It is used in reference to species with temperature-dependent sex determination, such as crocodilians and turtles. The extent of the TSP varies a little among species,  and development within the oviducts must be taken into account in species where the embryo is at a relatively late stage of development on egg laying e.
Temperature pulses during the thermosensitive period are often sufficient to determine sex, but after the TSP, sex is unresponsive to temperature. After this period, however, sex cannot be reversed see sex reversal.
Pattern I is found in turtles, e. Red-eared slider turtles Trachemys scripta , Olive Ridley sea turtles Lepidochelys olivacea , or Painted turtles Chrysemys picta. Pattern II has been found in American alligators Alligator mississippiensis and Leopard geckos Eublepharis macularius. In some species, this follows the pattern that eggs in extremely high or low temperatures become male and eggs in medium temperatures become female.
Very near or at the pivotal temperature of sex determination, mixed sex ratios and more rarely intersex individuals.
Also, experiments conducted at the pivotal temperature, where temperature is equivocal in its influence, have demonstrated an underlying genetic predisposition to be one sex or the other. The lizards were female in appearance and were capable of bearing offspring, despite having the ZZ chromosomes usually associated with male lizards.
Administering estradiol at male-producing temperatures generates females that are physiologically identical to temperature-produced females. Interestingly, hormones and temperature show signs of acting in the same pathway, in that less hormone is required to produce a sexual shift as the incubation conditions near the pivotal temperature.
It has been proposed  that temperature acts on genes coding for such steroidogenic enzymes , and testing of homologous GSD pathways has provided a genic starting point. While aromatase is involved in more processes than only TSD, it has also been shown to play a role in certain tumor development. One possible explanation that TSD is common in amniotes is phylogenetic inertia — TSD is the ancestral condition in this clade and is simply maintained in extant lineages because it is currently adaptively neutral or nearly so.
Consequently, the adaptive significance of TSD in all but the most recent origins of TSD may have been obscured by the passage of deep time, with TSD potentially being maintained in many amniote clades simply because it works 'well enough' i. Other work centers on a theoretical model the Charnov — Bull model ,   predicted that selection should favour TSD over chromosome -based systems when "the developmental environment 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.
This hypothesis is supported by the persistence of TSD in certain populations of spotted skink Niveoscincus ocellatus , a small lizard in Tasmania, where it is advantageous to have females early in the season. The warmth early in the season ensures female-biased broods that then have more time to grow and reach maturity and possibly reproduce before they experience their first winter, thereby increasing fitness of the individual. These chemicals block the conversion of testosterone to oestradiol during development so each sex offspring can be produced at all temperatures.
The turtles were incubated at temperatures that produce solely males, both sexes, and solely females. 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. Hatchlings from single-sex producing temperatures also had higher first-year survivorship than the hatchlings from the temperature that produces both sexes.
TSD may be advantageous and selected for in turtles, as embryo energy efficiency and hatchling size are optimized for each sex at single-sex incubation temperatures and are indicative of first-year survivorship. An alternative hypothesis of adaptive significance was proposed by Bulmer and Bull in  and supported by the work of Pen et al. They conjectured that disruptive selection produced by variation in the environment could result in an evolutionary transition from ESD to GSD Bull, Vogt, and Bulmer, Studying the spotted skink, they observed that the highland population was not affected by temperature, yet, there was a negative correlation between annual temperature and cohort sex ratios in the lowlands.
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. However, in the lowlands, temperatures are more constant and a longer activity season allows for favorable conditions for TSD. They concluded that this differentiation in climate causes divergent selection on regulatory elements in the sex-determining network allowing for the emergence of sex chromosomes in the highlands.
However, there is no evidence thus far that sex ratio is manipulated by parental care. 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.