Strange lizards can change sex in the womb

The spotted ball lizard (Carinascincus ocellatus), endemic to Tasmania, Australia, can change sex from female to male before birth. This is the first non-egg-laying animal discovered to have this ability. The new study was conducted by a team of experts at the University of Tasmania and published in the journal Proceedings of the Royal Society B on June 1.

Spotted ball lizard, endemic to Tasmania. (Photo: JMsayers)

Spotted ball lizards are sometimes born anatomically male, but are still genetically female, according to new research. The reason for this change, scientists say, is temperature.

In humans, sex depends on an inherited pair of chromosomes, but in reptiles this is not always the case. For some species, sex depends on incubation temperature. For others, this may depend on both, for example the lizard Pogona vitticeps. Normally, sex is determined by genes, but at temperatures above 32 degrees Celsius, the male genetically becomes a female with the correct function.

This is called "gender inversion" and occurs when genes that determine sex are also sensitive to temperature. Previously, sex reversal had only been observed in spawning animals including fish, amphibians and reptiles.

Spotted ball lizards give birth instead of laying eggs. In nature, the sex ratio of a population is influenced by temperature. The number of females will be more when warm and the number of males will be more when cool. In the new study, experts at the University of Tasmania looked to see if these differences in sex ratios were dictated by temperature-induced sex reversals.

The team traps 100 newly pregnant females from different altitude locations and cares for them at various temperatures in the laboratory. They then divided them into five groups of 20 each. In one experiment, two groups were exposed to a heater for four or 10 hours a day, with a temperature range of 10 degrees Celsius when the lights were off and 20 to 37 degrees Celsius when the lights were on. In another experiment, the remaining groups were kept at a constant temperature of 33 degrees Celsius, 29.5 degrees Celsius or 26 degrees Celsius during the day and 10 degrees Celsius at night.

When 423 baby lizards were born, experts sequenced the genes from the DNA sample on the tail of each individual to determine the sex by genes, and also examined the reproductive organs to determine the sex anatomical.

All females anatomically have two X chromosomes, which means they are also genetically female. There is no gender reversal from male to female. However, 31 juveniles, or 7%, had male reproductive organs and female (XX) chromosomes.

These XX males appeared in both experiments and were more common in females from low altitudes and when temperature was limited - i.e. when heaters were turned on for only 4 hours or when heat levels were controlled. at 26 degrees Celsius.

The study helps to explain the sex bias in favor of females in populations of spotted ball lizards in warm conditions. If XX males mate with XX females, all offspring will be genetically female because XX males lack a Y chromosome, leading to the possibility of more females in the second generation, says Benjamin expert. Geffroy at the French Marine Institute explains.