Abstract
Most organisms experience environments that vary continuously over time, yet researchers generally study phenotypic responses to abrupt and sustained changes in environmental conditions. Gradual environmental changes, whether predictable or stochastic, might affect organisms differently than do abrupt changes. To explore this possibility, we exposed terrestrial isopods (Porcellio scaber) collected from a highly seasonal environment to four thermal treatments: (1) a constant 20°C; (2) a constant 10°C; (3) a steady decline from 20° to 10°C; and (4) a stochastic decline from 20° to 10°C that mimicked natural conditions during autumn. After 45 days, we measured thermal sensitivities of running speed and thermal tolerances (critical thermal maximum and chill-coma recovery time). Contrary to our expectation, thermal treatments did not affect the thermal sensitivity of locomotion; isopods from all treatments ran fastest at 33° to 34°C and achieved more than 80% of their maximal speed over a range of 10° to 11°C. Isopods exposed to a stochastic decline in temperature tolerated cold the best, and isopods exposed to a constant temperature of 20°C tolerated cold the worst. No significant variation in heat tolerance was observed among groups. Therefore, thermal sensitivity and heat tolerance failed to acclimate to any type of thermal change, whereas cold tolerance acclimated more during stochastic change than it did during abrupt change.
Highlights
Organisms commonly modify their molecular and cellular structures to maintain performance as their environments change [1,2]
Fruit flies can alter their thermal tolerance within the course of a single day [5], whereas trees require much longer to alter their photosynthetic rates [6]
The benefit of acclimation during an initial change could be offset by a loss of performance following a reversal [9]
Summary
Organisms commonly modify their molecular and cellular structures to maintain performance as their environments change [1,2]. Such acclimatory responses have been demonstrated to occur over temporal scales ranging from hours to months [3,4]. When environmental conditions fluctuate slowly, an individual can continuously adjust its phenotype to match prevailing conditions (see [7]) In this way, organisms can tolerate variation in environmental conditions among seasons. Stochastic variation weakens an individual’s ability to anticipate future conditions and adjust its phenotype . These factors could explain why many organisms fail to acclimate to changes in their environment (reviewed by [10])
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