Models of primary sex ratios at a major flatback turtle rookery show an anomalous masculinising trend

Abstract

Background: Quantifying primary sex ratios is essential for assessing how global warming will influence the population dynamics of species with temperature-dependent sex determination (TSD). Process-explicit (mechanistic) models can accurately estimate primary sex ratios but require the resolution of the key physiological parameters that influence sex determination and validation of the model by testing predictions against empirical data.Results: To address these goals, we conducted incubation experiments on flatback sea turtle (Natator depressus) embryos from a large winter-nesting rookery at Cape Domett in the East Kimberley region of Western Australia. A TSD model fitted to laboratory and field nest data indicated that the pivotal temperature producing equal sex ratios was 29.4°C, with males produced below 27.7°C and females produced above 31.1°C. Back-switch experiments revealed that the thermosensitive period (TSP), when gonads differentiate into testes or ovaries, occurs between 43% and 66% of development to hatching. Integrating this new information with sand temperatures reconstructed from 23 years of historical climate data shows that male-biased sex ratios are likely if the TSP falls during the Austral winter. Annual variation in the simulated sand temperatures increased from 1990 to 2013, with cooler winters producing conditions that favoured male hatchlings for longer periods. The same model projected to 2030 and 2070 suggests that femalebiased primary sex ratios will become more prevalent over time. Conclusions: Our results show that accurate modelling of primary sex ratios depends on quantifying the thermal biology of embryos and on parameterising mechanistic models of sand temperatures with site-specific climate data.

Loggerhead sea turtle embryos (Caretta caretta) regulate expression of stress response and developmental genes when exposed to a biologically realistic heat stress

“…; Stubbs et al . ). Tacc3 was one of the genes downregulated under stress and encodes a protein that is integral to normal development in the brain tissue of developing mouse embryos (Aitola et al .…”

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

“…It is unknown how the genetic stocks across northern Australia, which are already primarily nesting during the cooler months, will adapt. At Cape Domett, the peak of nesting occurs when sand temperatures are lowest, and there are very few shaded nest sites that would mitigate rising temperatures (Stubbs, Kearney, Whiting, & Mitchell, ). Indications of gene flow between winter and summer nesting rookeries will be important in spreading genes that protect against the higher temperatures predicted from climate change (Tedeschi et al, ), or that influence pivotal temperatures.…”

Reptile embryos and climate change: Modelling limits of viability to inform translocation decisions

“…The reflectance of air-dried surface soil samples from each nest, measured using a spectrometer (300-2100 nm wavelength range), as described by Stubbs et al (2014). The average of three measurements per soil sample was calculated.…”

“…The mechanistic model used by Mitchell et al (2008), known as Niche Mapper™ (Porter and Mitchell, 2006), has since been applied in other studies of the embryonic stages of reptiles, especially those with a focus on modelling sex ratios (e.g. Fuentes and Porter, 2013;Stubbs et al, 2014;Cavallo et al, 2015).…”

“…The integration of these field data with a microclimate model then allows the prediction of nest temperatures under various climates and at different geographical locations. Such methodologies have been applied in several studies of the embryonic stages of reptiles, including Bynoe's gecko (Heteronotia binoei; Kearney and Porter, 2004), tuatara (Sphenodon guntheri; Mitchell et al, 2008;Carter, 2015), flatback turtles (Natator depressus; Stubbs et al, 2014) and green turtles (Chelonia mydas; Cavallo et al, 2015), all using the Niche Mapper™ framework. In this study we further aimed to integrate field and laboratory data to describe the sensitivity of P. umbrina embryos to the thermal environment, and to apply a customised mechanistic model to map locations within southwestern Australia where embryos would survive, and could potentially be translocated.…”