A baby born without a genetic father might sound like a divine miracle or a biblical tale but, this past summer, it happened at Mountsberg Conservation Area when a female Northern Watersnake gave birth to three baby snakes, without coming in contact with a male snake.
In Canada, the Northern Watersnake (Nerodia sipedon sipedon) can be found throughout southern Ontario, in and around almost any body of water, including lakes, rivers and wetlands and are often seen basking on rocks or slithering through reeds along the shoreline. Like most snake species, Northern Watersnakes breed in the spring, after emerging from hibernation, and give birth in late summer or early autumn.
However, the baby snakes that were recently born at Mountsberg were not like most. The mother, a Northern Watersnake named Mickey, came to Mountsberg to be part of the education program about five years ago and has not come in contact with a male during her time there.
That’s why Bobby Bowen, Resource Interpretor at Mountsberg, was so surprised to find a stillborn but fully developed baby snake in the tank where Mickey is held. He was even more shocked when, the following day, some of the other resource interpreters found two living baby snakes in the tank.
“I was amazed by the fully developed embryo but it didn’t cross my mind to check the enclosure for living babies,” Bowen says. “When I found out what they had discovered I was flabbergasted. They must have been hiding under some of the rocks or bark in her enclosure when I was cleaning it the day before.”
Of the two baby snakes that were born alive, one was born normal and healthy and one was born with a kinked spine. Another staff interpreter had put the baby snakes into a couple of small containers and then, the following day, staff set up two small glass tanks with heat pads, water dishes, shredded bark and a few hides. The healthier baby started eating about a week after it was born and had its first shed a couple of weeks after birth. The baby with the kinked spine didn’t eat for weeks and even months after birth.
“We were sure it was going to pass away,” says Bowen. “I didn’t give up on it though. I would always offer it food when its sibling ate. Suddenly, one day, it had a feeding response that it had never showed before and it ate a little minnow. It has been eating regularly ever since.”
As for how Mickey became pregnant, there are two possible options.
The first option is sperm retention also known as delayed fertilization. If Mickey had been in contact with a male snake before she came to Mountsberg, it is possible that she held onto sperm from the male, then used it to fertilize her own egg.
Sperm storage occurs in many species of snakes, including the Northern Watersnake, but it most often occurs during a shorter timespan of several months, rather than several years. According to Yves Scholten, Planning Ecologist at Conservation Authority, five years is likely too long for stored sperm to be viable. Scholten also mentions that Northern Watersnakes are less likely to store sperm, since the organ used for the purpose is less developed in the Northern Watersnake, than in other snake species.
The second possibility is parthenogenesis, which is a form of reproduction in which a female will produce offspring on her own, without the genetic contribution of a male. There are a number of species of fish, amphibians, birds and reptiles that can reproduce this way and Northern Watersnakes are one of them.
For this to occur, female snakes carry out meiosis, which is the division of cells that results in the formation of four egg-progenitor cells, one of which becomes the egg. In most cases, the body will reabsorb the other three egg-progenitor cells but, when parthenogenesis occurs, one of the remaining three cells will behave like sperm and fertilize the egg by fusing with it. The result is an embryo that only contains genetic material from the female. This embryo is either a clone or a half-clone of the mother, depending on the species. Offspring produced this way are technically referred to as parthenogens.
In nature, parthenogenesis occurs when a female snake is unable to find a male snake that she deems good enough to mate with or, if the female snake is kept in captivity, when there just aren’t any male snakes around. Watersnake parthenogens are missing important genetic information because they are half-clones of their mother, and thus highly in-bred. Being inbred in nature means that parthenogens are weak and less likely to survive. Because parthenogenesis is used as a last resort, snakes that are conceived this way are often stillborn, and, when they are born alive, are rarely healthy. This, Scholten says, would explain why one of the babies was stillborn and another was born with a kinked spine. It’s remarkable that two of the babies have survived if they are indeed parthenogens.
At nine years old, Mickey is nearing the end of her life and it is possible that parthenogenesis was a desperate attempt to pass on her genes. Parthenogenesis seems to be the most likely option but there are a couple of ways that staff will be able to determine how Mickey became pregnant. First, they would need to determine the sex of the baby snakes. Generally, If the babies are male, then it was a case of retained sperm because babies born from parthenogenesis can only be female, since they only contain genetic material from the mother. If the babies are female, they could be a case of retained sperm or parthenogenesis. Determining the sex of the baby snakes can be done using genetic analysis or visually by a herpetologist—a snake specialist—but nobody at Mountsberg has the specific skill to do this.
The only way to find out for sure how Mickey became pregnant would be to conduct a genetic analysis of the babies to determine if they have genetic material from a male snake and female snake or only a female snake. Genetic testing can be quite expensive but the staff at Mountsberg are looking into options, as having proof of parthenogenesis would be talk of the herpetology community.
For now, Mickey’s miraculous conception remains a mystery, with some educated guesses.
Last modified: November 29, 2017