Jos Snoeks

Royal Museum for Central Africa, Tervueren, Flemish, Belgium

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Publications (61)156.72 Total impact

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    ABSTRACT: The unparalleled biodiversity of Lake Tanganyika (Africa) has fascinated biologists for over a century; its unique cichlid communities are a preferred model for evolutionary research. Although species delineation is, in most cases, relatively straightforward, higher-order clas- sifications were shown not to agree with monophyletic groups. Here, traditional morphologi- cal methods meet their limitations. A typical example are the tropheine cichlids currently belonging to Simochromis and Pseudosimochromis. The affiliations of these widespread and abundant cichlids are poorly understood. Molecular work suggested that genus and species boundaries should be revised. Moreover, previous morphological results indicated that intraspecific variation should be considered to delineate species in Lake Tanganyika cichlids. We review the genera Simochromis and Pseudosimochromis using an integrative approach. Besides a morphometric study and a barcoding approach, monogenean Cichli- dogyrus (Platyhelminthes: Ancyrocephalidae) gill parasites, often highly species-specific, are used as complementary markers. Six new species are described. Cichlidogyrus raey- maekersi sp. nov., C. muterezii sp. nov. and C. banyankimbonai sp. nov. infect S. dia- gramma. Cichlidogyrus georgesmertensi sp. nov. was found on S. babaulti and S. pleurospilus, C. franswittei sp. nov. on both S. marginatus and P. curvifrons and C. frank- willemsi sp. nov. only on P. curvifrons. As relatedness between Cichlidogyrus species usu- ally reflects relatedness between hosts, we considered Simochromis monotypic because the three Cichlidogyrus species found on S. diagramma belonged to a different morphotype than those found on the other Simochromis. The transfer of S. babaulti, S. marginatus, S. pleurospilus and S. margaretae to Pseudosimochromis was justified by the similarity of their Cichlidogyrus fauna and the intermediate morphology of S. margaretae. Finally parasite data also supported the synonymy between S. pleurospilus and S. babaulti, a species that contains a large amount of geographical morphological variation.
    PLoS ONE 04/2015; 10(4). DOI:10.1371/journal.pone.0124474 · 3.53 Impact Factor
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    ABSTRACT: The species flocks of cichlid fishes in the East African Great Lakes are the largest vertebrate adaptive radiations in the world and illustrious textbook examples of convergent evolution between independent species assemblages. Although recent studies suggest some degrees of genetic exchange between riverine taxa and the lake faunas, not a single cichlid species is known from Lakes Tanganyika, Malawi and Victoria that is derived from the radiation associated with another of these lakes. Here, we report the discovery of a haplochromine cichlid species in Lake Tanganyika, which belongs genetically to the species flock of haplochromines of the Lake Victoria region. The new species colonized Lake Tanganyika only recently, suggesting that faunal exchange across watersheds and, hence, between isolated ichthyofaunas, is more common than previously thought.
    Royal Society Open Science 03/2015; 2(3-3):140498. DOI:10.1098/rsos.140498
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    ABSTRACT: The faunal diversity of Lake Tanganyika, with its fish species flocks and its importance as a cradle and reservoir of ancient fish lineages seeding other radiations, has generated a considerable scientific interest in the fields of evolution and biodiversity. The Tropheini, an endemic Tanganyikan cichlid tribe, fills a peculiar phylogenetic position, being closely related to the haplochromine radiations of Lakes Malawi and Victoria. Several problems remain regarding their genus-level classification. For example, the monotypic genus Interochromis is phylogenetically nested within Petrochromis; its only representative, I. loocki, has often been reclassified. As monogenean flatworms are useful markers for fish phylogeny and taxonomy, the monogenean fauna of Interochromis loocki was examined and compared to that of other tropheine cichlids. Three new monogenean species belonging to Cichlidogyrus are described from Interochromis loocki: Cichlidogyrus buescheri Pariselle and Vanhove, sp. nov., Cichlidogyrus schreyenbrichardorum Pariselle and Vanhove, sp. nov. and Cichlidogyrus vealli Pariselle and Vanhove, sp. nov. Their haptoral anchors remind more of congeners infecting species of Petrochromis than of all Cichli­dogyrus spp. hitherto described from other tropheine cichlids. Attachment organ morphology has been proven to mirror the phylogenetic affinities of Cichlidogyrus lineages. Therefore the monogenean parasite fauna of I. loocki reflects this host’s position within Petrochromis. Moreover, I. loocki differs in habitat choice from Petrochromis spp. This study hence confirms that host range and host-specificity in Cichlidogyrus spp. parasitizing tropheines is determined by the host’s phylogenetic position, rather than by a shared ecological niche.
