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Cambridge University Science Magazine

Scientists have known for decades that the sex of the developing embryo of reptiles and fish can be influenced by environmental cues such as temperature. The question challenging scientists is exactly what biochemical changes occur after heat exposure that cause a male embryo to develop ovaries instead of testes?

Using bearded dragon embryos as a model, Sarah Whiteley and Arthur Georges from University of Canberra, were able to identify possible clues as to how this phenomenon can be explained.

Upon exposing male bearded dragon embryos to high temperatures, two main events were observed simultaneously. Firstly, an ion channel (known as transient receptor potential channel) responded by increasing the number of calcium ions travelling into the cells of the embryo. Next, the mitochondria of embryonic cells metabolised at a faster rate, increasing the levels of reactive oxygen species (ROS). ROS are a normal by-product of aerobic respiration but at high levels can become toxic, placing cells into oxidative stress. The combination of calcium influx and oxidative stress results in gene expression changes of the developing embryo, leading to the development of ovaries instead of testes.

Furthermore, there are key differences in gene expression between the females defined by their chromosomes, compared to temperature-originated females, showing that there are two distinct pathways that determine sex in bearded dragons.

This is a fascinating find that makes you wonder about the future: as our planet continues to heat up, female reptiles may dominate leading to questions about how these species will survive.

Artwork by Mariadaria Ianni-Ravn