Mathbio proposal: Underwater survival in ticks

Mentors

Laura Fielden; Biology

David Garth; Mathematics & Computer Science

Project description

Background: Ticks can remain totally submerged in water for extended periods of time (days to weeks) using plastron respiration and metabolic depression (Fielden and Duncan 2012, Fielden et al. 2011). Ticks have two large spiracles for gas exchange. These spiracles are covered with a complex perforated sieve plate that traps air when the tick is submerged. This air-filled sieve plate functions as a plastron. Oxygen from the water diffuses into this plastron which is linked to the tracheal system - a system of tubes that conducts air into the body. This oxygen extracted from the water appears sufficient to keep the tick alive for long periods of time. Bach Ha (Mathbio research student 2005, 2006) helped develop the following mathematical model to predict survivability of submerged ticks under water.

T amount of time that a tick can survive underwater

Vvolume of airspace beneath the spiracular plate

Asurface area of air-water interface

qoxygen consumption rate/metabolic rate

ioinvasion coefficient of oxygen in water

popressure of oxygen in water

p*pressure of oxygen in the plastron

totension of oxygen in the air.

However, there is a great deal of interspecific variation in the underwater survivability of ticks (Fielden unpublished data; Gianelli et al. 2012). This difference in survivability may relate to the structure of the plastron (terms V and A) and the metabolic demands of the tick while submerged under water (term q).

Goal and significance: Our proposed research will investigate why different species of ticks have different survival abilities under conditions of flooding. We hypothesize that length of survival (t) is related to the efficiency of the plastron in extracting oxygen from the water (V and A), as well as the oxygen consumption of the tick (q) while submerged. We predict that species of ticks with an efficient plastron (i.e. large air-water interface and volume of air) in combination with a low metabolic rate will have higher survivability rates than ticks with less efficient plastrons and/ or higher oxygen consumption rates. 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.

Objectives: This research will examine

1) underwater survival, 2) plastron efficiency and 3) underwater oxygen consumption in five species of ticks *Dermacentor variabilis. *Amblyomma americanum,A. maculatum, *Rhipicephalus sanguineus and Ixodes scapularis. Three of these species (*) are maintained on site while the others can be obtained from commercial breeders or the Centers for Disease Control (Atlanta, GA). These species are selected to give diversity in in phylogeny and habitat preference. They are also indigenous to the Midwest and provide no risk of introduced species.

1)Underwater survival: Survival of ticks submerged under water for periods of time ranging from a few hours to a few weeks will be investigated using survival curve analysis. Long survival indicates an efficient plastron.

2)Plastron efficiency: Volume of the air film contained within the spiracular plate, and the plastron air/water interface will be determined by the area of air-water interface in relation to the respiring biomass of the animal. Calculation of the interface and volume of the air spaces requires estimates of the dimensions of the aeropyles (pores) in the spiracular plate using scanning electron microscopy and image analysis software (Image J).

3)The oxygen consumption of the submerged tick. Dissolved oxygen electrode has been found to be the most suitable method to determine oxygen uptake in individual ticks at various intervals of submergence (1, 5, 10 and 15 days). Preliminary studies on Dermacentor variabilis have demonstrated that oxygen consumption of ticks decreases with length of submergence.

Skills -research students

Biology Student

Apart from a strong commitment to research, no specific skills required but any experience in scanning electron microscopy or use of image analysis software would be a great advantage.

Math Student

Completion of Stat 290 and Math 365, Ordinary Differential Equations, during the first year of the project are desirable.

Citations

Fielden, L.J. and Duncan, F.D. (2012): The Respiratory System – Structure and Function in Sonenshine, D. and Roe, M (eds): Biology Of Ticks (2nd edition). Oxford University Press, London; In press

Fielden, L.J., Knolhoff, L.M., Villarreal, S.M., Ryan, P. (2011):Underwater survival in the dog tick Dermacentor variabilis (Acari: Ixodidae). Journal of Insect Physiology57:21-6.

Giannelli, A., Dantas-Torres, F., and Otranto, D. (2012): Underwater survival of Rhipicephalus sanguineus. Experimental and Applied Acarology57:171-178

Funding period

We request funding for two years according to the following anticipated time line.

Year 1

  • Boosting current colonies of ticks (*Dermacentor variabilis. *Amblyomma americanum, and *Rhipicephalus sanguineus) and establishing new colonies at Truman, (A. maculatum and Ixodes scapularis)
  • Training of students in electron microscopy skills
  • Survival studies for all species of ticks (this needs to be done before oxygen determinations so that we can target critical submergence times for oxygen consumption measurements)
  • Start electron microscopy studies on spiracular plate structure.
  • Ongoing data analysis

Year 2

  • Training of students in use of oxygen electrode
  • Oxygen consumption studies for all species of ticks
  • Complete electron microscopy studies on spiracular plate structure
  • Completion of data analysis
  • Preparation of manuscript for publication.

Recruitment of students

We will recruit our own students but would welcome any help from Mathbio.