Testing mechanistic models of growth in insects

Abstract

Insects are typified by their small size, large numbers, impressive reproductive output and rapid growth. However, insect growth is not simply rapid; rather, insects follow a qualitatively distinct trajectory to many other animals. Here we present a mechanistic growth model for insects and show that increasing specific assimilation during the growth phase can explain the near-exponential growth trajectory of insects. The presented model is tested against growth data on 50 insects, and compared against other mechanistic growth models. Unlike the other mechanistic models, our growth model predicts energy reserves per biomass to increase with age, which implies a higher production efficiency and energy density of biomass in later instars. These predictions are tested against data compiled from the literature whereby it is confirmed that insects increase their production efficiency (by 24 percentage points) and energy density (by 4 J mg 21 ) between hatching and the attainment of full size. The model suggests that insects achieve greater production efficiencies and enhanced growth rates by increasing specific assimilation and increasing energy reserves per biomass, which are less costly to maintain than structural biomass. Our findings illustrate how the explanatory and predictive power of mechanistic growth models comes from their grounding in underlying biological processes.

Integrating lipid storage into general representations of fish energetics

“…We have thus far limited our analysis to fishes. However, a tendency for lipid stores to increase throughout ontogeny has been reported in a wide range of other taxa species including insects (Maino, Kearney & Maino ), copepods and krill (Lee, Hagen & Kattner ), cladocerans (Goulden & Place ) and reptiles (Avery ). To what extent the model developed here extends to other taxa remains to be tested.…”

The effect of egg size on hatch time and metabolic rate: theoretical and empirical insights on developing insect embryos

“…We compare the explanatory power of this model with other theoretical models in the literature (Smith ; Gillooly et al . ; Kooijman ; Maino and Kearney , , ; see Discussion) on the basis of how much variance in the data was explained and Akaike Information Criteria values for each competing model (Burnham & Anderson ). These alternate models predict embryonic respiration to vary with time as some polynomial function (with a highest order of three) and can be thought of as special cases of a third‐degree polynomial function, which we represented by a best‐fit third‐degree polynomial function.…”

Evaluating the role and measures of juvenile growth rate: latitudinal variation in insect life histories

“…The most straightforward solution, i.e. dividing final size by developmental time may not be satisfactory due to the markedly nonlinear character of insect growth curves (Esperk and Tammaru , Tammaru and Esperk , Tammaru et al , Maino and Kearney ). Calculating growth rates is especially problematic when only integral measures of growth are available, the integral measures being here defined as those which are based on parameters of the entire growing period (final weight, developmental time) of the juvenile.…”