How can nest temperature determine the sex of some lizard hatchlings?

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black girdle-tailed lizard — lizard Black girdle-tailed lizard (*Cordylus nigra*).

In most lizard species, sex is determined by chromosomes at conception. However, in a small number of species—including certain iguanids, geckos, and wall lizards—there are no sex chromosomes. These species rely on temperature-dependent sex determination (TSD).1

In these cases, the specific temperatures experienced within the nest during the period of egg development act as the primary control for whether the hatchlings develop as male or female. While thermoregulation is a critical aspect of a lizard's life, TSD represents a unique biological mechanism where environmental thermal conditions directly influence the sexual differentiation of the developing embryo.12