Search publications of the members of the Royal Belgian institute of natural Sciences
-
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.
-
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.
-
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.
-
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.
-
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.
-
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.
-
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.
-
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.
-
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.
-
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.
-
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.
-
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.
-
Mitochondrial phylogeography of rock-dwelling cichlid fishes reveals evolutionary influence of historical lake level fluctuations of Lake Tanganyika, Africa
- The East African Lakes Tanganyika, Malawi and Victoria each harbour hundreds of endemic invertebrate and vertebrate species. Inferences about the ecological and evolutionary processes responsible for the origin of these species flocks will only be possible when they are made within historical and comparative frameworks. Specifically, the relative importance of intrinsic characteristics and extrinsic factors may offer information about the processes that drive diversification and speciation in these species. We investigated the sequence variation of a segment of the mitochondrial DNA control region of 32 populations representing all four nominal species in the three genera of eretmodine cichlids from Lake Tanganyika. Based on a phylogenetic analysis of these data we attempted to evaluate the importance of major lake level fluctuations on patterns of intralacustrine speciation. The geography of genetic variation reveals a high degree of within-lake endemism among genetically well- separated lineages distributed along the inferred shore lines of three historically intermittent lake basins. Seismic data indicate that extreme lowering of water levels in the Pleistocene caused the single Lake Tanganyika basin to split into three isolated ones. The strong phylogeographic structure of the Eretmodini, and the observation that some closely, related populations occur on opposite shores of the lake, agree with this geological scenario. The three-clade-three-basin phylogeographic pattern was repeated twice within this tribe of cichlids. The phylogeographic pattern of eretmodine cichlids suggests that major fluctuations in the level of the lake have been important in shaping their adaptive radiation and speciation. The mitochondrially defined clades are in conflict with the current taxonomy of the group and suggest that there has been convergent evolution in trophic morphology, particularly in the shapes of oral teeth, taxonomically the most diagnostic characters of the three genera.
-
Asexual reproduction in nonmarine ostracods
- Asexual reproduction has evolved repeatedly in nonmarine ostracods and takes a variety of forms from ancient asexuals to species in which sexual and asexual lineages coexist. Clonal diversity is highly variable. There is evidence that some of this diversity is maintained by ecological differentiation. Hybridization between asexual females and males, of the same or related species, contributes to clonal diversity. Molecular data suggest that some clonal lineages are surprisingly old (more than 5 Myr). In the ancient asexual Darwinula stevensoni, from a lineage that has apparently been without sex for more than 100 Myr, a remarkable lack of sequence variation in ITS1 may be explained by occasional automixis, gene conversion or somatic recombination, or by efficient DNA repair. Overall, the ostracods provide an excellent system in which to study the evolution of reproductive modes.
-
Congruence between allozyme and RAPD data in assessing macrogeographical genetic variation in the periwinkle Littorina striata (mollusca, gastropoda)
- The population genetic structure of the Macaronesian planktonic-developing periwinkle Littorina striata was analysed, using random amplified polymorphic DNA analysis (RAPD). Two primers, yielding six polymorphic loci, were surveyed to infer the population genetic structure of five geographically separated populations (i.e. 10-2000 km). Biased and unbiased allele frequency and heterozygosity levels were estimated and were found to be highly similar. As in previous allozyme studies, our results suggest that populations of L. striata display (i) only little amounts of genetic heterogeneity and population differentiation, (ii) high levels of gene flow, between geographically separated populations and within a single population, between two distinct shell morphs (i.e. nodulose and smooth shells) and (iii) a tendency for northern populations to be less heterozygous than southern populations. The current results reveal a high congruence between allozyme and RAPD data, suggesting that geographically separated populations and different shell morphs share a common gene pool. Given the fact that our RAPD loci might be considered as neutral markers, we conclude that the previously analysed allozymes were representative for L. striata's entire genome.
-
New Bactrosaurus (Dinosauria: Hadrosauroidea) material from Iren Dabasu (Inner Mongolia, P.R. China)
- In 1995, the Sino-Belgian dinosaur expedition discovered a rich bonebed in the Iren Dabasu Formation (Late Cretaceous) of Erenhot (Inner Mongolia PR China). This bonebed comprised the scattered skeletons of at least four specimens belonging to the primitive hadrosaur Bactrosaurus johnsoni Gilmore, 1933. The study of the new material allows an accurate osteological reconstruction of this species, eg definitely showing that it was a flat-headed hadrosaur. The superfamily Hadrosauroidea is diagnosed as a monophyletic groups characterized by 11 synapomorphies. Bactrosaurus johnsoni is the most basal taxon of the Hadrosauroidea, as it lacks numerous apomorphies observed in the other well known taxa within this superfamily. The basal position of Bactrosaurus johnsoni in hadrosaur phylogeny speaks for an early Late Cretaceous age for the Iren Dabasu Formation.
-
Improving the methodology of chironomid deformation analysis for sediment toxicity assessment: A case study in three Danish lowland streams
- This paper aims at improving the methodology of chironomid deformation screening as a biomonitoring tool in sediment toxicity assessment. Head capsule deformities were investigated in Chironomus riparius larvae in three contaminated Danish streams. A new scoring system for deformities of the mentum, mandibles and pecten was designed, in order to objectify and improve previously published scoring methods. A comparison of this new scoring system with deformation frequencies indicated that the more laborious scoring of deformities did not result in a higher resolution than the simple frequency counts of deformed larvae. However, the different mouthparts seem to react independently to pollution stress and display specific deformation frequency profiles. Hence, a separate calculation of their deformation frequencies remains essential for a correct evaluation. Using cluster analysis, all mouthpart deformation frequencies were combined into one sediment classification scheme. This classification could be adequately explained by the different levels of sediment contamination, as indicated by metal analyses and site-specific pollutant sources. However, when only mentum deformation frequencies were used, an almost identical classification was obtained. Deformation in mandibles, pecten, premandibles and antennae did not display a consistent relationship with sediment contamination by the paper mill. Hence, in the present study, a simple calculation of the frequencies of mentum deformation was the most efficient strategy for sediment toxicity assessment.
