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

Summary Body size scaling relationships allow biologists to study ecological phenomena in terms of individual level metabolic processes. Recently, dynamic energy budget (DEB) theory has been shown to offer novel insights on the effect of body size on biological rates. We test whether DEB theory and its unique partitioning of biomass into reserve and structural components can explain the effect of egg size on hatch time and the time course of respiration in insect embryos. We find that without any parameterization (calibration), DEB theory is able to predict hatch time for eggs sizes spanning four orders of magnitude from fundamental biological processes. We find, however, that the standard DEB model poorly predicts the time course of respiration, particularly in early embryonic development where a strong effect of egg size is observed. Further, we show that other theoretical models also poorly predict early embryonic respiration. By modifying the assumption that a fresh egg is entirely reserve, we show that embryonic respiration and hatch time can be better predicted by the DEB model. Useful theories in metabolic ecology, such as DEB theory, can help explain universal scaling patterns in development times. However, simple theoretical models must be expanded if they are to capture the scaling of metabolic rate in insect eggs. A Lay Summary is available for this article.