False vampire bats attack a rodent in India in 2010. Photograph by Stephen Dalton, Minden Pictures/Corbis

If bats ever used a cell phone, they could forgo the version with caller ID: The mammals can identify each other by their voices, a new study says.

Bats aren’t the only mammals to use voice recognition—people do it, too. Even in the days before caller ID, a simple “Hi, it’s me,” from a close friend or loved one was usually enough to figure out who’s on the other end. Recognizing a person by voice, however, requires previous knowledge: We can’t identify a stranger on the phone by voice alone because we have never met them before.

People can, however, discriminate between a familiar voice and an unfamiliar one, even if they’ve never met the other person. We can also distinguish between two individuals by voice alone even if we’ve never met them before.

Hanna Kastein and colleagues at the University of Veterinary Medicine in Hannover, Germany, wanted to know whether bats could perform these same tasks.

“Bats are totally interesting mammals to study voice perception since they are dependent on their vocalizations for orientation and communication due to their nocturnal lifestyle. In addition, they are socially living animals that frequently communicate acoustically with other members of their species,” Kastein said. (Also see “‘Whispering’ Bat Evolved to Trick Prey.”)

Besides their social lifestyles, bats and people share a number of physical characteristics. Both produce sounds using a combination of the larynx, vocal cords, and nasal cavities. These structures work together with an animal’s physical makeup to produce an individual’s unique voice.

“In stressful situations, voices become higher pitched, or ‘squeaky,’ in bats as in humans. Also, each individual bat has a slightly different morphology, and thus its voice sounds different from any other individual, just as voices in humans differ individually,” Kastein said.

You Had Me at Hello

Kastein and colleagues wanted to know whether bats could use vocal calls to identify individuals with which they shared a roost, and whether they could use these same calls to distinguish between two different individuals.

The researchers worked with the greater false vampire bat (Megaderma lyra) because the species has a rich array of calls that it uses in several contexts. (See “Vampire Bats Have Vein Sensors.”)

The team observed two groups of bats kept in separate artificial roosts for two months. They hypothesized that bats that had the most body contact while roosting would form the closest relationships. Kastein and colleagues then recorded various vocal calls from both groups of bats.

When Kastein played the recording of a vocal call over a loudspeaker, bats in both roosts universally turned their heads toward the speaker regardless of whether the call was from a bat with which they had close body contact, a bat from the same roost, or a bat from the other roost. (Interactive: Hear tropical bat calls.)

Given that the artificial roosts had much lower rates of vocal calls, due to the lack of stimuli, the researchers thought that this response could be due to the novelty of hearing any type of vocalization.

Discriminating Bat

So the team did a second set of experiments in which they had a bat listen to the call of their “friend” until the call didn’t create any type of behavioral response, such as turning the head. This means the listening bat had become habituated to the call, according to the study, published recently in the journal Animal Cognition.

Then, the scientists alternated playing a vocalization of the bat friend with that of an unfamiliar bat. The listening bats were significantly more likely to turn their heads toward the call of their friend—indicating both that they recognized their friend and that they could distinguish between individual vocalizations. (Also see “‘Talking’ Whale Could Imitate Human Voice.”)

“In our study, we found that the … false vampire bat is able to discriminate between different voices, including both known or unknown individuals,” Kastein noted.

“However, to what extent bats are able to label an unknown bat as unknown, we cannot say.” She suspects that in real life, recognizing other bats by their voices is aided by smell and, to a lesser extent, vision.

We’ve known for years that female black widow spiders and other arachnids eat males during mating.

Now, new research shows that males of a type of ground spider known as Micaria sociabilis also eat females, and scientists are trying to figure out what motivates this behavior.

A male M. sociabilis attacks his mate. Photograph courtesy Lenka Sentenská

More than just a first date from hell, sexual cannibalism happens when one member of a species kills and eats a member of the opposite sex immediately before, after, or during mating.

This behavior is most common in arachnids like the black widow, as well as other invertebrates like insects, gastropods, and copepods. Most commonly, the female eats the male—but occasionally, the reverse is true. Male sexual cannibalism has been observed in another species of spider, Allocosa brasiliensis, and in crustaceans, but previously researchers had no idea what factors drove this behavior. (Watch a video of a male spider attacking a female one.)

Ultimate Sacrifice

On the surface, this seems like a pretty weird way to pass along your genes to the next generation. To scientists, however, sexual cannibalism can make a lot of sense. When prey is scarce and males are abundant, males become extremely valuable as a food source to females, noted study co-author Lenka Sentenská, a biologist at Masaryk University in Brno, Czech Republic.

Females invest much more energy into egg production than males do in sperm production, which tends to make them pickier about who they mate with. (See “Male Spiders Give ‘Back Rubs’ to Seduce Their Mates.”)

As well, not all males seem to fight being cannibalized, said Sentenská, whose study appeared recently in the journal Behavioral Ecology and Sociobiology.

“Males of some species voluntarily sacrifice themselves to a female, because such behavior enables them to copulate longer and pass more sperm. Males who are trying to escape usually copulate for a shorter time. Sometimes, this behavior is also viewed as an extreme paternal investment of the male, who sacrifices his body to provide nutrients to his future offspring via the female,” she said.

