Developmental biologist Alexis Sperling became obsessed with something she saw in the lab when she was studying for her PhD. A praying mantis was fertilized and she gave birth spontaneously, without having previously had sex with a male. A virgin had had children.
This ability has never been observed in mammals, including of course humans, but in the rest of the animal world there are certain species capable of doing it. Many of the cases have been observed in zoos where the females had spent years alone, without the possibility of mating.
In 2015, a team discovered one of the first cases of sexless reproduction in the wild: Florida saw sharks, which were on the brink of extinction. Just two years ago, at the San Diego Zoo (United States), two females of the endangered California condor gave birth alone, despite the fact that in this case there were males available.
This phenomenon is called parthenogenesis (virgin birth) and it can be an advantage if the mother is well adapted to her environment and it is not very changeable. Her young, practically clones, will also be, and they will not need males to be able to give rise to new generations. In fact, her reproductive capacity is doubled in this way. It is still an enigma how, when and why parthenogenesis happens and the reason why mammals have it banned.
sperlingan evolutionary biologist at the University of Cambridge (United Kingdom), has cleared up some of these unknowns by creating the first genetically modified animal to be able to have children as a virgin: the fruit fly, or Drosophila melanogaster. The team has achieved this by intervening in three genes of the animal. After 40 days without a male to fertilize them—half their lives—the modified drosophilas turned on their new genetic superpower and produced young all on their own.
an inheritable power
“This is the first time that it has been shown how to induce the ability to have pups while being a virgin”, highlights Sperling. “Otherwise, the daughters are completely healthy and despite having inherited the power to carry out parthenogenesis, they also retain their ability to reproduce sexually,” adds the biologist, first author of the study that describes these experiments. in the specialized magazine Current Biology.
Parthenogenesis is one of the most unknown biological processes in the animal kingdom. As the eggs mature inside the mother, they divide several times until they are ready, with half of the genetic material needed to create a new individual — the other half provided by the male’s sperm. In this process, a fusion of the ovum with excess genetic material can occur, which gives rise to spontaneous fertilization. The process produces offspring that are very similar to the mother, but not identical, as the original genetic sequence is slightly remixed in the fusion process.
Attempts to get mammals to spontaneously have sexless young have failed. In these animals there is imprinting, which causes certain genes essential for the development of the embryo to be deactivated and turn on only when the genetic halves of the female and the male are mixed. In mice, this imprinting has been partially deactivated to generate offspring without the need for a father or sex, but it has always required a complex manipulation of the ovules, which then have to be implanted in a female for her to gestate. The biological barriers to parthenogenesis are probably much more complex in primates and humans, so the application of these techniques to assisted reproduction presents many difficulties.
old school genetics
Sperling’s team found the key to creating virgin births by studying the genome of two variants of another fly, the Drosophila mercator. One reproduces only sexually and the other only by parthenogenesis. This allowed us to identify two genes responsible for asexual fertilization: the pole —essential for cell proliferation and discovered in the late 1980s by David Glover, co-author of the present study— and the Desat2. The scientists found their equivalents in the fruit fly genome and began to cross different lineages until they got one that had the same functioning patterns as in the other species. And thus arose the first generation capable of asexual reproduction. If in addition the function of the gene is enhanced Myc, essential for cell growth, parthenogenesis becomes much more efficient. “This is old-school genetics,” Sperling acknowledges; but it works.
The discovery has required six years of work and the creation of more than 220,000 flies, something unthinkable with other laboratory animals with longer and much less manageable breeding times, explains Sperling.
cayetano gonzalezveteran researcher with Drosophila at the Barcelona Institute for Research in Biomedicine (IRB), believes that this is a “very surprising” experiment. “Not only have they found the magic combination of genes, but they are also using it to give a species that was not capable of parthenogenesis the ability to do so,” he points out. The finding shows one of the evolutionary pathways to asexual reproduction in animals, but there are likely many others that have yet to be discovered, she adds.
Sperling is going to redirect his investigation towards a worrying new phenomenon. Parthenogenesis is much more common in insects that are agricultural pests and can cause millions in losses. An example is the tomato borer —absolute tuta—, considered one of the worst agricultural pests globally. Although it was relatively controlled thanks to current pest management methods, in recent years the insects seem to have gained resistance.
One method of combating these pests is to flood the greenhouse with artificial female pheromones. The males become so saturated by these biochemical signals that they are unable to find the actual females, resulting in no reproduction. But it seems that female borers are increasingly capable of reproducing by parthenogenesis, and this in turn gives them an enormous advantage, since in each generation not only half of the individuals adapted to their environment can have offspring —50% females. , 50% males—but potentially 100%. Despite this, experiments have shown that only 2% of second generation fruit flies develop sexless offspring, and as long as there are no males around.
Sperling, who used to work in the Department of Genetics at Cambridge, has moved to the associated Crop Research Center at the same university. “I want to start to understand how this happens in pests,” he says. “I would like to test all the pesticides we use and see if any of them are promoting pathogenesis. To know if our means of mass agricultural production really favor the advance of this type of pest ”, he adds.
You can follow MATERIA on Facebook, Twitter and instagramor sign up here to receive our weekly newsletter.
#Created #modified #animal #children #sex