Tropical flatback turtle embryos (Natator depressus) are resilient to the heat of climate change

Abstract

Climate change is threatening reproduction of many ectotherms by increasing nest temperatures, potentially making it more difficult for females to locate nest sites that provide suitable incubation regimes during embryonic development. Elevated nest temperatures could increase the incidence of embryonic mortality and/or maladaptive phenotypes. We investigated whether elevated nest temperatures reduce hatching success in tropical flatback turtles (Natator depressus) nesting in the Gulf of Carpentaria, Australia. Egg incubation treatments began at 29.5°C and progressively increased in temperature throughout incubation, up to maxima of 31, 32, 33, 34 and 35°C. Elevated nest temperatures did not reduce hatching success or hatchling body size relative to control temperatures (29.5°C), but did speed up embryonic development. A combination of sudden exposure to high temperatures during the first 2 weeks of incubation (>36°C for 48 h) and prolonged warming throughout incubation (from 29.5-35°C) did not reduce hatching success. We also recorded an unusually high pivotal sex-determining temperature in this flatback turtle population relative to other sea turtle populations: an equal ratio of male and female hatchlings is produced at ∼30.4°C. This adaptation may allow some flatback turtle populations to continue producing large numbers of hatchlings of both sexes under the most extreme climate change scenarios. Some tropical populations of nesting flatbacks may possess important adaptations to high-temperature incubation environments, which are not found in more southerly temperate populations.

Climate change and temperature‐linked hatchling mortality at a globally important sea turtle nesting site

“…The upper thermal limit for sea turtle egg development is often cited as 33°C (Miller, ) or 35°C (Ackerman, ) although it is possible that for some species the upper thermal tolerance is higher (Howard, Bell, & Pike, , ). Additionally, it is now clear that sea turtle embryos become more tolerant of high incubation temperatures as incubation progresses (Maulaney, Booth, & Baxter, ).…”

“…Currently, most of the published data on temperature‐linked mortality stem from studies with loggerhead (e.g., Matsuzawa et al., ; Read, Booth, & Limpus, ) or green turtles (e.g., Weber et al., ), so studying the survival curves of individual species is limited by data availability. Very few data are available for Kemp's ridley turtles and only a few studies have studied flatback turtles (e.g., Howard et al., ; Van Lohuizen, Rossendell, Mitchell, & Thums, ). We reiterate here that there is a need to bridge this knowledge gap to assess how climate change will impact different populations and different species of turtles worldwide (Howard et al., ).…”

Phylogeography, genetic stocks, and conservation implications for an Australian endemic marine turtle

“…Flatback turtles of the eQld stock, where 50 years of data have been compiled, have shifted the beginning of the nesting season earlier to when temperatures are cooler (C. J. Limpus & A. Whiting, unpublished data). Moreover, there is evidence of variation in pivotal temperatures in flatback turtles relative to nesting phenology (Hewavisenthi & Parmenter, ; Howard, Bell, & Pike, ; Limpus, ). It is unknown how the genetic stocks across northern Australia, which are already primarily nesting during the cooler months, will adapt.…”

Are thermal barriers "higher" in deep sea turtle nests?

“…Differences in thermal tolerances are not only found among species but also intra-specifically and within populations at fine scales [42, 43]. For example, clutches laid by green turtles that nest on a dark beach of Ascension Island where temperatures are naturally high exhibit higher thermal tolerance than those laid by turtles that use a nearby lighter beach [42].…”