COS 118-1 - RESCHEDULING TBD - Thermoregulatory behaviors and effects of water characteristics on dive duration in Anolis aquaticus

Abstract: Participating in antipredator behavior, while necessary to survival, detracts from important activities, such as foraging, courtship, and territory defense. This is especially true of semi-aquatic ectotherms that use water as a means of escape. Such organisms may contend with the effects of reduced body temperatures as well as environmental challenges, such as water turbulence, that affect their ability to perform antipredator behavior effectively. Such is the case with the water anole, Anolis aquaticus. This small Costa Rican lizard can evade predators by diving underwater for long durations (over 15 minutes), a feat likely facilitated by rebreathing an air bubble that forms above its nares. Within this bubble, oxygen concentration decreases over time, strongly suggesting that A. aquaticus tolerates long dives by continuously extracting oxygen from this rebreathed bubble. Unfortunately, an understanding of the fitness tradeoffs associated with aquatic antipredator behavior, as well as tactics for compensation, is lacking. Our research focused on two distinct but related questions: 1) how do water characteristics such as flow and dissolved oxygen (DO) level affect dive duration? And 2) does A. aquaticus, while generally considered a thermoconformer, perform any thermoregulatory behaviors after diving? To answer our first question, we submerged lizards in varying levels of water flow (no flow, low flow, high flow) as well as varying levels of DO (low, medium, high), independently. We found that with greater water flow, lizards dove for significantly shorter durations, likely due to the energetic strain of remaining submerged while being jostled, or due to continuous loss of oxygen via disruption of the rebreathing bubble. There was also a positive trend between increased DO and longer dive duration, which may indicate oxygen from the surrounding aquatic environment is diffusing into the rebreathing bubble, as has been documented in some semi-aquatic invertebrates. To answer our second question, we cooled lizards to simulate the thermal effect of diving and put them in a tank with a thermal gradient along the floor ranging from ~4°C to ~32°C. The position of these lizards along the gradient was then compared to lizards that were not cooled. Preliminary results of this study do not suggest thermoregulatory behaviors occur. By addressing this knowledge gap, this research greatly expands our understanding of how ectothermic species balance mitigating predator risk with potentially extreme physiological costs.