Scientists Reveal How Molecular Switch for Sex Evolved in Honeybees

Scientists have made a surprising discovery when it comes to a certain insect. They’ve teased out how the molecular switch for sex gradually and adaptively evolved in the honeybee.

The first genetic mechanism for sex determination was proposed in the mid-1800s by a Silesian monk named Johann Dzierson. At that time, he was trying to understand how males and females were produced in honeybee colonies. He knew that the differences between queen and worker bees arose due to the different quality and quantity of food, but he wasn’t sure about the males.

In order to find out about these differences today, the researchers studied 14 natural sequence variants of the complementary sex determining switch (csd gene) for 76 genotypes of honeybees. In order to do so, the researchers identified genetic markers close to the complementary sex determining locus in order to map the genes.

So what did they find? It turns out that the honeybees high recombination rate–the process by which genetic material is physically mixed during sexual reproduction–is the highest of any known animal studied. This actually helped the scientists isolate, sequence and characterize the complementary sex determining locus. They were also able to knock out an allele and show how they could get a male from a diploid genotype.Image

Despite these findings, though, the questions of which alleles were key and how they worked together in combinations and why this system evolved were left unanswered. That’s why researchers reviewed what actually constitutes and allele.

“There has to be some segment of that gene that is responsible in this allelic series, where if you have two different coding sequences in that part of the gene you end up producing a female,” said Robert Page, one of the researchers, in a news release. “So we asked how different do two alleles do you have to be? Can you be off one or two base pairs or does it always have to be the same set of sequences? We came up with a strategy to go in and look at these 18-20 alleles and find out what regions of these genes are responsible among these variants.’

In the end, the scientists found at least five amino acid differences can control allelic differences to create a female through the csd gene. The findings reveal exactly how males and females form in honeybees. In addition, they suggest that incomplete penetrance may be the mechanism by which new molecular switches can gradually and adaptively evolve.

The findings are published in the journal Current Biology.


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