MASS SCALING OF STANDARD METABOLISM IN TICKS - A VALID CASE OF LOW METABOLIC RATES IN SIT-AND-WAIT STRATEGISTS

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 comp aring them with modern literature values for other arthropods (ants, b eetles, and spiders). By ANCOVA ants, beetles, and spiders share a com mon mass scaling of SMR (SMR = 906 BM(0.825), where SMR is in microwat ts at 25 degrees C and BM is body mass in grams). Previous investigati ons suggesting low SMRs in spiders utilized a questionable ''yardstick equation'' relating SMR to BM in arthropods. Ticks, in contrast are s hown by ANCOVA to have genuinely low SMRs-12% of the predicted value f or ants, beetles, or spiders of equivalent BM. We hypothesize that thi s low SMR is caused by an atypically low ratio of actively respiring t issue (ART) to BM. We hypothesize further that this low ART/BM ratio r esults from maintaining metabolically near-inert structures, such as e xcess integument, required for rapid engorgement during blood meals, a nd that this low ART/BM ratio has the synergistic effect of increasing energy storage capacity per unit ART, increasing survival time during fasting.