Predicting the fate of a living fossil: how will global warming affect sex determination and hatching phenology in tuatara?

Abstract

How will climate change affect species' reproduction and subsequent survival? In many egg-laying reptiles, the sex of offspring is determined by the temperature experienced during a critical period of embryonic development (temperature-dependent sex determination, TSD). Increasing air temperatures are likely to skew offspring sex ratios in the absence of evolutionary or plastic adaptation, hence we urgently require means for predicting the future distributions of species with TSD. Here we develop a mechanistic model that demonstrates how climate, soil and topography interact with physiology and nesting behaviour to determine sex ratios of tuatara, cold-climate reptiles from New Zealand with an unusual developmental biology. Under extreme regional climate change, all-male clutches would hatch at 100% of current nest sites of the rarest species, Sphenodon guntheri, by the mid-2080s. We show that tuatara could behaviourally compensate for the male-biasing effects of warmer air temperatures by nesting later in the season or selecting shaded nest sites. Later nesting is, however, an unlikely response to global warming, as many oviparous species are nesting earlier as the climate warms. Our approach allows the assessment of the thermal suitability of current reserves and future translocation sites for tuatara, and can be readily modified to predict climatic impacts on any species with TSD.

Turtle mating patterns buffer against disruptive effects of climate change

“…Many populations of species with TSD already exhibit offspring sex ratios skewed towards the sex produced at warmer temperatures, e.g. males in tuatara [3] and females in marine and freshwater turtle populations [4,5]. Future climate change scenarios are predicted to increase these sex ratio biases, with implications for population viability [2,3,6,7].…”

“…males in tuatara [3] and females in marine and freshwater turtle populations [4,5]. Future climate change scenarios are predicted to increase these sex ratio biases, with implications for population viability [2,3,6,7]. Potential consequences include a reduction in effective population size (N e ) that will exacerbate the negative effects of inbreeding and increase genetic drift in small populations [8], the inability to find mates leading to reduced fecundity or female infertility [9], and, under more extreme climate projections, the production of single sex cohorts [3,7].…”

Bite‐force performance of the last rhynchocephalian (Lepidosauria:Sphenodon)

“…It is the largest endemic non-avian reptilian and has significant cultural importance for Maori (Sharell 1966; Mot 1997;Ramstad et al 2007). Currently restricted to approximately 35 small islands and the subject of concerted conservation efforts Mlot 1997;Gaze 2001;Parkinson 2002;Mitchell et al 2008), Sphenodon is of great scientific significance because it is the only extant member of the Rhynchocephalia, a group that was diverse and globally distributed during the Mesozoic (Apesteguia & Novas 2003;Evans 2003;Jones 2008;Jones et al 2009). Being the closest living relative (sister group) to Squamata (lizards, snakes, amphisbaenians;Rest et al 2003;Evans 2003), Sphenodon has been the subject of much research and has played an essential role as an outgroup taxon in comparative studies of squamate biology (e.g., Schwenk 1986Schwenk , 2000McBrayer & Reilly 2002;Vitt et al 2003;Herrel et al 2007;Evans 2008; Jones et al in press).…”

Can behavior douse the fire of climate warming?

“…In addition, Kearney et al focus on adult ectotherms, which can use their mobility to thermoregulate. In contrast, their eggs are immobile, and thus warming-induced selection on eggs may be greater than on adults (17). Of course, if ''mother knows best,'' mobile moms can potentially use thermal cues to pick the best nest sites, which would represent a cross-generational behavioral buffering (18).…”