The direction of evolution in the Drosophila melanogaster species subgroup based on functional analysis of the crystal cells

Abstract

The crystal cells in the hemolymph of Drosophila melanogaster contain paracrystalline inclusions and phenol oxidase. Melanization of this type of blood cell can be induced by treatment of larvae with hot water. By using this functional criterion to establish cell homology we compared the shape of the inclusions in the crystal cells of the D. melanogaster species subgroup and a number of distantly related species of Drosophila . The crystal cell inclusions in four of the sibling species ( simulans, erecta, mauritiana, yakuba ) are the same as those found in D. melanogaster . In the fifth species, D. teissieri , the crystal cell inclusions resemble those found in the hemocytes of the other larval drosophilids that were examined rather than those of D. melanogaster . On the basis of these observations and the phylogenetic relationships deduced from analysis of chromosomal inversions by Lemeunier and Ashburner ('76), we propose that D. teissieri is closer to the ancestral form or is the ancestral species of the melanogaster species subgroup of Drosophila . This is the first instance in which a hemocyte type has been used to determine the direction of evolution within a subgroup of insect species.