title: Thermal preference and performance in a sub-Antarctic caterpillar: A test of the coadaptation hypothesis and its alternatives.
abstract: Physiological ecologists have long assumed that thermoregulatory behaviour will evolve to optimise physiological performance. The coadaptation hypothesis predicts that an animal's preferred body temperature will correspond to the temperature at which its performance is optimal. Here we use a strong inference approach to examine the relationship between thermal preference and locomotor performance in the caterpillars of a wingless sub-Antarctic moth, Pringleophaga marioni Viette (Tineidae). The coadaptation hypothesis and its alternatives (suboptimal is optimal, thermodynamic effect, trait variation) are tested. Compared to the optimal movement temperature (22.5°C for field-fresh caterpillars and 25, 20, 22.5, 25 and 20°C following seven day acclimations to 0, 5, 10, 15 and 5-15°C respectively), caterpillar thermal preference was significantly lower (9.2°C for field-fresh individuals and 9.4, 8.8, 8.1, 5.2 and 4.6°C following acclimation to 0, 5, 10, 15 and 5-15°C, respectively). Together with the low degree of asymmetry observed in the performance curves, and the finding that acclimation to high temperatures did not result in maximal performance, all, but one of the above hypotheses (i.e. 'trait variation') was rejected. The thermal preference of P. marioni caterpillars more closely resembles temperatures at which survival is high (5-10°C), or where feeding is optimal (10°C), than where locomotion speed is maximal, suggesting that thermal preference may be optimised for overall fitness rather than for a given trait.
authors.affiliation: Centre for Invasion Biology, Department of Botany and Zoology, Stellenbosch University, Private Bag X1, Matieland 7602, South Africa. Electronic address: THaupt-Schuter@environment.gov.za.
authors.forename: Tanya M
authors.initials: TM
authors.lastname: Haupt
authors.affiliation: Department of Biology, The University of Western Ontario, London, Ontario N6A 5B7, Canada.
authors.forename: Brent J
authors.initials: BJ
authors.lastname: Sinclair
authors.affiliation: School of Biological Sciences, Monash University, Victoria 3800, Australia.
authors.forename: Steven L
authors.initials: SL
authors.lastname: Chown
mesh_terms: D000064:Acclimatization; D000818:Animals; D000864:Antarctic Regions; D003080:Cold Temperature / Q000009:adverse effects; D062312:Islands; D007814:Larva / Q000254:growth & development / Q000502:physiology; D008124:Locomotion; D009036:Moths / Q000254:growth & development / Q000502:physiology*; D000071436:Thermotolerance
keywords: Caterpillars; Coadaptation; Fluctuating temperatures; Locomotion; Thermal performance curves; Thermal preference