Ramification of Relaxed Thermoregulation Under Climate Change

How animals respond to climate changes may be limited by their niche dimensions. Animals able to select microhabitats will be less affected than those that physically or behaviorally are unable to change their exposure. Hence the outcome of tick responses to climate change - which may affect transmission of diseases to humans - may not be obvious first-order effects. Tick species that actively move throughout their habitat searching for hosts may be able to utilize microhabitats that avoid the full effect of rising temperatures. Other tick species are more static since they wait for hosts to come to them. So even if a tick has a low preferred temperature, the need to be present in questing sites optimal for encountering hosts may force exposure to near lethal elevated temperatures. To further explore the questing behavior of Dermacentor variabilis and D. andersoni , and to test if regional variation is exhibited by adult D. variabilis , we reproduced a study that found that this species is an active hunter that orients and moves towards infrared radiation (IR) by use of Haller’s organs. We also tested if D. andersoni would move towards an exposed human hand, i.e. a host emitting a combination of IR, CO ₂ , and odors. This tested if the tick species exhibits sit-and-wait or active hunting. We found strong sit-and-wait behaviors by D. andersoni and D. variabilis . The ticks did not move toward the stationary exposed hand of an observer, and they were not attracted to infrared radiation. Tick may prioritize optimal locations to encounter potential hosts, over enzymatically optimal temperatures. Rather than evolving to detect hosts at a distance, Haller’s organs may have evolved to differentiate warm attachment sites from cooler fur. Our results suggest that Dermacentor questing behavior (remaining on station irregardless of preferred temperature) may make them particularly vulnerable to future rises in temperature.