The overwintering behaviour and physiology of Northern map turtles (Graptemys geographica) in Ontario

Northern map turtles (Graptemys geographica) are a freshwater turtle species that spends months of the year overwintering submerged under ice. They are anoxia intolerant, making their ability to survive submerged without access to atmospheric oxygen physiologically impressive. Overwintering behaviour and physiology were examined to understand how this species survives the winter. Biologgers recorded locomotor activity, temperature, and depth throughout overwintering. Locomotor activity was continuous during the winter. The amount of movement differed between adult females, juvenile females, and adult males. Temperature preference for all groups was near 1°C and each moved progressively shallower as winter progressed. Respirometry was used to measure adult female standard metabolic rates at under-ice temperatures. Metabolism was lower at lower temperatures (i.e., 1°C versus 4°C), indicating considerable metabolic savings at 1°C. The behaviours observed likely reflect this species working to meet winter oxygen and energetic needs which differ based on size specific physiological needs.