Meeting Abstract
Powered flight evolved at least twice in vertebrates. We tested for shared digestive adaptations in two extant volant lineages. Bats and birds, compared with nonflying mammals, share shorter intestines and smaller nominal intestinal surface areas (NSA), which lowers digestive mass carried and thus improves flight maneuverability and economy. The daily digestive “load” placed on the intestine (= ratio of daily energy needs to NSA) is at least twice higher in vertebrate flyers than nonflyers. Intestinal hydrolytic enzyme and nutrient transport activities appear similar among these groups per unit intestine, but lower over the entire intestine in the fliers, which translates to lower spare digestive capacity. Nutrients can also be absorbed paracellularly by passing through the tight junctions that link adjacent enterocytes. Seven bat species and 14 bird species, with a variety of natural diets, absorbed significantly more of ingested L-arabinose and other similarly sized, metabolically inert, nonactively transported monosaccharides than 18 species of nonflying mammals. These differences in nutrient-sized probe absorption were demonstrated at the tissue level comparing results from perfusion experiments (7 bat species, 1 bird, 5 nonflying mammals) that control for several potential confounding factors. Greater amplification of digestive surface area by villi and differences in expression patterns of junctional proteins (i.e., claudins and occludin) may provide mechanistic explanations for the observation of higher paracellular absorption in bats and birds relative to nonflying mammals. Supported by USA NSF (IOS-1025886) and Argentina CONICET.
