Relating Environmental Variation to Selection on Reaction Norms: An Experimental Test

Abstract

Theoretical models predict that selection on reaction norms should depend on the relative frequency of environmental states experienced by a population. We report a laboratory experimental test of this prediction for thermal performance curves of larval growth rate in Pieris rapae in relation to their thermal environment. We measured short-term relative growth rate (RGR) for each individual at a series of five temperatures, and then we assigned individuals randomly to warm or cool selection treatments, which differ in the frequency distributions of environmental temperatures. Selection gradient analyses of two independent experiments demonstrated significant positive selection for increasing RGR, primarily through its effects on survival to adulthood and on development rate. In both the warm and cool selection treatments, the magnitude of directional selection on RGR was consistently greater at lower (suboptimal) temperatures than at higher temperatures; differences in selection between the treatments did not match model predictions. The temporal order and duration of environmental conditions may affect patterns of selection on thermal performance curves and other continuous reaction norms, complicating the connections between variation in environment, phenotype, and fitness.

Geographic variation in thermal physiological performance of the intertidal crabPetrolisthes violaceusalong a latitudinal gradient

“…Gaussian, Lorentzian, Weibull) that could describe organismal performance as a function of temperature was analyzed using the Akaike Information Criterion (Angilletta, 2006). The AIC represents a balance between the likelihood explained by the model and the number of model parameters, with the best model minimizing AIC (Kingsolver and Massie, 2007). Thermal physiological traits obtained from the TPCs (i.e.…”

Ecological and evolutionary impacts of changing climatic variability

“…The reaction norm itself may evolve by natural selection (Scheiner & Lyman, 1991;Pigliucci & Schlichting, 1996;Scheiner & Callahan, 1999;Garland & Kelly, 2006;Baythavong & Stanton, 2010). Selection on reaction norms and performance curves in a population should be driven by the frequency (and predictability) of the environments experienced by organisms (Weis & Gorman, 1990;Gilchrist, 1995;Alpert & Simms, 2002;Kingsolver et al, 2007). Phenotypic plasticity should be important not only to deal with the increasing rate of climate change, but also with the increased unpredictability of climatic anomalies (Arias, Poupin & Lardies, 2011).…”

“…Nonetheless, stabilizing selection is less frequent and usually weaker than directional selection in natural populations (Kingsolver et al, 2001). In any event, increased levels of climatic complexity (the particular sequence and duration of environmental states) may complicate patterns of selection on thermal performance curves and other continuous reaction norms (Kingsolver et al, 2007;Valladares, Gianoli & Gómez, 2007). Moreover, a comprehensive and realistic analysis must take into account the role of correlations between characters of functional value, which may constrain the evolution of adaptive responses to climate change (Etterson & Shaw, 2001;Gianoli & Palacio-López, 2009).…”

Microgeographic variation in temperature-induced plasticity in an isolated amphibian metapopulation

“…Variation in local temperature conditions is expected to select for increased variation in thermal reaction norms among populations (Kingsolver and Gomulkiewicz 2003;Kingsolver et al 2007). In larval amphibians, higher water temperature usually leads to earlier metamorphosis, at smaller size, whereas lower water temperatures lead to a later metamorphosis at larger size (Atkinson 1996).…”