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SOLVED: THE MYSTERY OF JAPAN’S ALL-FEMALE COLONIES

Researchers from The University of Sydney have uncovered the origins of the recently discovered female termite colonies in Japan.

Back in 2018, scientists from The University of Sydney made a remarkable discovery in the forests of Japan, having found, for the first time, a number of all-female termite colonies. Aside from a lack of males, the colonies’ queens contained no sperm in their sperm storage organs and their eggs remained unfertilised. Now, the same team of researchers – including Professor Nathan Lo and postdoctoral researcher Dr Toshihisa Yashiro – have found the answer as to how these all-female colonies came to exist.

Published in Proceedings of the National Academy of Sciences in December 2021, the research team found that the all-female colonies of drywood termites (Glyptotermes nakajimai) developed through accidental human-assisted hybridisation. Genetic testing revealed that at some time during in the last century, females from one lineage mated with males from another. The males were originally from a small island off the coast of Japan, but must have been unknowingly transported, likely via boat, to mainland Japan, where they mated with the resident termite population.

The result of the two lineages mating is the creation of genetically diverse and highly robust offspring that can reproduce asexually. The all-female colonies can clone themselves and do not require a male to procreate, resulting in double the amount of breeding. According to the researchers, this is bad news for the incumbent, non-hybrid species, which can be outcompeted by its hybrid relatives.

It’s also potentially bad news for property owners. Drywood termites, as their name suggests, do not require moist conditions to burrow into and eat wooden beams, walls, floors or furniture, and are commonly moved around the world by trade, opening the door to hybridisation events. Once an infestation occurs, it can be difficult to eradicate, potentially leading to structural damage to a building, or even collapse.

 

Cooperative colony foundation by multiple queens of an asexual female population of Glyptotermes nakajimai (photo credit: University of Sydney)

 

Professor Lo, who co-led the study, said his findings have implications for Australian biosecurity:

“We already have a number of very damaging termite species here. However, our study highlights the importance of making sure termites from overseas are not permitted to establish themselves. If they were to hybridise with our local termites, it might lead to even nastier lineages of termites for homeowners to deal with.”

Aside from discerning how the female colonies evolved, the researchers also studied several drywood termite colonies that contained both males and females. Genetic testing of the male termites revealed something very unusual – the sperm of males consisted of either 15 Y or 15 X chromosomes. In most species, including humans, male sperm have only a single Y or X chromosome. To have 15, rather than just one, is very unusual indeed.

“It’s really weird,” commented Professor Lo, who believes the genetic quirk occurred as a clever way for termites to breed successfully.

“Termite offspring can inherit nests from their parents, saving them the trouble of venturing into the dangers of the outside world, burrowing into wood, and creating their own nests. The problem with nest inheritance is that it results in a lot of inbreeding – sisters mate with brothers, and offspring may even mate with parents. “

As a solution, male termites probably evolved to have multiple Y chromosomes, making them harbour more genetic diversity than females. So, even if a sister and brother mate, they can produce viable offspring.”

The researchers say that this chromosomal pattern is found in some other organisms, including plants and huntsman spiders, but not usually to the extremes found in drywood termites.

 

References:

1 Yashiro, Toshihisa et al. Enhanced heterozygosity from male meiotic chromosome chains is superseded by hybrid female asexuality in termites. Proceedings of the National Academy of Sciences, 2021; 118 (51): e2009533118 DOI: 10.1073/ pnas.2009533118

Reworked article from: ‘Rise of termite clone queendoms offers clue to curb invasions: Preventing a homeowner headache’. Science Daily, January 28, 2022.

 

More information on termite nests and termite reproduction.