Trait variation in extreme thermal environments under constant and fluctuating temperatures

Area of Science:

• Ecology
• Evolutionary Biology
• Environmental Science

Background:

• Climate change introduces novel environmental conditions, potentially altering phenotypic variation.
• Extreme environments are theorized to reveal cryptic phenotypes and increase trait variation.
• Organismal responses to temperature vary between constant and fluctuating regimes.

Purpose of the Study:

• To investigate how common, rare, and novel temperatures affect hidden phenotypic variation.
• To determine the impact of constant versus fluctuating temperature regimes on trait variation in fathead minnows.
• To examine the relationship between temperature stress and phenotypic plasticity.

Main Methods:

• Fathead minnows (Pimephales promelas) were exposed to five fluctuating and four constant temperature regimes.
• Measurements included weekly length, critical thermal maximum (CTmax), five morphometric traits, and fluctuating asymmetry (FA).
• Data were analyzed to assess changes in trait means and variances under different thermal conditions.

Main Results:

• Length-at-age and critical thermal maximum (CTmax) decreased with increasing temperature in both regimes.
• Variance in length-at-age decreased with temperature under fluctuating conditions.
• Variance in CTmax decreased in warmer waters, and no consistent patterns were observed for other traits or FA.

Conclusions:

• Environmental stress, including elevated temperatures, can lead to a decrease in the variance of key traits like length-at-age and CTmax in fathead minnows.
• The study suggests that established theories on increased trait variation under extreme conditions may not universally apply.
• Findings highlight the complexity of predicting phenotypic adaptation to rapid environmental change and the role of plasticity.