Meeting Abstract
P3-17 Sunday, Jan. 6 15:30 – 17:30 The convergent evolution of blinking in mudskippers and tetrapods STEWART, TA*; AIELLO, BR; GAU, GF; BHAMLA , S; SHUBIN, NH; University of Chicago; Georgia Institute of Technology; Georgia Institute of Technology; Georgia Institute of Technology; University of Chicago tomstewart@uchicago.edu http://www.tomstewart.com
Approximately 360 million years ago, tetrapods colonized the terrestrial environment. This water-to-land transition is marked by a suite of behavioral and morphological adaptations. Among these, was the origin of blinking – the periodic occlusion of the eye by one or more membranes. Blinking behaviors coat the cornea in a liquid film, which is critical for epithelial cell health, lubrication, and cleaning the eye of debris. Mudskippers (Oxudercidae) are a second lineage of fishes that have evolved to spend the majority of their day on land. Here we describe how mudskippers have evolved the ability to blink, convergent with tetrapods, by studying the Indian mudskipper Periophthalmus septemradiatus. High speed kinematics show that the eye is retracted ventrally and this displaces the dermal cup (an epithelial fold analogous to the lower eyelid of tetrapods), which moves dorsally to cover the cornea. Rates of blinking are associated with ambient humidity, indicating the behavior functions for eye-wetting. To characterize how this anatomy has evolved, we compare P. septembradiatus with the closely related fully-aquatic round goby, Neogobius melanostomus; specimens were soft-tissue contrast stained by phosphomolybdic acid and CT-scanned. We also describe histology of the eyes and the dermal cup, which reveals that, unlike extant tetrapods, mudskippers lack associated ‘tear’ glands. Collectively, these behavioral and anatomical data show how complex behavior, such as blinking, can occur in systems that are unexpectedly simple (i.e., without new associated musculature or glands), and this informs the range of strategies that could have been deployed during initial stages of the water-to-land transition of tetrapods.
