Energy metabolism and the postprandial response of the Chilean tarantulas, Euathlus truculentus (Araneae: Theraphosidae)

One of the most ubiquitous consequences of feeding in animals is specific dynamic action (SDA), a drastic increment in metabolic rate after a meal, which lasts from a few hours to several days. According to a recent exhaustive review by Secor (2009), studies in SDA are abundant, encompassing all kinds of vertebrates and invertebrates. However, important exceptions are arachnids, as few studies have characterized SDA in this group. Here, we measured the standard metabolic rate (SMR) of the Chilean tarantulas Euathlus truculentus (body mass = 7.32 ± 0.7 g; N = 32; TA = 25 °C), its inter-individual variation (i.e., repeatability) and its SDA. We measured SMR three or four times in each individual, and we also conducted predation experiments where a prey was consumed by each spider, during a respirometry trial. The SMR of E. truculentus was 0.00049 ± 0.000079 mlCO2 g−1 min−1 which corresponds to 1524 μW (assuming a protein-based diet), 108.4% of the predicted value for arachnids. According to the standard nomenclature for SDA studies, the scope of the SDA for a meal size of 1.26 ± 0.04 g (18% of the spider size) was 6.55 ± 1.1 times the baseline, the time to peak was 45 min, and the magnitude of the SDA was 0.28 ± 0.03 kj, which is 85% of the expected value for invertebrates. Our SMR data are in concordance with previous findings suggesting remarkably low energy metabolism in arachnids, compared with other arthropods. On the other hand, the exceedingly high scope of the postprandial response contrasts with the comparatively low SDA. This fact suggests that spiders spend most of the energy for digestion in a short period after prey capture, which could be a consequence of their external digestion.