Insect homeostasis: past and future.

Most of my work has been on the hormonal control of fluid secretion by insect Malpighian tubules. My present purpose is mostly to describe some previously unpublished results in this area and put them in context of what was already known. In this, I hope to draw attention to some areas where future research might be productive.

Limitation of size by hypoxia in the fruit fly Drosophila melanogaster.

The size of an organism is of fundamental importance in all biological processes. It dictates many of the critical interactions and physical factors that delimit the envelope within which an organism can grow. We investigated the effects of reduced oxygen on size and development in the fruit fly Drosophila melanogaster, and showed that limiting the oxygen in the environment limits both whole animal and cell size.

Dual origin of the renal tubules in Drosophila: mesodermal cells integrate and polarize to establish secretory function.

Organs are made up of cells from separate origins, whose development and differentiation must be integrated to produce a physiologically coherent structure. For example, during the development of the kidney, a series of interactions between the epithelial mesonephric duct and the surrounding metanephric mesenchyme leads to the formation of renal tubules. Cells of the metanephric mesenchyme first induce branching of the mesonephric duct to form the ureteric buds, and they then respond to signals derived from them.

Amino acids modulate ion transport and fluid secretion by insect Malpighian tubules.

Insect haemolymph typically contains very high levels of free amino acids. This study shows that amino acids can modulate the secretion of ions and water by isolated Malpighian tubules of Rhodnius prolixus and Drosophila melanogaster. Secretion rates of Rhodnius tubules in amino-acid-free saline increase after addition of serotonin to a peak value, then slowly decline to a plateau.