Evolution toward a new adaptive optimum: phenotypic evolution in a fossil stickleback lineage

Area of Science:

• Evolutionary biology
• Paleontology
• Quantitative genetics

Background:

• Demonstrating natural selection's role in fossil lineages is challenging.
• Previous analyses of stickleback armor reduction were inconclusive, indistinguishable from neutral drift.
• Indirect evidence suggested natural selection, but direct proof was lacking.

Purpose of the Study:

• To re-evaluate the stickleback armor reduction case study using novel analytical approaches.
• To compare neutral evolution with adaptive evolution models on equal footing.
• To infer the relationship between evolutionary change and the adaptive landscape in fossil lineages.

Main Methods:

• Utilized the Akaike Information Criterion (AIC) to compare neutral and adaptive models.
• Modeled adaptive evolution as an Ornstein-Uhlenbeck process (population ascending an adaptive peak).
• Analyzed an evolutionary time series of skeletal features in a fossil stickleback lineage.

Main Results:

• The adaptive model, incorporating an Ornstein-Uhlenbeck process, significantly outperformed neutral evolution for all measured skeletal features.
• This adaptive model provided a better explanation for the observed evolutionary trajectories than neutral drift.
• The study successfully inferred the influence of natural selection on trait evolution.

Conclusions:

• Natural selection plays a significant role in shaping evolutionary trajectories in fossil lineages, even in cases previously attributed to neutral drift.
• The applied analytical framework, comparing adaptive and neutral models using AIC and Ornstein-Uhlenbeck processes, is effective for inferring selection in paleontology.
• This study demonstrates the possibility of linking fossil evolutionary changes to adaptive landscape dynamics under favorable conditions.