Effects of semi-constant temperature on embryonic and hatchling phenotypes of six-tubercled Amazon River turtles, Podocnemis sextuberculata
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2022-08
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Elsevier Ltd.
Abstract
Purpose: We evaluated how constant incubation temperatures affect life-history traits pre-hatching and post-hatching of the six-tubercled Amazon River turtle, Podocnemis
sextuberculata.
Methods: We incubated eggs from natural nests at ten constant temperatures between 22°C and 37.5°C (2013) and at six temperatures between 26°C and 36°C (2016). In 2013, we raised hatchling for 90 days to evaluate effects of temperature on early hatchling growth. We evaluated maternal effects in 2016.
Results: P. sextuberculata displays temperature-dependent sex determination and produces females at warmer temperatures (TSD Ia). The estimated pivotal temperature was 33.73 ± 0.15°C and the transitional range temperature 1.16 ± 0.59°C. Constant temperatures below 26°C and above 38°C were lethal. Intermediate temperatures (32.25°C and 31.5°C, respectively) were optimal for hatching success and produced larger hatchlings that grew slower early in life compared to colder or warmer conditions, which produced smaller hatchlings. Warmer incubation temperatures accelerated embryonic development (except at the highest value which increased incubation duration). Comparison between growth and mass gain rates of 30, 60 and 90 days-old suggests that higher temperatures induced lower growth and mass gain rates posthatching. Therefore, incubation temperature effects on hatchling size disappeared by 3 months of age.
Conclusions: Six-tubercled Amazon River turtles showed the highest pivotal temperature ever documented for a turtle species. Their relatively narrow transitional range temperature may limit its evolutionary potential of this vulnerable turtle in the face of global warming. Future incubation experiments at a finer scale (33°C-36°C) are warranted to refine the sex-ratio reaction norm. Field studies that monitor natural nests are imperative to evaluate conservation measures and the effect of female-biased illegal hunting and climate change. By providing data about the thermal biology of an understudied lineage of non-model species, our study helps fill gaps in our understanding of the evolution of vertebrate sex determination and its potential adaptive value.
Methods: We incubated eggs from natural nests at ten constant temperatures between 22°C and 37.5°C (2013) and at six temperatures between 26°C and 36°C (2016). In 2013, we raised hatchling for 90 days to evaluate effects of temperature on early hatchling growth. We evaluated maternal effects in 2016.
Results: P. sextuberculata displays temperature-dependent sex determination and produces females at warmer temperatures (TSD Ia). The estimated pivotal temperature was 33.73 ± 0.15°C and the transitional range temperature 1.16 ± 0.59°C. Constant temperatures below 26°C and above 38°C were lethal. Intermediate temperatures (32.25°C and 31.5°C, respectively) were optimal for hatching success and produced larger hatchlings that grew slower early in life compared to colder or warmer conditions, which produced smaller hatchlings. Warmer incubation temperatures accelerated embryonic development (except at the highest value which increased incubation duration). Comparison between growth and mass gain rates of 30, 60 and 90 days-old suggests that higher temperatures induced lower growth and mass gain rates posthatching. Therefore, incubation temperature effects on hatchling size disappeared by 3 months of age.
Conclusions: Six-tubercled Amazon River turtles showed the highest pivotal temperature ever documented for a turtle species. Their relatively narrow transitional range temperature may limit its evolutionary potential of this vulnerable turtle in the face of global warming. Future incubation experiments at a finer scale (33°C-36°C) are warranted to refine the sex-ratio reaction norm. Field studies that monitor natural nests are imperative to evaluate conservation measures and the effect of female-biased illegal hunting and climate change. By providing data about the thermal biology of an understudied lineage of non-model species, our study helps fill gaps in our understanding of the evolution of vertebrate sex determination and its potential adaptive value.
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This is a preprint of an article published as Camillo, Cassia S., Nicole Valenzuela, and Steve A. Johnson. "Effects of semi-constant temperature on embryonic and hatchling phenotypes of six-tubercled Amazon River turtles, Podocnemis sextuberculata." Journal of Thermal Biology 108 (2022): 103292. doi:10.1016/j.jtherbio.2022.103292. © 2022 Elsevier Ltd. Posted with permission.