One hypothesis is that the temperature is sensed by neurons in the central nervous system and transduced to the bipotential gonad by nerve fibers see Lance Journal of Animal Ecology. Spencer and Janzen found that hatchlings from mixed-sex nests were less energy efficient and grew less than their same-sex counterparts incubated in single-sex producing temperatures.
It is quite possible that there are other species of reptiles with more complicated scenarios of temperature reversal of chromosomal sex. Valenzuela, Nicole. Although other environmental influences can have similar effects, temperature is the most wide-spread factor that alters aromatase activity and sex determination.
In most species, gender is determined during fertilization. Sign up for our email newsletter. This is called temperature-dependent sex determination, or TSD. Other work centers on a theoretical model the Charnov — Bull model  predicted that selection should favour TSD over chromosome -based systems when "the developmental temperature dependent sex determination is seen in in Lismore differentially influences male versus female fitness";  this theoretical model was empirically validated thirty years later  but the generality of this hypothesis in reptiles is questioned.
Current research suggests that warming trends due to climate change may result in more female turtles being born!
However, there is evidence that during climactic extremes, changes in the sex determining mechanism itself to GSD are selected for, particularly in the highly-mutable turtles. Very near or at the pivotal temperature of sex determination, mixed sex ratios and more rarely intersex individuals.
New Jersey: Pearson Education, The highlands are colder with a higher magnitude of annual temperature fluctuation and a shorter activity season, delaying maturity, thus GSD is favored so sex ratios are not skewed.
It appears that the enzyme aromatase which can convert testosterone into estrogen is important in temperaturedependent sex determination. PLOS One. Charles Deeming. Likewise, additional experiments in sockeye salmon Oncorhynchus nerka reported in Azuma et al.
Sunderland MA : Sinauer Associates; What is the reliability of the original data used to assign TSD in the different species that survived our analysis?