The developmental basis for allometry in insects

Within all species of animals, the size of each organ bears a specific rela tionship to overall body size. These patterns of organ size relative to tot al body size are called static allometry and have enchanted biologists for centuries, yet the mechanisms generating these patterns have attracted litt le experimental study, We review recent and older work on holometabolous in sect development that sheds light on these mechanisms. In insects, static a llometry can be divided into at least two processes: (1) the autonomous spe cification of organ identity, perhaps including the approximate size of the organ, and (2) the determination of the final size of organs based on tota l body size. We present three models to explain the second process: (1) all organs autonomously absorb nutrients and grow at organ-specific rates, (2) a centralized system measures a close correlate of total body size and dis tributes this information to all organs, and (3) autonomous organ growth is combined with feedback between growing organs to modulate final sizes. We provide evidence supporting models 2 and 3 and also suggest that hormones a re the messengers of size information. Advances in our understanding of the mechanisms of allometry will come through the integrated study of whole ti ssues using techniques from development, genetics, endocrinology and popula tion biology.