Search publications of the members of the Royal Belgian institute of natural Sciences
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Lake level fluctuations synchronize genetic divergences of cichlid fishes in African Lakes
- Water level fluctuations are important modulators of speciation processes in tropical lakes, in that they temporarily form or break down barriers to gene flow among adjacent populations and/or incipient species. Time estimates of the most recent major lowstands of the three African Great Lakes are thus crucial to infer the relative timescales of explosive speciation events in cichlid species flocks. Our approach combines geological evidence with genetic divergence data of cichlid fishes from the three Great East African Lakes derived from the fastest-evolving mtDNA segment. Thereby, we show for each of the three lakes that individuals sampled from several populations which are currently isolated by long geographic distances and/or deep water form clusters of equally closely related haplotypes. The distribution of identical or equally closely related haplotypes in a lake basin allows delineation of the extent of lake level fluctuations. Our data suggest that the same climatic phenomenon synchronized the onset of genetic divergence of lineages in all three species flocks, such that their most recent evolutionary history seems to be linked to the same external modulators of adaptive radiation. A calibration of the molecular clock of the control region was elaborated by gauging the age of the Lake Malawi species flock through the divergence among the utaka-cichlid and the mbuna-cichlid lineages to minimally 570,000 years and maximally 1 Myr. This suggests that the low-lake-level period which established the observed patterns of genetic relatedness dates back less than 57,000 years, probably even to 17,000-12,400 years ago, when Lake Victoria dried up and Lakes Malawi and Tanganyika were also low. A rapid rise of all three lakes about 11,000 years ago established the large-scale population subdivisions observed today. Over that period of time, a multitude of species originated in Lakes Malawi and Victoria with an impressive degree of morphological and ecological differentiation, whereas the Tanganyikan taxa that were exposed to the same habitat changes hardly diverged ecologically and morphologically. Our findings also show that patterns of genetic divergences of stenotopic organisms provide valuable feedback on geological and sedimentological time estimates for lake level changes.
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Microsatellite data reveals weak population substructuring in Copadichromis sp. `virginalis kajose', a demersal cichlid from Lake Malawi, Africa
- Small but significant differences were found in allele frequencies among five populations (overall F ST estimate (θ)=0.004, P=0.006; overall R ST estimate (RHO)=0.019, P<0.00001) of the demersal cichlid Copadichromis sp. `virginalis kajose', collected from five locations in Lake Malawi. Pairwise F ST estimates revealed significant differences between the most southerly population (Cape Maclear), and the three most northerly populations (Mbamba Bay, Metangula and Chilola). Pairwise R ST estimates also revealed significant differences between some populations, but no geographical pattern was discernible. There was no evidence of isolation by distance using either the shortest straight-line distance between samples, or the distance around the shoreline following a 50 m depth contour. F ST, estimates were considerably lower than found in previous studies on the mbuna (rock-dwelling species), but higher than those found in a study of three pelagic cichlid species from Lake Malawi. Substructuring in C. sp. `virginalis kajose' appears to be on a similar scale to the Atlantic cod. © 2001 The Fisheries Society of the British Isles.
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Morphological variation within and between four closely related phyllotreta species: P. dilatata, P. flexuosa, P. ochripes and P. tetrastigma (Coleoptera: Chrysomelidae)
- Phyllotreta dilatata Thomson. 1866. P. flexuosa (Illiger, 1794) P. ochripes (Curtis, 1837) and P. tetrastigma (Comolli, 1837) are four closely related, morphologically similar flea beetle species which are usually distinguished according to elytral colour pattern and also show morphological differences in the genitalia. Here both uni- and multivariate analyses are used to study intra-and interspecific morphological variation for the four species. All species seem to differ in overall morphology and the results also support the idea of regarding P. tetrastigma and P. flexuosa as two different systematic entities.
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On the Cyprideis species flock (Crustacea, Ostracoda) in Lake Tanganyika, with the description of four new species
- Four new species, belonging to three genera, of ostracods from Lake Tanganyika are described: Mesocyprideis nitida sp.nov., Romecytheridea belone sp.nov., R. plegma sp. nov. and Cyprideis loricata sp. nov. The Cyprideis species flock of Lake Tanganyika now consists of 17 formally described species (16 endemic) in 6 genera (4 endemic). The geographical and ecological distribution of the four species is briefly discussed and some supplementary remarks on the radiation of the Cyprideis species flock in Lake Tanganyika are offered.
