Seven python taxa, two elapid species and one acrochordid were used in laboratory experiments over two years. This study examined the metabolic rates among species and temperatures, and also between seasons. Pythons were used in feeding experiments to determine the extent of specific dynamic action (SDA) at four temperatures. Digestive efficiency and energy budgets were also determined for the pythons at each temperature. Python metabolic rate follows the general allometric pattern for reptiles but it is lower than in most other reptiles. The thermal sensitivity of metabolism is similar to other reptiles. Standard metabolic rate (SMR) did not differ between seasons or on a daily cycle. Preferred body temperatures are similar between seasons for most pythons, although they did change for some non python species. An increase in metabolic rate associated with feeding in animals is known as specific dynamic action. In this study the maximum increase due to SDA was 42 times SMR, but the typical increase was about 7 times SMR. The increase due to SDA, relative to SMR, was insensitive to temperature. The magnitude of SDA was related to meal size when relatively small meals were consumed (<25% body mass), but the magnitude of SDA plateaued for relative meal sizes >25% of body mass. This plateau occurred for a range of relative food masses between 25 and 51.1% body mass. The increase in peak metabolic rate after feeding relative to SMR did not differ between the four experimental temperatures. This may indicate that in pythons, activity of digestive enzymes are temperature dependent and have a thermal sensitivity similar to standard metabolic rate. Digestive efficiency (DE) of pythons was much higher than all other reptiles. Hair was removed from the initial analysis because it is indigestible. DE was insensitive to temperature, and was about 99% at all temperatures examined. The energy available to pythons from a meal decreased with increasing temperature. This decline in energy available was due to increasing energy costs associated with SMR and SDA. Empirical equations allow estimation of the energy allocated to each of the components of the energy budget including SMR, SDA, shedding, growth and activity. Pythons assimilate more energy per gram of food ingested at low digesting temperatures due to the reduced metabolic cost of SDA. This result suggests that digestion at lower temperatures may be advantageous if food is scarce. However, at high temperatures, digestion time is reduced, allowing more food to be ingested within a given time compared to digestion at low temperatures. Although at high temperatures the metabolic cost of SDA is high, it is possible for pythons to assimilate more energy compared to digestion at lower temperatures by consuming more food per unit time. This suggests that digestion at higher temperatures may be advantageous if food is abundant.
|Date of Award||Nov 1996|
|Supervisor||Keith Christian (Supervisor)|