Molting else matters: An extended bioenergetic model for Gammarus fossarum that links molt and reproduction

In crustaceans, molting is a vital process that occurs throughout the organism’s life. Non-continuous growth models are sometimes accurate to describe such process. However, clarifications are needed when molting is intrinsically linked to growth and reproduction, as is the case with tiny amphipods. This study demonstrates how the molting process can be modeled and incorporated into the description of Gammarus fossarum physiology, an amphipod widely used as a test species for water quality and with non-continuous reproduction. To this end, we extend the Dynamic Energy Budget theory by modeling the reproduction with a molting event linked to the organism physiology (rather than using a fixed time step). Simulations are realized by using AddMyPet estimated parameters to calibrate the model in an optimal and constant environment (i.e. temperature and food source ad libitum ). We compared the predictions with those in the literature, which enabled us to demonstrate that our extended DEB model is well adapted to predict growth traits (such as length and weight) as well as reproductive output (the number of oocytes produced) when the molting is taken into account. This study therefore provides a basis for making predictions about populations facing environmental fluctuations, such as changes in temperature or resources, or even other stressors, such as toxic compounds.