Search publications of the members of the Royal Belgian institute of natural Sciences
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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Growth and regeneration rates of the calcareous skeleton of the Caribbean coralline sponge Ceratoporella nicholsoni: A long term survey
- The growth rate of the aragonitic skeleton of the Caribbean 'sclerosponge' Ceratoporella nicholsoni has been studied by in situ staining of specimens with calcein in a reef tunnel, 28m depth, near Discovery Bay, Jamaica. Experiments were performed up to five times from 1984 to 1997 on a population of 10 specimens ranging from 10-20cm maximum diameter. In each experiment small skeletal samples were removed from the periphery of sponges, and specimens were left in place for further studies on growth and regeneration. Perpendicular sections, ground to a thickness of about 10μm, were photographed by fluorescence microscopy. Annual skeletal growth rates were calculated from measurements of the linear extension between calcein stained lines along growth axes. Data indicate that although average annual growth rates remained in the same range for different periods (214.6±54.5-233.3±33.0μm yr -1), significant differences occurred from one individual to another within the same period. The annual growth rate of a given individual also varied significantly in time (191.1±30.0-269.9±37.0μm yr -1). A second population of smaller individuals, measured after a single period of one year, revealed a strikingly lower average annual growth rate (124.4±35.0μm yr -1). Regeneration of the skeleton of injured specimens was also characterised by an initial slower growth rate. Nevertheless, after the first year, it was comparable to normal growth, and exceeded it slightly thereafter. This first long term study of Ceratoporella provides important information on the variability in growth rates, with implications on the use of sclerosponges as paleoenvironmental proxies.
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Two new living species of Loxotaphrus (Gastropoda: Cancellariidae: Plesiotritoninae) from Queensland, Australia and Mozambique, East Africa
- Until now, the only living species assigned. to the cancellariid genus Loxotaphrus Harris, 1897 was the West African species L. deshayesii (Duval, 1841). Two new living species are described here, L. limpusi n. sp., from the Swain Reefs, Queensland, and L. rosadoi n. sp., from off southern Mozambique. L. limpusi most closely resembles the type species of the genus, L. variciferus (Tate, 1888) (Miocene, southern Australia). Although L. rosadoi resembles L. variciferus and L. limpusi more closely than it does L. deshayesii, it differs from all other species, assigned to Loxotaphrus in having weak sculpture, apart from the prominent, sharp nodules around the peripheral keel.
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Pathological findings in two fin whales (Balaenoptera physalus) with evidence of morbillivirus infection
- Two immature female fin whales stranded on the Belgian and French coastlines, were examined post mortem. The main gross findings were massive parasitic infestation, associated with a large thrombus in one whale, and severe emaciation. Microscopical investigations revealed multinucleated syncytia with large intranuclear inclusion bodies in various tissues, and positive immunolabelling for morbillivirus antigens. Other evidence of morbillivirus infection was provided by the demonstration of specific viral structures in syncytia and in cell cultures, and the detection of neutralizing antibodies to canine distemper virus. To the authors' knowledge, this is the first firm report of morbillivirus infection in baleen whales. (C) 2000 Harcourt Publishers Ltd.
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Is there a geographical pattern in the breeding system of a complex of hermaphroditic slugs (Mollusca: Gastropoda: Carinarion)?
- Allozyme analyses of the hermaphroditic slugs Arion (Carinarion) fasciatus, A. (C.) circumscriptus and A. (C.) silvaticus have suggested that the three species in North America and north-west Europe predominantly reproduce uniparentally, most probably by selfing. We used allozyme electrophoresis to investigate the population genetic structure of these species throughout a larger part of their native European distribution. Our results show that the previously reported 'species' specific allozyme markers are no longer valid if populations from central Europe are investigated, and A. fasciatus and A. silvaticus appear to be 'paraphyletic' taxa. In contrast to the general belief that selfing organisms show low gene diversities, the high selfing rates in N-NE European Carinarion do not necessarily result in low gene diversities. Moreover, our data suggest a geographical pattern in the prevalence of outcrossing, at least in A. fasciatus, with selfing in N-NE Europe and a mixed breeding system (i.e. selfing and outcrossing) in central Europe. Possible scenarios for the disjunct distribution of breeding systems in Carinarion are discussed.
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Trends in the ecological strategies and evolution of millipedes (Diplopoda)
- Five main morphotypes (polyxenoid, glomeroid, juloid, polydesmoid, and platydesmoid) are denoted and five ecomorphotypes, i.e. life-forms (stratobionts, troglobionts, geobionts, subcorticolous xylobionts, and epiphytobionts) are outlined in the Class Diplopoda. Their distribution and that of separate higher taxa show a number of marked ecological and geographical trends. The Diplopoda as a whole is believed to be originally a forest floor-dwelling group, with stratobionts dominating everywhere, this life-form having given rise to all other derivative, apparently synchronously evolved life-forms. The poor development of the derived life-forms points to their recent evolution, probably brought about by the great climatic changes of the last 2-3 Ma. The European fauna is characteristically dominated by the life-form of stratobionts and in most areas by the juloid morphotype. However, the distribution of orders is strongly skewed. The habitats in Europe with richest millipede faunas seem to be temperate forests in the Adantic zone and central mountain chains, where the Order Chordeumatida is strongly represented. This area contains several long-term, or Ice Age, refugia. Further to the north, south and east, especially in open landscapes, along with an increasingly continental/Mediterranean climate, representatives of the juloid morphotype, mainly members of the Order Julida, become proportionately more common, while general species diversity falls. The ecological strategies of millipedes are rooted both in the group's phylogeny and in the Earth's history. In Europe this history is peculiar owing to the eastwest lic of the principal mountain chains, and repeated glaciations have led to the development of a mixed, fully migratory, recent European faunal kernel, or nucleus, which is forced south and cornered in the largely mountainous western and central parts of the Continent during glaciations. Many local endemics have evolved in these areas, including a substantial proportion of cavernicolous species. (C) 2000 The Linnean Society of London.
