Quantifying visual acuity of Terrapene carolina triunguis utilizing optokinetic response

Abstract

Vertebrates belonging to the order Testudines, commonly referred to as turtles, are a distinct clade of reptiles that can be characterized by fused rib plates that form shells. The order is comprised of 356 species distributed worldwide that can be fully aquatic, fully terrestrial, or semi-aquatic. 1 Three-toed box turtles (Terrapene carolina triunguis) are semi-aquatic turtles classified within the genus Terrapene. The genus contains four recognized species (T. carolina, T. ornata, T. nelsoni, and T. coahuila) and several subspecies within the genus. This genus of turtles is distinguished by their ability to close their plastron via a movable hinge. 2 Although T. c. triunguis are considered semi-aquatic, much like other Terrapene spp., their habitat selection is much more terrestrial than aquatic turtles. In cases of high temperatures and drought, Terrapene spp. may choose to enter bodies of water to thermoregulate and prevent dehydration 3 ; otherwise, they spend the majority of their time on land. Due to their vast differences in environments, there should be an expected difference in visual physiology between fully aquatic turtles and semi-aquatic turtles such as T. c. triunguis.