GROWTH-MODELS OF COMPLEX ALLOMETRIES IN HOLOMETABOLOUS INSECTS

Allometries among body parts of adult holometabolous insects differ fr om allometries among body parts of many other animals because adult st ructures (many of which are derived from imaginal disks) do not grow s ynchronously with the body. Imaginal structures grow little during lar val life but experience most of their growth during the prepupal and p upal period, after food intake and somatic growth have ceased. Growth of imaginal tissues thus occurs in a closed system at the expense of n utrients accumulated during larval life. In a closed system, growing i maginal tissues compete for available nutrients, and the growth trajec tory and final size of one tissue (or disk) are influenced by the grow th of others. We use the Gompertz growth equation and a model of growt h in a closed system in which imaginal disks compete for nutrients to model the growth of imaginal disks and the resulting allometric relati ons among them. By incorporating known features of ant caste developme nt, such as reprogramming of the critical size for metamorphosis in ma jor workers (soldiers) and reprogramming of developmental parameters i n individuals larger than a critical size, we show that the nonlinear and discontinuous allometries of ants with polymorphic castes result f rom normal developmental processes during the metamorphosis of holomet abolous insects. The imaginal disk competition model predicts that whe n one disk is reprogrammed, others will show a compensatory response. Such correlated developmental responses may play a role in the evoluti on of body proportions in ants, rhinoceros beetles, and other insects.