Phenotypic plasticity drives phenological changes in a Mediterranean blue tit population

Area of Science:

• Ecology
• Evolutionary Biology
• Animal Behavior

Background:

• Climate change is causing earlier phenology, like bird breeding times, in natural populations.
• Understanding if these shifts are plastic or evolutionary is crucial for predicting population responses.
• Laying date in birds is known to be heritable and under selection, suggesting potential for evolution.

Purpose of the Study:

• To determine if the observed advancement in Corsican blue tit laying dates over 40 years is due to phenotypic plasticity or evolutionary change.
• To compare the predictions of the breeder's equation and the Robertson-Price (STS) equation with observed genetic changes in laying date.
• To investigate the role of fitness proxies (fledgling and recruitment success) in driving phenological shifts.

Main Methods:

• Analysis of a 40-year dataset of Corsican blue tit laying dates and fitness proxies.
• Application of the breeder's equation and the Robertson-Price (STS) equation to assess evolutionary change.
• Use of statistical models accounting for zero inflation in fitness data.
• Distinguishing between within-individual and between-individual covariance to understand selection on plastic traits.

Main Results:

• The breeder's equation predicted significant genetic change, aligning with heritability and selection observations.
• No genetic correlation was found between laying date and fitness proxies (fledgling/recruitment success).
• The Robertson-Price (STS) equation accurately predicted no evolution in breeding time, consistent with the absence of trend in breeding values.
• Phenotypic covariance was partly explained by within-individual covariance, highlighting selection on plastic traits.

Conclusions:

• The phenological advancement in Corsican blue tit laying dates is primarily driven by environmental plasticity rather than genetic evolution.
• The lack of genetic correlation between laying date and fitness suggests limited potential for rapid evolutionary response in this trait.
• Accounting for within-individual covariance is essential for accurately assessing selection intensity on plastic traits under fluctuating conditions.