Search publications of the members of the Royal Belgian institute of natural Sciences
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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.
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Zonation and structuring factors of meiofauna communities in a tropical seagrass bed (Gazi Bay, Kenya)
- This study deals with the relation between tropical meiofauna and environmental variables by comparing the 'benthic' (i.e. in the bare sediment adjacent to seagrass plants) and the 'epiphytic' (i.e. in samples including seagrass plants) meiofauna associated with five seagrass species from the high intertidal to the high subtidal zone in Gazi Bay (Kenya), Ordination and variance analysis revealed three distinct 'benthic' and two 'epiphytic' meiofauna assemblages. These assemblages corresponded entirely with those identified for the seagrass species: a high intertidal pioneer association (Halophila ovalis/Halodule wrightii), an intertidal climax assemblage (Thalassia hemprichii) and a high subtidal pioneer association (Halophila stipulacea/ Syringodium isoetifolium). These data support the hypothesis that meiofaunal communities correspond to the characteristic zonation of the seagrass vegetation in Gazi Bay. In beds of the pioneer seagrass species, the close relationship between sediment characteristics and both 'benthic' and 'epiphytic' meiofauna communities suggests that these pioneer communities were mainly driven by physical factors. The 'benthic' communities adjacent to the climax seagrass species T. hemprichii were more structured by biogenic factors, e.g. \% TOM, chlorophyll a and c, fucoxanthin, habitat complexity and growth form of the seagrass species. For its associated 'epiphytic' meiofauna the latter conclusion was even more striking. These data corroborate the importance of physical factors in disturbed environments (intertidal zone, near pioneer seagrasses) and of biotic factors in more stable conditions (subtidal zone, near climax seagrasses). © 2001 Elsevier Science B.V.
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Intersex and sterility in the periwinkle Littorina littorea (Mollusca: Gastropoda) along the Western Scheldt estuary, the Netherlands
- In this study we present the results of an intersex survey of Littorina littorea along the heavily polluted Western Scheldt estuary (the Netherlands), and record for the first time the intersex phenomenon in L. littorea from Dutch waters. Intersex differed significantly between localities and was the highest in the vicinity of the harbours of Antwerp and Vlissingen, as reflected by the ISI distribution along the estuary. In contrast, sterility did not differ significantly between the different sites, but nonetheless, followed the ISI distribution as well, ranging from 0 to 33\%. Despite the current ISI levels are high (maximum=1.26), they are still much lower than the ISI levels reported for L. littorea in some German harbour areas. Copyright © 2001 Elsevier Science Ltd.
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Esterase variation in the periwinkle Littorina littorea, along the western and eastern Scheldt estuarium
- Variation in esterase expression (EST) has been investigated in 360 specimens of the periwinkle Littorina littorea, collected at nine sites along the polluted western Scheldt and the relatively clean eastern Scheldt estuary. Mean number of EST bands differed among the sites, while a Dice similarity based multi-dimensional scaling along with a minimum spanning tree procedure, revealed an estuary based structuring, clustering the most polluted and least saline like sites together. The underlying factors and mechanisms (i.e. selection, regulation) which are responsible for this structuring remain to be determined © 2001 Elsevier Science Ltd. All rights reserved.
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Heavy metal levels in the sediments of four Dar es Salaam mangroves accumulation in, and effect on the morphology of the periwinkle, Littoraria scabra (Mollusca: Gastropoda)
- Heavy metals were determined in the soft tissue and shells of the littorinid, Littoraria scabra, and in the sediments of four mangrove areas along the Dar es Salaam coastline where L. scabra was collected. Several metals accumulate, preferentially in the animals' soft body parts, but do not seem to affect the shell morphology of this species. Sediment-metal levels, measured in the direct vicinity of Dar es Salaam have increased dramatically over the last decade. Nonetheless, these levels are still lower compared to metal-sediment levels reported in polluted European and American estuaries. Soft-tissue metal levels detected in L. scabra are, nevertheless, with the exception of Cr and Zn, comparable to metal levels reported in other gastropod species. © 2001 Elsevier Science Ltd. All rights reserved.
