Data and code from: The evolution of developmental thresholds and reaction norms for age and size at maturity

Developing organisms typically mature earlier and at larger sizes in
favorable growth conditions, while in rarer cases maturity is delayed. The
rarer reaction norm is easily accommodated by general life history models,
whereas the common pattern is not.  Theory suggests that a
solution to this paradox lies in the existence of developmental thresholds
that define the minimum size at which maturation or metamorphosis can
commence, and in the evolution of these threshold sizes in response to
environmental variation. For example, more ephemeral environments might
favor the evolution of smaller thresholds, enabling earlier maturation.
The threshold model makes two unique and untested predictions; first,
reaction norms for age and size should steepen, and even change sign, with
decreases in the threshold size, and second, food reductions at sizes
below the threshold should delay maturation, while those occurring after
the threshold should accelerate maturation. We test these predictions by
performing targeted food manipulations in a suite of five damselfly
species, which theory suggest should differ in threshold size. The results
provide strong support for the threshold model’s predictions. In all
species, early food reductions delayed maturation, while late reductions
accelerated maturation. Reaction norms were steeper, and the effect of
food reductions changed from decelerating to accelerating at a much
smaller size in fast-developing species from ephemeral habitats. These
results support the view that developmental thresholds can account for the
widespread observation of negative correlations between age and size at
maturity. Moreover, evolution of the threshold appears to be both central
to the observed diversity of reaction norms for age and size at maturity,
and is predictable.