Planet Earth

Termite Queen Clones Herself by Making Eggs Impervious to Sperm

InkfishBy Elizabeth PrestonNov 21, 2014 12:58 PM

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Even kings and queens that have six legs and live underground aren't immune to royal machinations. In one Asian termite species, queens choose to shut their mates out of the picture when it's time to breed a successor. They simply clone themselves to make new queens. To keep the king's genes away, the queen makes special eggs that have no entrances for sperm—all their drawbridges are pulled up tight. The lives of Reticulitermes speratus termites are worthy of an HBO series. The story starts when a new colony is founded by a single termite pair, the king and queen. They mate in the usual way and fill the colony with workers, their offspring. No one reproduces except for the royal pair. Everyone in this humble kingdom of dirt knows their places. The queen can live for more than 11 years, and as she ages, the order of things starts to get muddy. New queens-in-training appear throughout the colony and begin to produce their own young. Who's the father? The king—but he isn't breeding with his daughters; it's not that kind of drama. The secondary queens are essentially clones of the mother, made from her eggs without any sperm. This sort-of-virgin birth is called parthenogenesis. It's used by many insects and occasionally by certain lizards, sharks, and other vertebrates. (The termite queen's fatherless daughter isn't a true clone, because she doesn't have her mother's exact complement of genes. Half the mother's genes go into the egg, and those genes are doubled to make up for the missing sperm contribution.) Gradually these "secondary queens" take over reproduction in the colony from their mother. It's not a system the king should be happy to go along with. By cloning herself, the queen shrinks the king's genetic legacy. So how does she get away with it? Scientists discovered the structure of royal succession in Reticulitermes speratus in 2009

, but the way queens make fatherless daughters remained a mystery. The female termite's body stores sperm from her mate and dumps some on each egg as it's laid, so it would seem there's no way to prevent fertilization. Toshihisa Yashiro and Kenji Matsuura at Japan's Kyoto University believe they've found the answer. Ordinarily, sperm enter a Reticulitermes speratus egg through tiny tunnels called micropyles on the egg's surface. The researchers collected eggs from 60 termite colonies and found that the numbers of these tunnels varied widely. On average there were about 9 micropyles per egg, but other eggs had up to 33, and some had only one. Every one of these eggs held an embryo containing both the queen's and the king's DNA, Yashiro and Matsuura found. Even with just one entry point on an egg, sperm could find its way in. But in several colonies, the scientists also found eggs with no micropyles at all. The drawbridges were shut and sealed. Inside these impenetrable eggs, the scientists found termite embryos with only the queen's DNA

. These were the future queens. A young termite queen doesn't need to think about replacing herself. Accordingly, when the scientists examined eggs from queens of different ages, they found that young queens' eggs all have micropyles. Only aging queens produce the sealed-up eggs. With the time of their succession drawing closer, they begin to shut out sperm and fill the colony with their chosen daughters. "We [were] surprised so much because this is exactly what we predicted," Matsuura says of the micropyle-free eggs. "It is [a] really smart system." Matsuura says there are certain cells responsible for forming micropyles, and the queen makes fewer of these cells as she ages. Even with the king at her side, this means she can control her sexual and asexual reproduction—and there's nothing he can do about it. Because she hands over control to her parthenogenetic daughters, the scientists write, "The founder queen can be considered genetically immortal until the colony dies." Game of Clones, anyone?

Image: Reticulitermes speratus colony, by Keisotyo (via Wikimedia Commons)

Yashiro T, & Matsuura K (2014). Termite queens close the sperm gates of eggs to switch from sexual to asexual reproduction. Proceedings of the National Academy of Sciences of the United States of America PMID: 25404335

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