What term describes reptile embryos' sex being determined by incubation temperature?

The term for reptile embryos’ sex being determined by incubation temperature is temperature-dependent sex determination. It is a form of environmental sex determination in which temperature during development influences whether an embryo develops as male or female.

In many turtles and crocodilians, the critical period is the middle third of incubation, called the thermosensitive period. Different species respond in different ways: in some, warmer eggs produce mostly females and cooler eggs mostly males; in others, the pattern is reversed or intermediate temperatures produce one sex while both extremes produce the other.

Temperature-dependent sex determination is not universal among reptiles. Many reptiles use sex chromosomes, while some species combine chromosomal cues with temperature effects. The underlying biology involves temperature-sensitive gene and hormone pathways, including genes such as DMRT1 in some species.

Scientists first described the phenomenon in the lizard Agama agama in 1966. It is also important in climate research because changing nest temperatures can alter offspring sex ratios in wild turtle and crocodilian populations.