Abstract
BackgroundFor many fish species, retinal function changes between life history stages as part of an encoded developmental program. Retinal change is also known to exhibit plasticity because retinal form and function can be influenced by light exposure over the course of development. Aside from studies of gene expression, it remains largely unknown whether retinal plasticity can provide functional responses to short-term changes in environmental light quality. The aim of this study was to determine whether the structure and function of the fish retina can change in response to altered light intensity and spectrum—not over the course of a developmental regime, but over shorter time periods relevant to marine habitat disturbance.ResultsThe effects of light environment on sensitivity of the retina, as well as on cone photoreceptor distribution were examined in the Atlantic tarpon (Megalops atlanticus) on 2- and 4-month timescales. In a spectral experiment, juvenile M. atlanticus were placed in either ‘red’ or ‘blue’ light conditions (with near identical irradiance), and in an intensity experiment, juveniles were placed in either ‘bright’ or ‘dim’ light conditions (with near identical spectra). Analysis of the retina by electroretinography and anti-opsin immunofluorescence revealed that relative to fish held in the blue condition, those in the red condition exhibited longer-wavelength peak sensitivity and greater abundance of long-wavelength-sensitive (LWS) cone photoreceptors over time. Following pre-test dark adaption of the retina, fish held in the dim light required less irradiance to produce a standard retinal response than fish held in bright light, developing a greater sensitivity to white light over time.ConclusionsThe results show that structure and function of the M. atlanticus retina can rapidly adjust to changes in environmental light within a given developmental stage, and that such changes are dependent on light quality and the length of exposure. These findings suggest that the fish retina may be resilient to disturbances in environmental light, using retinal plasticity to compensate for changes in light quality over short timescales.
Highlights
For many fish species, retinal function changes between life history stages as part of an encoded developmental program
Strong anti-rhodopsin and anti-cone opsin immunofluorescence was observed in the M. atlanticus retina, Fig. 2 Effects of light spectrum and exposure time on the spectral sensitivity of juvenile Megalops atlanticus
The results of the present study indicate that photoreceptor abundance, absolute sensitivity and spectral sensitivity of the M. atlanticus retina all undergo significant change in response to light condition within a 2- to 4-month timescale during the juvenile developmental stage
Summary
Retinal function changes between life history stages as part of an encoded developmental program. The ability of individual organisms to adapt to environmental change (i.e., phenotypic plasticity) supports fitness by allowing the colonization of new environments [1] and survival during environmental disturbance [2]. Aquatic habitats are dynamic because factors including depth [3], suspended sediment [4], and dissolved organic matter can alter underwater light quality [5]. The life history of fish typically includes metamorphosis from a larval stage to one or more juvenile stages before reaching adult sexual maturity Between these stages, many marine fish migrate to new light environments, which requires changes in visual function [9,10,11,12,13,14,15,16]. Retinal change is thought to occur in anticipation of or in concert with shifts in habitat [17,18,19,20,21], the outcomes of which can be strongly influenced by changes in light exposure over life history [e.g., 22]
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