Les chromosomes polytènes de Neanura monticola Cassagnau (Collemboles) - I. Polymorphisme écologique du chromosome X

Abstract

In the Collembolan Neanura monticola (2 n ♀ = + XX, 2 n ♂ = 12 + XO) only the autosomes have classical polytene structure in salivary glands. - In a valley of the Pyrenees-mountains, the X-chromosome shows an intense polymorphism with 13 different types of pattern. These differences are revealed in the pairing in bundles of elementary fibres, in the apparition of transversal bands, in a progressive overcharge of α-heterochromatin in certain points, briing a radiant structure of chromosome (25 differents types of heterogametic females have been observed). - In the damp forests at lesser altitude, the X-chromosome remains flaky, as in polyploid nuclei of other tissues. The structure with parallel bundles appears in cold forests between 1 600 and 1 800 m of altitude. In subalpine biotopes the astral-ray type becomes preponderant and from 2 200 m the exclusive form with hypertrophy of α-heterochromatic block. Various hypothesis are discussed that explain the selective advantage an α-heterochromatic overcharge might give to the subalpine populations. © 1974 Springer-Verlag.