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Molluscan diversity in tidal marshes along the Scheldt estuary (The Netherlands, Belgium)
- The mollusc fauna of 64 sites in 31 tidal marshes was surveyed along a salinity gradient from freshwater to marine conditions in the river Scheldt (Belgium-The Netherlands). A total of 10 649 specimens involving 31 taxa were identified. Salinity turned out to be a major factor in mollusc assemblages in the Scheldt estuary, but other factors can not be excluded. In the marine part five species were common, compared to the brackish part where only Assiminea grayana was abundant. In the freshwater zone species richness was highest (24). There was a significant correlation between flooding frequency and species richness in the tidal freshwater marsh 'Durmemonding'. Finally, the survey confirmed the distribution of the amphibious hygromiid snail Pseudotrichia rubiginosa, a species which in Belgium only occurs in the marshes of the tidal freshwater part of the Scheldt and its tributaries.
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Ostracods and fore-reef sedimentology of the Frasnian-Famennian boundary beds in Kielce (Holy Cross Mountains, Poland)
- Four major microfacies have been recognized in the Psie Górki section and the bioclastic content indicates an open marine environment in the photic zone close to an algal shole. Sedimentological studies point to a regressive episode starting close to the Frasnian-Famennian boundary. The regressive microfacies pattern is revealed by the presence of semi-restricted algal microbreccias that compose all of the lower part of the Famennian. The regression was accompanied by meteoric water invasion as the sea level fell. Seventy-six ostracod species are recorded. The ostracod assemblage, dominated by podocopids, belongs to the Eifelian ecotype and is indicative of a well-oxygenated marine environment below fair-weather wave base in the Frasnian part of the section, and of shallower environments in the base of the Famennian. No ostracod assemblage characteristic of hypoxic or semi-restricted water conditions has been recorded. The rate of extinction of ostracod species (70\%) close to the Frasnian-Famennian boundary is comparable with that known on the same level in several other sections investigated in the world. Five new ostracod species are proposed by J.-G. Casier and F. Lethiers: Selebratina vellicata, Samarella? minuta, Bairdiocypris ventrorecta, Acratia pentagona, and "Bairdia" psiegorkiensis.
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Evaluation of a high-resolution time-of-flight mass spectrometer for the gas chromatographic determination of selected environmental contaminants
- A benchtop high-resolution time-of-flight mass spectrometer (TOF MS) was evaluated for the determination of key organic microcontaminants. The major advantage of the TOF MS proved to be the high mass resolution of about 0.002 Da (10 ppm). Consequently, the detectability of polar pesticides, polynuclear aromatic hydrocarbons and polychlorinated biphenyls is excellent, and detection limits are in the order of 1-4 pg injected mass. Best mass spectral resolution was obtained for medium-scale peaks. It is a disadvantage that the calibration range is rather limited, viz. to about two orders of magnitude. The high mass spectral resolution was especially useful to improve the selectivity and sensitivity when analyzing target compounds in complex samples and to prevent false-positive identifications. © 2002 Elsevier Science B.V. All rights reserved.
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Isolation and characterization of microsatellite loci in Galápagos caterpillar hunters (Coleoptera, Carabidae, Calosoma)
- Five microsatellite loci were isolated from the Galápagos caterpillar hunter Calosoma granatense. Polymorphism ranges from four to 14 alleles, and observed and expected heterozygosities range from 0.138 to 0.889 and 0.197-0.902, respectively. Cross-amplification of the developed primers was successful in the related species C. leleuporum.
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Some gastronomic aspects of bird species in still life paintings of Frans Snyders (Antwerp, 1579-1657)
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Post-mortem findings and causes of death of harbour porpoises (Phocoena phocoena) stranded from 1990 to 2000 along the coastlines of Belgium and Northern France
- Between the years 1990 and 2000, an attempt was made to determine the causes of death of 55 harbour porpoises stranded along the Belgian and northern French coasts. From 1990 to 1996, only five carcasses were collected as against seven in 1997, eight in 1998, 27 in 1999 and eight in 2000. The sex ratio was normal and most of the animals were juvenile. The most common findings were emaciation, severe parasitosis and pneumonia. A few cases of fishing net entanglement were observed. The main microscopical lesions were acute pneumonia, massive lung oedema, enteritis, hepatitis and gastritis. Encephalitis was observed in six cases. No evidence of morbillivirus infection was detected. Pneumonia was associated with bacteria or parasites, or both. The causes of death and the lesions were similar to those previously reported in other countries bordering the North Sea. The cause of the increased numbers of carcasses in 1999 was unclear but did not include viral epizootics or net entanglement. A temporary increase in the porpoise population in the southern North Sea may have been responsible. © 2002 Elsevier Science Ltd. All rights reserved.
