Yellow crazy ants break the rules of reproduction.
Every male ant contains separate populations of cells from two distinct genetic lineages, making them “chimeras,” researchers report in the April 7 Science. Yellow crazy ants (Anoplolepis gracilipes) are the first known species that requires chimerism to create fertile males.
It’s “an elegant response to the kinds of unusual mating systems we’ve observed in other ants,” says evolutionary geneticist Waring “Buck” Trible of Harvard University, who was not involved in the study. “We might consider this as the next evolutionary step” in ants.
Most animals develop from a sperm cell and an egg cell uniting into one, combining their DNA. As a creature grows, all of the subsequent cells, save for sex cells, carry two sets of DNA-bearing chromosomes, one from each parent. In other words, these somatic cells all carry the same genetic information. Sperm and egg cells contain just one set of chromosomes.
But in many ants, along with other insects like wasps and bees, only females have somatic cells with chromosome pairs. Males typically develop from unfertilized eggs. So their somatic cells hold just one set of chromosomes.
A 2007 study, however, found that about half of the sampled male yellow crazy ants possessed two different copies of the same genes, just like the species’ female worker ants.
But “it didn’t make any sense that all males in this species would be diploid,” or have two sets of chromosomes in each somatic cell, says evolutionary biologist Hugo Darras of Johannes Gutenberg University Mainz in Germany. When this happens in other ants, the males are usually sterile, he says. “Nobody had any explanation.”
So Darras and colleagues collected hundreds of yellow crazy ants from across East and Southeast Asia. Analyzing females — queens and workers — revealed that royalty in this species has a genetic source. Reproductive queens came from…
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