightly younger Lake Tanganyika is very scarce. This is partly due to an obvious lack of studies, as the oligochaete fauna of other great African lakes is virtually unknown, but this might be the result of an environment in these lakes less favourable to oligochaetes. Some factors likely to interact with speciation in oligochaetes are discussed but nothing can be concluded to date. A recent interest in African great lakes revealed a more diverse oligochaete fauna than previously assumed but a better study of this fauna is still badly needed.