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Multivariate morphometrics of soft body parts in terrestrial slugs: Comparison between two datasets, error assessment and taxonomic implications
- Ten flexible characters for two collections of a pulmonate land slug that differed in their method of preservation (ethanol or freezer/ethanol), were measured four times - twice with calipers and twice with a stage micrometer - by two different people. Repeated measurements were used to estimate the measurement error (ME) associated with the ten characters. ME ranged from 2\% to 90\% and differed significantly between the characters. Characters with low mean values and a high flexibility showed the largest ME. With the stage micrometer, one measurer obtained significantly higher ME, but both measurers obtained the same ME with calipers. There was no detectable effect of preservation method on the size and shape of characters, yet, results differed when characters were measured with either calipers or a stage micrometer. One measurer obtained significantly larger mean values for three characters with calipers. Additionally, presumed species differences between three Carinarian species (Arion fasciatus, A. silvaticus and A circumscriptus; subgenus Carinarian Hesse 1926) were tested using principal component analysis and canonical discriminant analysis. Despite possible measurer biases and high ME, the different datasets yielded highly similar results, indicating that biometrical data of soft, flexible structures may yield valuable and reliable data which can be examined statistically. Our results indicate that A. fasciatus is larger than the other two species, but it is hard to distinguish from both of the other species when size is not considered. Arion silvaticus and A. circumscriptus can be separated only when colour characters are used. © 2002 The Linnean Society of London.
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Mouthpart deformities and nucleolus activity in field-collected Chironomus riparius larvae
- Chironomid mouthpart deformities and aberrations of their polytenic chromosomes are sublethal responses to toxic stress. These endpoints have been used in several cases as bioindications for sediment pollution. In the present study we aimed to establish whether there was an association between mouthpart deformities and nucleolus activity in the polytenic chromosomes. Such information could be useful to gain insight into the mechanisms involved in the occurrence of mouthpart deformities and their consequences on the larvae. Third-instar larvae of Chironomus riparius were collected at a site downstream of a sewage treatment plant mostly contaminated by pesticides. Larvae were then raised in the laboratory in aquaria containing sediment and water from the study location. During a 16-day period, larvae ready to molt to the fourth instar were reared individually. Within a few hours of their molt, the larvae were preserved. The presence of mouthpart deformities (menturn, mandibles, and pecten epipharyngis) and the percentage of active nucleoli were assessed. Those larvae presenting menturn deformities had a significantly higher incidence of active nucleoli in their polytenic chromosomes than nondeformed larvae. Because a high number of active nucleoli generally indicates increased rRNA synthesis, deformed larvae seemed to exhibit a higher protein synthesis than normal individuals. The synthesis of additional proteins may increase deformed larva tolerance to toxicants.
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Isoelectric focusing as a tool to evaluate carabid beetles as predatory agents of the pest slug Arion lusitanicus
- Isoelectric focusing was investigated to detect esterases of the pest slug Arion lusitanicus in the crop contents of predatory carabid beetles. The method is exceptionally well suited for field studies, as it is fast, cheap, easy to apply, and almost species-specific. The identification of A. lusitanicus was enabled by four characteristic, stable esterase electromorphs. The profile clearly differed from the band patterns of the digestive enzymes of the carabid beetles, from esterases of other potential prey species and even from the enzymes of early developmental stages of the slug. To test the heaviest stained isoenzyme for its decay under controlled conditions, three carabid species were fed on a fixed amount of slug hepatopancreas. In Carabus cancellatus and Pterostichus melanarius the enzyme lost 35\% of its activity after 16 h, fitting a logarithmic curve, whereas in Carabus granulatus the same decay status was already reached after 8 h following a linear regression. Both, the similarities and differences between beetle species might be due to their mode of extra- versus intraintestinal digestion and the amount of hepatopancreas fed. The temperature during digestion was also influential, as the regression slopes of esterase activity between the two temperature regimes tested in C. granulatus were significantly different. The volume of crop contents decreased during digestion in both Carabus species, corresponding to the decline in esterase. In contrast, the crop volume of P. melanarius reached its maximum almost 4 h after ingestion. This was interpreted as an effect of its mode of ingestion and time-elapsed enzyme production. © 2002 Elsevier Science Ltd. All rights reserved.