    Contributions to zoology Bijdragen tot de dierkunde 01/2015; 84(1):25-38. · 2.03 Impact Factor
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    ABSTRACT: 1. In semi-arid regions, the construction of small reservoirs is important in alleviating water shortage, although many have poor water quality with high turbidity and dense blooms of algae and cyanobacteria, and there are large differences in the ecology of such reservoirs. 2. We took advantage of two exceptionally dry years in northern Ethiopia to study the effect of a dry period and the associated fish kills on reservoir ecology and water quality. We studied 13 reservoirs, seven of which dried up in 2009. Four of the latter dried up again in 2010. We monitored the ecology of these reservoirs from 2009 to 2011, hypothesising that the pattern of reservoir drying would explain ecological differences among them. 3. Reservoirs that refilled after drying had a significantly lower fish biomass, lower biomass of phytoplankton (expressed as chlorophyll-a) and cyanobacteria (Microcystis), clearer water, greater macrophyte cover and lower nutrient concentrations than reservoirs that did not dry. Although the differences in water quality were most striking in the wet season after a drying event, there were persistent effects on reservoir ecology. The three categories of reservoirs we distinguished, based on their behaviour in 2009 and 2010, also showed differences in 2004, a year during which none of the reservoirs dried out. While drying evidently results in better water quality, we could not disentangle the effects of drying per se from that of reductions in fish biomass. The total combined effect was highly significant in all 3 years, whereas the separate effects of drying and loss of fish were only significant in 2004. 4. Our results suggest that differences in water quality and ecology among reservoirs depend on their propensity to dry out. Drying might be used as a restoration measure to reduce potentially harmful cyanobacterial blooms in reservoirs. Keywords: Ethiopia, fish biomass, Microcystis, reservoir ecology, water clarity
    8th International Shallow Lakes Conference,, Antalya, Turkey; 10/2014
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    ABSTRACT: Riverine fish that colonize reservoirs can have a strong influence on the ecology of these systems. To understand this impact, it is important to know what they feed upon. In the reservoirs, they are exposed to different food sources compared to the riverine environment. We studied diet of 404 specimens belonging to two species of the riverine cyprinid genus Garra (G. blanfordii and G. dembecha) from six reservoirs in the highlands of northern Ethiopia using gut contents analysis. Detritus was an important food resource for both species. There was a significant difference in diet composition between G. blanfordii and G. dembecha. While detritus was the dominant food item in both, the diet of G. dembecha is distinguished from that of G. blanfordii by a lower detritus proportion, an additional dominance of chironomid food items. The diet composition of G. dembecha was similar in all reservoirs, whereas the diet composition of G. blanfordii varied among reservoirs and depended on prey availability. The benthic feeding habits of Garra in the reservoirs, reflected by high proportion of detritus and chironomids may contribute to sediment resuspension by disturbing the bottom sediment, and may thus affect reservoir ecology through nutrient enrichment.
    8th International Shallow Lakes Conference, Antalya, Turkey; 10/2014
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    ABSTRACT: Labeo rosae, a species with a native range in Southern Africa, was discovered in the Congo basin by re-identification of two museum specimens previously identified as Labeo mesops. The occurrence of this species in the upper Congo implies a range extension of the species of more than 1000 km. Although the species' distribution is mirrored by that of some other Cypriniformes, its occurrence in the Congo might be due to introduction by humans.
