Ola Svensson et al, Royal Society Open Science
The cichlid fish that grew a pair to reproduce.
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.
Smithsonian's National Zoo
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!
Smithsonian's National Zoo
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.
A typical-looking female fish in the aquarium room at U.K.'s Hull University recently shocked researchers when it was discovered that she had developed a male sex organ, fertilized her own eggs and produced four offspring.
The tropical freshwater fish known as a cichlid gave birth to 42 more offspring over the subsequent year, becoming the first documented cases of "selfing" in an otherwise sexually reproducing vertebrate (animal with a backbone and/or spinal column), according to a paper published in the journal Royal Society Open Science.
Selfing essentially refers to having sex with oneself and breeding. It was previously discovered among mangrove killifish, but for those fish, selfing is a primary mode of reproduction.
"In the mangrove killifish, selfing is an adaptation," lead author Ola Svensson explained to Discovery News. "It is believed that it can be hard for them to find a mate, and selfing is better than not producing at all."
Svensson, a researcher from the University of Gothenburg's Department of Biological and Environmental Sciences, and colleagues had previously crossed two different species of cichlids to produce what they thought was a normal, albeit hybrid, female fish. Such hybridizations do occur in nature and have often happened before in laboratory settings.
Upon the fish's death, the scientists determined that the individual had both ovaries and a male testis, so the fish at this point was intersex. Breeding was an all-oral event.
Senior author Cock van Oosterhout of the University of East Anglia explained to Discovery News, "These are mouth brooding fish, and fertilization takes place in the mouth. If some spermatozoa are released together with the eggs, they may be fertilized upon release, or in the mouth of the fish."
Many cases of "virgin births" have been reported in various species ranging from sharks to scorpions. That type of reproduction, however, is referred to as parthenogenis, and involves no fertilization.
What makes the recent event so different and unusual is that the individual was both mother and father to the offspring.
"It is a case of sexual reproduction," Svensson said.
Some of the offspring were male, while others were females. They were able to reproduce normally, and none of their offspring were capable of selfing.
Nevertheless, the progeny suffered from what the researchers called "inbreeding depression," showing minimal genetic diversity evident among them. Svensson said that many of their colleagues have therefore wondered, "If this is such an unsuccessful form of reproduction, why might it have evolved in the first place?"
Lukas Schärer from the University of Basel and his team share the view of Svensson's group that some reproduction for certain species is better than none at all.
Schärer and his team discovered selfing in the flatworm species Macrostomum hystrix. In that case, the process is doubly unusual because the intersex worms must inject sperm directly into their own heads in order to reproduce.
"To us this sounds traumatic, but to these flatworms it may be their best bet if they cannot find a mate but still want to reproduce," Steven Ramm of Bielefeld University, who studied the phenomenon, said.
So selfing is not always an evolutionary dead end, since it can result in some offspring that may reproduce. Time will tell if the process may occur in vertebrates other than certain fish. Van Oosterhout indicated that scientists now have clues on what to look for in different species.
He said, "Selfing would be advantageous in a species that has a low population size or excellent colonizing potential because, under these circumstances, finding a mate may be most difficult."