Evol Ecol Res 17: 111-124 (2016)     Full PDF if your library subscribes.

Temperature variability and thermal performance in ectotherms:
acclimation, behaviour, and experimental considerations

Francisco Bozinovic1,2, Pablo Sabat2,3, Enrico L. Rezende4 and Mauricio Canals3,5

1Departamento de Ecología, Facultad de Ciencias Biológicas, Pontificia Universidad Católica de Chile, Santiago, Chile,  2Center of Applied Ecology and Sustainability, Pontificia Universidad Católica de Chile, Santiago, Chile,  3Departamento de Ciencias Ecológicas, Facultad de Ciencias, Universidad de Chile, Santiago, Chile,  4Department of Life Sciences, Centre for Research in Ecology, University of Roehampton, London, UK and  5Programa de Salud Ambiental, Escuela de Salud pública, Facultad de Medicina, Universidad de Chile, Santiago, Chile

Correspondence: F. Bozinovic, Departamento de Ecología, Pontificia Universidad Católica de Chile, Santiago 6513677, Chile.
e-mail: fbozinovic@bio.puc.cl


Background: Among the predictions of the effect of future climate change, the impact of thermal conditions at local levels on the performance of individuals and their acclimation capacities is key to understanding animals’ responses to global warming. Woodlice (the terrestrial isopod Porcellio laevis) exhibit a readily observed behaviour that may reflect their acclimation capacities. When they find themselves on their back, they sometimes roll over (i.e. right themselves). Whether they do, and how fast they do it, are measures of their behaviour and performance that vary with ambient temperature.

Goal: Measure experimentally the effect of acclimation to environmental thermal variability on the rollover behaviour of Porcellio laevis.

Methods: Maintain woodlice in 24°C laboratory environments. Each individual lived in one of three thermal treatments: constant temperature regime (δ = 0); a regime with alternating temperatures of 27°C during daytime and 21°C at night (δ = 3); and a regime with alternating temperatures of 32°C during daytime and 16°C at night (δ = 8). After 3 months, measure the rollover behaviour (percentage that rolled over) and rollover speed of the woodlice at 5, 15, 25, 32, and 38°C. Rollover speed is the inverse of the time it took an individual to right itself.

Results: At 5 and 38°C, most woodlice seemed to be in thermal coma and had very slow rollover speed. At 15, 25, and 32°C, rollover speed was in the range 0.12–0.18 rollovers per second. At 15, 25, and 32°C, 52% of individuals righted themselves in ∼4 s. At these temperatures, most individuals either rolled quickly or remained inactive for the entire 10-min test period. When we examined rollover speed in the cooler (night) and warmer (daytime) periods, individuals subjected to the three regimes of temperature variation differed: woodlice acclimated to δ = 8 roll over very fast when temperature (T ) is low and very slowly when T is high; woodlice acclimated to δ = 3 roll over fairly fast when T is low and somewhat slowly when T is high; and woodlice acclimated to δ = 0 roll over quite quickly when T is low and quite slowly when T is high. However, the higher and lower speeds at different regimes neutralized each other so that average rollover speed over the course of a whole day did not depend on the size of the daily fluctuation.

Conclusions: The impact of temperature variability must be taken into consideration. Behavioural responses that are seemingly costly in the very short term may be beneficial in the longer term.

Keywords: acclimation, global warming, performance variance, thermal variability.

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