Tuatara tuesday – how cold is too cold for a tuatara?

ResearchBlogging.org Tuatara like it cold.  Unusually so, for a reptile.  While reptiles in most other countries are happiest with temperatures over 25 degrees celcius, here in New Zealand our reptiles prefer much lower temperatures.  Alison Cree’s group at the University of Otago has been investigating exactly which temperatures tuatara prefer, with a view to determining whether new populations of tuatara could be established in the southern South Island.

Research just published in Animal Conservation by PhD student Anne Besson examined the effects of cool temperature on juvenile tuatara sourced from Stephens Island, the southern-most natural population.  Sub-fossil remains tell us that tuatara were once present in Otago and Southland, but they have been extinct in this region for possibly hundreds of years.  Temperatures on Stephens Island are on average 3-4 degrees warmer than those at proposed translocation sites in Otago, and it is possible that tuatara originally living in the deep south had special adaptations to enable them to withstand the cold that are absent in animals from more northerly present-day populations.  To test whether Stephens Island tuatara are likely to be able to survive in the deep south, Besson compared tuatara behaviour at low temperatures with that of three lizard species found in the wild in Otago (common geckos, jewelled geckos and McCann’s skinks), hypothesizing that if tuatara have the same responses as these lizard species, then its likely they will be able to survive similar temperatures.

Besson investigated feeding behaviour at 20, 12 and 5 degrees, measuring the time it took an animal to catch, handle and digest prey at the three different temperatures.  She found few differences between tuatara and the lizards.  For all species, feeding performance dropped off significantly at 5 degrees as animals became very sluggish at catching and handling their food, and neither skinks or tuatara could digest food at this temperature.  However, one important difference between tuatara and lizards was seen at 12 degrees.  At this temperature lizards were able to digest food, albiet more slowly than at warmer temperatures, but tuatara were not.  Besson also measured preferred body temperature and critical thermal minimum (i.e. the temperature at which animals can effectively no longer function) across the four species and again found little difference between tuatara and the lizard species.

Besson’s results suggest that Stephens Island tuatara would survive a move south, but their inability to digest food at temperatures of 12 degrees or lower has important implications for choosing translocation sites in Otago, given that ambient temperatures rarely rise above 12 degrees in winter in this region.  As tuatara do not hibernate and still feed throughout the winter, Besson and Cree recommend that proposed translocation sites for tuatara should provide plenty of opportunities for animals to bask in the sun in order to digest their food.

Testing physiological and behavioural responses to investigate whether animals are likely to be survive in new environments is something that is rarely done in conservation studies, but is likely to become increasingly important in the face of climate change.  Tuatara are particularly vulnerable to warming temperatures, as sex determination in tuatara is temperature-dependent and warming temperatures are likely to produce an excess of males.  Establishing new populations further south may be one way of countering future temperature rises.  Besson’s research shows that this is likely to be a viable strategy for conservation management of tuatara, but whether they can produce self-sustaining populations at cooler temperatures still needs to be tested.

Besson, A., & Cree, A. (2010). Integrating physiology into conservation: an approach to help guide translocations of a rare reptile in a warming environment Animal Conservation DOI: 10.1111/j.1469-1795.2010.00386.x

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2 Responses to Tuatara tuesday – how cold is too cold for a tuatara?

  1. Chameleon says:

    How interesting that the lizard needs to be warmer to digest its food than it does to catch it. Hopefully the temperature changes with global warming won’t affect the population dynamics too badly.

  2. hilaryml says:

    Yes the global warming question is interesting from lots of angles for tuatara as they have temperature-dependent sex determination, where males are produced at higher temperatures. I think this is the subject for another post 🙂

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