Term of Award

Summer 2018

Degree Name

Master of Science in Biology (M.S.)

Document Type and Release Option

Thesis (open access)

Copyright Statement / License for Reuse

Creative Commons License
This work is licensed under a Creative Commons Attribution 4.0 License.

Department

Department of Biology

Committee Chair

Christine Bedore

Committee Member 1

Johanne Lewis

Committee Member 2

Christian Cox

Abstract

Many reef fishes exhibit dynamic coloration and body patterns that can change under nervous or hormonal control. Several species of benthic sharks and rays likely alter melanin in the skin to provide background matching for camouflage. The yellow stingray (Urobatis jamaicensis) is a benthically-oriented elasmobranch with elaborate spot patterns that provide effective camouflage within its habitats. This patterning, when coupled with the ability to alter melanin in response to background color, could increase background matching effectiveness in these species. The yellow stingray has been anecdotally noted to lighten or darken skin color.However, it is unclear whether this type of change is controlled by Morphological or Physiological change. Manipulation melanin content to produce a color change is termed Morphological color change. The movement of pigment granules alone to produce a color change is termed Physiological color change. Despite the wide array of studies conducted on color change for enhanced background-matching capabilities in bony fish, this ability and its mechanism remains understudied among elasmobranchs. To investigate this, we housed rays in either black or white tanks for one week and photographed the rays daily. On the last day, blood and skin samples were taken to quantify melanin concentrations, and cell morphology. Stingrays in black tanks significantly darkened skin color over the seven-day period whereas rays in white tanks significantly lightened their skin color during the same period. However, skin melanin concentrations did not differ between rays maintained in black or white tanks after seven days. Furthermore, stingrays had the same cell density after seven days but the melanophore index values (Hogben and Slome, 1931) were different between tank treatments. These results demonstrate that yellow stingrays do regulate their body color in response to background color. Furthermore, the results suggest that stingrays undergo physiological (not morphological) color change in order to regulate body color. This is the first study to both quantify the background matching response and evaluate the physiological regulation of that response in a stingray species.

Research Data and Supplementary Material

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