Locomotor Exercise Exerts No Systemic Effect On The Dentary In The American Alligator

RM 210

Exercise appears to exert systemic effects on skeletal growth in mammals, causing increased bone deposition in skeletal elements not under direct mechanical loading. Such potential effects in nonmammalian vertebrates have not received much attention. We studied effects of locomotor regimen on the lower jaw histomorphometry in the American alligator (Alligator mississipiensis). Animals were assigned to one of three groups: sedentary, running, swimming (n=20 each), and exercised to exhaustion every other day for 18 months. Surgery was used to render the animals’ circulatory system in-series (experimental n=24), or retain the original in-parallel design (sham n=36). Whole body growth of animals was tracked biweekly, with fluorescent dye injections used to quantify the mineral apposition rate (MAR). Periosteal MAR of the dentary correlated with both mass and linear growth at the lateral margin of the mandibular ramus, but not at the ventral margin. Exercise regimen and shunt ability had no effect on MAR at either site. This suggests that skeletal integrity of the feeding apparatus in crocodilians is not influenced by systemic effects of exercise. This may be of selective advantage in sit-and-wait predators, which rely on robust jaws despite long periods of inactivity. Similar experiments on modern birds are needed to discern whether non-avian dinosaurs showed systemic sensitivity to exercise. Supported by NSF IOB 0445680 to JWH.