The phenotypic flexibility of the gut is energetically cheap in Burmese pythons: feeding frequency does not affect growth efficiency.

The overall energetic expenditure related to the upregulation and downregulation of the mass and function of the gastrointestinal (GI) organs in response to feeding and fasting in vertebrates has attracted great interest. While it is generally considered energetically favourable to downregulate intestinal mass when food is scarce, very few direct experimental studies address the actual costs. Here, we specifically address the costs of phenotypic flexibility by comparing growth, body composition and oxygen consumption of snakes fed on two different feeding regimes. One group was fed intermittently to allow for the gut to be downregulated during the fasting intervals, while the other group was fed more continuously to maintain a chronic upregulated GI tract. We demonstrate that these two feeding regimes result in very similar growth, growth efficiency and overall oxygen consumption, and thus point to upregulation and maintenance of the GI tract being energetically inexpensive. These findings challenge the prevailing assumption that maintaining a functional GI tract is metabolically costly. Although replenishing and maintaining a functional GI tract probably incurs some energetic cost, it probably represents only a minor component of the specific dynamic action (SDA) response.