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Phylogenetic and body size patterns in intestinal paracellular solute absorption
Author(s) -
Karasov William H,
McWhorter Todd J,
CaviedesVidal Enrique
Publication year - 2006
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.20.5.a1275-b
Subject(s) - paracellular transport , biology , clade , absorption (acoustics) , zoology , phylogenetic tree , ecology , biochemistry , gene , physics , membrane , acoustics , permeability (electromagnetism)
The nutritional significance of paracellular solute absorption is controversial. Earlier studies suggested that reliance on this route, vs active transport, is greater in birds than mammals, and is greater with increasing body size within mammals. We studied additional species in different taxonomic clades (subclasses, orders, families) in order to survey this feature across mammals (14 species in 7 clades, 50% of species studied by us), birds (12 species, 6 clades, 91% by us), and reptiles (2 species, 2 clades, 100% by us). We measured fractional absorption of nonmetabolizable, nonactively transported carbohydrates by total urine collection or by appearance in blood post oral administration. We find no trend for increasing reliance on paracellular absorption with increasing size in either mammals or birds. Paracellular absorption is greater in birds than in mammals and reptiles, but the differences decline at larger body sizes. Mammalian species in only two clades, the Old and New World bats, exhibit paracellular absorption as high as in small birds. Coincidently, bats and birds share a relatively low intestinal surface area compared to non‐flying mammals, but the difference diminishes with increasing size. Paracellular absorption is high in birds with a variety of diets, and in the species with the highest paracellular absorption, uptake via this pathway can account for the majority of glucose absorption. A parsimonious explanation for evolution of high paracellular absorption is as a compensatory mechanism for reduced intestine size, especially in flying vertebrates. Supported by NSF IBN‐0216709 to WHK, UNSL22/Q451 to EC‐V.