Search publications of the members of the Royal Belgian institute of natural Sciences
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Over 100 years of biodiversity research on Lake Tanganyika fishes
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Patterns of evolutionary change in Baikalian gammarids inferred from DNA sequences (Crustacea, Amphipoda).
- The Baikalian gammarids (Crustacea, Amphipoda) are the most widely known and most spectacular example of an adaptive radiation among contemporary freshwater invertebrates. To study the phylogeny of the Baikalian gammarids we sequenced a 622-bp-long fragment of the nuclear gene coding for 18S rRNA from species of 18 endemic Baikalian genera and Gammarus pulex-a non-Baikalian taxon. Some important morphological characters appear independently in both lineages and suggest parallelism in the development of gigantism and body armament. The first lineage comprises benthic, mostly unarmed taxa. The second lineage contains predominantly armed taxa, most of which are detrivorous or carnivorous.
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Phylogeny and evolution of African shrews (Mammalia: Soricidae) inferred from 16s rRNA sequences.
- Current phylogenetic hypotheses on the African Crocidurinae (Soricidae) are based upon morpho-anatomical, karyological, and allozyme studies. The present study attempts to resolve the interrelationships among African Crocidurinae and their relationships to Eurasian Crocidurinae and to the subfamily Soricinae, on the basis of partial mitochondrial 16s rRNA sequences (549 bp). This is the first molecular study to include all but one of the nine currently recognized African shrew genera. In agreement with current views, two major lineages emerge. The first lineage includes Myosorex and Congosorex and supports the existence of a myosoricine taxon. The second lineage includes the six remaining genera. The genus Sylvisorex appears to be polyphyletic, whereas species of the controversial genus Crocidura are monophyletic. The genus Suncus presumably originated in Africa. The monospecific genera Ruwenzorisorex and Scutisorex and the two representatives of Paracrocidura cluster with species of other genera. Grouping patterns of species from different continents suggest that there have been multiple exchanges between Africa and Eurasia. The time estimates of these exchanges, inferred from two independent fossil-based calibrations of a molecular clock, coincide with the time estimates for migration events in other mammalian taxa.
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Phylogeny of the Lake Tanganyika cichlid species flock and its relationship to the Central and East African haplochromine cichlid fish faunas.
- Lake Tanganyika, the oldest of the East African Great Lakes, harbors the ecologically, morphologically, and behaviorally most complex of all assemblages of cichlid fishes, consisting of about 200 described species. The evolutionary old age of the cichlid assemblage, its extreme degree of morphological differentiation, the lack of species with intermediate morphologies, and the rapidity of lineage formation have made evolutionary reconstruction difficult. The number and origin of seeding lineages, particularly the possible contribution of riverine haplochromine cichlids to endemic lacustrine lineages, remains unclear. Our phylogenetic analyses, based on mitochondrial DNA sequences of three gene segments of 49 species (25\% of all described species, up to 2,400 bp each), yield robust phylogenies that provide new insights into the Lake Tanganyika adaptive radiation as well as into the origin of the Central- and East-African haplochromine faunas. Our data suggest that eight ancient African lineages may have seeded the Tanganyikan cichlid radiation. One of these seeding lineages, probably comprising substrate spawning Lamprologus-like species, diversified into six lineages that evolved mouthbrooding during the initial stage of the radiation. All analyzed haplochromines from surrounding rivers and lakes seem to have evolved within the radiating Tanganyikan lineages. Thus, our findings contradict the current hypothesis that ancestral riverine haplochromines colonized Lake Tanganyika to give rise to at least part of its spectacular endemic cichlid species assemblage. Instead, the early phases of the Tanganyikan radiation affected Central and East African rivers and lakes. The haplochromines may have evolved in the Tanganyikan basin before the lake became a hydrologically and ecologically closed system and then secondarily colonized surrounding rivers. Apparently, therefore, the current diversity of Central and East African haplochromines represents a relatively young and polyphyletic fauna that evolved from or in parallel to lineages now endemic to Lake Tanganyika.
