Phylogenetic constraints on digesta separation: Variation in fluid throughput in the digestive tract in mammalian herbivores

Dennis W.H. Müller, Judith Caton, Daryl Codron, Angela Schwarm, Roger Lentle, W. Jürgen Streich, Jürgen Hummel, Marcus Clauss*

*Corresponding author for this work

    Research output: Contribution to journalArticlepeer-review

    58 Citations (Scopus)

    Abstract

    The relevance of the mean retention time (MRT) of particles through the gastrointestinal tract (GIT) is well understood and MRTparticleGIT is an important parameter in digestion models. Solute markers have been used to estimate MRTsoluteGIT (or 'fluid passage') in animals, but the relevance of this measure is less evident and is usually sought in its relation to MRTparticleGIT. The ratio between the two measures indicates the degree of 'digesta washing', with little washing occurring at ratios of 1, aborad washing at ratios >1 (where the solute marker travels faster than the particle marker), and orad (retrograde) washing at ratios <1 (where the solute marker travels slower than the particle marker). We analysed digesta washing in a dataset of 98 mammalian species including man of different digestion types (caecum, colon and nonruminant foregut fermenters, and ruminants), controlling for phylogeny; a subset of 72 species allowed testing for the influence of food intake level. The results indicate that MRTsoluteGIT and the degree of digesta washing are related to digestion type, whereas variation in MRTparticleGIT is influenced mainly by effects of body mass and food intake. Thus, fluid throughput and digesta washing emerge as important correlates of digestive anatomy. Most importantly, primates appear constrained to little digesta washing compared to non-primate mammalian herbivores, regardless of their digestion type. These results may help explain the absence of primates from certain herbivore niches and represent a drastic example of a physiologic limitation in a phylogenetic group. More experimental research is required to illuminate relative benefits and costs of digesta washing.

    Original languageEnglish
    Pages (from-to)207-220
    Number of pages14
    JournalComparative Biochemistry and Physiology -Part A : Molecular and Integrative Physiology
    Volume160
    Issue number2
    DOIs
    Publication statusPublished - Oct 2011

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