The chromosomal inversion polymorphism in natural populations of D. subobscura was investigated near Zürich, Switzerland, in 1986 and 1987. These data are compared with earlier data from 1963, 1964 and 1984, collected in the same region. In all five acrocentric chromosomes, significant differences in the proportions of the dominant gene arrangements occurred; in the chromosomes A, I, O and U the standard order decreased from the sixties to the eighties, whereas the arrangements I1, O3+4, O3+4+8 and U1+2 became more frequent.
In alpine grasslands pale colour morphs of the snail Arianta arbustorum are more frequent than dark ones As pale morphs absorb less solar radiation, they may forage for longer in sunlight and/or have a lower mortality risk from overheating This hypothesis was tested Equal numbers of pale and dark morphs were kept in enclosures in an alpine meadow During the day, more pale morphs were seen than dark ones, the latter obviously remaining hidden The difference was not significant in enclosures set up in a nearby forest, confirming that the inequality in behaviour depends on the amount of sunlight Dark snails are on average warmer than pale ones
Experiments were also conducted in grassland on a mountain slope at altitudes between 1200 and 2000 m Snails were marked with a paint which fades in light, and released When recaptured several days later, the marks were more faded in pale morphs than in dark, suggesting that they had been more exposed to sunlight, supporting our hypothesis The difference in fading was more pronounced at high than at low altitude
The question is posed whether karyotype frequencies in the active fraction of Drosophila subobscura populations vary consistently in the course of a day, or in accordance with weather changes. Significant daily variation occurred in all chromosomes with the exception of the sex chromosome. The proportions of the karyotypes Ust/1+2 and Ist/st decreased from early to late morning and increased during the evening. Ist/1 displayed a complementary behaviour. The homokaryotypes Ost/st and Est/st decreased both during the morning and the evening. Weather disturbances caused a remarkable variation in the frequencies of the standard gene arrangements.
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