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.
Owls don't need eyes in the back of their heads to see what's behind them — they can just swivel their heads all the way around. In fact, many owl species, such as the barred owl, can rotate their heads 270 degrees in each direction, which means they can look to the left by rotating all the way to the right, or vice versa.
But how do they do it without severing their arteries or preventing blood from reaching the brain? An illustrator and a physician at the Johns Hopkins University School of Medicine teamed up to find out.
"Until now, brain imaging specialists like me who deal with human injuries caused by trauma to arteries in the head and neck have always been puzzled as to why rapid, twisting head movements did not leave thousands of owls lying dead on the forest floor from stroke," said study author Dr. Philippe Gailloud, in a statement from the university.
If humans tried to rotate our heads so rapidly or far, we'd tear the lining of our arteries, which would cause clots to form and lead to a stroke (besides also breaking our necks), he added. "The carotid and vertebral arteries in the neck of most animals — including owls and humans — are very fragile and highly susceptible to even minor tears of the vessel lining."
Looking inside owls
To get a glimpse of the owl's blood vessels when their necks were turning, the duo injected dye into the blood vessels of a dozen dead owls and used a CT scan to visualize the shimmering fluid spreading throughout the birds' arteries like blood, said Fabian de Kok-Mercado, who performed the work while getting a master's in medical illustration at Johns Hopkins. (He is now an illustrator at the Howard Hughes Medical Institute in Chevy Chase, Md.) The researchers then twisted the dead owls' heads to see what happened. [Video: Watch the owls' necks twist.]
After creating the CT scan images, the researchers injected a plastic-like substance into the veins of dead snowy, barred and great horned owls and dissected the animals, drawing the routes and locations of the vessels.
They found a number of previously undiscovered and unique traits, de Kok-Mercado told OurAmazingPlanet. For one, the owls' neck bones, or vertebrae, contain holes that are much larger than those found in other birds or humans. In humans, the hole in the vertebra is about the same size as the artery, but in owls the hole is about 10 times larger than the artery, according to the study, published today (Jan. 31) in the journal Science. These holes, or canals, likely hold air sacks meant to cushion the twisting motion of the head, de Kok-Mercado said.
"We also noticed right away that these canals were absent in the bottom two vertebra of the neck," de Kok-Mercado said. This gives the cord-like vessels some slack when the bird twists its head.
Fabian de Kok-Mercado (left) and Dr. Philippe Gailloud give a CT scan to a dead owl to learn how its blood vessels withstand the rapid, up-to-270-degree turns their heads make.Fabian de Kok-Mercado and Dr. Philippe Gailloud
The large holes and "slack" at the bottom of the neck help explain why the vessels don't break. But they don't explain why the supply of blood isn't cut off when an owl turns its head — with so much twisting, the vessels are bound to become partially blocked.
Blood to the brain
The team noticed that the vertebral artery enlarges slightly as it approaches the brain, which is unusual and not seen in many other animals (like the trunk of a tree, vessels generally get smaller as they get farther from the heart). The authors think that these enlarged areas may function as reservoirs in which blood can pool, so that the brain has extra blood to work with as the head swivels around, de Kok-Mercado said.
The blood vessels near the brain are also highly connected. A vessel called the patent trigeminal artery connects the front and the back of the owl's brain, which helps supply the organ with as much blood as possible.
Why do owls need to crane their necks to such an extreme degree? It's because their eyes are tubular, built almost like telescopes, giving them amazing vision, de Kok-Mercado said. But unlike humans, who have roughly spherical eyes, owls cannot move them about easily, so they have to rotate their heads.
The finding is just another example of how the birds are perfectly adapted to suit their environment, enabling them to see despite having relatively fixed eyes.
"I hope it gives people more of an appreciation of the life on this planet," de Kok-Mercado said.
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