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Sex? Female Stick Insects Can Take It Or Leave It

Fuseworks Media
Fuseworks Media
Sex? Female Stick Insects Can Take It Or Leave It

Wellington, NZPA - Male stick insects may not be good stick men, as research shows New Zealand's female stick insects don't actually need them to get on with a brood.

Not only that, the females capable of reproducing without male help always produce female offspring, according to the research, by Massey University's Mary Morgan-Richards.

Southern females were more likely to go it alone.

Her work, Geographic Parthenogenesis and the Common Tea-tree Stick Insect of New Zealand, which described the distribution and evolutionary relationships of sexual and asexual populations of the stick insect, is being published in the International journal Molecular Ecology.

In collaboration with Steve Trewick and the Department of Conservation's Ian Stringer, Dr Morgan-Richards conducted several experiments involving the reproduction of the species.

They found some populations had equal numbers of males and females that reproduced sexually, but others had unmated females that laid eggs that hatched and produced offspring identical to the mother -- known as parthenogenesis.

"All of the parthenogenic populations of stick insect are to the south in New Zealand compared to the sexual populations more to the north," Dr Morgan-Richards said.

They did not have a clear idea exactly of why that was but it seemed to fit with the idea of range expansion -- organisms moving to warmer places further north when the climate cools and expanding their population mid-range by going south when the climate warms.

The team also took females out of sexual populations and raised them on their own. Despite the lack of a male to mate with, the stick insects that usually reproduced sexually were capable of reproducing asexually.

Females from sexual populations that had access to mates did not reproduce asexually, even though they were capable of doing so.

Also, females from parthenogenic populations were able to reproduce sexually if they were given a male, but only about 10 percent of their offspring were the result of sex.

"It seemed that reverting to being sexual isn't an easy step."

The research also indicates that all of the southern parthenogenic populations seem to have the same common ancestor.

"That was unexpected. It seems extraordinary when any single female is capable of reproducing parthenogenically," Dr Morgan-Richards said.

The next phase of the research will try to determine the cause of such low rates of sexual reproduction from formerly parthenogenic populations.

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