Limits to phenotypic plasticity: flow effects on barnacle feeding appendages.

Area of Science:

• Marine biology
• Ecology
• Evolutionary biology

Background:

• Phenotypic plasticity allows organisms to adapt morphology to environmental conditions.
• Acorn barnacles (Balanus glandula) show plastic changes in feeding leg length with water flow velocity.
• Previous studies explored this plasticity only at velocities below 4.6 m/s.

Purpose of the Study:

• To investigate the upper limit of phenotypic plasticity in Balanus glandula feeding leg length in response to water flow.
• To determine if leg length plasticity persists at higher velocities found on wave-exposed shores.

Main Methods:

• Measuring leg lengths of Balanus glandula at 15 sites in Monterey, California.
• Assessing water flow velocities ranging from 0.5 to 14.0 m/s across these sites.
• Analyzing the relationship between leg length and water velocity.

Main Results:

• A plastic response in leg length was observed at sites with velocities below 3 m/s.
• No significant plastic response in leg length was found at sites with velocities above 3 m/s, despite a 4-fold speed variation.
• The upper limit for this plastic response was determined to be between 2-4 m/s.

Conclusions:

• The phenotypic plasticity of Balanus glandula feeding leg length has an upper velocity limit of 2-4 m/s.
• This limit is frequently exceeded in the typical wave-exposed habitats of the species.
• The adaptive significance of this plasticity may be constrained in high-flow environments.