Figure 1 used with permission of (Secor and Diamond, 1998)
Pay Before Pumping Theory |
|
One theory on the energetic costs of digestion after feeding is that the energy needed to up-regulate the digestive system initially comes form energy stores within the python and not within the prey. This theory is consistent with the fact that organ growth, digestive enzyme synthesis and the increase in metabolic rate, which all require energy, begin within 1-2 days of feeding while the prey is still largely intact and within the snakes stomach.
Figure 1 used with permission of (Secor and Diamond, 1998) |
As seen in the graph above, it is not until about 6 days after feeding that the ingested meal completely travels from the stomach into the small intestines. Therefore, the energy from the prey has not been absorbed by the time the digestive system begins to up-regulate As a result, the energy needed for the growth and synthesis of the digestive processes must come from the snake's own stored energy. This theory is supported by the 160 fold increase in the level of plasma triglycerides observed in the snake, which reflects the depletion of the fat stores within the snake to be used as energy to up-regulate the digestive system (Secor and Diamond, 1998). Thus, the digestive system of pythons resembles a gas station in which you have to "pay before pumping".
 |
On average a python spends 32% of the ingested food's energy on digestion compared humans who spend only 9% of the food's energy on digestive processes (Secor and Diamond, 1998). This high energetic cost is due to the energy needed to start up the python's digestive organs and processes which have been turned off during fasting. Evolutionarily, it seems un adaptive to expend that percentage of energy to digest a single meal. However, because a python can turn off its digestive system during fasting periods it is believed that the python is able to save energy in the maintenance of these processes when they are not in use. Therefore, it is hypothesized that there is an energetic benefit in digestive up-regulation because the energy associated with up-regulating the digestive organs is less than the cost of maintaining those organs continuously.
Topics
in Animal Physiology