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Factors affecting the divergence of mate recognition systems in the Limnocytherinae (Crustacea, Ostracoda)
- Specific Mate Recognition Systems (SMRS) consist of a set of morphological, behavioural and physiological traits which allow mate recognition. The Limnocytherinae, a lineage of non-marine podocopid Ostracoda, have a relatively wide diversity of copulatory modules, a concept largely congruent with the morphological part of the SMRS. The present paper describes the various copulatory modules in some detail and discusses potential mechanisms responsible for the divergence of these modules. Although none of the processes was thus far demonstrated directly, resulting patterns provide indirect evidence that four different mechanisms contribute. Stochastic processes (chance) as well as developmental and other phylogenetic constraints are involved in the initial selection (choice) of modified structures. Subsequent (positive) directional sexual selection on traits of the recognition systems causes radiative speciation within lineages. At all times, natural selection acts on the development of these structures, either stabilising or negative directional. A number of potential tests for these hypotheses are suggested.
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Parasites, predators and the Red Queen
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The use of chironomid deformation in an in situ test for sediment toxicity
- An in situ bioassay using mouthpart deformities in Chironomus riparius larvae was developed to monitor sediment toxicity. Second-instar larvae, along with a standardized amount of food and sediment taken from the study locations, were enclosed in cages that were placed on the sediment surface of rivers. Mouthpart deformities were screened after larval molting to the fourth instar (exposure time: 7-10 days). Mouthpart deformities of caged and field larvae (when present) were related to the estimated sediment toxicity. By summing toxicant concentrations and normalizing them to the organic matter and clay contents, a significant relationship between toxicity levels and mouthpart deformities in the mentum was revealed. Results suggest that the pattern of observed deformities was indicative of site toxicity rather than a characteristic of the laboratory larval population used. The main advantage of the proposed in situ bioassay is the possibility to assess the incidence of deformities at sites where C. riparius does not occur naturally. (C) 2000 Academic Press.
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Volatile organic compounds in various marine organisms from the southern North Sea
- The concentration levels of 12 priority volatile organic compounds (VOCs) were determined in two species of vertebrates and four species of invertebrates from sampling stations in the southern North Sea, using a modified Tekmar LSC 2000 purge and trap system coupled to gas chromatograph-mass spectrometer (GC-MS). In general, concentration levels of VOCs found in this study were of the same order of magnitude as those previously reported in the literature. The concentrations of the chlorinated hydrocarbons (CHCs), with the exception of chloroform, tended to be lower than those of the monocyclic aromatic hydrocarbons (MAHs). The experimental data were statistically evaluated using both cluster analysis and principal component analysis (PCA). From the results of cluster analysis and PCA, no specific groups could be distinguished on the basis of geographical, temporal or biological parameters. However, based on the cluster analysis and the PCA, the VOCs could be divided into three groups, C2-substituted benzenes, CHCs and benzene plus toluene. This division could be related to different types of sources. Finally, it was shown that organisms can be used to monitor the presence of VOCs in the marine environment and the observed concentrations levels were compared with proposed safety levels. (C) 2000 Elsevier Science Ltd.
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The ontogeny of the cypridid ostracod Eucypris virens (Jurine, 1820) (Crustacea, Ostracoda)
- The chaetotaxy (shape, structure and distribution of setae) of appendages and valve allometry during the post embryonic ontogeny of the cyprididine ostracod Eucypris virens are described. It is shown that the basic ontogenetic development of E. virens is very similar to that of other species of the family Cyprididae. During ontogeny, the chaetotaxy shows continual development on all podomeres of the limbs with the exception of the last podomere on the antennulae. The long setae on the exopodite and protopodite of the antennae have a natatory function until the actual natatory setae develop in later instars. Aesthetascs (presumed chemoreceptors) ya and y3 are the first to develop and may have an important function in the first instars. Cyprididae require a pediform limb in the posterior of the body presumably to help them to attach to substrates and this is reflected by the pediform nature of one limb at all times throughout all ipstars. This study has also shown that the fifth limb is most probably of thoracic origin and hence ostracods have only one pair of maxillae.
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Eradication of exotic species [3] (multiple letters)
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Exposure of Chironomus riparius larvae (diptera) to lead, mercury and β-sitosterol: Effects on mouthpart deformation and moulting
- Mouthpart deformation in chironomid larvae is induced by exposure to chemical contaminants and is becoming an established bio-indicator in sediment assessment programmes. However, concentration-response relationships with causal agents have only been established occasionally and with varying success, In this laboratory study, instar II and III larvae were exposed to sub-lethal concentrations of lead, mercury and β-sitosterol. A significant deformation response was induced in the pecten with lead and mercury. Deformation frequencies of the mentum after metal exposures were not significantly different from the control. Moulting was retarded by both metals and was well correlated with mouthpart deformation. The β-sitosterol is an endocrine disruptor, which was used to test the hypothetical cause-effect relation between disruption of ecdyson functioning and chironomid deformation. In the present study, exposure to sublethal concentrations of β-sitosterol did not result in any effect on deformation or moulting. As such, the proposed hypothesis of endocrine disruptors as primary casual agents of chironomid deformation could not be substantiated. Acetone, which was used as a solvent to apply β-sitosterol caused a significant increase of mentum deformation. The ground filtration paper used as substrate seemed to induce deformities as well. Substrate contamination, acetone and (especially) inbreeding were most probably responsible for the high deformation frequencies in the control conditions. (C) 2000 Elsevier Science Ltd.
