From form to function: Stingray sensory superstars
Sharks and stingrays are sensory superstars! They have successfully navigated and hunted the Earth's oceans for ~400 million years! With over 1100 species and counting, there are a variety of different configurations of sensory systems found in the elasmobranch group. Within the lateral line and electrosensory systems, I found distinct differences in anatomy between three species commonly found in California's waters. To see if these structural differences had any functional consequences I put some stingrays to the test!
First I had to catch them! Each species has it's own unique behaviors and habitat, meaning I needed different strategies to catch each one so I could safely bring them back to the lab and study their response to various sensory signals. For round stingrays, Urobatis halleri, this meant using a seine net that I could carefully take out into the water and drag toward shore over a shallow mud flat habitat (with the help of a great volunteer). For bat rays, Myliobatis calirornica, I had to go a bit deeper and don my SCUBA gear and catch each one individually with a large net and a good dive buddy! Since bat rays can get so big (over 6 ft across!) I selected only small rays to bring back to the tanks (picture below left). Finally, for the pelagic stingrays, Pteroplatytrygon violacea, I needed the most help because they live out in the open ocean. Fortunately, the folks at NOAA helped safely deliver some of the rays caught on longlines to the lab (see Shark Cruising! for more on NOAA shark cruises and pelagic stingrays).
At Wrigley Marine Science Center on Santa Catalina Island I had two tanks to use for my stingray behavioral experiments, one for holding them and one for conducting experiments. Above you can see the general set-up for the experimental tank (right). To test responses to water flow, I created a weak water jet (in the center of the blue circles shown on the experimental plate in the center photo). To determine sensitivity to electric fields, I created dipole electrodes (black circles with center line in center photo). Four of each of these were arranged on the flat plate at the bottom of the tank so that one could be activated at a time. To measure and analyze the stingrays' responses, I filmed all experimental trials from a camera situated above the tank.
Were there any differences in detection capabilities of water jet and electrical signals? Yes and no! The bat rays appeared to be the most likely to respond to water jet signals but all three rays were extremely sensitive to electric fields. There were some really interesting differences in their behavior and the differences I found corresponded well with the anatomy and with the ecology, including prey type and feeding habitat, of each species. For more details on this research see "Publications" in About Laura. For a glimpse at some of my Catalina Island adventures see Adventure.
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