    Journal of Fish Biology 08/2014; 85(5). DOI:10.1111/jfb.12491 · 1.73 Impact Factor
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    ABSTRACT: A checklist of the fishes of the Upper Luapula area, situated in the Bangweulu-Mweru ecoregion (Upper Congo) between the Bangweulu swamps and the Mumbatuta falls, is presented, with details of the distribution and com- mon names in English and Bemba. Seventy-one species are recorded, 33 of which belong to the Cyprinidae and Cichlidae. Ichthyofaunal comparisons confirm the inclusion of the Upper Luapula area within the species-poor Bangweulu–Chambeshi subregion. This subregion was previously thought to have a Zambezian rather than a Congolese ichthyofauna. However, ichthyofaunal comparisons showed a higher similarity with the Congo basin. This study presents an updated list of the fishes of Kasanka National Park, the sole protected area within the Upper Luapula area. Five synomymies are presented and the recent introduction of an exotic species, Oreochromis andersonii, is reported.
    Ichthyological Exploration of Freshwaters 04/2014; 24(4):329-345. · 2.28 Impact Factor
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    ABSTRACT: The status of the Distichodus antonii assemblage, all large-sized, banded Distichodus species with a brownish-greenish colour pattern from the Congo basin, incorporating Distichodus antonii, Distichodus atroventralis, Distichodus fasciolatus, Distichodus langi and Distichodus mossambicus, has been revised. Distichodus antonii, D. fasciolatus and D. langi are found to be valid species, though the latter has long been considered a possible junior synonym of D. antonii. A detailed redescription for each of these three species is provided. Reports of D. mossambicus from the Congo basin are based on misidentifications; these specimens are assigned to the D. atroventralis complex, a seemingly polyspecific complex in need of further in-depth revision. An identification key to the large-sized Distichodus species from the Congo basin is provided.
    Journal of Natural History 03/2014; 48(27-28):1707-1735. DOI:10.1080/00222933.2013.862312 · 0.93 Impact Factor
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    ABSTRACT: In semi-arid regions, the construction of small reservoirs is important in alleviating water shortage, although many have poor water quality with high turbidity and dense blooms of algae and cyanobacteria, and there are large differences in the ecology of such reservoirs.We took advantage of two exceptionally dry years in northern Ethiopia to study the effect of a dry period and the associated fish kills on reservoir ecology and water quality. We studied 13 reservoirs, seven of which dried up in 2009. Four of the latter dried up again in 2010. We monitored the ecology of these reservoirs from 2009 to 2011, hypothesising that the pattern of reservoir drying would explain ecological differences among them.Reservoirs that refilled after drying had a significantly lower fish biomass, lower biomass of phytoplankton (expressed as chlorophyll-a) and cyanobacteria (Microcystis), clearer water, greater macrophyte cover and lower nutrient concentrations than reservoirs that did not dry. Although the differences in water quality were most striking in the wet season after a drying event, there were persistent effects on reservoir ecology. The three categories of reservoirs we distinguished, based on their behaviour in 2009 and 2010, also showed differences in 2004, a year during which none of the reservoirs dried out. While drying evidently results in better water quality, we could not disentangle the effects of drying per se from that of reductions in fish biomass. The total combined effect was highly significant in all 3 years, whereas the separate effects of drying and loss of fish were only significant in 2004.Our results suggest that differences in water quality and ecology among reservoirs depend on their propensity to dry out. Drying might be used as a restoration measure to reduce potentially harmful cyanobacterial blooms in reservoirs.
