Meeting Abstract
Passive, paracellular transport of small, water-soluble nutrients can be an important pathway for nutrient absorption, particularly for small, flying vertebrates. This has been hypothesized to be an efficient way to overcome the combined constraints of high-energy demands, reduced gut size, and fast digesta passage faced by small flying vertebrates. However, young saltwater crocodiles also show high paracellular absorption, despite being neither small nor flying. We hypothesized that fast-growing juvenile crocodiles may also rely on high paracellular absorption to fuel the energy demands of growth. Fractional absorption (bioavailability) of metabolically-inert carbohydrate probes decreased with probe size, as expected, and fractional absorption of both arabinose (absorbed only paracellularly) and 3-O-methyl D-glucose (absorbed by both mediated and paracellular transport) decreased with body mass across four size/age classes of saltwater crocodiles ranging from 250 to 33,000g. The higher paracellular absorption in small crocodiles may suggest that the pattern of reliance on high paracellular absorption is not limited to small flyers, but is more general, whereby any vertebrate with high energy demands should rely on energetically-cheap paracellular absorption to fuel growth, survival, or other energetic expenses.
