Circadian histories: latitudinally determined responses to light
pollution
- Victoria E. Amaral,
- Coşkun Güçlü,
- Louise A. Ashton,
- Timothy C. Bonebrake,
- Avalon C. S. Owens,
- Caroline Dingle,
- Michael J. W. Boyle
Abstract
Circadian rhythms are highly conserved across the tree of life, with
light serving as the primary cue for the circadian timer. Photoperiod
variation follows a latitudinal gradient, reflecting fluctuations in
seasonality that increases towards the poles. As photoperiod variability
intensifies at higher latitudes, organisms must develop mechanisms to
maintain circadian timing during prolonged periods of light or darkness.
Consequently, latitudinal gradients in photic sensitivity occur, as
populations in northern latitudes have physiologically adapted to
significant seasonal variations in day length. However, the rise of
urbanization has introduced artificial light on a global scale, creating
new photoperiods for organisms to navigate. This artificial extension of
the natural photoperiod is now interacting with evolutionarily
established circadian rhythms. Because photic sensitivity follows a
latitudinal gradient, this may also inform biogeographic patterns of
vulnerability to light pollution. We introduce the term "circadian
histories" to describe an organism's evolutionary history of circadian
entrainment, which may influence its response to novel light pollution.