    Freshwater Biology 02/2014; 59(4). DOI:10.1111/fwb.12312 · 2.91 Impact Factor
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    ABSTRACT: Intra-specific morphological variation in the cichlid Tropheus duboisi from 10 localities over its entire known distribution area along the central eastern and northern shore of Lake Tanganyika was investigated. This revealed significant differences between various populations that are geographically isolated. These morphological observations only partially correspond to the results of a haplotype network, based on mtDNA. In addition, a difference in the timing of the onset of the adult colour pattern was discovered for one isolated population. The occurrence of morphological intra-specific differentiation is discussed with respect to the basal position of T. duboisi within Tropheus as well as to the presumed morphological stasis of the genus.
    Hydrobiologia 11/2013; 748(1). DOI:10.1007/s10750-013-1692-5 · 2.21 Impact Factor
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    7th International Symposium on Monogenea, Rio de Janeiro, Brazil; 08/2013
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    ABSTRACT: Garra species are among the most abundant fish in small rivers of northern Ethiopia. Many manmade reservoirs in the region have been colonized by Garra, which often are the only fish species present and have become very abundant. Little is known about the ecology of these reservoir populations of riverine species. In this study we investigated the distribution patterns and gut fullness of 2 dominant species, G. blanfordii and G. geba, in 3 recently created reservoirs (Gereb Awso, Tsinkanet, and Mai Gassa I) in Tigray, northern Ethiopia. Species composition differed among reservoirs. Our data on fish catch densities and the fullness of the foregut suggest that the ecology of the Garra populations in the reservoirs is likely influenced by the avoidance of predation by birds. G. blanfordii, and to a lesser extent G. geba, foraged most actively after sunset.
    Inland Waters 04/2013; 3(3):331-340. DOI:10.5268/IW-3.3.572 · 1.43 Impact Factor
  • E Decru, E Vreven, J Snoeks
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    ABSTRACT: An α-taxonomic revision of the African pike, Hepsetus odoe, from Lower Guinea is provided. The results show that three different species occur in Lower Guinea instead of one. Hepsetus akawo, recently described from West Africa, is present in the northern part of Lower Guinea; Hepsetus lineata, the most widespread species within Lower Guinea, is known from the Sanaga (Cameroon) in the north to the Shiloango (Democratic Republic of the Congo) in the south and Hepsetus kingsleyae sp. nov. is endemic to the Ogowe Basin. The new species H. kingsleyae is described and H. lineata, which is elevated here to the species level, is redescribed. Hepsetus lineata can easily be recognized by its prominent horizontal line pattern on the flanks and differs further from H. akawo and H. kingsleyae in the number of lateral-line scales and the number of gill rakers. Hepsetus kingsleyae differs from H. lineata and H. akawo by its narrow head, elongated snout and narrow, knife-shaped body. All three species are also distinguishable from H. odoe and the recently revalidated H. cuvieri. A few exceptional specimens could not be allocated to one of the three species and may represent hybrids because of their mixed diagnostic characters or their intermediate values.
    Journal of Fish Biology 04/2013; 82(4):1351-75. DOI:10.1111/jfb.12079 · 1.73 Impact Factor
  • 02/2013; DOI:10.5852/ejt.2013.39
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    ABSTRACT: BACKGROUND: Adaptation to different ecological environments is thought to drive ecological speciation. This phenomenon culminates in the radiations of cichlid fishes in the African Great Lakes. Multiple characteristic traits of cichlids, targeted by natural or sexual selection, are considered among the driving factors of these radiations. Parasites and pathogens have been suggested to initiate or accelerate speciation by triggering both natural and sexual selection. Three prerequisites for parasite-driven speciation can be inferred from ecological speciation theory. The first prerequisite is that different populations experience divergent infection levels. The second prerequisite is that these infection levels cause divergent selection and facilitate adaptive divergence. The third prerequisite is that parasite-driven adaptive divergence facilitates the evolution of reproductive isolation. Here we investigate the first and the second prerequisite in allopatric chromatically differentiated lineages of the rock-dwelling cichlid Tropheus spp. from southern Lake Tanganyika (Central Africa). Macroparasite communities were screened in eight populations belonging to five different colour morphs. RESULTS: Parasite communities were mainly composed of acanthocephalans, nematodes, monogeneans, copepods, branchiurans, and digeneans. In two consecutive years (2011 and 2012), we observed significant variation across populations for infection with acanthocephalans, nematodes, monogeneans of the genera Gyrodactylus and Cichlidogyrus, and the copepod Ergasilus spp. Overall, parasite community composition differed significantly between populations of different colour morphs. Differences in parasite community composition were stable in time. The genetic structure of Tropheus populations was strong and showed a significant isolation-by-distance pattern, confirming that spatial isolation is limiting host dispersal. Correlations between parasite community composition and Tropheus genetic differentiation were not significant, suggesting that host dispersal does not influence parasite community diversification. CONCLUSIONS: Subject to alternating episodes of isolation and secondary contact because of lake level fluctuations, Tropheus colour morphs are believed to accumulate and maintain genetic differentiation through a combination of vicariance, philopatric behaviour and mate discrimination. Provided that the observed contrasts in parasitism facilitate adaptive divergence among populations in allopatry (which is the current situation), and promote the evolution of reproductive isolation during episodes of sympatry, parasites might facilitate speciation in this genus.