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A red data book of empidid flies of Flanders (northern Belgium) (Diptera, Empididae s.1.): Constraints and possible use in nature conservation
- To enable use of Empididae s.l. (Diptera) as a tool in nature conservation, a Red Data Book of this taxonomical group was generated for Flanders, Belgium. All distribution data on species in Belgium between 1887 and 1999 were gathered from collections as well as personal sampling efforts by the first two authors. This resulted in about 21,000 records of Empididae, Hybotidae, Microphoridae and Atelestidae with 16,119 records for Flanders (northern Belgium) and 4776 for Wallony (southern Belgium). All species were assigned to Red Data Book categories which are based on a combination of a rarity and a trend criterion. Rarity is expressed as the proportion of the total number of UTM 5 km squares sampled in which the species have been found since 1981. The trend criterion is interpreted as the change of the species rarity between 1887-1980 and 1981-1999. A comparable number of UTM 5 km squares was investigated during the two time periods. A total of 259 species were recorded in Flanders. Twenty-seven or 10\% of them are considered as 'extinct in Flanders', 10 (4\%) as 'critically endangered', 12 (5\%) as 'endangered', 11 (4\%) as 'vulnerable', 99 species (38\%) as 'susceptible' or 'rare', 65 species (25\%) as 'safe' or 'at low risk' and 34 species (13\%) are assigned to the category 'data deficient' due to taxonomic problems or a lack of ecological data. Only one of the common species shows a recent decrease of more than 50\% and is classified as 'nearly threatened'. Current threats in most species are related to the alteration or destruction of their favoured habitats. The results are discussed in the light of recent criticism of the use of Red Data Books in nature conservation.
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Morphological deformities in Chironomus riparius meigen larvae after exposure to cadmium over several generations
- In order to test the potential of chironomid deformities for biomonitoring, induction of morphological deformities in Chironomus riparius larvae was assessed after chronic exposure (static with renewal) of eggs and subsequent instars to sublethal nominal cadmium concentrations of 0, 3 (NOEC), 9 (intermediate) and 27 (chronic LC'50) μg Cd 1-1 during 7 to 10 generations. Deformities which could be associated with an indirect or direct cadmium effect were split medial mentum teeth (more frequent in 9 and 27 μg Cd 1-1) and premandible deformities (especially in 3 μg Cd 1-1). The control contained more larvae with additional teeth in mentum and mandible than the metal-exposed conditions. In the 9 μg Cd 1-1 condition the frequencies of larvae with split medial mentum teeth increased in the last four generations, to reach 40\%. The unpredictability of fluctuations of deformity frequencies over the generations was associated with parental effects and experimental manipulation. The deformity percentages correlated positively with the mortalities and could be related to the induction of tolerance to cadmium, as was concluded on the basis of life cycle analysis in a previous paper. This experiment demonstrated a concentration-response relationship between deformities and sublethal levels of cadmium. However, the observed generation fluctuations caution for (1) the use of single-generation experiments for defining ecotoxicological threshold values, and (2) experimentally induced genetical drift in multi-generation experiments.
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Genetic and morphological variation in the land winkle Pomatias elegans (Müller) (Caenogastropoda: Pomatiasidae)
- Population genetics and shell morphology have been studied in 11 populations of the poorly colonizing land caenogastropod Pomatias elegans. The total area of suitable habitats in northwest Europe is shrinking and many isolated populations are becoming vulnerable to extinction. In this study we tested whether the concept of management units (i.e. groups of population with significantly different allele frequencies due to demographic independence) is applicable to the conservation of P. elegans. F st values indicated strong genetic differentiation and thus little genetic exchange between populations. Allozyme differentiation could be explained with an isolation by distance model, whereas morphological differentiation could not. A morphological difference exists between sexes but not sufficient to discriminate males and females. A Mantel test showed no significant relationship between morphological distance (size corrected or not) and genetic distance. Since allele frequencies differed even among populations in areas where P. elegans is not threathened, we conclude that in the case of P. elegans, defining management units with allozymes may not be an appropriate way to select the most suitable populations for conservation.
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Food-induced body pigmentation questions the taxonomic value of colour in the self-fertilizing slug Carinarion spp.
- Body pigmentation is a popular taxonomic marker in slugs to discriminate closely related species. However, the genetic background of body pigmentation is known only for a few species, while in many others body pigmentation is influenced by age, food and/or climate. In this study, we investigated the effects of different food items on body pigmentation expression in two selfing pulmonate gastropods, Arion (Carinarion) silvaticus and Arion (Carinarion) fasciatus. Both species mainly differ in the distribution of yellow-orange granules on the body, which in A. fasciatus are concentrated in lateral bands, and in A. silvaticus are evenly scattered. Animals were raised individually under the same conditions, while they laid eggs as a consequence of selfing. This F1 generation was afterwards divided into two groups, which were fed with different food items. A diet of carrot, lettuce or paper had no effect on the distribution of the yellow-orange granules in A. silvaticus, but provoked a loss of the yellow-orange lateral bands in A. fasciatus so that externally these F1 specimens became similar to A. silvaticus. In both species, a diet of nettle resulted in a strong yellow-orange pigmentation, which often formed yellow-orange lateral bands. These results indicate that food can probably influence the 'species-specific' body pigmentation in Carinarion, and thus question the reliability of colour traits to distinguish A. silvaticus and A. fasciatus.