Deadly Dinner Date

Researchers have traditionally focused on female sexual cannibalism, both because of its relative frequency and perhaps because of humanity’s attraction to the femme fatale.

A female M. sociabilis. Photograph courtesy Stano Pekar

But in some species, such as M. sociabilis, females are also in danger of being eaten by males. Sentenská and her colleague Stano Pekár examined what factors drove male sexual cannibalism in this particular species. (Watch a video of the world’s largest spider.)

These small brown spiders commonly live in trees in Central Europe. M. sociabilis has two generations of offspring each year—one in spring and one in early summer. Whereas females born in the springtime frequently survive to see the arrival of the second generation in June or July, male numbers drop precipitously in May. This creates some significant factors that the authors believe could lead to sexual cannibalism.

Males can choose among females of different size and quality—for instance, by mating with older females from the spring generation or with virgin females from the summer generation. (See pictures of spiders up close.)

To test whether these factors actually affect whether males ate females, Sentenská and Pekár paired adult male M. sociabilis with females of various ages and sizes. They found that larger males were more aggressive and much more likely to attack a female regardless of her age or size. Overall, however, males of any size were more likely to attack and eat females from the older generation.

Picky Males

Between 44 and 52 percent of the time, the males and females mated. In 20 percent of all of these trials, the male attacked and ate the female during copulation. However, the frequency of cannibalism varied depending on time of year. (See “‘Castrated’ Spiders Are Better Fighters, Study Says.”)

“Males are usually viewed as nondiscriminatory machines eager to impress and mate with every female encountered. Our study shows that males can be choosy and that they can present their choice in a quite extreme way—by killing unpreferred females. Moreover, despite the rarity of such behavior, this strategy seems to be advantageous for them,” Sentenská said.

These results might help explain male sexual cannibalism in other species, the researchers concluded.

However, Sentenská quipped, “I definitely would not encourage readers to try this strategy in their personal life.”

The species, named Tinkerbella nana after Peter Pan’s miniscule assistant, averages 250 micrometers long. That’s 0.01 of an inch—little wider than the diameter of a human hair.

The new fairyfly is named after Tinkerbell. Photograph courtesy Jennifer Read

T. nana is a type of wasp known as a fairyfly (Mymaridae). Don’t be fooled by its sweet-sounding name, small size, or the delicate fringe on its wings—T. nana and other fairyflies are parasites that live on the eggs of other insect species. (Also see “Parasitic Wasp Swarm Unleashed to Fight Pests.”)

Finding such small insects is no easy task—researcher John Huber of Natural Resources Canada and entomologist John Noyes of the Natural History Museum in London, England, found the fairyflies only by sifting through leaf litter and debris, looking for eggs. Huber and Noyes recently published their find in the Journal of Hymenoptera Research.

Despite its microscopic size, T. nana isn’t the smallest known insect. That particular honor goes to Kikiki huna, a species of fairyfly found on Hawaii. This fly is only half as long as T. nana, and scientists don’t know whether it’s possible for insects to get any smaller.

Meet some other members of the animal kingdom known for their remarkably petite physiques.

Smallest primate. Southeast Asia’s pygmy tarsiers (Tarsius) and Madagascar‘s mouse lemurs (Microcebus) seem to be in a running competition for world’s smallest primate.

A tarsier munches on an insect in the Philippines. Photograph by Erik Sellgren, Your Shot

At approximately 4 inches (10 centimeters) long, the pygmy tarsier can fit inside a person’s fist, and full-grown adults frequently weigh in at less than two ounces (57 grams). Mouse lemurs have a combined head, body, and tail length of less than 10.6 inches (27 centimeters), according to the National Primate Research Center at the University of Wisconsin.  The smallest mouse lemur, M. berthae, weighs about 1.1 ounces (31 grams). (Read about new mouse lemurs discovered in 2006.)

A new species of mouse lemur found in Madagascar. Photograph by Mark Thiessen, National Geographic

Primatologist Mireya Mayor holding a newfound mouse lemur in Madagascar. Photograph by Mark Thiessen, National Geographic

Smallest vertebrate. The world’s smallest vertebrate, a frog known as Paedophryne amanuensis, was discovered in 2009 in Papua New Guinea. The frog measures only 0.3 of an inch (7.7 millimeters), according to a 2012 study in the journal PLoS ONE.

Dwarfed by a dime, Paedophryne amauensis inhabits New Guinean rain forests. Photograph courtesy Christopher Austin

Scientists found the frog the way they found T. nana—by sorting through leaf litter, although no one currently knows exactly what it eats or how it lives.

Smallest mammal. The Kitti’s hog-nosed bat (Craseonycteris thonglongyai), a.k.a. the bumblebee bat, has been dubbed one of the world’s smallest mammals. A threatened native of Thailand and Myanmar (Burma), the bumblebee bat weighs in at 0.071 of an ounce (2 grams) and measures only 1.1 to 1.3 inches (2.8 to 3.3 centimeters) in length.

Kitti’s hognosed bat, or the bumblebee bat, is the world’s smallest bat. Photograph by Merlin D. Tuttle, