Search publications of the members of the Royal Belgian institute of natural Sciences
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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.
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Centipede communities in the forests of flanders
- During a year-round pitfall sampling campaign in 56 Flemish forest stands, a total number of 21 centipede species were caught. Community analyses on the basis of the species composition revealed that three distinct clusters of forests could be recognised which are separated geographically. The Campine Region with a lot of pine forests, which is characterised by its sandy soils, contained the lowest diversity of centipedes and only Lithobius forficatus and L. calcaratus were common. Sandy Flanders with a lot of oak forests contained more species including Cryptops hortensis, the most characteristic species of this region. The Loamy Region contained a lot of oak and beech forests and Cryptops parisi and Lithobius dentatus were especially characteristic for this region.
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Effects of metal contamination on the activity and diversity of carabid beetles in an ancient Pb-Zn mining area at Plombières (Belgium)
- Carabid beetles were monthly sampled with pitfall traps in the ancient Pb-Zn mining area of Plombières during one year. Based on the total soil concentrations of lead, zinc, cadmium and copper, it was expected that zinc would probably have the most adverse effects on the populations. Activity and species richness of carabid beetles were, however, not significantly correlated with total zinc concentration nor with the water soluble and the calciumchloride extractable concentration. In fact, despite the high soil concentrations, carabid beetles did not seem to be affected in the study area. The apparent lack of effects at the high observed zinc concentrations is probably caused by the low bioavailability of zinc to the beetles in the litter of the study sites which was also reflected in the low observed water soluble zinc concentrations.
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Echiuropus bekmanae n.sp. (Crustacea, Amphipoda, Carinogammaridae) from Lake Baikal, retrieved by a new deep-water sampling device
- Lake Baikal is well known for its exceptional diversity of gammarid amphipods, with 95\% of endemics from its 270 described species representing about 20\% of the world freshwater fauna. Echiuropus (Asprogammarus) bekmanae n.sp. was collected by an 'autonomous trap system', a sampling device thoroughly described here. Although not necrophagous itself, this new species was found in two baited trap samples (at 750 and more than 1600 m) from 1995 and 1996. This rather small (13 mm) deep water species is the eighth species of the subgenus Asprogammarus, of the Baikal endemic genus Echiuropus. Diagnoses of the subgenus and the closer species are given.
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Dolichopodid biodiveristy and site quality assessment of reed marshes and grasslands in Belgium (Diptera: Dolichopodidae)
- The conservation value of grassland and reed marsh habitats in Belgium was determined on the basis of dolichopodid communities (Diptera: Dolichopodidae). Four grassland and one reed marsh sites within the 'Bourgoyen-Ossemeersen' Nature Reserve (B.O.) (Ghent) were sampled with white water traps from March 1993 until March 1994. Subsequently, these soil faunas were compared with those of reed marsh habitats in 'Het Meetjeslandse Krekengebied' (M.K.) sampled in 1990. Comparisons of species communities were carried out by means of multivariate analysis techniques. The DCA and CCA on the B.O. sites produced a clear separation between the grassland and the reed marsh communities. Light intensity and soil humidity were among the most important factors determining species distributions. The comparison between the B.O. and M.K. communities revealed that sampling sites were clustered according to their geographical location rather than to habitat type. Overall species richness and diversity was not significantly different between grasslands and reed marshes. However, conservation quality estimates of the sites using the Site Conservation Quality Index (SCQI) indicated that reed marshes comprise a considerably larger number of rare and Red Data Book species. Moreover, besides typical reed marsh-inhabiting species, reed marshes also house species with other ecological affinities sometimes in rather high abundance. As a result, reed marshes are considered highly valuable for the survival of several wetland dolichopodid species.
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First evidence of possible outcrossing in the terrestrial slug Arion intermedius (Gastropoda: Pulmonata)
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Evolutionary convergence of body shape and trophic morphology in cichlids from Lake Tanganyika
- A recent phylogenetic analysis of mitochondrial DNA sequences from eretmodine cichlids from Lake Tanganyika indicated independent origins of strikingly similar trophic specializations, such as dentition characters. Because genetic lineages with similar trophic morphologies were not monophyletic, but instead were grouped with lineages with different trophic phenotypes, raises the question of whether trophic morphology covaries with additional morphological characters. Here, we quantified morphological variation in body shape and trophically associated traits among eretmodine cichlids using linear measurements, meristic counts and landmark-based geometric morphometrics. A canonical variates analysis (CVA) delineated groups consistent with dentition characters. Multivariate regression and partial least squares analyses indicated that body shape was significantly associated with trophic morphology. When the phylogenetic relationships among taxa were taken into account using comparative methods, the covariation of body shape and trophic morphology persisted, indicating that phylogenetic relationships were not wholly responsible for the observed pattern. We hypothesize that trophic ecology may be a key factor promoting morphological differentiation, and postulate that similar body shape and feeding structures have evolved multiple times in independent lineages, enabling taxa to invade similar adaptive zones.
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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.
