Metabolic rate does not scale with body size or activity in some tick species

Respiration in ticks is highly efficient and exceptionally low. Ticks can survive years between bloodmeals by having low activity and respiration to conserve energetic resources. Our objective was to compare metabolic (VCO₂) and activity rates across 6 tick species. We predicted that VCO₂ would be different among species and scale linearly with activity and body mass. Activity and CO₂ production were measured for 32 h in 6 tick species: Dermacentor andersoni, D. variabilis, Haemaphysalis longicornis, Rhipicephalus appendiculatus, R. microplus, and R. sanguineus. Individual ticks were measured for 30 min three times to ensure breathing occurred. Absolute and mass-specific VCO₂, total activity, body mass, and ventilation patterns were compared among species. As expected, ticks did not always breathe during the 30-minute measurements, especially R. sanguineus. Ventilation patterns differed among species with R. microplus having primarily cyclic patterns and R. appendiculatus having discontinuous gas exchange. VCO₂ did not scale with body mass in most species. Haemaphysalis longicornis and R. sanguineus had the lowest VCO₂; however, H. longicornis was the second most active species. Life history, including questing behavior and range expansion, could be contributing to differences between species. For instance, H. longicornis had exceptionally low metabolic rates despite above average activity levels, suggesting an energetic advantage which may underlie recently documented range expansions in North America. Our results demonstrate how ticks utilize energetic resources to maximize longevity. Future research describing questing behavior and distribution modeling may help explain differences in metabolic rates and activity and impacts on life history traits.