Locomotor and energetic consequences of behavioral thermoregulation in the sanguivorous leech Hirudo verbana.

Medicinal leeches (Hirudo verbana) thermoregulate with respect to their sanguivorous feeding behavior. Immediate postprandial preferences are for warmer than their initial acclimation temperature (T, 21°C, Petersen et al. 2011), while unfed leeches have a lower preferred temperature (T, 12.5°C). This may reduce energy expenditure and defer starvation if feeding opportunities are limited. Energetic benefits may have an associated cost if low temperatures reduce mobility and the ability to locate further hosts. These costs could be limited if mobility is unimpaired at low temperatures, or if acclimation can restore locomotor performance to the levels at T. The transition from T to the unfed T significantly reduced speed and propulsive cycle frequency during swimming, and extension and retraction rates during crawling. Aerobic metabolic rate was also reduced from 0.20±0.03Wkg at T to 0.10±0.03Wkg at T. The Q values of 1.7-2.9 for energetic and swimming parameters indicate a substantial temperature effect, although part of the decline in swimming performance can be attributed to temperature-related changes in water viscosity. 6 weeks at T resulted in no detectable acclimation in locomotor performance or aerobic metabolism. The energetic savings associated with a lower T in unfed leeches effectively doubled the estimated time until depletion of energy reserves. Given that some mobility is still retained at T, and that acclimation is in itself costly, the energetic benefits of selecting cooler temperatures between feedings may outweigh the costs associated with reduced locomotor performance.