Hot off the Press, Holiday Edition: Hatchling Turtle Overwintering
The holiday season has returned – when thoughts turn away from sun and scaley creatures, to snow, Santa, and ice! Yet, temperate zone reptiles are still out in the wild – being exposed and challenged by the winter season.
Winter is a huge energetic challenge, and reptiles within the northern hemisphere have developed adaptations to survive this season. These vary between species, and even within the same species! These adaptations can be behavioural to avoid low temperatures (i.e., habitat selection), as well as physiological to allow survival at low temperatures (i.e., reduced metabolic rate, biochemical changes). Many species utilize more than one adaptation, which combine to form an overwintering strategy. For example, many hatchling turtles have both physiological adaptations that promote survival at freezing temperatures (e.g., supercooling), and also select habitats that promote their survival overwinter (e.g., remain in their natal nest or emerge and find an alternative overwintering location).
In two of my most recent publications, collaborators and myself examined why sometimes hatchlings turtles remain in their natal nest while others disperse?
First, a 20 year study in Pennsylvania, USA collected data on whether 6 freshwater turtle species emerged from the nest before winter or remained in the nests overwinter and emerged in spring. We found that small species tended to emerge early, and larger species tended to remain in their nests over winter. These tendencies remained consistent every year. Also, we found that precipitation was correlated to the number of hatchlings that delayed emergence until the following spring. Overall, we found that delaying emergence until the following spring tended to be the primary overwintering strategy utilized.
Second, a two-year study on Painted Turtle hatchlings in Ontario, Canada examined what might trigger hatchlings to emerge from a nest in the fall, versus stay in their nest overwinter. We found that smaller hatchlings emerged early, and this may be to increase fat reserves to ensure survival overwinter. Also, nest infestation by predatory Sarcophagid fly larvae triggered hatchlings to emerge from nests before winter. In Painted Turtles, emerging early is most likely a plastic response to increase their survival (either by increasing their fat reserves for winter, or avoiding a predator).
Finally, writing these two papers highlighted to me that a lot about overwintering strategy and behaviour in reptiles is unknown. More research in these chilly winter months on reptiles is required to fully understand how our cold-blooded friends survive such extreme temperatures. All I am sure about it that it's impressive!
Lovich, J. E., Ernst, C. H., Ernst, E. M. and Riley J. L. 2014. A 21 year study of seasonal and interspecific variation of hatchling emergence in a Nearctic freshwater turtle community: to overwinter or not to overwinter? Herpetological Monographs, 28: 93-109. (download PDF here)
Riley, J. L., Tattersall, G. J. and Litzgus, J. D. 2014. Potential sources of intra-population variation in painted turtle (Chrysemys picta) hatchling overwintering strategy. Journal of Experimental Biology, 217: 4174-4183. (download PDF here)