Graduation Year

2023

Document Type

Campus Only Senior Thesis

Degree Name

Bachelor of Science

Department

Neuroscience

Reader 1

Dr. Lars Schmitz

Reader 2

Dr. Findley Finseth

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Terms of Use for work posted in Scholarship@Claremont.

Abstract

Geckos are a diverse infraorder of Squamata that provide an important model of the visual system due to the unique evolutionary history of their photoreceptors. This paper is a portion of Dr. Lars Schmitz’s larger project attempting to link the electrical responses of gecko photoreceptors with their diel activity patterns and habitat ecology using electroretinography (ERG). ERG administers a light stimulus with predetermined characteristics to an animal's eye and records the electrical output of rods, cones, and bipolar cells. The flash section of this project helps elucidate how sensitivity to light in the nocturnal species Gecko gekko varies with brightness, and showed that despite photoreceptor transmutation favoring low-light vision, this species showed greater electrical (µV) response by the visual system to stimuli at 10 cd*s/m2 than 3 cd*s/m2 , 0.01 cd*s/m2 or 0.002 cd*s/m2. This thesis also tested critical flicker fusion frequency, which refers to the maximum speed a light stimulus can blink on and off before an organism perceives it as one light. Flicker fusion frequency is of adaptive importance for nocturnal animals, who often have a slower visual cycle to collect as many photons as possible in a dark environment. These results are preliminary, and foremost showed a strange phenomena in which the animal’s voltage responses cycled in an exactly repetitive way over time, despite expected noise and natural variation. If results are replicated, there is evidence that the nocturnal species Gecko gekko can perceive light flashes as fast as 55 Hz, far higher than previously recorded. Regardless, this thesis established a testing protocol for replication of flicker results from G. gekko as well as new results for the nocturnal Coleonyx brevis and a diurnal Phelsuma. All together, data from these species will allow for comparison between species based on diel activity pattern and habitat ecology.

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