Directional-disruptive selection in Drosophila melanogaster

Directional selection in lines founded from different parts of the phenotypic distribution of sternopleural chaetae number in Drosophila melanogaster

Divergent directional selection lines were initiated from base populations founded from parents taken from different parts of the sternopleural chaetae distribution in a cage population of Drosophila melanogaster. Lines founded from parents taken from the central part of the distribution showed greater response and higher realised heritability than lines derived from parents with extreme high or extreme low chaetae number. The results suggest that centrally derived phenotypes have higher heterozygosity for chaetae factors than extreme phenotypes and that these factors have a large effect on the character.

Quantitative genetics and fitness: lessons from Drosophila

This paper examines patterns of heritability and genetic covariance between traits in the genus Drosophila. Traits are divided into the categories, morphology, behaviour, physiology and life history. Early theoretical analyses suggested that life history traits should have heritabilities that are lower than those in other categories. Variable pleiotrophy, environmental variation, mutation and niche variation may, however, maintain high heritabilities. In Drosophila the heritabilities of life history traits are lower than morphological or physiological traits but may exceed 20 per cent. The pattern of variation in the heritability of behavioural traits is similar to that of life history traits. Genetic covariance between morphological traits and between morphological and life history traits are all positive but those between life history traits have variable sign. Negative covariance between traits supports the variable pleiotropy hypothesis but other factors such as environmental heterogeneity, or mutation cannot be excluded.