MOSCOW, June 15, Tatyana Pichugina.Immaculate conception, when a child is born without the participation of a father, is considered a miracle in all religions. And only for scientists, this is not surprising. Same-sex reproduction, or parthenogenesis, is common among plants and small invertebrates, such as bees and termites. In vertebrates — much less frequently, mainly in lizards. The other day reported the first case of spontaneous conception in crocodiles. Why is this important for science?In 2002, a two-year-old female sharp-snouted crocodile was placed in a reptile park in Costa Rica. She lived in isolation. After 16 years, a clutch of 14 eggs was found in her aviary. Half appeared to be fertilized and they were taken to the incubator. When no one hatched after three months, the eggs were opened. Only one contained a fully formed fetus, unfortunately dead.
Science knows the ability of females to store sperm for a long time, more than six years. To exclude such a case, scientists isolated DNA from the shed scales of the parent and from the heart muscle of the fetus. The match is 99.9 percent. Then we analyzed small sections of the genome using the open source program ParthenoGenius. Not finding paternal genes, they concluded that spontaneous conception. This discovery was reportedin Biological Letter, Royal Society of Great Britain Journal. crop-width=»600″ data-crop-height=»400″ data-source-sid=»cc_by-sa_20″ class=»lazyload» width=»1920″ height=»1281″ decoding=»async» />< br />
Who doesn't need a male
Bisexual reproduction is when a zygote is formed, that is, a fertilized egg containing hereditary material from the mother and father, when a spermatozoon fuses with an egg. In the process of division, the zygote forms an embryo. In many animals, including humans, sex is determined at the time of fertilization due to the set of chromosomes. But crocodiles, turtles, lizards and hatterias do not have sex chromosomes, the sex is set by the temperature in the environment. At 30-33 degrees Celsius, males are born, higher or lower — females. It was 29-30 degrees in a Costa Rican incubator, so that single fetus was female, scientists say.
In parthenogenesis, the embryo develops only from the mother's egg. This was first identified in aphids in the middle of the 18th century. After a century and a half, they already knew that this happens with domestic chickens, pigeons, turkeys. Similar cases with mammals in nature are unknown. However, there are successful experiments with laboratory mice.
There are species that reproduce exclusively by parthenogenesis. For example, Armenian rock lizards — this was established in the 1950s by the Soviet herpetologist Igor Darevsky.
With the development of molecular biology and the accumulation of data from zoos, the number of vertebrate species, capable of virgin conception, constantly grew. So, in 2001, hammerhead sharks were added to the list.
In articleTwo years ago, two California condor chicks are mentioned hatching from unfertilized eggs at the San Diego Zoo in the United States. This is an endangered species, restored from literally two dozen special ones. They are grown and then released into the wild. To identify kinship, certain sections of DNA are analyzed in birds. And so they found two cubs, conceived immaculately. Moreover, their mothers were in the enclosure along with the males and brought offspring from them. Both parthenogenetic chicks (males) quickly died because they were weaker and smaller than the others.
Same-sex reproduction produces non-viable, weakened offspring with various disorders. So it's no surprise that the Costa Rica crocodile fetus didn't survive. For example, in turkeys, only three percent of parthenogenetic eggs hatch into chicks. At the same time, such offspring, having lived to adulthood, are capable of procreation. There are known precedents for ordinary and imperial boas, royal pythons.
Legacy from time dinosaurs
Scientists believe that parthenogenesis in crocodiles could not be noticed for a long time. Firstly, egg layings during long-term isolation are considered by default to be unviable, they are disposed of. Secondly, parthenogenetic offspring appears in the presence of males — then they simply do not pay attention to it. Thirdly, in crocodiles, abnormal cubs, unlike snakes, do not stand out so much in color. Only genetic research will help.
Meanwhile, the discovery of parthenogenesis in crocodiles has an important consequence. Diagnostics showed that it is based on the same mechanism as in birds and other reptiles, when a fertilized egg is formed by fusion (automixis) with another, intermediate, sex cell, the polar body.
Crocodiles belong to a large group of animals called archosaurs, from which they split off about 240 million years ago. Dinosaurs and pterosaurs then split, giving rise to birds. That is, crocodiles and birds are the only representatives of archosaurs that have survived to this day.
The ancestor of crocodiles, common with scaly reptiles, lived 267-312 million years ago. But lizards and snakes also have parthenogenesis, and with the same mechanism as in crocodiles (terminal fusion automixis). It did not arise independently in different lines of animals, but was inherited from common ancestors, the researchers believe. «The discovery sheds light on the possible reproductive behavior of extinct relatives of crocodiles and birds, the famous pterosaurs and dinosaurs,» the authors write. However, nothing can be firmly established without the genetic material of these fossil animals.