An Amazonian ant has dispensed¹ of sex and developed into an all-female species, researchers have found.

研究人员已经发现，一种亚马逊蚂蚁已经不需要性并且进化到全是雌性的物种。

These ants do not need males

The ants reproduce（再生，繁殖） via cloning - the queen ants copy themselves to produce genetically³ identical（相同的，同一的） daughters.

This species - the first ever to be shown to reproduce entirely⁴ without sex - cultivates a garden of fungus⁵（真菌，霉菌）, which also reproduces asexually（无性地）.

The finding of the ants' "world without sex" is published in the journal Proceedings⁶ of the Royal Society B.

Anna Himler, the biologist from the University of Arizona who led the research, told BBC News that the team used a battery of tests to verify their findings.

Unusual evolution

By "fingerprinting⁷" DNA⁸ of the ant species - Mycocepurus smithii - they found them all to be clones of the colony's queen.

And when they dissected⁹（解剖） the female insects, they found them to be physically¹⁰ incapable¹¹ of mating, as an essential part of their reproductive system known as the "mussel organ" had degenerated¹².

Asexual reproduction of males from unfertilised eggs is a normal part of some insect reproduction, but asexual reproduction of females is "exceedingly rare in ants", write the researchers.

"In social insects, there are a number of different types of reproduction," explained Dr Himler. "But this species has evolved its own unusual mode."

She and her colleagues do not know exactly why this particular species has become fully¹³ asexual, and how long the ago the phenomenon evolved.

They are carrying out further genetic² experiments, which will enable them to estimate how long ago the evolutionary¹⁴ change occurred.

No sex please

There are advantages to life without sex, as Dr Himler explained.

"It avoids the energetic cost of producing males, and doubles the number of reproductive females produced each generation from 50% to 100% of the offspring（子孙，后代）."

But combining genetic material in sexual reproduction gives future generations many more advantages.

"If we're more diverse（不同的，相异的）, we're more resistant¹⁵（抵抗的，反抗的） to parasites¹⁷（寄生现象） and disease," explained Laurent Keller, an expert in social insects from the University of Lausanne.

"In a colony of clones, if one ant is susceptible¹⁸ to a parasite¹⁶, they will all be susceptible. So if you're asexual（无性的;，无性生殖的）, you normally don't last very long.

"But in ants we're seeing more and more reports of unusual methods of reproduction," added Professor Keller, who was not involved in this study.

He also points out that social insects, like ants, may be particularly well suited to this type of reproduction because it enables the queen to control the caste（排他的社会团体） and sex of all the offspring in her colony.

More interested in gardening than sex 

The first farmers

Dr Himler's interest in Mycocepurus smithii was originally sparked not by their unusually biased¹⁹（有偏见的） sex ratio（比，比率）, but by their ability to cultivate crops.

"Ants discovered farming long before we did - they have been cultivating fungus gardens for an estimated 80 million years

"They collect plant material, insect faeces（粪，排泄物） and even dead insects from the forest floor and feed it to their crops," she said.

Many different species of ant - including the famous leafcutter ants - cultivate fungi²⁰, relying on it for nutrition.

But this particular species is able to grow "a greater number of crops than other ant species", she explained.

"When we started to study this species more closely, we just weren't finding any males. That's when we started to look at them in a different way."

Since the fungus crop reproduces asexually, Dr Himler thinks it might give the ants some kind of advantage "not to operate under the usual constraints²¹（规定参数） of sexual reproduction".

"There is certainly more work to be done in this system," she added. "We're quite excited about the direction this research might take us, and its implications（蕴涵式）."