Zoology (Jena) 2006 7;109(4):310-7. Epub 2006 Sep 7.
Department of Biology, Biocenter Martinsried, University of Munich (LMU), Grosshadernerstrasse 2, D-82152 Planegg-Martinsried, Germany.
The African rhombic egg eater (Dasypeltis scabra) is a colubrid snake feeding exclusively on bird eggs. Frequency of feeding is governed by the seasonal availability of bird eggs; i.e., long fasting intervals change with relatively short periods when plenty of food is available. Intermittent feeding snakes show a remarkable postprandial increase of metabolic rate and digestive organ size. The postprandial increase in metabolic rate (specific dynamic action, SDA) in snakes is affected by meal size, temperature, and meal composition. A major portion of SDA in snakes is allocated to gastric function and the breakdown of the meal. We hypothesize that SDA in egg eaters is lower than in other snake species, because egg eaters feed on "liquid" food that does not require enzymatic breakdown in the stomach. We also hypothesized that other components of the postprandial response of egg eaters (e.g., size changes of the intestine and the liver) do not differ from other snakes. The standard metabolic rate and metabolic response to feeding were measured using closed-chamber respirometry. Size changes of small intestine and liver were measured using high-resolution transcutaneous ultrasonography. Standard metabolic rates of fasting egg eaters were in the same range of mass specific values as known from other snakes. Within 24h after feeding, oxygen consumption doubled and peaked at 2 days after feeding. At the same time, the size of the small intestine and the cross-sectional diameter of the liver increased. Within 2 days after feeding, the size of the mucosal epithelium doubled its thickness. Liver size increased significantly within 24h reaching maximum size 2-4 days after feeding. The size of both organs returned to fasting values within 7-10 days after feeding. The postprandial response of African rhombic egg eaters shows the same pattern and dynamics as known from other snake species. However, the factorial increase of metabolic rate during SDA is the lowest reported for any snake. A comparison with literature data supports the idea that SDA is mainly determined by gastric function and that it is low in egg eaters because they do not have to break down solid meals in the stomach as other snake species do.