Abstract
Potamotrygon motoro has been shown to use vision to orient in a laboratory setting and has been successfully trained in cognitive behavioral studies using visual stimuli. This study explores P. motoro’s visual discrimination abilities in the context of two-alternative forced-choice experiments, with a focus on shape and contrast, stimulus orientation, and visual resolution. Results support that stingrays are able to discriminate stimulus-presence and -absence, overall stimulus contrasts, two forms, horizontal from vertical stimulus orientations, and different colors that also vary in brightness. Stingrays tested in visual resolution experiments demonstrated a range of visual acuities from < 0.13 to 0.23 cpd under the given experimental conditions. Additionally, this report includes the first evidence for memory retention in this species.
Highlights
Potamotrygon motoro has a distribution that overlaps that of other Potamotrygonid rays, such as Potamotrygon wallacei, Paratrygon aiereba (Oliveira et al 2017), and Potamotrygon falkneri (Garrone Neto and Uieda 2012)
Similar discrimination experiments conducted on the grey bamboo shark (Chiloscyllium griseum) showed that sharks could discriminate between forms and objects, based on shape and contrast but not color (Fuss et al 2014; Schluessel et al 2014; Schluessel 2015)
The retina of P. motoro has a visual cell layer that is comprised of rod-shaped and cone-shaped cells in a ratio of 6–7:1, which is low by comparison to other elasmobranchs (Ali and Anctil 1974) and may be an indication that photopic vision is important to the species (Schluessel and Bleckmann 2005)
Summary
Potamotrygon motoro has a distribution that overlaps that of other Potamotrygonid rays, such as Potamotrygon wallacei, Paratrygon aiereba (Oliveira et al 2017), and Potamotrygon falkneri (Garrone Neto and Uieda 2012). The retina of P. motoro has a visual cell layer that is comprised of rod-shaped and cone-shaped cells in a ratio of 6–7:1, which is low by comparison to other elasmobranchs (Ali and Anctil 1974) and may be an indication that photopic vision is important to the species (Schluessel and Bleckmann 2005) Several batoids are both physiologically (Bedore et al 2013; Hart et al 2004; Theiss et al 2007) and behaviourally (Van-Eyk et al 2011) able to perceive and discriminate colour, using multiple cone visual photopigments. This together with Potamotrygon motoro’s ability to discriminate colors (Seifert 2017) could demonstrate that photoreceptors in elasmobranchs function to the rods and cones in teleost and mammal retinae.
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