Data from: Rapid shifts in the thermal sensitivity of growth but not development rate causes temperature-size response variability during ontogeny in arthropods

Size at maturity in ectotherms commonly declines with warming. This
near-universal phenomenon, formalised as the temperature-size rule, has
been observed in over 80% of tested species, from bacteria to fish. The
proximate cause has been attributed to the greater temperature dependence
of development rate than growth rate, causing individuals to develop
earlier but mature smaller in the warm. However, few studies have examined
the ontogenetic progression of the temperature-size response at high
resolution. Using marine planktonic copepods, we experimentally determined
the progression of the temperature-size response over ontogeny.
Temperature-size responses were not generated gradually from egg to adult,
contrary to the predictions of a naïve model in which development rate was
assumed to be more temperature-dependent than growth rate, and the
difference in the temperature dependence of these two rates remained
constant over ontogeny. Instead, the ontogenetic progression of the
temperature-size response in experimental animals was highly episodic,
indicating rapid changes in the extent to which growth and development
rates are thermally decoupled. The strongest temperature-size responses
occurred temporally mid-way through ontogeny, corresponding with the point
at which individuals reached between ~5- 25% of their adult mass. Using
the copepod Oithona nana, we show that the temperature-dependence of
growth rate varied substantially throughout ontogeny, whereas the
temperature dependence of development rate remained constant. The
temperature-dependence of growth rate even exceeded that of development
rate in some life stages, leading to a weakening of the temperature-size
response. Our analyses of arthropod temperature-size responses from the
literature, including crustaceans and insects, support these conclusions
more broadly. Overall, our findings provide a better understanding of how
the temperature-size rule is produced over ontogeny. Whereas we find
support for the generality of developmental rate isomorphy in arthropods
(shared temperature dependence of development rate across life stages),
this concept should not apply to growth rates.