All-female fish species shows sex is overrated

An all-female freshwater fishspecies called the Amazon molly that inhabits rivers and creeksalong the Texas-Mexico border is living proof that sexualreproduction may be vastly overrated.

Scientists said on Monday they have deciphered the genome ofthe Amazon molly, one of the few vertebrate species to rely uponasexual reproduction, and discovered that it had none of thegenetic flaws, such as an accumulation of harmful mutations or alack of genetic diversity, they had expected.

They found that the Amazon molly, named after the fiercefemale warriors of ancient Greek mythology, boasts a hardy
genetic makeup that makes it equally fit, or even more so, thanfish using sexual reproduction in which both maternal andpaternal genes are passed along to offspring.

"The Amazon molly is doing quite well," said biologistManfred Schartl of the University of Wuerzburg in Germany.
"Unexpectedly, we did not find the signs of genomic decay aspredicted."

Sperm stealer

The fish reproduces using a strategy in which a female's eggcell develops into a baby without being fertilized by a male'ssperm cell. But that does not mean the fish does not need somehanky panky.

"The Amazon molly female produces clones of itself by dupinga male of a closely related species to mate with her. Theasexual mode of reproduction termed gynogenesis requires thefemale to mate with a male but none of the male's genome ispassed to the offspring," said geneticist Wesley Warren of theMcDonnell Genome Institute at Washington University in St.Louis.

The Amazon molly's egg cells are activated to develop intoan embryo by a sperm cell that degenerates without fusing withthe egg's nucleus.

The fish is up to about 3 inches (8 cm) long and eatsinsects, plants, algae and other food. The study showed itoriginated when two other species, the Atlantic molly and theSailfin molly, mated about 100,000 to 200,000 years ago.

Animals that reproduce asexually are rare compared to theoverwhelming majority that exist as males and females and
reproduce sexually.

"It was long thought that vertebrates would not be able toexist in such a way. It was a sensation when the Amazon mollywas the first asexual vertebrate discovered in 1932," Schartlsaid.

About 50 vertebrates are known to use asexual reproductionincluding fish, amphibians and reptiles.

The research was published in the journal Nature Ecology &Evolution.