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Presence of Anopheles culicifacies B in Cambodia established by the PCR-RFLP assay developed for the identification of Anopheles minimus species A and C and four related species
- A polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) assay developed for identification of five species of the Anopheles minimus Theobald group and a related mosquito species of the Myzomyia Series (Diptera: Culicidae) was applied to morphologically identified adult female specimens collected in Ratanakiri Province, north-eastern Cambodia. In addition to finding An. aconitus Dönitz, An. minimus species A and An. pampanai Büttiker & Beales, some specimens showed a new restriction banding pattern. Siblings of specimens that exhibited this new PCR-RFLP pattern were morphologically identified as An. culicifacies James sensu lato. Based on nucleotide sequences of the ribonuclear DNA internal transcribed spacer 2 region (ITS2) and the mitochondrial cytochrome oxidase I gene (COI), these specimens were recognized as An. culicifacies species B (sensu Green & Miles, 1980), the first confirmed record of the An. culicifacies complex from Cambodia. This study shows that the PCR-RFLP assay can detect species not included in the initial set-up and is capable of identifying at least seven species of the Myzomyia Series, allowing better definition of those malaria vector and non-vector anophelines in South-east Asia.
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The east carpathian loess record: A reference for the middle and late Pleniglacial stratigraphy in central Europe [La sequence loessique du domaine est-carpatique: Une référence pour le pléniglaciaire moyen et supérieur d'Europe centrale]
- The East Carpathian regional sequence established for the middle and late pleniglacial loess is based on records from the Palaeolithic sites Molodova V (Ukraine), Mitoc-Malu Galben (Romania) and Cosautsi (Moldova). The special importance of this long sequence lies 1) in the high quality of the pedosedimentary and climatic records favoured by the position of the three sites within the terrace system of the Dniester and Prut basins and 2) in the high chronological resolution within the period posterior to 33,000 BP determined by the archaeological context of the multilayered Palaeolithic sites. A large number of these layers with a quite regular distribution within the sequence appeared to be rich in good quality organic material for accurate radiometric dating. This made possible to establish a well documented pedosedimentary and climatic succession encompassing the main part of the middle pleniglacial and almost the whole upper pleniglacial, with a resolution degree around one millennium or several centuries. The analysis of this new sequence revealed a quite coherent internal structure that illustrates the complexity of the sedimentary and climatic dynamics within the time span 33,000-10,000 BP.
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Palynology, paleoenvironments, and organic carbon isotope evolution in lagoonal Paleocene-Eocene boundary settings in North Belgium
- Integration of new data in sedimentology, micropaleontology and carbon isotope analysis of the Paleocene-Eocene boundary sequence in northern Belgium enables differentiation of a series of biotic and tectonic events, generally associated with the brief episode of global warming, known as the Initial Eocene Thermal Maximum (IETM, formerly LPTM), and to establish their succession in time. The onset of the carbon isotope excursion (CIE), positioned at the base of the Tienen Formation, is shown to precisely coincide with the onset of a massive Apectodinium abundance, and to be coincident or very close to the development of deeply incised paleovalleys. The organic carbon isotope curve recorded in the lagoonal settings of northern Belgium, presents a complex structure, marked by multiple anomalies and, consequently, is not believed to result from a single instantaneous event. The most negative values (-26\%) are recorded in the Apectodinium-dominated interval (75\%) in the lower part of the Tienen Formation. However, the range of the Apectodinium acme (50\%) suggests that the IETM probably lasted until the end of the deposition of the Tienen Formation. The kaolinite influxes at its base and within its middle part are proved to be unrelated to the CIE. The integration of the dinoflagellate cyst and the carbon isotope data has led to the establishment of a refined chronostratigraphic framework, allowing the depositional history of the southern North Sea Basin to be deciphered. During pre-IETM and post-IETM times widely uniform marine depositional regimes existed throughout the area because of tectonic quiescence. This strongly contrasted with the IETM interval, which is marked by restricted complex lagoonal conditions and differential subsidence. In spite of the extreme warm climate and the tectonic instability of the area, vegetation was relatively stable across the IETM and marked by low extinction and first-occurrence rates. © 2003 Geological Society of America.
