Mass Scaling of Standard Metabolism in Ticks: A Valid Case of Low Metabolic Rates in Sit-and-Wait Strategists

Abstract

Ticks can survive for a year or more between blood meals, making them the ultimate "sit-and-wait" strategists. We accordingly hypothesize that their standard metabolic rates (SMRs) are unusually low. We test this hypothesis by measuring the SMRs of several tick species and comparing them with modern literature values for other arthropods (ants, beetles, and spiders). By ANCOVA ants, beetles, and spiders share a common mass scaling of SMR (SMR = 906 BM0.825, where SMR is in microwatts at 25° C and BM is body mass in grams). Previous investigations suggesting low SMRs in spiders utilized a questionable "yardstick equation" relating SMR to BM in arthropods. Ticks, in contrast, are shown by ANCOVA to have genuinely low SMRs-12% of the predicted value for ants, beetles, or spiders of equivalent BM. We hypothesize that this low SMR is caused by an atjpically low ratio of actively respiring tissue (ART) to BM. We hypothesize further that this low ART/BM ratio results from maintaining metabolically near-inert structures, such as excess integument, required for rapid engorgement during blood meals, and that this low ART/BM ratio has the synergistic effect of increasing energy storage capacity per unit ART, increasing survival time during fasting.