In early January of 2018, zookeepers at a zoo in Costa Rica found that one crocodile had laid her eggs. What was peculiar about this was that this crocodile has been living alone for 16 years! While crocs can lay sterile eggs that never develop, some of the eggs in this mama’s clutch looked perfectly fine, so scientists put them in an incubator to mature. Luck was not on their side, however, as the baby crocs developed but never hatched.
As an egg cell matures in its mother’s body, it divides repeatedly to generate an egg with exactly half the genes needed for an individual. Three smaller cellular sacs containing chromosomes, known as polar bodies, are formed as byproducts. Polar bodies usually wither away. But in vertebrates that can perform parthenogenesis (reproduction from an ovum without fertilization), one polar body sometimes fuses with the egg, creating a cell with the necessary complement of chromosomes to form an individual. That may be the reason for the virgin birth.
But why is this happening? Well, when a female is looking for a mate, she will produce parthenogens. This way she has more time to go and look for a mate, but it is also possible that it is just a trait that doesn’t have enough downsides for evolution to move on from it.
In 2020, scientists discovered that lizards could lay a clutch of eggs with some that are fertile and some that contain parthenogens. This hinted at the hypothesis that lizards can turn the trait on and off, but can crocs? They ran tests and collected data but there was no solid evidence that proved crocodiles can do it too. “We’ll never be able to prove they could do it,” said Dr. Booth, a scientist that led the study, “but it suggests they had the ability.”
As an egg cell matures in its mother’s body, it divides repeatedly to generate an egg with exactly half the genes needed for an individual. Three smaller cellular sacs containing chromosomes, known as polar bodies, are formed as byproducts. Polar bodies usually wither away. But in vertebrates that can perform parthenogenesis (reproduction from an ovum without fertilization), one polar body sometimes fuses with the egg, creating a cell with the necessary complement of chromosomes to form an individual. That may be the reason for the virgin birth.
But why is this happening? Well, when a female is looking for a mate, she will produce parthenogens. This way she has more time to go and look for a mate, but it is also possible that it is just a trait that doesn’t have enough downsides for evolution to move on from it.
In 2020, scientists discovered that lizards could lay a clutch of eggs with some that are fertile and some that contain parthenogens. This hinted at the hypothesis that lizards can turn the trait on and off, but can crocs? They ran tests and collected data but there was no solid evidence that proved crocodiles can do it too. “We’ll never be able to prove they could do it,” said Dr. Booth, a scientist that led the study, “but it suggests they had the ability.”
