Relating environmental variation to selection on reaction norms: an experimental test

Area of Science:

• Evolutionary biology
• Ecology
• Genetics

Background:

• Theoretical models predict that selection on reaction norms is influenced by the frequency of environmental states.
• Understanding how populations adapt to varying thermal environments is crucial for predicting responses to climate change.

Purpose of the Study:

• To experimentally test the prediction that selection on thermal performance curves depends on the frequency distribution of environmental temperatures.
• To investigate the relationship between larval growth rate, thermal environment, and fitness in the cabbage white butterfly, Pieris rapae.

Main Methods:

• Larval growth rate (RGR) was measured across five temperatures for individual Pieris rapae.
• Individuals were randomly assigned to warm or cool selection treatments with different temperature frequency distributions.
• Selection gradient analyses were used to quantify selection on RGR, considering survival and development rate.

Main Results:

• Significant positive selection for increased RGR was observed, primarily through effects on survival and development rate.
• The magnitude of directional selection on RGR was consistently greater at lower (suboptimal) temperatures than at higher temperatures.
• Observed differences in selection between warm and cool treatments did not align with theoretical predictions.

Conclusions:

• Environmental temperature frequency alone may not fully predict selection on thermal performance curves.
• The temporal order and duration of environmental conditions can influence selection patterns, complicating the link between environment, phenotype, and fitness.
• Further research is needed to understand the complex interplay of environmental factors in shaping adaptation.