Does size-selective harvesting erode adaptive potential to thermal stress?

Area of Science:

• Evolutionary Biology
• Ecology
• Aquaculture

Background:

• Overharvesting poses a significant threat to fish populations globally.
• Directional selection on traits like body size can reduce phenotypic diversity.
• The impact of reduced diversity on population resilience to environmental stress is poorly understood.

Purpose of the Study:

• To investigate if directional selection, by reducing phenotypic diversity, impairs the response of fish populations to thermal stress.
• To compare the adaptive capacity of size-selected zebrafish lines versus a randomly selected line under varying temperatures.

Main Methods:

• Three zebrafish (Danio rerio) selection lines were created: directional selection for large body size, directional selection for small body size, and random selection (control).
• Lines were exposed to three temperatures: low (22°C), ambient (28°C), and elevated (34°C).
• Life history (growth, reproduction), physiological (metabolic rate, critical thermal maximum), and behavioral (activity, feeding) traits were assessed.

Main Results:

• Size-selected lines exhibited reduced growth rates under thermal stress compared to the random-selected line.
• Directional selection led to a shift in the average phenotype in response to thermal stress.
• Populations under directional selection showed a more limited capacity to respond to thermal stress than those with random selection.

Conclusions:

• Directional selection, often a consequence of exploitation, can diminish a population's ability to adapt to environmental stressors like temperature fluctuations.
• Reduced phenotypic diversity may compromise the resilience of fish populations to environmental change.
• Understanding these impacts is crucial for managing natural fish stocks facing both exploitation and climate change.