Sawfish Have Virgin Births: First in the Wild
No sex is required for some mothers in the wild who are reproducing via virgin birth.
The first known virgin births in the wild have been documented among critically endangered smalltooth sawfish in Florida waters.
The discovery, reported in the journal Current Biology, marks the first time that living offspring from virgin births -- births where the mother did not mate with a male -- have been found in a normally sexually reproducing animal in nature.
Lead author Andrew Fields explained to Discovery News that "with fragmented habitat and low abundance," it is likely that female smalltooth sawfish, known for their iconic tooth-studded rostrum or "saw," are having trouble findings males. Lack of mating can then trigger the unusual births among certain adult females, he and his team suspect.
Fields, a researcher at the Stony Brook University's School of Marine and Atmospheric Science, and his colleagues were conducting routine DNA fingerprinting of the sawfish (a type of ray related to sharks) in a Florida estuary when they determined that about 3 percent of those studied arose due to virgin birthing, a process technically known as parthenogenesis.
This phenomenon is thought to occur when an unfertilized egg absorbs a genetically identical sister cell. The resulting offspring have about half of the genetic diversity of their mothers and often die. In this case, however, the "parthogens" looked to be in perfect health, so the scientists just tagged and released them as part of an ongoing study that they are conducting on sawfish movements.
As for how those individuals might then reproduce later in life, Fields said, "They may give birth sexually or asexually."
It is likely that virgin births are more common than previously thought among sharks and rays, both in captivity and in the wild. It is harder to detect and confirm the latter, given that DNA testing would be needed. Such births over the years, though, have surprised many aquarium staff members, who have found baby sharks suddenly appearing in tanks inhabited for lengthy periods by a lone female or multiple females and no males.
Senior author Demian Chapman, also from Stony Brook University, told Discovery News, "We know of parthenogenesis in blacktip, bonnethead, whitetip reef, whitespotted bamboo, and zebra sharks in captivity, so (there are) 5 species total."
More species are expected to be added to that list. Some birds and reptiles have also undergone parthenogenesis in captivity.
For the smalltooth sawfish, the discovery is a dire warning about the species' dwindling population. Fields said that it and other sawfish "are on the brink of extinction."
He says that, for the smalltooth sawfish, "there is no accurate estimated population size, but it seems to be at 1–5 percent of historical levels based on the best evidence available. The primary threats are entanglement during fishing and habitat loss."
While the virgin births could help to keep the population going for a while longer, they are not significant enough to save the sawfishes from extinction.
The study "should serve as a wake-up call that we need serious global efforts to save these animals," Kevin Feldheim of the Pritzker Laboratory at the Field Museum of Chicago said.
Field said that, even if strong conservation measures are put in place and properly enforced, it will take a lengthy period to bring smalltooth sawfish and other sawfish back to healthier population levels. He explained that they "are a long-lived species that take a long time to mature and do not produce a large number of offspring at a time, so the process will be very slow."
While scientists continue to investigate virgin births, so far, the phenomenon has not been reported for any mammal outside of a lab setting. The researchers suspect that genetic imprinting prevents mammals from undergoing such births naturally.
Another team of researchers from the Institute of Reproductive Medicine and Genetics in Los Angeles, however, has created "artificial sperm," consisting of multiple compounds that caused parthenogenesis to occur among their test mammals, which were mice.
Juvenile smalltooth sawfish in the Charlotte Harbor estuarine system, Florida.
Birds do it. Bees do it. Even bats, penguins, cheetahs and elephants do it. Sex spans the animal kingdom. But the way animals get the job done varies tremendously from one species to the next. Most of those reproductive strategies, according to a new study, have been completely ignored by science. WATCH: The world's most promiscuous bird is a sparrow that lives in tidal marshes in the northeastern United States. Researchers found that in most nests, saltmarsh sparrow chicks had multiple fathers. Jorge Ribas gets the sordid details.
