Clitarchus hookeri stick insects, male and female pair

This female Clitarchus hookeri stick insect (green) is mating with a male (brown), but some females reproduce asexually. Credit: Steve Trewick

Evolution

The insect that lost its homeland — and its sex life

A pioneering group of stick insects that settled in the United Kingdom lost all of its males, leaving females that reproduce asexually.

In an evolutionary blink, populations of a New Zealand stick insect can give up sex — or embrace it again.

Some populations of the stick insect Clitarchus hookeri reproduce sexually and contain equal numbers of males and females; other populations consist entirely of females that forgo sex and reproduce asexually. One lonely population of asexual females lives on a cluster of small islands off the coast of the United Kingdom. The insects probably hitchhiked there on imported plants, perhaps as early as 1911.

Mary Morgan-Richards at Massey University in Palmerston North, New Zealand, and her colleagues traced the UK population’s genetic ancestry to a sexual New Zealand population. This indicates that the emigrant insects made the switch to asexuality within a 100-year period, or about 100 generations.

Two New Zealand populations, meanwhile, switched from asexual to sexual reproduction. One population consisted almost entirely of asexual females in 2003, but had transitioned to half male — and showed genetic evidence of sexual reproduction — by just 13 years later.

The insects could help scientists to understand the relative merits of sexual and asexual reproduction.