EAPSI: Bright coloration and the startle response: an experimental test of a possible anti-predator mechanism

Reinke Beth, Hanover NH

Investigators

Abstract

Freshwater turtle species worldwide are declining due to habitat destruction, harvesting, and high mortality early in life. Hatchlings of many species have brightly colored plastrons (ventral shell) that fade over the course of development, but very little is known about the function of this coloration. Because hatchlings experience high predation rates while overwintering in or emerging from the nest, the bright coloration of hatchling plastrons may have an anti-predatory function to increase the likelihood of survival during the first year of life. This project will investigate the function of turtle hatchling plastron coloration by 1) using visual modeling to determine the conspicuousness of painted turtle (Chrysemys picta) and diamondback terrapin (Malaclemys terrapin) plastrons against substrates as viewed by common predators and 2) quantifying the startle response and re-engagement time of predators to differently colored replicas of turtle hatchlings to estimate the likelihood of escape from a predator. This work will be done in collaboration with Dr. Devi Stuart-Fox at University of Melbourne in Australia, an expert in visual modeling and signal coloration. The combination of visual modeling and behavioral experimentation will provide novel information on visual signaling in turtles in general, and may contribute to the conservation of freshwater turtles. Irradiance at the nest site and reflectance measurements will be obtained from hatchling C.picta and M.terrapin plastrons and from undisturbed ground near the nest to obtain background reflectance measurements. These measurements allow chromatic and achromatic contrasts to be calculated with visual models that include spectral sensitivities of predators to determine conspicuousness. Hatchling righting responses will be measured by flipping each individual on its carapace (dorsal shell) and measuring the average time it takes to right itself. By comparing the individual hatchling righting time to the conspicuousness of the hatchling against its background and the startle response and re-engagement time of each predator, this project will determine if bright plastron coloration has an anti-predatory function. This NSF EAPSI award is funded in collaboration with the Australian Academy of Science.