Resolving the energy restriction at high altitude: variation in the digestive system of Phrynocephalus vlangalii

Hypothermic and hypoxic environments create strong selective pressure on native species by affecting, among other things, the relationship between energy intake and allocation. In order to detect the adaptation of Phrynocephalus vlangalii to such energy limitation, the morphological structure and argyrophil cells of the digestive tract of 80 individuals from two different altitudes in the Qinghai-Tibet Plateau were compared using overall anatomy as well as paraffin sectioning of specific organs. Compared with the low-altitude population, the high-altitude individuals were found to have a significantly longer stomach and duodenum, longer and wider villus in the small intestine, larger surface area in duodenum and jejunum, and more argyrophilic cells in stomach and duodenum. Our results indicate that the morphological and histological change of the digestive tract may be conductive to the plateau adaptability of P. vlangalii by enhancing the efficiency of digestion and absorption. For a more general conclusion to be drawn, comparison of more populations at both altitudes is required in addition to verifying how phenotypically flexible these traits are.