Inbred invasive ants eat their sterile sons

JCU and CSIRO PhD student Pauline Lenancker led the study of the tropical fire ant (Solenopsis geminata), an invasive species that is a significant agricultural and ecological pest in Australia.

“Despite these ants being a threat, little is known about their social biology – how they operate as a group,” she said.

Ms Lenancker said it was a particular mystery how the ants got through what biologists call the ‘genetic bottleneck’.

“When invasive ants move to a new area the pioneers may be one or a few colonies. Because they are isolated, they inbreed, and are subject to genetic issues, including production of sterile sons. Yet they somehow survive and spread,” said Ms Lenancker.

She said when queens have newly mated, they fly off to start their own colonies. If they do not quickly rear daughters that can forage, the queens will starve to death.

The research team found that queens that had mated with closely related males regularly produced ‘useless’ sterile male sons instead of daughters. The researchers maintained 1187 queens in 487 colonies in the lab to examine strategies the queens used to overcome this genetic burden.

“We found that queens often abandoned their sterile male sons in the colony ‘trash pile’ before eating them or feeding them to their daughters,” said Ms Lenancker.

Ms Lenancker said this had the advantage of allowing the queens to redirect nutrients to productive members of their colony.

The researchers also found that colonies containing groups of queens reared more daughters than those with a single queen and therefore would likely have a better chance of survival.

“Queens could also reduce the likelihood of producing sterile sons if they ‘sleep around’ because they would then have a greater chance of mating with a male that is genetically different than they are,” stated Ms. Lenancker. However, the team found no evidence of promiscuity.

Associate Professor Lori Lach, who co-supervised the project said the findings provided an important insight into the fascinating biology of invasive ants.

“Governments, industries, and land managers around the world are spending millions to control or eradicate species like the tropical fire ant, red imported fire ant, and the yellow crazy ant. The more we learn about their biology, the closer we can come to novel methods of preventing their establishment, spread, and impacts,” she said.

Link to paper here

Link to images here