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| Scheepmaker, Maarten. |
| Morphologically distinct populations of the Gammarus pulex group which should be attributed to at least three species applying morphological criteria postulated by Karaman & Pinkster (1977) have been reported in the Massif de la Sainte Baume (southern France). These populations proved to be completely interfertile and thus were considered conspecific. This group of populations, in which three major forms A, B and C were distinguished, has been described as Gammarus stupendus Pinkster, 1983. Systematic sampling was carried out to determine the distribution of the various forms of G. stupendus in the Massif de la Sainte Baume and adjacent areas, and the relation between morphological and genetic differentiation has been investigated. Genetic... |
| Tipo: Article / Letter to the editor |
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| Ano: 1987 |
URL: http://www.repository.naturalis.nl/record/504296 |
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| Scheepmaker, Maarten. |
| Bij milieu-inventarisaties zoals die door verschillende Provinciale Waterstaten worden uitgevoerd, worden verschillende methodieken toegepast. Eén aspect is het onderzoek naar de samenstelling van de makrofauna. Provinciale Waterstaat van Noord-Holland monstert hiervoor twee keer per jaar, één keer in het voor jaar (maart) en één keer in juli-augustus. Het tijdstip van de tweede monstername is voornamelijk bepaald door het tijdstip waarop de sloten geschoond worden. Hierbij wordt uitgegaan van de veronderstelling, dat door het schonen de samenstelling van de makrofauna-gemeenschap ernstig verstoord wordt. Bewijs voor deze veronderstelling is er echter niet. Incidenteel (dus niet hierop gericht) onderzoek door studenten en medewerkers van het ITZ heeft... |
| Tipo: Article / Letter to the editor |
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| Ano: 1982 |
URL: http://www.repository.naturalis.nl/record/506381 |
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| Platvoet, Dirk; Scheepmaker, Maarten; Pinkster, Sjouk. |
| During two and a half decades periodic survey programs have been carried out to follow the dispersal of Gammarus tigrinus. Since the last survey in the period 1985-1986 the species consolidated its position and showed a minor range extension in the southeastern part of the country. Gammarus specimens from the island Terschelling were electrophoretically investigated and compared with known G.tigrinus and G.zaddachi from the mainland. These experiments demonstrated the presence of G.tigrinus on this island. Crangonyx pseudogracilis which showed some range extension in the 1985-1986-survey, again was found outside its hitherto known distribution area. |
| Tipo: Article / Letter to the editor |
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| Ano: 1989 |
URL: http://www.repository.naturalis.nl/record/505504 |
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| Scheepmaker, Maarten. |
| Genetic differentiation of morphologically variable members of the G. pulex-group in northwestern Europe was investigated by electrophoresis at 20 enzyme loci. Five recently described related forms were examined with reference to the “classical” species G. pulex, G. wautieri and G. fossarum. G. pulex and G. wautieri were shown to be genetically homogeneous and clearly distinct species. In the other species, morphologically similar forms were shown to be genetically distant, and inter-areal intraspecific genetic differentiation may warrant recognition of subspecies or sibling species. In some cases, levels of reproductive isolation of the forms involved could be assessed by cross-breeding experiments. To estimate dispersal capabilities, gene flow levels... |
| Tipo: Article / Letter to the editor |
Palavras-chave: Taxonomy; Distribution; Population structure; Intra-specific divergence; Gammarus. |
| Ano: 1990 |
URL: http://www.repository.naturalis.nl/record/504326 |
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| Janssen, Hans; Scheepmaker, Maarten; Couwelaar, Matthijs van; Pinkster, Sjouk. |
| 1. Gammarus aequicauda (Martynov, 1931) and Gammarus insensibilis Stock, 1966 have been the subject of a quantitative ecological research project in the lagoon system of Bages-Sigean (France, dépt. Aude). From April 1976 till August 1977 samples have been taken at 31 different stations all over the lagoon at intervals of about 2 weeks. With the samples thus obtained we studied the biology and distribution of the two species in relation to environmental factors, the most important being chlorinity and temperature. 2. Both species reproduce throughout the year and have a regular reproductive pattern with maxima in spring and autumn. In G. aequicauda. as compared to the other species, this peak is earlier in spring and later in autumn. This is caused by a... |
| Tipo: Article / Letter to the editor |
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| Ano: 1979 |
URL: http://www.repository.naturalis.nl/record/504129 |
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| Scheepmaker, Maarten; Meer, Frits van der; Pinkster, Sjouk. |
| Populations of five related species belonging to the Gammarus pulex group from the Iberian Peninsula and southern France have been studied electrophoretically at 21 enzyme loci. Morphologically distinct forms from the same side of the Pyrenees proved to be genetically more similar than morphologically very similar forms from opposite sides of this barrier. With reference to published data, genetic differentiation between French and Iberian species was observed at the generic level. Inter-areal intraspecific genetic differentiation in Iberian species may warrant recognition of subspecies or sibling species. However, cross-breeding experiments performed did not assess levels of reproductive isolation of the forms involved. A dendrogram derived from genetic... |
| Tipo: Article / Letter to the editor |
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| Ano: 1988 |
URL: http://www.repository.naturalis.nl/record/504502 |
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| Scheepmaker, Maarten; Dalfsen, Jan van. |
| Genetic differentiation among G. fossarum Koch, 1835 from different stations in Germany, Switzerland, Belgium and northern France, and the closely related Belgian form G. caparti Pètre-Stroobants, 1980 was investigated by electrophoresis at 20 enzyme loci. Although morphologically variable, geographically distant populations of G. cf. fossarum were hitherto considered conspecific. In the present study, populations of G. cf. fossarum and G. caparti were examined with reference to G. pulex pulex as an estimate for genetic differentiation at the species level. With G. p. pulex as a standard, genetic differentiation among geographically distant populations of G. cf. fossarum is occasionally observed at species level. The populations of G. caparti studied were... |
| Tipo: Article / Letter to the editor |
Palavras-chave: Taxonomy; Distribution; Morphology; Genetic variability; Gammarus. |
| Ano: 1989 |
URL: http://www.repository.naturalis.nl/record/504137 |
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| Scheepmaker, Maarten. |
| Genetic differentiation among population samples of G. gauthieri on both sides of the Strait of Gibraltar was investigated by enzyme electrophoresis at 20 enzyme loci with reference to G. gauthieri and G. ibericus from different areas in the Iberian peninsula. Levels of divergence resolved suggest that G. gauthieri reached North Africa from the Iberian peninsula, and not vice versa. With reference to geological evidence, this was likely to occur during the Messinian (6—5 My ago). As the opening of the Strait of Gibraltar represents a well dated geological event, an attempt has been made to calibrate the molecular clock for the G. pulex-group. Indirect estimations of gene flow levels were shown to be extremely low. Probably as a consequence of frequently... |
| Tipo: Article / Letter to the editor |
Palavras-chave: Distribution; Genetic divergence; Gene flow; Molecular clock; Gammarus. |
| Ano: 1990 |
URL: http://www.repository.naturalis.nl/record/503962 |
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