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A perspective on the importance of reproductive mode in astrobiology
- Reproduction is a vital characteristic of life, and sex is the most common reproductive mode in the eukaryotic world. Sex and reproduction are not necessarily linked mechanisms: Sexuality without reproduction exists, while several forms of asexual reproduction are known. The occurrence of sexuality itself is paradoxical, as it is very costly in evolutionary terms. Most of the hypotheses (more than 20) attempting to explain the prevalence of sex fall into two categories: Sex either creates good gene combinations for adaptation to environments or eliminates bad gene combinations counteracting the accumulation of mutations. In spite of this apparent wealth of beneficial effects of sex, asexuality is not rare. Most eukaryotic, asexual lineages are short-lived and can only persist through the presence of sexual roots, but at least two animal groups, bdelloid rotifers and darwinulid ostracods, seem to claim the status of ancient asexuals. Research on (a)sexuality is relevant to astrobiology in a number of ways. First, strong relationships between the origin and persistence of life in extreme environments and reproductive mode are known. Second, the "habitability" of nonterrestrial environments to life greatly depends on reproductive mode. Whereas asexuals can do equally well or better in harsh environments, they fail to adapt fast enough to changing abiotic and biotic environments. Third, it has been shown that plants reproduce mainly asexually in space, and sperm production and motility in some vertebrates are hampered. Both findings indicate that extraterrestrial life under conditions different from Earth might be dominated by asexual reproduction. Finally, for exchange of biological material between planets, the choice of reproductive mode will be important. © Mary Ann Liebert, Inc.
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Valve surface structure of Candona neglecta Sars, 1887 (Crustacea, Ostracoda)
- The valves of Candona neglecta Sars, 1887, a common freshwater ostracod occurring throughout the Holarctic, were formerly described to bear tiny tubercles and spinules. It is here shown with the help of the scanning electron microscope that the valves of this species actually appear to be smooth. The tubercles and spinules described by previous authors correspond to conspicuously wide pore canals that mimic tiny surface structures when observed in the stereomicroscope. The taxonomic importance of this character is briefly discussed and a diagnosis of the neglecta-group of Candona Baird, 1845 is given. The genus name Neglecandona, which was introduced in 2001, is unavailable in the sense of the International Code of Zoological Nomenclature.
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Meris imagery of belgian coastal waters: Mapping of suspended participate matter and chlorophyll-A
- This paper describes a first application-oriented analysis of MERIS products for Suspended Particulate Matter (SPM) and Chlorophyll-a (CHL) concentration in Belgian coastal waters. Regional algorithms designed for Belgian waters have been implemented and compared with the standard MERIS products, termed Total Suspended Matter and Algal2 respectively. The standard and regional SPM products seem robust and give similar data. Notwithstanding a more complete match-up validation analysis, these products seem sufficiently mature for use in applications such as sediment transport model validation. Results for CHL products are less convincing and further analysis is required before this data can be reliably used. In particular the MERIS Product Confidence flags have not yet been validated. The red and near infrared bands are particularly important in turbid coastal waters and should be considered a priority for further validation. MERIS full resolution mode is attractive for SPM mapping when compared with other sensors. For CHL mapping in coastal waters the superior spectral resolution and algorithm design give MERIS a distinct advantage over other ocean colour sensors. The disadvantages of MERIS, particularly for SPM mapping, are the reduced frequency (related to swath and sunglint) and availability of data.
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Mapping of chlorophyll and suspended particulate matter maps from CHRIS imagery of the oostende core site
- The image set created on 5 August 2003 by CHRIS/PROBA is analyzed to assess the feasibility of producing suspended particulate matter (SPM) and chlorophyll (CHL) maps. To produce these maps images are first destriped, atmospherically corrected and georeferenced. Once the data processing is finished, the results are compared with seaborne measurements and data products retrieved from other ocean colour sensors. The data processing with its associated problems, the comparison with seaborne and other data and the creation of SPM and CHL maps are described in this paper. Conclusions and recommendations are made in the context of considering CHRIS/PROBA as a model for the future generation of small ocean colour missions.
