Beneficial acclimation hypothesis

The Beneficial Acclimation Hypothesis (BAH) is the physiological hypothesis that acclimating to a particular environment (usually thermal) provides an organism with advantages in that environment. First formally defined and tested by Armand Marie Leroi, Albert Bennett, and Richard Lenski in 1994, it has however been a central assumption in historical physiological work that acclimation is adaptive. Further refined by Raymond B. Huey and David Berrigan under the strong inference approach, the hypothesis has been falsified as a general rule by a series of multiple hypotheses experiments.

History and Definition

Acclimation is a set of physiological responses that occurs during an individual’s lifetime to chronic laboratory-induced environmental conditions (in contrast to acclimatization). It is one component of adaptation. While physiologists have traditionally assumed that acclimation is beneficial (or explicitly defined it as such), criticism of the adaptationist program by Stephen Jay Gould and Richard Lewontin led to a call for increased robustness in testing adaptationist hypotheses.

The initial definition of the BAH, as published in 1994 in the Proceedings of the National Academy of Sciences by Leroi et al., is that

“acclimation to a particular environment gives an organism a performance advantage in that environment over another organism that has not had the opportunity to acclimate to that particular environment.”

This definition was further reworked in an article in American Zoologist 1999 by Raymond B. Huey, David Berrigan, George W. Gilchrist, and Jon C. Herron. They determined that, following Platt’s strong inference approach, multiple competing hypotheses were needed to properly assess beneficial acclimation. These included:

1. Beneficial Acclimation. Acclimating to a particular environment confers fitness advantages in that environment.

2. Optimal Developmental Temperature. There is an ideal temperature to develop at so individuals reared at an optimal temperature compete better in all environments.

3. Colder (bigger) Is Better. In ectotherms, individuals reared in colder environments tend to develop to a larger body size. These individuals therefore have a fitness advantage in all environments.

4. Warmer (smaller) Is Better. The inverse of Colder Is Better. Smaller individuals have a fitness advantage.

5. Developmental Buffering. Development temperature does not affect adult fitness.

Current State

The majority of studies have concluded the Beneficial Acclimation Hypothesis is not true in all cases, and that alternate hypotheses should be tested. In addition to this, recent studies of the hypothesis have provided additional complications, such as trade-offs evident only in field environments and interactions with behavior and life history traits. The study of developmental and phenotypic plasticity continues.