Adaptive Interplay between Feeding Habits and Digestive Physiology for Pitvipers

Secor, Stephen M. Department of Biological Sciences University of Alabama Tuscaloosa, Alabama, USA ssecor@ua.edu

Castoe, Todd A. Department of Biology University of Texas Arlington Arlington, Texas, USA

Mackessy, Stephen P. School of Biological Sciences University of Northern Colorado Greeley, Colorado USA

The sit-and-wait foraging tactic of pitvipers is characterized by extended episodes of fasting between potentially large meals. An adaptive correlate that has evolved with their infrequent feeding is the capacity to widely regulate gastrointestinal performance with feeding and fasting. For pitvipers, feeding triggers a dramatic increase in metabolic rate, hypertrophy of organs, and the rapid up-regulation of gastric acid production, digestive enzymes, and intestinal nutrient transport. Upon the completion of digestion, metabolism is depressed, tissues undergo atrophy, and function is down-regulated. It is hypothesized that the selective force driving the down-regulation of tissue performance between meals resides in achieving a low standard metabolic rate, therefore enhancing the capacity to survive between infrequent meals utilizing endogenous energy stores. The cellular mechanism employed by pitvipers to regulate intestinal function involves altering the functional surface area of the intestinal epithelium via the modulation of microvillus length. Driving this remodeling response are gene and protein expression patterns that cascade through trafficking, cytoskeletal, cell cycling, and membrane pathways. An adaptive interplay between feeding habits and digestive physiology, and their underlying mechanisms, has evolved independently through snake evolution. This has generated an apparent dichotomy between frequently feeding species (acrochordids and colubrids) that modestly regulate organ performance and infrequently feeding species (boas, pythons, and pitvipers) that widely regulate digestive performance.