How Ants Evolved Their Sex Determination Traits

Being male or female can make a huge difference. Now, scientists have discovered the two ancient genetic components of sex determination in ants.

In many animals, sex is determined by sex chromosomes. For example, in humans the Y chromosome triggers male development. However, hundreds of thousands of insects, such as ants, wasps and bees, have a fundamentally different sex determination system called haplodiploidy.

In haplodiploid organisms, sex is typically determined by a mechanism called "complementary sex determination." Females are diploid, which means that they have two complementary versions of sex-determining genes, one set inherited from the father and one from the mother. Males, though, are haploid since they have just a single version of these genes.

A different situation comes with inbreeding. When ants are born with two of the same sex determination gene sets, they become sterile diploid males, even if they should develop as females. Generating sterile males is a flaw in this reproduction, since for ants the males do not work and their main function is to reproduce.

In this latest study, the researchers took a closer look at the mechanism of reproduction in ants. They created genetic crosses between brothers and sisters. This induced the production of sterile males, which allowed the researchers to see which genomic regions were associated with this phenomenon.

In the end, the scientists found that 25 percent of the progeny was sterile, and this was due to the presence of two separate sex determination regions in the ants' DNA. The first region is more than 100 million years old, and it contains two genes, which are also involved in honey bee sex determination.

"Sex determination systems are believed to evolve rapidly, but these data suggest that elements of the sex determination system used by bees and ants actually date to the time of the dinosaurs," said Alexander Mikheyev, one of the researchers, in a news release. "These findings also show that there is still much more to learn about the molecular diversity of sex determination mechanisms."

The findings are published in the journal PLOS Genetics.

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