Dermal secretion physiology in Metastriata ticks; thermoregulation in the lone star tick Amblyomma americanum

Abstract

Ticks are blood feeding ectoparasites that transmit a wide range of pathogens. The lone star tick, Amblyomma americanum, is one of the most widely distributed ticks in the Midwest and Eastern United States. Lone star ticks, like most three-host ixodid ticks, can survive in harsh environments for extended periods without consuming a blood meal. Physiological mechanisms that allow them to survive during hot and dry season include thermal tolerance and water homeostasis. Large quantity of dermal fluid secretions induced by mechanical stimulation of tick legs has been described in metastriate ticks including Amblyomma. We hypothesize that a function of tick dermal secretion is similar to the sweating in large homeothermal animals. In this study, we found that a contact with a heat probe at 45oC can trigger dermal secretion. We demonstrated that dermal secretion plays a role in evaporative cooling when ticks are exposed to high temperature. We observed that direct contact to a heat probe for 5 seconds at ~ 52oC caused an exhaustive dermal secretion with ~ 4% loss of body weight and resulted in the lethality in 24-hour, indicating that the secretion is associated with significant costs of water loss. We identified type II dermal glands having paired two cells forming large glandular structures. The secretion is triggered by an injection of serotonin and the serotonin-mediated secretion was suppressed by a pretreatment of Ouabain, a Na/K-ATPase blocker, implying that the secretion is controlled by serotonin and the downstream Na/K-ATPase.