Plastron respiration in ticks or how do ticks mange to live under water?
This research proposes to determine the mechanism by which ticks are able to survive submersion under water. Preliminary research has shown that unfed adult ticks (Dermacentor variabilis) can remain submerged in water for up to three weeks. Ticks have two large spiracles for external gas exchange. These spiracles are covered with a sieve plate in which there are numerous small holes or aeropyles. This sieve plate could serve as a plastron. A plastron is a type of physical gill consisting of a thin layer of air trapped by hydrophobic hairs or other cuticular projections (Schmidt-Nielsen 1997). Oxygen diffuses into this plastron which is linked to the tracheal system - a system of tubes that conducts air into the body. Plastron respiration has evolved independently in several groups of tracheate arthropods including, insects and mites. Arthropods that use plastron respiration can remain submerged for extended periods of time (hours to days). This study represents the first time that this respiratory mechanism has been investigated in ticks. This research project will (1) confirm the spiracular plate as the site of plastron respiration in ticks. 2) Develop a model for plastron efficiency and 3) test this model on different species of ticks, which show variation in spiracular morphology. This study will involve working with several different species of ticks in submersion experiments, investigating the spiracular structure of ticks using scanning electron microscopy and determining oxygen consumption of ticks using respirometry techniques. The significance of this work relates to understanding why ticks are able to survive several years under natural conditions. Extreme longevity is one of the reasons why ticks are important vectors of disease since they have the capability to outlive their hosts and thus serve as disease reservoirs. This research will contribute to our understanding of why ticks are amongst the most long-lived of arthropods. The ability of ticks to survive submersion must be critical for their survival under circumstances of heavy rainfall and/or periodic flooding.