For the first time, scientists have used genetic engineering to trigger a ‘virgin birth‘ in female animals that normally need a male partner to reproduce. Researchers generated young mice and frogs without genetic input from the male parent. But these offspring were produced by tinkering with egg cells in lab dishes rather than giving the female animals the ability to give birth to virgins, also known as parthenogenesis.
Previous research has identified candidate genes for parthenogenesis, says study co-author Alexis Sperling, a developmental biologist at the University of Cambridge in the UK. But her team, she says, not only pinpointed these genes, but also confirmed their function by activating them in another species.
No man is needed
In mammals, offspring are born when a male’s sperm fertilizes a female’s eggs. But many insects and lizards, as well as other animals, have evolved parthenogenesis, which requires no genetic input from the male, as an alternative to sex.
to identify the genes that underlie parthenogenesis, Sperling and her colleagues sequenced the genomes of two strains of the fly Drosophila mercatorum: one that reproduces sexually and one that reproduces through parthenogenesis. The researchers then compared gene activity in eggs from flies capable of parthenogenesis with those from flies capable of sexual reproduction only, to identify genes that work during one process but not the other.
The comparison allowed the authors to identify 44 genes potentially involved in parthenogenesis. The researchers altered the equivalent genes in the fruit fly Drosophila melanogaster, which normally cannot reproduce asexually.
After altering various combinations of genes, the researchers came across a combination that induced parthenogenesis in about 11% of female fruit flies. Some of the offspring of these genetically engineered flies were also capable of parthenogenesis.
Although parthenogenetic flies received genes only from their mothers, they were not always clones of their parents. Some had three sets of chromosomes, while eggs laid by mothers reproducing by parthenogenesis usually have only two.
Less complicated than sex
“Parthenogenesis is the most efficient method of reproduction. In animals, sex is very complicated,” says Tanja Schwander, an evolutionary biologist at the University of Lausanne in Switzerland who has studied parthenogenesis in stick insects. Studying parthenogenesis, he says, helps biologists understand the benefits and trade-offs associated with sexual reproduction.
The new work could also help biologists understand the evolution of parthenogenesis itself, says Chau-Ti Ting, an evolutionary biologist at the National Taiwan University in Taipei. She hopes to find out if other fly species have genes for parthenogenesis similar to those in D. mercatorum; this might help her piece together how this behavior developed.
Sperling notes that some agricultural pests use parthenogenesis to reproduce rapidly, amplifying their power to damage crops. In the United Kingdom, for example, one species of moth has turned to parthenogenesis due to the widespread use of pesticides that disrupt the reproduction of male moths. Now moths have become a major pest, Sperling says. He hopes to study which pest management policies and strategies could cause the pests to rely on parthenogenesis knowledge that could help keep the pests under control.
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