Investigating evolutionary lag using the species-pairs evolutionary lag test (SPELT)

Area of Science:

• Evolutionary biology
• Phylogenetics
• Quantitative genetics

Background:

• Correlated trait evolution can lead to evolutionary lag, where one trait lags behind another.
• Detecting evolutionary lag is crucial for understanding trait co-evolutionary dynamics.
• The species-pairs evolutionary lag test (SPELT) is a phylogenetic method designed to identify such lags.

Purpose of the Study:

• To statistically evaluate the performance of the species-pairs evolutionary lag test (SPELT).
• To assess the influence of lag magnitude, sample size, and trait association strength on SPELT's power.
• To investigate SPELT's Type I error rates and its applicability in empirical studies.

Main Methods:

• Simulated trait evolution under two distinct models: time-dependent lag and random walk with lagged trait dependency.
• Assessed SPELT's statistical power and Type I error rates across varying simulation parameters.
• Applied SPELT to two real-world biological datasets.

Main Results:

• SPELT demonstrated Type I error rates close to the nominal 5% level, indicating low false-positive rates.
• Approximately 140 species pairs are needed to achieve 80% statistical power for detecting evolutionary lag.
• The degree of lag and the strength of trait associations significantly impacted the test's power.

Conclusions:

• SPELT is a statistically robust method for detecting evolutionary lag on phylogenies.
• Sufficient sample size (species pairs) is essential for adequate statistical power.
• Incorporating a branch length scaling parameter (κ) can enhance lag detection with SPELT.