Selection on the morphology-physiology-performance nexus: Lessons from freshwater stickleback morphs

Area of Science:

• Evolutionary biology
• Ecology
• Animal physiology

Background:

• Conspecifics in different environments often show varied traits, but trait interrelationships and fitness impacts are unclear.
• Understanding trait evolution in response to environmental divergence is crucial for evolutionary studies.

Purpose of the Study:

• Investigate population differentiation in morphology, metabolic rate, and swimming performance in three-spined sticklebacks.
• Test if reduced lateral plate size in freshwater morphotypes evolved due to selection.
• Examine how morphology, physiology, and performance co-evolved in response to marine vs. freshwater selection.

Main Methods:

• Utilized a multivariate QST-FST framework to analyze population differentiation.
• Quantified lateral plate coverage, burst and critical swimming speeds, and standard and active metabolic rates.
• Raised pure-bred second-generation sticklebacks from marine and two freshwater populations.

Main Results:

• Detected directional selection on metabolic physiology and lateral plate coverage.
• Confirmed selection drives reduced lateral plate coverage in a small-plated stickleback population.
• Observed multivariate selection among traits, excluding swimming performance metrics.
• Freshwater-marine divergence exceeded neutral expectations for morphology, physiology, and performance traits.

Conclusions:

• Freshwater adaptation in sticklebacks involves diverse trait combinations across populations.
• Demonstrated the complex interplay between morphology, physiology, and performance in local adaptation.
• Provided a framework for investigating trait evolution in response to environmental pressures.