    BMC Evolutionary Biology 02/2013; 13(1):41. DOI:10.1186/1471-2148-13-41 · 3.41 Impact Factor
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    ABSTRACT: Fishes normally restricted to inland waters are valuable model systems for historical biogeography, inter alia, because of their limited dispersal abilities and concordance with the distribution patterns of other freshwater taxa (Zogaris et al. 2009). The comparison of fish species assemblages has been the major biogeographical tool for delineating African aquatic ecoregions as the fossil record is often meagre and merely offers complementary information. This is, for example, the case for the Zambezian and Congolian ichthyofaunal provinces, which display substantial contemporary fish diversity (Stewart 2001). Between both regions lies the Bangweulu-Mweru ecoregion (sensu Scott 2005), known for its high percentage of endemicity. Although hydrographically belonging to the Congo Basin, the Bangweulu-Mweru ecoregion has a high affinity with the Zambezi province (Scott 2005), due to historical river connections (Tweddle 2010). Studies comparing the Zambezi and Congo ichthyofaunal provinces are rare and hampered by lack of data from the Congo Basin. The latter harbours more than 1250 fish species (Snoeks et al. 2011) while in the Zambezi, only 120 freshwater fishes are found (Tweddle 2010). Indeed, species richness declines in all major African teleost families from the Congo Basin southwards, riverine haplochromine cichlids forming a notable exception to this rule (Joyce et al. 2005). Although it was hypothesized by Tweddle (2010) that the origin of many Zambezian fish species is in the Congo Basin, the haplochromines Serranochromis Regan, Sargochromis Regan, Pharyngochromis Greenwood and Chetia Trewavas, together forming the serranochromines, have their centre of diversity in the rivers of the Zambezian ichthyofaunal province (Joyce et al. 2005). Therefore, the biogeographical history of Cichlidae across the Zambezi- Congo watershed is not only key to cichlid biogeography on an African scale, but also complementary to biogeography of all other teleosts in the region. Yet, colonisation and speciation patterns are difficult to unravel due to complex hydrological history (Katongo et al. 2007; Schwarzer et al. 2012).
