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J Comp Physiol A (2014) 200:949957 DOI 10.1007/s00359-014-0941-z
ORIGINAL PAPER
Differences in lens optical plasticity in two gadoid shes meeting in the Arctic
Mikael Jnsson ystein Varpe Tomasz Kozowski Jrgen Berge Ronald H. H. Krger
Abstract Arctic and boreal/temperate species are likely to be evolutionary adapted to different light regimes. Currently, the boreal/temperate Atlantic cod (Gadus morhua) is coexisting with the native polar cod (Boreogadus saida) in the Arctic waters around Svalbard, Norway. Here, we studied light/dark adaptative optical plasticity of their eye lenses by exposing sh to bright light during the polar night. Schlieren photography, high-denition laser scanning and ray tracing were used to determine the optical properties of excised crystalline lenses. Both species have multifocal lenses, an optical adaptation for improved color vision. In polar cod, the optical properties of the lens were independent of light exposure. In the more southern Atlantic cod, the optical properties of the lens changed within hours upon exposure to light, even after months of darkness. Such fast optical adjustment has previously only been shown in a tropical cichlid. During the polar night the Atlantic cod lens seems to be unregulated and dysfunctional since it had an unsuitable focal length and severe spherical aberration. We present a system, to our knowledge unique, for studying visual plasticity on different timescales in relation to
Received: 19 March 2014 / Revised: 27 July 2014 / Accepted: 9 September 2014 / Published online: 21 September 2014 Springer-Verlag Berlin Heidelberg 2014
evolutionary history and present the rst study on the polar cod visual system.
Keywords Experiment Fish Multifocal lens
Visual plasticity Global warming
Abbreviations
BCD Back center distanceBEP Beam entrance positionLSA Longitudinal spherical aberration R Lens radiusRIG Refractive index gradientRMM Retinomotor movement
Introduction
Physiological plasticity helps animals to cope with variable environmental conditions by adjusting appropriate traits to current or predictable future conditions (Reed et al. 2010). However, the type and level of plasticity vary greatly between species. Some environmental conditions change in predictable cycles of different time scales, e.g. daily, lunar, or annual cycles. Animals exposed to short-term environmental cycles should be adapted to such variability, while animals accustomed to more stable conditions or slow cycles should be less exible, i.e., have less plasticity or slower response times. Through the effects of...