Contributions of digestive plasticity to the ability of white-tailed deer to cope with a low-quality diet

Many herbivores exhibit phenotypic variations of their digestive system in response to changes in quality of food resources. This digestive plasticity is considered an adaptive trait for individuals to help them cope with variation in food resources and to fulfill nutritional needs. We investigated whether digestive phenotypic variations could contribute to sustain the population of introduced white-tailed deer (Odocoileus virginianus) on Anticosti Island (Quebec, Canada) facing a winter diet of low-quality forage. We compared digestive morphology and in vitro digestibility of winter forage to that of deer from the original mainland population. Deer on Anticosti Island had a higher ruminal volume and digesta load (43% and 62%, respectively), greater absorption surface of the ruminal papillae, and greater relative mass of all forestomachs than deer from the mainland. Woody forage digestibility was similar between the 2 populations, even though faster kinetic digestion may occur for deer on Anticosti Island. Digestive plasticity appears to play a central role in sustaining high deer densities facing harsh forage conditions on Anticosti Island. Comparisons of digestive morphology and digestibility between populations that have access to forage of variable quality contribute to our understanding of the digestive response and the role of digestive plasticity for individuals facing a decline in diet quality.