Among the multitude of physiological processes, those that influence energy and resource acquisition are the most likely to have an effect on an animal’s behavior, ecological and trophic interactions. However, given the importance of digestive processes in determining an animal’s ecology, digestive physiology is not investigated as often as might be warranted. Here, I will share how studying the digestive physiology of fishes and lizards provided insight into their ecology not granted by studying diet alone. I will start by exploring the genetics underlying adaptations for herbivory in prickleback fishes (family Stichaeidae), which features dietary variation in sympatric species, sister taxa with different diets, and convergent evolution of herbivory. Whole genome sequencing, transcriptomics, digestive biochemistry, and whole animal digestibility experiments reveal how the convergently evolved herbivores partition resources on the digestive and metabolic levels as opposed to diet choice. Next, I will share how understanding the digestive physiology of parrotfishes has allowed for a better understanding of their biology and roles in coral reef systems. I will conclude by discussing how a lizard species from islets of the Adriatic Sea evolved complex digestive adaptations for herbivory in just 30-40 generations.
Overall, the gut is a dynamic biochemical system that has been relatively understudied in terms of its role in ecology and evolution, and many investigations, particularly those seeking to understand how animals might respond to global change, can benefit by understanding post-ingestive processes.