Variation of Scutellar Bristles In Drosophila XIV. Effects of Temperature and Crowding

Abstract

Several lines of D. melanoga8ter which were selected for increased numbers of scutellar bristles have been analysed for their response to temperature and larval density. Genetic data are summarized which indicates that two different polygenic systems have been separately involved in the selection responses. The one system, designated as the oo-modifiers, has been involved in the presence of 8cute+ and shows a correlated response in the presence of 8cute alleles. The other system, designated as the .a-modifiers, has been involved in several lines which also possess a major gene, provisionaJIy called extra-vert. This gene is a chromosome III recessive which manifests itself by increasing the number of dorsocentral and vertical as well as scutellar bristles. The effects of temperature and larval densities permit a further discrimination between these two genetic systems involved in bristle determination. A model is presented for the interaction of these two systems.