Introduction: food processing and nutritional assimilation in animals.

How animals process and absorb nutrients from their food is a fundamental question in biology. Despite the continuity and interaction between intraoral food processing and post-oesophageal nutritional extraction, these topics have largely been studied separately. At present, we lack a synthesis of how pre- and post-oesophageal mechanisms of food processing shape the ability of various taxa to effectively assimilate nutrients from their diet. The aim of this special issue is to catalyse a unification of these distinct approaches as a functional continuum. We highlight questions that derive from this synthesis, as well as technical advances to address these questions. At present, there is also a skew toward vertebrates in studies of feeding form-function mechanics; by including perspectives from researchers working on both vertebrates and invertebrates, we hope to stimulate integrative and comparative research on food processing and nutritional assimilation. Below, we discuss how the papers in this issue contribute to these goals in three areas: championing a functional-comparative approach, quantifying performance and emphasizing the effects of life history, and food substrate and extrinsic factors in current and future studies of oral food processing and nutritional assimilation. This article is part of the theme issue 'Food processing and nutritional assimilation in animals'.