The developmental control of size in insects

Abstract

The mechanisms that control the sizes of a body and its many parts remain among the great puzzles in developmental biology. Why do animals grow to a species-specific body size, and how is the relative growth of their body parts controlled to so they grow to the right size, and in the correct proportion with body size, giving an animal its species-characteristic shape? Control of size must involve mechanisms that somehow assess some aspect of size and are upstream of mechanisms that regulate growth. These mechanisms are now beginning to be understood in the insects, in particular in Manduca sexta and Drosophila melanogaster. The control of size requires control of the rate of growth and control of the cessation of growth. Growth is controlled by genetic and environmental factors. Insulin and ecdysone, their receptors and intracellular signaling pathways are the principal genetic regulators of growth. The secretion of these growth hormones, in turn, is controlled by complex interactions of other endocrine and molecular mechanisms, by environmental factors such as nutrition and by the physiological mechanisms that sense body size. Although the general mechanisms of growth regulation appear to be widely shared, the mechanisms that regulate final size can be quite diverse.

Life history evolution and cellular mechanisms associated with increased size in high‐altitude Drosophila

“…For body size, the cellular mechanisms driving final adult size in insects are relatively well understood (Brodsky and Uryaeva 1977; Conlon and Raff 1999; Nijhout et al. 2014), and have been implicated in natural variation in body and appendage size (Scholes et al. 2013).…”

“…In spite of copious amounts of natural variation within and among species, the complexity of size and growth determination has made it incredibly challenging to characterize the genetic basis of evolutionary shifts in body or appendage size (Nijhout et al. 2014). Size is a complex trait at the genetic level, and many hundreds of genes may affect growth in Drosophila melanogaster (Turner et al.…”

Positional specification in the segmental growth pattern of an early arthropod

“…However, if segment differential growth rate in A. koninckii was under the control of a morphogen signal, with effect, for instance, on the level of expression of some growth hormone receptors or of members of the signalling pathways downstream of them [5,28,29], as is likely when it is considered that genes and hormones involved in tissue growth are remarkably conserved in all animals [30], this signal was apparently transduced linearly into an isomorphic growth gradient response.…”

Metamorphosis is induced by food absence rather than a critical weight in the solitary bee,Osmia lignaria

“…The insect body size model integrates genetic, tissue signaling, and hormonal elements that regulate the developmental basis of adult size variation (12). In tandem with increasingly detailed identification and characterization of mechanisms shaping body size (12)(13)(14)(15), there has been an effort to simplify this complexity for the purposes of generalization and predictability (8,16).…”

“…In tandem with increasingly detailed identification and characterization of mechanisms shaping body size (12)(13)(14)(15), there has been an effort to simplify this complexity for the purposes of generalization and predictability (8,16). Three factors contribute to adult body size and serve as proxies for the endocrine regulation of metamorphosis: larval growth rate, the critical weight that induces metamorphosis, and the interval between the critical weight and cessation of growth (8,(16)(17)(18)(19).…”