A staging scheme for the development of the moth midge Clogmia albipunctata.

Model organisms, such as Drosophila melanogaster, allow us to address a wide range of biological questions with experimental rigour. However, studies in model species need to be complemented by comparative studies if we are to fully understand the functional properties and evolutionary history of developmental processes. The establishment of new model organisms is crucial for this purpose. One of the first essential steps to establish a species as an experimental model is to carefully describe its life cycle and development. The resulting staging scheme serves as a framework for molecular studies, and allows us to homologise developmental processes between species. In this paper, we have characterised the life cycle and development of an emerging non-drosophilid dipteran model system: the moth midge Clogmia albipunctata. In particular, we focus on early embryogenesis (cleavage and blastoderm cycles before gastrulation), on formation and retraction of extraembryonic tissues, and on formation of the germ line. Considering the large evolutionary distance between the two species (approximately 250 million years), we find that the development of C. albipunctata is remarkably conserved compared to D. melanogaster. On the other hand, we detect significant differences in morphology and timing affecting the development of extraembryonic tissues and the germ line. Moreover, C. albipunctata shows several heterochronic shifts, and lacks head involution and associated processes during late stages of development.