Dynamic energy budget modelling of anuran metamorphosis

Abstract

The metamorphosis of aquatic anuran tadpoles to the air-breathing (terrestrial) tetrapod life form is a process that is sensitive to the impacts of natural and anthropogenic stressors. Therefore, metamorphosis is of particular interest in environmental hazard and risk assessment. Current Dynamic Energy Budget (DEB) models that deal with anuran metamorphosis do not have a particular focus on the plasticity of the metamorphosis climax and can thus not be used to evaluate those impacts. In order to remedy this issue, we have developed two independent modeling modules describing anuran metamorphosis, and its plasticity and implemented them in the standard DEB model. Our model meets three important criteria. First, adequately fed tadpoles should be able to emerge as viable frog/toadlets, which is important as tadpoles do not feed during the metamorphosis climax. Second, the model should allow the partial repurposing of structural mass, e.g., resources contained in the tail and gills, during the metamorphosis climax. Third, the model should be able to predict that moderate temperature increases will cause frog- and toadlets to emerge quicker and at a smaller size. The model successfully describes various endpoints, such as the start and end of the metamorphosis climax, and weight and length of the tadpoles from hatching to the completion of metamorphosis as functions of food availability and temperature. This was done for anuran species from four distinct families, namely the common frog Rana temporaria (Ranidae), the common toad Bufo bufo (Bufonidae), the African clawed frog Xenopus laevis (Pipidae) and the gray tree frog Dryophytes versicolor (Hylidae). It is to be expected that the developed modules can be universally applied to other anuran species and likely also to other amphibian species such as urodeles that also undergo metamorphosis. We propose to use this model for establishing a normal operating range that can be used as a baseline in the environmental hazard and risk assessment of pesticides.