By: Hannah Rosenblatt | SQ Staff Writer | SQ Online 2016-17
Although appearing as a bland blend of beige and black at first glance, catsharks and other bony fish species emit biofluorescence in dazzling greens, yellows, and oranges (1). This unique biofluorescence enables these marine organisms to reflect specific and complex concoctions of light wavelengths that illuminate their bodies to other members of their species. This finding is one of many that highlights how an organism’s visual system evolves to suit its specific ecological needs.
The Deheyn lab at Scripps Institution of Oceanography focuses on understanding how organisms bend and emit light to produce and perceive a diverse array of colors. Recently, their work has concentrated on catsharks who, like other biofluorescent organisms, have unique fluorescent proteins in their skin that when struck with a certain wavelength of light become excited and emit a lower-energy wavelength (perceived by us as a fluorescent glow)(2). When viewed from a shark’s eye, this underlying fluorescence increases the contrast between a shark’s exterior and its dark surroundings (2). This fluorescent glow and vision system appear to have evolved together because of their high specificity and uniqueness to the species.
The development of a vision system primed for viewing important objects in an oceanic environment is just one example of how creatures are able to evolve practical ways to perceive their world. Some organisms, such as the mantis shrimp, have developed elaborate vision systems, allowing them to discern a large array of wavelengths that remain unseen to humans. A mantis shrimp’s eye contains twelve different cell types, each aimed at detecting a narrow range of wavelengths, including UV and polarized light (for comparison, humans possess three). This gives them the ability to respond rapidly to changes in their environment and communicate with discrete light-based signals (3).
These adaptations are not reserved for seemingly bizarre or rare creatures. Many mollusks and cephalopods, such as cuttlefish and octopuses, are also able to sense polarized light — a capability absent in humans and other mammals (4). Honeybees and other insects rely heavily on polarized vision to navigate large spaces while searching for food or returning home (5). These adaptations demonstrate that organisms are capable of developing a means to see the world that is beneficial to them specifically. They have vision systems that emphasize what is important to them against murky, deep blue waters, and have gained ways to always orient themselves towards where they need to go. However, there are also remarkable similarities between these systems. Bees possess similar vision capabilities to cuttlefish and octopuses despite inhabiting very different niches.
Upon further inspection, the vision systems of different organisms are more closely related than they appear. All animals, including humans use the same basic protein family, ospin, to absorb light (6). Opsin originated in ancient bacteria, and the genetic coding for this molecule has simply been altered, copied, deleted, and moved around throughout evolution by each species to suit their specific needs (6). These seemingly minor genetic alterations explain the stark differences in how organisms perceive their surroundings.
Our eyes are unequipped to see the polarized light guiding a bee home or the specific fluorescent patterns of a catshark, because at some point in history, our vision system was optimized to suit our needs and filter out unnecessary wavelengths. Although our eyes contain the same basic machinery as most organisms, the fact that we are all wired slightly differently enables us to see entirely different worlds despite facing the same surroundings. Amidst a deeply connected web, different species are still capable of achieving great diversity.
- Sparks, John S., Robert C. Schelly, W. Leo Smith, Matthew P. Davis, Dan Tchernov, Vincent A. Pieribone, and David F. Gruber. “The Covert World of Fish Biofluorescence: A Phylogenetically Widespread and Phenotypically Variable Phenomenon.” PLoS ONE 9.1 (2014).
- Gruber, David F., Ellis R. Loew, Dimitri D. Deheyn, Derya Akkaynak, Jean P. Gaffney, W. Leo Smith, Matthew P. Davis, Jennifer H. Stern, Vincent A. Pieribone, and John S. Sparks. “Biofluorescence in Catsharks (Scyliorhinidae): Fundamental Description and Relevance for Elasmobranch Visual Ecology.” Sci. Rep. Scientific Reports 6 (2016): 24751.
- Thoen, H. H., M. J. How, T.-H. Chiou, and J. Marshall. “A Different Form of Color Vision in Mantis Shrimp.” Science 343.6169 (2014): 411-13.
- Cronin, T. W. “Polarization Vision and Its Role in Biological Signaling.” Integrative and Comparative Biology 43.4 (2003): 549-58.
- Wehner, Rudiger. “Polarization Vision – A Uniform Sensory Capacity?” The Journal of Experimental Biology 204 (2001): 2589-596.
- Shubin, Neil. Your Inner Fish: A Journey into the 3.5-billion-year History of the Human Body. New York: Pantheon, 2008.