    Zootaxa 01/2013; 3608(5):398-400. DOI:10.11646/zootaxa.3608.5.8 · 1.06 Impact Factor
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    ABSTRACT: The megadiverse haplochromine cichlid radiations of the East African lakes, famous examples of explosive speciation and adaptive radiation, are according to recent studies, introgressed by different riverine lineages. This study is based on the first comprehensive mitochondrial and nuclear DNA dataset from extensive sampling of riverine haplochromine cichlids. It includes species from the lower River Congo and Angolan (River Kwanza) drainages. Reconstruction of phylogenetic hypotheses revealed the paradox of clearly discordant phylogenetic signals. Closely related mtDNA haplotypes are distributed thousands of kilometres apart and across major African watersheds, whereas some neighbouring species carry drastically divergent mtDNA haplotypes. At shallow and deep phylogenetic layers, strong signals of hybridization are attributed to the complex Late Miocene/Early Pliocene palaeohistory of African rivers. Hybridization of multiple lineages across changing watersheds shaped each of the major haplochromine radiations in lakes Tanganyika, Victoria, Malawi and the Kalahari Palaeolakes, as well as a miniature species flock in the Congo basin (River Fwa). On the basis of our results, introgression occurred not only on a spatially restricted scale, but massively over almost the whole range of the haplochromine distribution. This provides an alternative view on the origin and exceptional high diversity of this enigmatic vertebrate group.
    Proceedings of the Royal Society B: Biological Sciences 09/2012; 279(1746):4389-4398. DOI:10.1098/rspb.2012.1667 · 5.29 Impact Factor
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    ABSTRACT: We present a comprehensive phylogenetic analysis of the Utaka, an informal taxonomic group of cichlid species from Lake Malawi. We analyse both nuclear and mtDNA data from five Utaka species representing two (Copadichromis and Mchenga) of the three genera within Utaka. Within three of the five analysed species we find two very divergent mtDNA lineages. These lineages are widespread and occur sympatrically in conspecific individuals in different areas throughout the lake. In a broader taxonomic context including representatives of the main groups within the Lake Malawi cichlid fauna, we find that one of these lineages clusters within the non-Mbuna mtDNA clade, while the other forms a separate clade stemming from the base of the Malawian cichlid radiation. This second mtDNA lineage was only found in Utaka individuals, mostly within Copadichromis sp. "virginalis kajose" specimens. The nuclear genes analysed, on the other hand, did not show traces of divergence within each species. We suggest that the discrepancy between the mtDNA and the nuclear DNA signatures is best explained by a past hybridisation event by which the mtDNA of another species introgressed into the ancestral Copadichromis sp. "virginalis kajose" gene pool.
    05/2012; 2012:865603. DOI:10.1155/2012/865603
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    ABSTRACT: Cette étude porte sur la variabilité morphologique de Tilapia kottae Lönnberg, 1904, un Cichlidae endémique de deux lacs de cratères (Barombi Kotto et Mboandong) situés sur la ligne volcanique du Cameroun ainsi que sur les affinités morphologiques de T. kottae avec d’autres espèces de Tilapia de la région. L’Analyse en Composantes Principales (effectuée sur des caractères morphométriques et méristiques classiques) montre l’existence, dans chaque lac, de deux phénotypes de T. kottae. Cette différenciation morphologique concerne le diamètre de l’oeil, la longueur de la base des nageoires dorsale et anale, ainsi que la hauteur du corps. De plus, les populations des deux lacs divergent significativement, d’une part, par la longueur pré-dorsale et la longueur de la tête et, d’autre part, par le nombre de branchiospines et de rangées de dents maxillaires internes. C’est avec les Tilapias échantillonnés dans les lacs Ejagham et Bermin que les individus de T. kottae prélevés à Barombi Kotto et Mboandong présentent le plus d’affinités morphologiques comme l’a démontré la Classification hiérarchique des groupes. Cela est conforme avec des résultats moléculaires connus dans la littérature pour les Cichlidae du genre Tilapia de cette région. Nos résultats mettent en évidence le rôle de l’isolement géographique résultant de la fragmentation des habitats sur la variabilité morphologique de cette espèce.

Publication Stats

1k Citations
156.72 Total Impact Points

Institutions

  • 2003–2015
    • Royal Museum for Central Africa
      • Department of Biology
      Tervueren, Flemish, Belgium
  • 2014
    • Mekelle University
      • Department of Chemistry
      Makalle, Tigray, Ethiopia
  • 1990–2013
    • University of Leuven
      • Section of Ecology, Evolution and Biodiversity Conservation
      Louvain, Flanders, Belgium