Yellow crazy ants reproduce in a way never seen before
Sashithorn Hasin
Most male yellow crazy ants have two separate sets of DNA derived from sperm and egg cells that do not mix genetic material after fertilization.
This means that males are chimeras – individuals with one set of genes in one part of their body and another set in other parts. Depending on the DNA in the sperm cell that fertilizes, it develops into either a worker bee or a queen bee, but the male offspring can themselves be chimeras.
The discovery, which solves a 15-year-old mystery of insect genetics, reveals a previously “scientifically unknown” mode of reproduction, says Hugo Dallas of Germany’s Johannes Gutenberg University Mainz.
“There were a lot of crazy hypotheses to explain what was going on with these ants, but none were as crazy as what we discovered,” he says.
Ants typically reproduce by either sexual reproduction (a male sperm fertilizes a female egg) or clonal reproduction (i.e., the queen ant produces offspring without adding the genes of the second parent) . Generally, males are born from unfertilized eggs and females from fertilized eggs. In most cases, the queen bee is genetically similar to the worker bees of the same colony, but it develops into a queen bee because it is given special care and nourishment.
In 2007, scientists studied the genome of the yellow crazy ant (Anoprolepis gracilipes) And to my surprise, I found that the men had a mix of genetics, as if they had two parents. Six years later, another team found that all queen bees in a colony descended from the same genetic lineage, while worker sisters all descended from a very different second lineage.
Intrigued by this puzzle, Dallas and his colleagues sequenced the DNA of 53 yellow crazy queens and 91 workers collected from 14 locations in Southeast Asia. The queen bees were inbred, he says, but the worker bees had much higher genetic diversity. In other words, the queen bee appeared to be born from the same pedigree parents, whereas the worker bees were born from different pedigree parents.
Assuming this meant the colony contained two lineages of males, the researchers collected 574 males from the same colony as the queen and worker bees and sequenced their leg DNA. They found that some males appear to share a genetic lineage with the queen, while others appear to be more closely related to worker bees.
If males came from fertilized eggs, it might make sense, says Dallas. But his team’s analysis revealed that, like most male ants, bees and wasps, each chromosome appears to come from an unfertilized egg, since he has only one copy. .
Perplexed, the team tested DNA from individual cells of 20 males. They found that within the same individual insect, about half of the cells carried genes of one lineage and the other half carried genes of the other. Looking specifically at sperm cells, the research team found that one lineage (the lineage that led to worker bees) was much more abundant than the other.
Further analysis revealed that the two strains of these males were derived from two parents. This means that males were actually born from fertilized eggs, but unlike females, the nucleus of the egg did not fuse with the nucleus of the sperm. In this way, the male will have two different sets of her chromosomes carried in different parts of the body.
In retrospect, the researchers realized that most of the male yellow mad ants were probably chimeras, and that DNA samples from the insect’s legs only showed the genetic material of that particular leg. , says Darras.
Ants may have evolved such strange reproductive systems because of old conflicts between lineages, he says. If it always creates infertile females, it can survive for generations if it can slip into an egg without fusion. It becomes a “selfish” system.
“But this is just speculation,” says Darras. “We are only at the beginning of understanding.”
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