Using conservation translocations to assess the impact of anthropogenic climate change on a cold-adapted reptile, the tuatara (Sphenodon punctatus)
Authors:   , Price Stephanie J. 
Published: November 2021

<p>Anthropogenic climate change is progressing at a rate unprecedented in the past 65 million years and is a significant conservation concern. The associated biotic and abiotic impacts are expected to have substantial effects on global biodiversity, with some species potentially more vulnerable than others. The tuatara (Sphenodon punctatus) is a New Zealand endemic reptile and of particular interest as it is a slowly reproducing, range-restricted, cold-adapted ectotherm with temperature-dependent sex determination. Consequently, tuatara could be particularly vulnerable to rising air temperatures and conservation translocations have been key components of tuatara conservation efforts. Knowledge of how the tuatara might be affected by warmer climates will help inform where future conservation efforts are best directed, practices to avoid and which sites might be most suitable for the establishment of populations. The translocation of 176 adult tuatara in October 2012 from Stephens Island in New Zealand’s Cook Strait to four latitudinally distant North Island sites offered the opportunity to study the responses of tuatara in a range of environments. The comparatively warmer, drier climates of several sites provided surrogates for temporal climate change, enabling an assessment of how a warming climate might impact tuatara, and how they might respond. Using field observations, laboratory analysis and controlled experiments I investigated the short-term success of the translocations, the influence of translocation and climate on tuatara enteric bacterial communities and parasites, as well as how warmer climates might influence nocturnal activity, thermoregulatory opportunities and learning ability. I found several translocated populations to be progressing favourably, and found evidence that tuatara may exhibit enhanced growth at warmer, less densely-populated sites, suggesting that further translocations to lower latitude sites might be a viable conservation strategy. However, high population density at one translocation site was a concern and management recommendations were made to enable the dispersal of individuals. I detected Salmonella Saintpaul for the first time in a live tuatara, Campylobacter spp. was identified as a likely common commensal organism, and no measurable impact of translocation or climate on bacterial prevalence was observed, suggesting no substantial risk of climate warming to the susceptibility of tuatara to these bacteria. Tick populations were negatively impacted by translocation-associated factors following release but subsequently recovered at most sites and mites were not found on any translocated tuatara. Diurnal and nocturnal activities were positively influenced by air temperature, up to an upper threshold, and assessment of the site-specific thermal climates suggested that tuatara at warmer sites may benefit from increased opportunities for emergence and the attainment of preferred body temperatures throughout the year, though a higher frequency of restrictive air temperatures over summer may also reduce emergence opportunities. Experimental work showed that warmer air temperatures may enhance learning in tuatara, which could improve their ability to cope with challenging environments under climate change. However, body size was also an influential component of learning ability and further research is needed to build on these initial findings. I conclude that tuatara may experience overall benefits from further translocations to warmer sites and warming climates at currently cooler sites, which suggests that other cold-adapted reptiles with similar thermal tolerances may also see initial benefits under climate warming, though further monitoring is required to determine longer-term translocation success. Equally, while warmer air temperatures were not found to be detrimental to tuatara, they still pose a risk to population viability and further work is required on the impacts of associated abiotic factors like drought, and how populations of this long-lived species may be affected if and when climate warming exceeds the upper temperature rise of ~5°C predicted by the 2100s.</p>