The ins and outs of integrative digestive biology.

The digestive system facilitates exchanges between animals and their environments. It not only converts resources into energy and growth but also shapes ecosystem processes through waste outputs, all while mediating an animal's relationship with complex microbial communities. The Special Issue: The Integrative Biology of the Gut delves into many aspects of this expansive relationship. Further, this Commentary collects the special issue papers under themes to highlight and explore the physiology of the digestive system and the plasticity that enables its acclimatization to dietary and environmental changes. The themes that have been identified portray the gastrointestinal (GI) tract as an integrative moderator of physiology, and show that when this system is explored using novel techniques or by asking innovative questions, one can reveal phenomena with applications well beyond digestive biology. Further, we discuss how embracing multidisciplinary approaches - including systems biology, evolutionary comparisons and environmental considerations - will allow us to use the unique physiology of the GI tract to form critical insights into evolved organismal biology, microbial symbioses and ecological stewardship. Ultimately, the pivotal role of the GI tract in connecting internal physiology with external ecological dynamics across taxa exemplifies its value as a model system.