Trichoniscus pusillus

Abstract: The distribution of two sexual sibling species and a triploid parthenogenetic form of Fridericia galba, and the genetic variation within each biotype were studied within an area covering appr. 7 ha. The parthenogenetic form tends to reach its highest relative frequencies in stations at intermediate elevations and with generally favourable water conditions, whereas the two sexual species dominate in lower occasionally waterlogged resp. higher lying occasionally dry habitats. While the sexual sibling species show no intraspecific differentiation, they differ strongly in genetic heterogeneity. Based upon 5 polymorphic loci, 13 major clones were identified in the parthenogenetic form. The distribution of some clonal groups is nonrandom and correlated with the relative frequencies of the two sexual sibling species. These findings are discussed in relation to a previous study on the likewise sexual/asexual isopod, Trichoniscus pusillus, within the same area. In both species the parthenogens successfully compete with their sexual congeners in parts of this heterogeneous environment, and they comprise a number of ecologically diverse clones. It is suggested, that parthenogenesis may result in a differential distribution of ecologically diverse clones, and thereby, perhaps, in an efficient exploitation of a spatially variable niche.

Abstract: The common woodlouse, Trichoniscus pusillus Brandt, is represented in the British Isles by a diploid bisexual form, f. provisorius, and a triploid parthenogenetic form, f. pusillus. Identification of individual specimens is seldom possible, but populations can be assessed for the presence of the two forms by using the sex ratio of a numerically large sample. Using this method, a survey of 139 sites throughout the British Isles has mapped the distribution of the two forms. No clear trends in the distributions are found with either latitude, longitude, altitude or seven climatic variables using multivariate statistics. A clear association off. provisorius with calcareous habitats is noted, however, and this is discussed in the light of previous descriptions of the phenomenon of geographic parthenogenesis.

Abstract: Biochemical systematics and evolutionary relationships in the Trichoniscus pusillus complex (Crustacea, Isopoda, Oniscidea)

Abstract: L'acidite du sol a ete influencee par des depots provenant de la pollution aerienne, qui peuvent provoquer des changements dans la composition en especes de la communaute des invertebres du sol. Ce travail met en evidence la preference pour le facteur pH chez cinq especes d'isopodes, Oniscus asellus, Trichoniscus pusillus, Porcellio scaber, Philoscia muscorum et Armadillidium vulgare, dans le but d'identifier des bioindicateurs possibles de l'acidification du sol. Les isopodes ont ete soumis aux tests selon une procedure standardisee. On a realise les tests dans des chambres en anneau divise a la base en compartiments remplis de sable et ajustes aux valeurs de pH dans la zone 2 a 9 au moyen de tampons de McIlvaine. Les solutions des tampons ont ete diluees jusqu'a une osmolarite identique pour tous les pH (.)