Adaptive photoperiod interpretation modulates phenological timing in Atlantic salmon

Area of Science:

• Environmental Physiology
• Animal Behavior
• Aquaculture Science

Background:

• Photoperiod serves as a crucial phenological cue for many animals, influencing vital biological processes.
• The precise mechanism by which light intensity variations are translated into perceived photoperiod remains largely unknown.
• Understanding photoperiod perception is critical for predicting species' responses to environmental changes.

Purpose of the Study:

• To investigate how variations in light intensity affect the perceived photoperiod in Atlantic salmon (Salmo salar).
• To determine if photoperiod interpretation is fixed above a detection threshold or adaptive based on recent light exposure.
• To assess the impact of adaptive photoperiod interpretation on smoltification and sexual maturation timing.

Main Methods:

• Exposed male parr to eight different light regimes (12-hour light/12-hour dark) with varying high and low daytime intensities.
• Subdivided light regimes based on nighttime light intensity (100%, 10%, 1%, 0% of daytime intensity).
• Compared frequencies of smoltification and sexual maturation across experimental groups.

Main Results:

• Atlantic salmon exhibit adaptive photoperiod interpretation above a minimum detection threshold, which varies with recent light exposure.
• Adaptive photoperiod interpretation significantly modulates the timing of parr-smolt transformation and sexual maturation.
• Photoperiod interpretation differences were observed even between closely related families of Atlantic salmon.

Conclusions:

• Photoperiod perception in Atlantic salmon is adaptive and influenced by light intensity history.
• This adaptive mechanism plays a key role in regulating critical life-history events like smoltification and maturation.
• Integrating photoperiod interpretation is essential for understanding how climate change-induced thermal niche shifts will affect salmon populations.