The Effects of Heavy Noise Levels on the Production of Corticosterone in the Squirrel Tree Frog (Hyla squirella)

Abstract

Background and Objective: Urbanization of the environment is making animal communication more difficult. Sounds degrade over the distance traveled and therefore by adding additional noises, like roadside traffic, the interpretation of ‘the message’ becomes increasingly difficult (Naguib, 2013). This increase in difficulty to communicate day-to-day messages can lead to negative effects on the animal. Previous research has been conducted with female wood frogs, Lithobates sylvaticus, on the effects of traffic noise on the production of corticosterone, a hormone related to stress also known as CORT (Tennessen, 2014). The research with the wood frogs determined that not only did the production of corticosterone increase but the females’ ability to travel and find a mate was impaired (Tennessen, 2014). Previous research conducted on the Gulf Toadfish focused on the production CORT levels released during exposure to a playback (Remage-Healey, 2014). The Gulf Toadfishes that were exposed to aggressive vocalizations playbacks had an increase in CORT levels (Remage-Healey, 2014). This leads us to believe that using playbacks of traffic noise will give us an accurate conclusion on the effects of heavy noise on CORT production. The objective of the following research focuses specifically on squirrel tree frogs (Hyla squirella) and the effects of increasing traffic noise on CORT production. We hypothesized that H. squirella exposed to higher levels of roadside noise will display higher concentrations of CORT production. Methods: Frogs (n=33) were placed in cages lined with terrarium moss. Temperature and humidity were monitored daily. Corticosterone levels were measured through a noninvasive waterborne technique. Frogs were placed in 50 ml conical centrifuge tubes with 10 ml of water for 30 minutes, CORT diffused out of the frog’s skin and into the 10 ml of surrounding water. The CORT was extracted on three different occasions; once before exposure, another time after 3 weeks of exposure, and the final CORT extraction was 6 weeks after beginning treatment. The water/CORT samples were then passed through C-18 columns to separate corticosterone away from the water. The columns were eluted with 3mL of methanol to recover the corticosterone and stored in a -30 °C freezer until ready to be thawed for extraction. Using a centro-vap, the excess methanol was removed. Samples were then suspended in assay buffer and analyzed via a corticosterone enzyme-linked immunoassay kit. Results: The frogs within the experimental cage were observed outside of the refugia more frequently and the coloration of these frogs dulled over time. There was no significant change in mass (g) detected. There was no significant difference in baseline CORT prior to treatment. Upon 3 weeks of noise exposure, experimental cages had an average corticosterone level significantly higher than both of the control cages. No significant difference between experimental and controls was detected at the final extraction. Implications: It appears that overall there is a stress related reaction with frogs exposed to heavy noise compared to those frogs not exposed. As predicted, it appears that if the frogs are exposed for a long period then eventually the frogs will acclimate. This is probably due to the fact that producing high stress for a long amount of time has physiological effects and may eventually lead to death if the animal is unable to adjust.