Colonies of the termite species Glyptotermes nakajimai are doing without males, something that may be increasingly tempting for many. Although other species have been known to reproduce asexually, this is the first time the phenomenon has been seen in termites, whose social status makes for a particularly interesting case study.
Previous studies of termite colonies always found males present. Moreover, the sexes existed in equal numbers, unlike among most social insects where workers are all female. This makes the evolution of all-female populations more surprising than previous reports among ants and honey bees.
Nevertheless, a paper in BMC Biology announces the discovery of entirely male-free colonies of G. nakajimai from coastal Japan. The authors compared 37 of these colonies with an equal number where the sexes were mixed. They confirmed the males were not just living separately, Gate to Women's Country style, or hiding in female-looking bodies but that most termite queens store sperm in organs called spermathecae. However, in female-only colonies, the spermathecae were empty and eggs unfertilized.
This didn't stop a new generation of termites, all female naturally, hatching from the unfertilized eggs with an extra chromosome and larger genome than in sexual colonies.
The female-only colonies had fewer members of their soldier caste but made up for this by being better at their primary defensive tactic of plugging tunnels using their heads. The greater consistency in head width in asexual colonies appears to make for better plugs. The need to expend less of the colony's resources on defense may be one of the reasons all-female colonies are flourishing.
“Interestingly, we observed the occasional development of unfertilized eggs in the mixed-sex populations too. This suggests the ability to produce offspring from unfertilized eggs may have originated in mixed-sex ancestors and provided a potential pathway to the evolution of all-female colonies.” Dr Toshihisa Yashiro of the University of Sydney said in a statement.
The authors propose that some unusual nakajimai traits set the scene for asexuality to flourish. This includes colonies being founded collectively by multiple queens and wide geographic dispersal by rafting across water barriers.
In other animals, asexual reproduction usually proves relatively short lived – without the genetic reshuffling sex provides, animals are less able to survive changing conditions, such as the arrival of a new parasite. However, the sexual and asexual nakajimai populations diverged 14 million years ago, and while asexuality itself may have appeared more recently, it appears to have considerable staying power.
Ominously for some, the paper concludes that its findings provide “evidence that males are dispensable for the maintenance of advanced animal societies.”