-
Metazoan relationships on the basis of 18S rRNA sequences: A few years later
- The 18S rRNA database is continuously growing and new tree construction methods are being developed. The present study aims at assessing what effect the addition of recently determined animal 18S rRNA sequences and the use of a recently developed distance matrix calculation method have on the results of some previously published case studies on metazoan phytogeny. When re-assessing three case studies, part of their conclusions was confirmed on the basis of the present 18S rRNA data set: 1) the monophyly of Arthropoda; 2) the monophyly of the Vestimentifera-Pogonophora and their protostome character, 3) the doubt about the monophyletic origin of Echiura-Sipuncula and 4) the coelomate character of Nemertea. Yet, it is also demonstrated that some of the previous results are no longer warranted when updating the analyses: 1) the monophyly of both the Annelida and the Eutrochozoa; 2) the sister-group relationship of Echiura to Vestimentifera-Pogonophora and 3) the polyphyly of the Mesozoa and their close relationship to Myxozoa and Nematodes. In addition, some new very preliminary evidence is provided for: 1) a common ancestry of Platyhelminthes and Mesozoa and the monophyly of the latter group and 2) the monophyly of Clitellata, Hirudinida and Oligochaeta. Finally, doubt is casted on the monophyly of the Polychaeta and the poiychaete orders Spionida, Phyllodocida, and Sabellidae. Of course, these hypotheses also need further testing.
-
The aptian stratigraphy of Southern Tuarkyr (Nw Turkmenistan, Central Asia)
- The ammonite successions of Turkmenistan, particularly those of the Greater Balkhan and Tuarkyr areas, are considered references for the Aptian Stage. Six sections across the uppermost Barremian - basal Upper Aptian interval were studied in the Tuarkyr desert in October 1997, and ammonites and bivalves were collected. Data are compared with those from a section sampled by a Russian team in 1959. The stratigraphic distribution of the faunas in the sections is discontinuous, as the fossiliferous levels intercalate with terrigenous sediments. The ammonite faunas, at least in the intervals sampled, show low diversity and are dominated by the genus Deshayesites in the lower Aptian and the genus Epicheloniceras, associated with the less common Caspianites, in the basal upper Aptian. The Turkmenistan sections contain species present also in the Caucasus, England, Germany, France and Switzerland, indicating that the Turkmenian faunas reflect impoverishement rather than geographic isolation. The chronologic equivalence between the Turkmenian Epicbeloniceras sitbnodosocostatum Zone and the Epicheloniceras martinioides Zone in England seems questionable because the Epicheloniceras-bearing beds of the Tuarkyr correspond to the upper part of the E. martinioides Zone, i. e. the Epichcloniccras buxtorfi Subzone. The bivalve fauna consists mainly of pteriids, Exogyrinae oysters and trigoniids. These groups undoubtedly indicate a very shallow, fairly warm and fully marine environment, typical of the Tethyan Lower Cretaceous. The heterodonts are too rare to give further bathymetric indications. None of the taxa indicate deep burrowing and all are assumed to be very littoral. The bivalve fauna shows strong affinities with that of the English Lower Greensand.
-
Cuticular linings and remodelisation processes in Crambe Crambe (Demospongiae: Poecilosclerida)
- The common Mediterranean sublittoral sponge Crambe crambe goes through a resting, non-feeding period with cellular restructuring which may have biological and ecological significance. This red encrusting sponge reproduces in summer and larvae released during July-August. After reproduction, from the end of August until the end of October, some specimens appeared covered with a glassy cuticle, obliterating the ostia and oscula. No water pumping and, hence, no feeding occurs during this stage. At the end of October and during November some specimens displayed a strongly hispid surface, with spicules retaining entangled debris. This hispid form is interpreted as an intermediate stage between the resting phase and the active period. SEM examination of the surface during the non-feeding period confirmed the absence of inhalant orifices and the presence of an acellular cuticle markedly different from the glycocalyx layer associated with the pinacoderm of active specimens. In some individuals, micro-organisms were found adhering to the outer side of the cuticle which were absent from the surface of active specimens. In TEM, the cuticle appeared as a complex 2.5-3μm thick structure made up of three layers: a proximal dense layer (0.06-0.12μm), an intermediate amorphous layer (0.15-0.3μm), and an outer granular layer also of variable thickness (more than 2μm) which progressively disintegrated. Collagen debris appeared between the proximal and intermediate layers. The zone beneath this triple-layered cuticle was either completely devoid of cells or showed scarce degenerating cellular components (mainly from pinacocytes and spherulous cells), and sparse collagen fibrils. The choanosome appeared rather disorganised, with most choanocyte chambers disintegrated, with abundant phagocytosing archeocytes, sclerocytes, spherulous cells, degenerated cells and cell debris. Later in the season the cuticle appeared broken in many places. It was cast off and a new pinacoderm with ostia developed below; filtering activity of the sponges resumed. Spicules, previously protected by the cuticle, were uncovered, giving rise to a hispid phase. Subsequently the emergent spicules were cast off and smoothness of the sponge surface was restored. These changes in sponge cell structure and activity may be explained as reorganisation processes after reproduction, but other causes, such as adverse water temperature, may have similar effects.