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Phylogeographic structure and regional history of Lemniscomys striatus (Rodentia: Muridae) in tropical Africa
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Phylogeographical patterns of genetic divergence and speciation in African mole-rats (Family: Bathyergidae)
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Phylogeography and cryptic diversity of the solitary-dwelling silvery mole-rat, genus Heliophobius (family: Bathyergidae)
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Pleistocene desiccation in East Africa bottlenecked but did not extirpate the adaptive radiation of Lake Victoria haplochromine cichlid fishes.
- The Great Lakes region of East Africa, including Lake Victoria, is the center of diversity of the mega-diverse cichlid fishes (Perciformes: Teleostei). Paleolimnological evidence indicates dramatic desiccation of this lake ca. 18,000-15,000 years ago. Consequently, the hundreds of extant endemic haplochromine species in the lake must have either evolved since then or refugia must have existed, within that lake basin or elsewhere, from which Lake Victoria was recolonized. We studied the population history of the Lake Victoria region superflock (LVRS) of haplochromine cichlids based on nuclear genetic analysis (12 microsatellite loci from 400 haplochomines) of populations from Lake Kivu, Lake Victoria, and the connected and surrounding rivers and lakes. Population genetic analyses confirmed that Lake Kivu haplochromines colonized Lake Victoria. Coalescent analyses show a 30- to 50-fold decline in the haplochromine populations of Lake Victoria, Lake Kivu, and the region ca. 18,000-15,000 years ago. We suggest that this coincides with drastic climatic and geological changes in the late Pleistocene. The most recent common ancestor of the Lake Victoria region haplochromines was estimated to have existed about 4.5 million years ago, which corresponds to the first radiation of cichlids in Lake Tanganyika and the origin of the tribe Haplochrominii. This relatively old evolutionary origin may explain the high levels of polymorphism still found in modern haplochromines. This degree of polymorphism might have acted as a "genetic reservoir" that permitted the explosive radiation of hundreds of haplochromines and their array of contemporary adaptive morphologies.
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Population structure in two sympatric species of the Lake Tanganyika cichlid tribe Eretmodini: evidence for introgression.
- Patterns of genetic differentiation were analysed and compared in two sympatric species of the endemic Lake Tanganyika cichlid tribe Eretmodini by means of mitochondrial DNA (mtDNA) sequences of the control region and six microsatellite DNA loci. The sample area covers a total of 138 km of mostly uninterrupted rocky shoreline in the Democratic Republic of Congo and includes the entire distribution range of Tanganicodus cf. irsacae that stretches over a distance of 35 km. Both markers detected significant genetic differentiation within and between the two species. T. cf. irsacae contained lower overall genetic variation than Eretmoduscyanostictus, possibly due to its more restricted range of distribution and its smaller effective population sizes. Complete fixation of Tanganicodus mtDNA haplotypes was observed in Eretmodus at two localities, while at two other localities some Tanganicodus individuals possessed Eretmodus mtDNA haplotypes. Taking into account the relatively large average sequence divergence of 6.2\% between the two species, as well as the geographical distribution of mtDNA haplotypes in the lake, the observed pattern is more likely to be a consequence of asymmetric introgression than of shared ancestral polymorphism. As there is significant population differentiation between sympatric Tanganicodus and Eretmodus populations, the events of introgressions may have happened after secondary contact, but our data provide no evidence for ongoing gene flow and suggest that both species are reproductively isolated at present time.
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Providing access to Albertine Rift biodiversity data: a queryable website on taxon and specimen information for selected Albertine Rift species: birds, butterflies (Papilionidae (Papilio, Graphium), Nymphalidae (Charaxes)), flowering plants (coffee family, Rubiaceae), and lacustrine fishes (Cichlidae)
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Rapid chromosomal evolution in the mesic four-striped grass rat Rhabdomys dilectus (Rodentia, Muridae) revealed by mtDNA phylogeographic analysis
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Rapidly evolving lineages impede the resolution of phylogenetic relationships among Clitellata (Annelida).
- The phylogenetic relationships of the Clitellata were investigated using a data set with published and new complete or partial 18S rRNA and mtCOI gene sequences of 13 and 49 taxa representing 8 and 14 families, respectively. Three different alignments were considered for 18S, and the possible influence of departures from rate constancy among sites was evaluated by analyses using a Gamma model of rate heterogeneity. Maximum-likelihood estimates of the shape parameter alpha of the Gamma distribution were very low, whatever the alignment or the gene considered, suggesting that phylogenetic reconstructions taking into account the rate heterogeneity among sites are likely to be the most reliable. Analyzed separately, the two genes did not resolve the relationships among the Clitellata, but the consensus tree was congruent with the morphology-based relationships. Our data suggest the inclusion of the Euhirudinea, Acanthobdellida, and Branchiobdellida in the Oligochaeta and suggest the Lumbriculidae as the link between both assemblages. Although separate analyses of both genes, as well as different alignments for the 18S rRNA sequences, yielded conflicting results concerning the phylogenetic position of leeches and leech-like worms vis-à-vis the Oligochaeta, subsequent analyses using the Gamma model greatly reduced the observed inconsistencies. Our analyses show that among the Clitellata, the leeches and the leech-like and gutless worms represent significantly faster evolving lineages. It is suggested that the observed higher mutation rates may be explained by the fact that these lineages contain almost exclusively commensal and/or parasitic taxa.
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Recensie: PW Hochachka & TP Mommsen (eds.): Molecular biology frontiers
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Reduced gene flow at pericentromeric loci in a hybrid zone involving chromosomal races of the house mouse Mus musculus domesticus.
- The West European house mouse, Mus musculus domesticus, is a particularly suitable model to investigate the role of chromosomal rearrangements in reproductive isolation. In fact, it exhibits a broad range of chromosomal polymorphism due to Robertsonian (Rb) fusions leading to various types of contact zones between different chromosomal races. In the present study, we analyzed a parapatric contact in central Italy between the Cittaducale chromosomal race (CD: 2n= 22) and the surrounding populations with standard karyotype (2n= 40) to understand if Rb fusions play a causative role in speciation. One hundred forty-seven mice from 17 localities were genotyped by means of 12 microsatellite loci. A telomeric and a pericentromeric locus situated on six chromosome arms (four Rbs and one telocentric) were selected to detect differences in the amount of gene flow for each locus in different chromosomal positions. The analyses performed on the two subsets of loci show differences in the level of gene flow, which is more restricted near the centromeres of Rb chromosomes. This effect is less pronounced in the homozygotes populations settled at the border of the hybrid zone. We discuss the possible cause of the differential porosity of gene flow in Rbs considering "hybrid dysfunctions" and "suppressed recombination" models.
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Repeated unidirectional introgression of nuclear and mitochondrial DNA between four congeneric Tanganyikan cichlids.
- With an increasing number of reported cases of hybridization and introgression, interspecific gene flow between animals has recently become a widely accepted and broadly studied phenomenon. In this study, we examine patterns of hybridization and introgression in Ophthalmotilapia spp., a genus of cichlid fish from Lake Tanganyika, using mitochondrial and nuclear DNA from all four species in the genus and including specimens from over 800 km of shoreline. These four species have very different, partially overlapping distribution ranges, thus allowing us to study in detail patterns of gene flow between sympatric and allopatric populations of the different species. We show that a significant proportion of individuals of the lake-wide distributed O. nasuta carry mitochondrial and/or nuclear DNA typical of other Ophthalmotilapia species. Strikingly, all such individuals were found in populations living in sympatry with each of the other Ophthalmotilapia species, strongly suggesting that this pattern originated by repeated and independent episodes of genetic exchange in different parts of the lake, with unidirectional introgression occurring into O. nasuta. Our analysis rejects the hypotheses that unidirectional introgression is caused by natural selection favoring heterospecific DNA, by skewed abundances of Ophthalmotilapia species or by hybridization events occurring during a putative spatial expansion in O. nasuta. Instead, cytonuclear incompatibilities or asymmetric behavioral reproductive isolation seem to have driven repeated, unidirectional introgression of nuclear and mitochondrial DNA into O. nasuta in different parts of the lake.
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Replicated evolution of trophic specializations in an endemic cichlid fish lineage from Lake Tanganyika.
- The current phylogenetic hypothesis for the endemic Lake Tanganyika cichlid fishes of the tribe Eretmodini is based solely on morphology and suggests that more complex trophic morphologies derived only once from a less specialized ancestral condition. A molecular phylogeny of eretmodine cichlids based on partial mitochondrial DNA cytochrome b and control-region sequences was used to reconstruct the evolutionary sequence of trophic adaptations and to test alternative models of morphological divergence. The six mitochondrial lineages found disagree with the current taxonomy and the morphology-based phylogeny. Mitochondrial lineages with similar trophic morphologies are not grouped monophyletically but are typically more closely related to lineages with different trophic phenotypes currently assigned to other genera. Our results indicate multiple independent origins of similar trophic specializations in these cichlids. A pattern of repeated divergent morphological evolution becomes apparent when the phylogeography of the mitochondrial haplotypes is analyzed in the context of the geological and paleoclimatological history of Lake Tanganyika. In more than one instance within Lake Tanganyika, similar morphological divergence of dentitional traits occurred in sympatric species pairs. Possibly, resource-based divergent selective regimes led to resource partitioning and brought about similar trophic morphologies independently and repeatedly.
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Research day
- Numerous official bodies (e.g. the Federal Public wo Services), scientific institutions and almost all universities of the country accepted the invitation. The researchers of RBINS could welcome almost 100 external participants rom around 20 institutions. The Universities of Liège and Leuven, the National nstitute of Criminalistics and Criminology, the Royal Museum for Central Africa, sent particularly large delegations. No less than 57 posters presented the Institute and its research activities; participants had been given the opportunity to register for 22 guided tours hrough the labs and the collections’ storage rooms. The program of the guided tours has proven to be very seducing; some groups got three times more visitors than foreseen. The posters were also continuously visited and discussed all along the day. The participants had to make a choice between different possibilities in the program, which caused sometimes understandable regrets.
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Resistance to water pollution in natural gudgeon (Gobio gobio) populations may be due to genetic adaptation.
- Anthropogenic disturbances cause the environment to change relatively fast. It is reasonable to assume that it is very unlikely for individuals to develop genetic adaptations to their polluted habitats, since adaptation through natural selection is a relatively slow process. Nevertheless, several studies have shown that such adaptations to changing environmental conditions may develop faster than anticipated. This study investigates the impact of historical metal pollution on a natural population of the gudgeon, Gobio gobio. Specimens from a contaminated site and a reference population were subjected to a series of three exposure experiments to cadmium after an acclimation period to reconstituted fresh water of 36 days. First, we performed an acute toxicity test on a sub-sample of both experimental groups to determine times-to-death (TTD) and lethal body burdens (LBB). The remaining individuals were used in a chronic Cd-exposure experiment, after which total Cd-body concentration, as well as Cd-concentrations and metallothionein-like protein (MTLP) levels in liver and gill tissue were determined. From the specimens that were not sacrificed for these measurements, a random subsample was subjected to a second acute toxicity test to evaluate the effect of chronic Cd-exposure (acclimation) on TTD and LBB. Our results show that, particularly after an extra acclimation period to a sublethal Cd-concentration, specimens originating from the contaminated sample area survived the acute exposure experiments better, despite the fact that neither the average Cd-accumulation rate, nor the lethal body concentrations differed between fishes from both groups. We also find that gudgeons from both populations translocated Cd from the gills (and probably also from other compartments) to the liver, where it can be more efficiently detoxified by MTLPs. Indeed, MTLP levels were found to increase faster in liver and gill tissue of specimens from the contaminated site, resulting in significantly higher MTLP-levels in the organs of these fishes. Although this study does not provide direct evidence for a genetic basis of Cd resistance (i.e. at the gene level), our results indicate that the regulation of MTLP-gene expression may involve a genetic component.
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Response to Comment on “ Origin of the Superflock of Cichlid Fishes from
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Seit über 100 Jahren im Blickpunkt der Forschung: Die vielvalt der Tanganjikaseefische (translated from English)
