Tick Ventilation and Respiratory Water Loss

Lighton, John

Abstract

Tick ventilation and respiratory water loss. Ticks are among the most significant disease vectors known, accounting for direct and indirect effects on humans and livestock worth billions of dollars per annum. In most tick species, the abundance and distribution of the off-host (fasting) stages--a very important epidemiological parameter--is profoundly affected by temperature and relative humidity levels. We have discovered that adult and nymphal fasting ticks employ a discontinuous ventilation cycle (DVC) similar to that found in insects. The function of the DVC is to reduce respiratory water loss (RWL). The DVC thus allows gas exchange to take place while conserving body water reserves, and facilitates maintenance of ionic homeostasis for periods ranging from weeks to years while the tick fasts between blood meals. In spite of the obvious significance of the DVC to the survival of adult and nymphal ticks, and hence to the epidemiology of a host of diseases including Rocky Mountain spotted fever, tularemia, Q fever and Lyme disease, we currently understand little or nothing of the DVC's occurrence, regulation, RWL correlates, modulation strategies, or control mechanisms. We propose to undertake the first in-depth study of tick ventilation, utilizing research methodologies and techniques--notably computer-controlled ultra-high- resolution flow-through respirometry--already developed in our laboratory for investigating insect ventilation. This places us in a unique position to solve problems to investigate tick ventilation: all of the proposed experiments utilize, and all of the stated aims are achievable with the aid of our up-and-running, proven capability in this field of research. The result will be an in-depth understanding of tick ventilation and its correlates for tick water balance, perhaps the most important single variable in the long-term survival of ticks. This knowledge will be a valuable tool for students of tick biology, with significant possible consequences for predictive modeling and the formulation of control strategies. As a spin-off, tick ventilation (and real-time metabolic rate, which is measured simultaneously) can be employed as a sensitive assay for the effects of acaricidal agents, hormones, pheromones and other variables on ticks.