Female cichlid develops male organs to fertilise herself

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A female cichlid held in isolation has managed to self fertilise herself and produce offspring.

The cichlid, living at Hull University, was an experimental cross between two species: Pundamilia pundamilia and Neochromis omnicaeruleus. 

She was kept in a tank on her own, like dozens of her siblings — but despite the lack of a mate, she still managed to produce more than 40 youngsters over a two-year period.

This is known as ‘selfing’ or self fertilisation. It’s a fairly common method of reproduction among flowers and insects — but in vertebrates it’s very rare. 

The Mangrove killifish (Kryptolebias marmoratus) is one of the few species known to self fertilise. It’s thought to have developed the ability as finding a mate isn’t always easy and selfing is better than not reproducing at all, despite the obvious inbreeding risks such a method poses.

The reason for the selfing in the hybrid cichlid — the only one of 80 similar hybrid females to do so — is unclear, but it could be a genetic 'innovation' caused by the hybrid nature of the fish, due to its parents having different sex-determining genes, say the researchers. 

The fish was a mouthbrooder, and she reproduced by fertilising eggs held in her mouth with the sperm she released into the water and then sucked up.

Seventeen of the 40-odd youngsters she produced grew to adulthood. These fish were also kept in isolation but while they were fertile, none of them exhibited the same selfing ability. However, these offspring all suffered from what scientists call ‘inbreeding depression’ — minimal genetic diversity, which can lead to birth defects in subsequent generations.

On dissection of the selfing female, it was found that she had developed sperm-containing tissue — a testicle of sorts — next to her normal reproductive organs.

The study was published in the journal Royal Society Open Science.