Data from: A dynamical model of growth and maturation in Drosophila

The decision to stop growing and mature into an adult is a critical point
in development that determines adult body size, impacting multiple aspects
of an adult’s biology. In many animals, growth-cessation is a consequence
of hormone release that appears to be tied to attainment of particular
body size or condition. Nevertheless, the size-sensing mechanism animals
use to initiate hormone synthesis is poorly understood. Here we develop a
simple mathematical model of growth cessation in Drosophila melanogaster,
which is ostensibly triggered by attainment of a critical weight early in
the last instar. Attainment of critical weight is correlated with
synthesis of the steroid hormone ecdysone, which causes a larva to stop
growing, pupate and metamorphose into the adult form. Our model suggests
that, contrary to expectation, the size-sensing mechanism that initiates
metamorphosis occurs before the larva reaches critical weight; that is,
the critical-weight phenomenon is a downstream consequence of an earlier
size-dependent developmental decision, not a decision point itself.
Further, this size-sensing mechanism does not require a direct assessment
of body size, but emerges from the interactions between body size,
ecdysone and nutritional signaling. Because many aspects of our model are
evolutionarily conserved among all animals, the model may provide a
general framework for understanding how animals commit to maturing from
their juvenile to adult form.