Abstract
ABSTRACTThe ‘disco’ clam Ctenoides ales (Finlay, 1927) is a marine bivalve that has a unique, vivid flashing display that is a result of light scattering by silica nanospheres and rapid mantle movement. The eyes of C. ales were examined to determine their visual capabilities and whether the clams can see the flashing of conspecifics. Similar to the congener C. scaber, C. ales exhibits an off-response (shadow reflex) and an on-response (light reflex). In field observations, a shadow caused a significant increase in flash rate from a mean of 3.9 Hz to 4.7 Hz (P=0.0016). In laboratory trials, a looming stimulus, which increased light intensity, caused a significant increase in flash rate from a median of 1.8 Hz to 2.2 Hz (P=0.0001). Morphological analysis of the eyes of C. ales revealed coarsely-packed photoreceptors lacking sophisticated structure, resulting in visual resolution that is likely too low to detect the flashing of conspecifics. As the eyes of C. ales are incapable of perceiving conspecific flashing, it is likely that their vision is instead used to detect predators.
Highlights
Marine invertebrates communicate through diverse channels, including visual (Adams and Caldwell, 1990; Adams and Mesterton-Gibbons, 1995; Marshall et al, 2015), chemical (Daloze et al, 2013; O’Connell, 1986; Scheuer, 1977), tactile (Caldwell and Dingle, 1976; Knowlton, 1996), and acoustic (Caldwell, 1979) signals
The small size of the eye combined with the irregular shape of the retina makes it difficult to determine an accurate focal length or receptor separation length, which would allow for a calculation of the inter-receptor angle and maximum resolvable spatial frequency (Land and Nilsson, 2002)
The morphological description of the eye of C. scaber by Bell and Mpitsos (1968) and of C. mitis by Morton (2000) are similar to the morphology of the eye of C. ales found in this study
Summary
Marine invertebrates communicate through diverse channels, including visual (Adams and Caldwell, 1990; Adams and Mesterton-Gibbons, 1995; Marshall et al, 2015), chemical (Daloze et al, 2013; O’Connell, 1986; Scheuer, 1977), tactile (Caldwell and Dingle, 1976; Knowlton, 1996), and acoustic (Caldwell, 1979) signals. Visual communication can be achieved through the use of light (including UV, fluorescence, and polarization) (Bok et al, 2014; Chiou et al, 2008; Cronin, 2006; Miya et al, 2010), color (Kohda et al, 2005; Sugimoto, 2002), countershading (Penacchio et al, 2014), and shape (Allen et al, 2014; Baker, 2010). Received 2 February 2017; Accepted 29 March 2017 considering the evolution of vision, simple light-sensitive cells can evolve to a complex camera-type eye in a mere few hundred thousand years (Nilsson and Pelger, 1994), which may explain the extreme diversity of vision throughout the animal kingdom
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