The Same Old Species
Of the more than 12,000 studies published in major journals over the last decade, more than 90 percent focused on the same old species, scientists reported in the journal Molecular Reproduction & Development. Mice, rats and cows topped the list. Such a narrow focus is a major opportunity lost, said David Wildt, head of the Center for Species Survival at the Smithsonian Conservation Biology Institute in Front Royal, Va. By tapping into the diversity of animal reproduction, he said, scientists could better protect threatened species. A broader view might also help human couples coping with infertility. "There's this powerful biological diversity out there," Wildt said. "And most species have never been studied." WATCH: Synchronized wing beats help mosquitoes meet their mates. James Williams discovers what the flap is about.
In 1998, a mere 124 giant pandas lived in captivity around the world, most of them in China. Breeders there were having an impossible time getting the animals to make babies. Part of the problem was that nobody knew the details about how the animals reproduce. After some basic research, scientists discovered that female giant pandas become fertile just once a year for a tiny window of time, lasting between 24 and 72 hours. Males, meanwhile, are sexually active for about half year, from October through May. "We learned so much through all of this," Wildt said, "that we started turning around the breeding program." Today, there are 293 captive giant pandas worldwide, 253 of them in China. In just a decade, the number of animals in captivity has more than doubled. For such an endangered species, a strong captive community is like an insurance policy for shrinking wild populations. WATCH: Why is it so special when a giant panda cub is born? The problems associated with panda reproduction is explored in this Animal Planet video.
Big, cute mammals aren't the only animals that can benefit from some attention to their sex lives. Consider seahorses. Most people know that male seahorses carry the pregnancies, even though they also provide the sperm. For a long time, scientists assumed that a male seahorse ejaculated through an opening in his baby-carrying pouch to fertilize eggs that were placed there by the female. Careful dissections, however, revealed that seahorse sperm actually travels outside the body and into the pouch. What's more, the male produces only a very tiny amount of sperm, and almost every one fertilizes an egg. Those findings suggest that good water quality is essential for seahorse sperm to get to their destinations safely. Seahorse numbers are dwindling as many of them are scooped out of the sea for use in Chinese traditional medicine, said Bill Holt, a reproductive biologist at the Zoological Society of London. Basic studies on the reproductive systems of these and other animals are crucial to keep life going. "The more biology you know," he said, "the easier it is for people preserving seahorses to make sure they get everything right." WATCH: Seahorse dads are an anomaly in the animal kingdom, because they are the ones who are impregnated and go through labor. Not only that, but they can actually give birth to up to 1500 babies at a time!
Conservation Through Copulation
As a growing number of people struggle with infertility, there may be a vat of untapped insight in the way other animals manage to create life. Female bats, for example, are able to store sperm for an extraordinarily long period of time before fertilization occurs. Giant pandas produce sperm that freezes well. Pigs and koalas have resilient sperm that resist DNA damage, unlike rhinoceros sperm, whose DNA deteriorates faster than any other animal. These details inform conservation strategies: To do artificial insemination on a rhino, for example, you have to be quick! But that's not all. WATCH: In this Animal Planet video, Saba Douglas-Hamilton lingers too long in rhino country. When an aggressive male rhino takes notice of her, she has only a log for protection.
Borrowing From Nature
Figuring out the reproductive strengths and weakness of other species could lead to better ways of preserving vulnerable human sperm for fertility treatments. The research could also aid agricultural breeding programs. "If we could understand why rhinos and sheep are so susceptible to DNA damage -- and we have a number of ideas about this -- we could find treatments," Holt said. If treatments become available, he added, "then, there would be applications to humans." WATCH: We've cloned sheep, mice, dogs and more. So are humans next?
Cheetahs Are Not Cows
Considering the reproductive systems of overlooked species can foster an appreciation for the multitude of ways that mating occurs in the animal kingdom -- even when species are closely related to each other. Female domestic cats, for example, only ovulate after they've mated. Clouded leopards, on the other hand, release eggs spontaneously. Cheetahs produce a lot of abnormal sperm, while ocelots produce a large percentage of normal ones. These are all types of cats, but differences among groups are significant. "When you do comparative studies, you find out that not only are cows not cheetahs, cheetahs aren't even tigers, and tigers aren't even leopards," Wildt said. "There's an amazing variation among species in terms of reproductive mechanisms." WATCH: From the archives of Discovery: Watch as this group of cheetahs feasts on gazelle and zebras. Learn more about cheetahs and hunting in this video.