A Developmental Perspective on the Evolution of Insect Wings and Imaginal Discs

University Of Connecticut, Storrs CT

Investigators

Abstract

0091005 Jockusch Insect wings and imaginal discs are two key innovations that have contributed to the spectacular success of the clades that they characterize. However, the developmental basis for the origins of these traits remains poorly understood. The work proposed here is a comparative analysis of wing development in two species of insects that retain morphologically more ancestral modes of wing development, the beetle Tribolium castaneum and the grasshopper Schistocerca americana, and a parallel analysis in one primitively wingless hexapod, the thysanuran Thermobia domestica. These comparisons will be used to address two significant questions in insect evolution: Did the origin of imaginal discs require major changes in both primordium allocation and disc patterning or did it result from more limited developmental changes? Are wings homologous to dorsal branches of ancestral arthropod legs or did they arise de novo from the dorsal thorax? Presently, most of what is known about wing development comes from a single species, the fruit fly Drosophila melanogaster. At a morphological level, wing development in Drosophila is derived. This grant proposes to use comparative molecular data to determine in what respects Drosophila wings develop by retained ancestral mechanisms and to what extent by novel mechanisms that may be related to the evolution and early allocation of imaginal discs. This work has three specific aims: (1) to examine the conservation of the Drosophila appendage allocation mechanism (involving, in part, interactions among the genes wingless, ecapentaplegic, and distal-less) in other insects using studies of gene expression and function; (2) to compare the expression of four genes important in Drosophila wing development- snail, escargot, apterous and wingless- in the developing wings of Schistocerca and Tribolium, and in the thoracic lobes of Thermobia to establish whether the mechanisms that pattern the wing are broadly conserved; (3) to identify the embryonic source of wing cells in these species using a combination of lineage tracing and laser ablation techniques.