Bats and birds share digestive adaptations to an aerial lifestyle

EDWIN R. PRICE; ANTONIO BRUN; CAVIEDES-VIDAL E; KARASOV WH

West Palm Beach

Congreso; SICB Annual Meeting; 2015

Powered flight evolved at least twice in vertebrates. We tested forshared digestive adaptations in two extant volant lineages. Bats andbirds, compared with nonflying mammals, share shorter intestinesand smaller nominal intestinal surface areas (NSA), which lowersdigestive mass carried and thus improves flight maneuverability andeconomy. The daily digestive "load" placed on the intestine (= ratioof daily energy needs to NSA) is at least twice higher in vertebrateflyers than nonflyers. Intestinal hydrolytic enzyme and nutrienttransport activities appear similar among these groups per unitintestine, but lower over the entire intestine in the fliers, whichtranslates to lower spare digestive capacity. Nutrients can also beabsorbed paracellularly by passing through the tight junctions thatlink adjacent enterocytes. Seven bat species and 14 bird species, witha variety of natural diets, absorbed significantly more of ingestedL−arabinose and other similarly sized, metabolically inert,nonactively transported monosaccharides than 18 species ofnonflying mammals. These differences in nutrient−sized probeabsorption were demonstrated at the tissue level comparing resultsfrom perfusion experiments (7 bat species, 1 bird, 5 nonflyingmammals) that control for several potential confounding factors.Greater amplification of digestive surface area by villi anddifferences in expression patterns of junctional proteins (i.e., claudinsand occludin) may provide mechanistic explanations for theobservation of higher paracellular absorption in bats and birdsrelative to nonflying mammals. Supported by USA NSF(IOS−1025886) and Argentina CONICET.