Le polymorphisme de coloration abdominale de Drosophila erecta est-il gouverné par un gène sélectivement neutre?

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Thoracic trident pigmentation in Drosophila melanogaster: Differentiation of geographical populations

A phenotypic classification of trident pigmentation allowed the characterization ol any natural population by a pigmentation score, ranging from 0 to 3. After some training, independent observers could produce very similar score values. Growth temperature influences pigmentation intensity and the response curves exhibit a U-shape, with a minimum at about 25 "C. For the description of natural populations, 2 different growth temperatures, 17 °C and 25 °C were chosen. Crosses between a dark French strain and a light Afrotropical strain produced intermediate offspring, but a clear maternal effect differentiated the reciprocal Fl’s. Numerous populations from various part of the world were investigated and results arranged according to the latitude. For temperate populations collected between 34 and 48 ° of latitude a steep cline was observed (pigmentation being much more darker in high latitude) suggesting an adaptive pressure on this phenotype: environmental factors which may explain this cline being temperature, insolation and desiccation. In tropical populations on the other hand a large variability was observed but without any relation to latitude