Active sensing in ticks: a comparative study between actively hunting Hyalomma marginatum and passively questing Ixodes ricinus ticks

• Applicant: Rock Lim, Ph.D.
• Subject Area: Cognitive, Systems and Behavioural Neurobiology ; Sensory and Behavioural Biology ; Biological Psychology and Cognitive Neuroscience
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 558695258

The purpose of this study is to research the function of the Haller's organ - a chemical/odor sensing organ on the first pair of ticks' forelegs, - when it comes to seeking hosts. This organ contains sensors for carbon dioxide, an important chemical signal for ticks which indicates presence of mammal hosts. When seeking prey, ticks wave their forelegs in the air, which is useful for grasping hosts and also moves the Haller's organ through airborne odorants. Recent research showed ticks can sense carbon dioxide with Haller's organs disabled, which implies that it provides some information benefit beyond simply knowing carbon dioxide is present at all. The movement of the Haller's organ through the air may be important for finding odor sources, similar to how insects wave antennae in the air to locate resources such as food. However, the specific behaviors and neural pathways of the Haller's organ have not been well-studied. This study will investigate the use of the Haller's organ in two species, one which is a passive ambusher, Ixodes ricinus, and one which is an active hunter, Hyalomma marginatum. Researching the use of the Haller's organ in species using different strategies will provide insight into how the organ is used in general. This will improve understanding how ticks sense odors and help develop methods to repel or otherwise mitigate the public health threat posed by disease-carrying ticks. The study has 3 key objectives: 1. To study the spatial olfactory accuracy of ticks' locating odor sources. 2. To investigate the role of the forelegs in active sensing and active interaction with odor plumes. 3. To identify and deorphanize olfactory receptors. Together, these objectives will show how ticks use the Haller's organ to find odor sources, such as hosts. They will be addressed through two behavioral experiments and one neuroscientific experiment which will collect data on tick movement, Haller's organ waving, and odorant receptor activity in response to carbon dioxide. The first objective will establish that ticks can orient and move toward sources of carbon dioxide. The second will show that ticks move their forelegs when exposed to carbon dioxide and quantify these movements. The third will identify olfactory receptors that respond to carbon dioxide.

• DFG Programme: WBP Position