The digestive adaptation of flying vertebrates

High intestinal paracellular absorption compensates for smaller guts

E Caviedes-Vidal, Todd McWhorter, S Lavin, J Chediak, Christopher Tracy, William Karasov

    Research output: Contribution to journalArticleResearchpeer-review

    Abstract

    Anecdotal evidence suggests that birds have smaller intestines than mammals. In the present analysis, we show that small birds and bats have significantly shorter small intestines and less small intestine nominal (smooth bore tube) surface area than similarly sized nonflying mammals. The corresponding >50% reduction in intestinal volume and hence mass of digesta carried is advantageous because the energetic costs of flight increase with load carried. But, a central dilemma is how birds and bats satisfy relatively high energy needs with less absorptive surface area. Here, we further show that an enhanced paracellular pathway for intestinal absorption of water-soluble nutrients such as glucose and amino acids may compensate for reduced small intestines in volant vertebrates. The evidence is that L-rhamnose and other similarly sized, metabolically inert, nonactively transported monosaccharides are absorbed significantly more in small birds and bats than in nonflying mammals. To broaden our comparison and test the veracity of our finding we surveyed the literature for other similar studies of paracellular absorption. The patterns found in our focal species held up when we included other species surveyed in our analysis. Significantly greater amplification of digestive surface area by villi in small birds, also uncovered by our analysis, may provide one mechanistic explanation for the observation of higher paracellular absorption relative to nonflying mammals. It appears that reduced intestinal size and relatively enhanced intestinal paracellular absorption can be added to the suite of adaptations that have evolved in actively flying vertebrates. � 2007 by The National Academy of Sciences of the USA.
    Original languageEnglish
    Pages (from-to)19132-19137
    Number of pages6
    JournalProceedings of the National Academy of Sciences of the United States of America
    Volume104
    Issue number48
    Publication statusPublished - 2007

    Fingerprint

    vertebrate
    bird
    mammal
    bat
    surface area
    monosaccharide
    amplification
    glucose
    energetics
    amino acid
    flight
    nutrient
    cost
    energy
    analysis
    water

    Cite this

    Caviedes-Vidal, E ; McWhorter, Todd ; Lavin, S ; Chediak, J ; Tracy, Christopher ; Karasov, William. / The digestive adaptation of flying vertebrates : High intestinal paracellular absorption compensates for smaller guts. In: Proceedings of the National Academy of Sciences of the United States of America. 2007 ; Vol. 104, No. 48. pp. 19132-19137.
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    abstract = "Anecdotal evidence suggests that birds have smaller intestines than mammals. In the present analysis, we show that small birds and bats have significantly shorter small intestines and less small intestine nominal (smooth bore tube) surface area than similarly sized nonflying mammals. The corresponding >50{\%} reduction in intestinal volume and hence mass of digesta carried is advantageous because the energetic costs of flight increase with load carried. But, a central dilemma is how birds and bats satisfy relatively high energy needs with less absorptive surface area. Here, we further show that an enhanced paracellular pathway for intestinal absorption of water-soluble nutrients such as glucose and amino acids may compensate for reduced small intestines in volant vertebrates. The evidence is that L-rhamnose and other similarly sized, metabolically inert, nonactively transported monosaccharides are absorbed significantly more in small birds and bats than in nonflying mammals. To broaden our comparison and test the veracity of our finding we surveyed the literature for other similar studies of paracellular absorption. The patterns found in our focal species held up when we included other species surveyed in our analysis. Significantly greater amplification of digestive surface area by villi in small birds, also uncovered by our analysis, may provide one mechanistic explanation for the observation of higher paracellular absorption relative to nonflying mammals. It appears that reduced intestinal size and relatively enhanced intestinal paracellular absorption can be added to the suite of adaptations that have evolved in actively flying vertebrates. � 2007 by The National Academy of Sciences of the USA.",
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    The digestive adaptation of flying vertebrates : High intestinal paracellular absorption compensates for smaller guts. / Caviedes-Vidal, E; McWhorter, Todd; Lavin, S; Chediak, J; Tracy, Christopher; Karasov, William.

    In: Proceedings of the National Academy of Sciences of the United States of America, Vol. 104, No. 48, 2007, p. 19132-19137.

    Research output: Contribution to journalArticleResearchpeer-review

    TY - JOUR

    T1 - The digestive adaptation of flying vertebrates

    T2 - High intestinal paracellular absorption compensates for smaller guts

    AU - Caviedes-Vidal, E

    AU - McWhorter, Todd

    AU - Lavin, S

    AU - Chediak, J

    AU - Tracy, Christopher

    AU - Karasov, William

    PY - 2007

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    AB - Anecdotal evidence suggests that birds have smaller intestines than mammals. In the present analysis, we show that small birds and bats have significantly shorter small intestines and less small intestine nominal (smooth bore tube) surface area than similarly sized nonflying mammals. The corresponding >50% reduction in intestinal volume and hence mass of digesta carried is advantageous because the energetic costs of flight increase with load carried. But, a central dilemma is how birds and bats satisfy relatively high energy needs with less absorptive surface area. Here, we further show that an enhanced paracellular pathway for intestinal absorption of water-soluble nutrients such as glucose and amino acids may compensate for reduced small intestines in volant vertebrates. The evidence is that L-rhamnose and other similarly sized, metabolically inert, nonactively transported monosaccharides are absorbed significantly more in small birds and bats than in nonflying mammals. To broaden our comparison and test the veracity of our finding we surveyed the literature for other similar studies of paracellular absorption. The patterns found in our focal species held up when we included other species surveyed in our analysis. Significantly greater amplification of digestive surface area by villi in small birds, also uncovered by our analysis, may provide one mechanistic explanation for the observation of higher paracellular absorption relative to nonflying mammals. It appears that reduced intestinal size and relatively enhanced intestinal paracellular absorption can be added to the suite of adaptations that have evolved in actively flying vertebrates. � 2007 by The National Academy of Sciences of the USA.

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