Abstract
Many ecologically and economically important marine fish species worldwide spend portions of their lives in coastal regions that are increasingly inundated by artificial light at night. However, while extensive research illustrates the harmful effects of inappropriate light exposure on biological timing in humans, rodents and birds, comparable studies on marine fish are virtually nonexistent. This study aimed to assess the effects of light on biological clock function in the marine fish retina using the Atlantic tarpon (Megalops atlanticus) as a model. Using anti-opsin immunofluorescence, we observed robust rhythms of photoreceptor outer segment position (retinomotor movement) over the course of the daily light–dark cycle: cone outer segments were contracted toward the inner retina and rods were elongated during the day; the opposite occurred at night. Phase shifting the daily light–dark cycle caused a corresponding shift of retinomotor movement timing, and cone retinomotor movement persisted in constant darkness, indicating control by a circadian clock. Constant light abolished retinomotor movements of both photoreceptor types. Thus, abnormally-timed light exposure may disrupt normal M. atlanticus clock function and harm vision, which in turn may affect prey capture and predator avoidance. These results should help inform efforts to mitigate the effects of coastal light pollution on organisms in marine ecosystems.
Highlights
Predictable abiotic variations in the natural environment including the daily light–dark cycle and seasonal fluctuations of day length and temperature exert selective pressures that have shaped much of life on Earth, permitting organisms to exploit temporal as well as spatial niches [1,2,3]
The work reported here was undertaken to assess whether retinal photoreceptor cells exhibit circadian rhythms of retinomotor movement in a marine fish species associated with potentially light-polluted habitats
This investigation was conducted as part of a larger effort to understand how alterations of the natural light–dark cycle may affect the biology of marine species inhabiting coastal and other areas inundated by artificial light at night
Summary
Predictable abiotic variations in the natural environment including the daily light–dark cycle and seasonal fluctuations of day length and temperature exert selective pressures that have shaped much of life on Earth, permitting organisms to exploit temporal as well as spatial niches [1,2,3]. Most organisms do not respond to cyclic changes in the environment, . Rather they have evolved precise internal timekeeping mechanisms that allow anticipation of and preparation for environmental change, and coordination of physiological and behavioral states with environmental characteristics [1,2,3,4,5,6]. Rhythmic physiological and behavioral outputs of biological clocks persist even when natural time cues may be temporarily obscured [2,7]. Coastal marine fish represent fascinating animals in which to study clock function because they are subject to environmental cycles of multiple distinct periodicities (daily, tidal and lunar), and because many coastal marine fish have significant ecological and economic value. Biological timekeeping mechanisms and the rhythms they control are poorly studied in fish outside the freshwater model organism Danio rerio [7,10], morphological examinations in a few other freshwater species including the [7,10], morphological examinations in a few other freshwater species including the green sunfish g(Lreepeonmsisucnyfiasnhell(uLse)p[o1m1–is13c]y,abnleulelugsi)ll[(1L1e–p1o3m]i,sbmluacergoiclhl ir(Luesp) o[1m4i]samndaccriocchhliirduss)[1[]7a],nadndcilcihmliidtesd[s1t5u–d1i7e]s, aonf dclolicmk iotepderasttiuodnieisn soofmcelomckaroinpeersaptieocniesinsuscohmaes tmhearbinlueesstpriepceiedsgsruucnht (aHsaetlhmeublolnuessctiurirpuesd) [1g8r,u1n9t] (aHnadelgmreuylosnnsacpiupreurs)(L[1u8tj,a1n9u] sangdrisgeruesy) [s1n9a]p. per (Lutjanus griseus) [19]
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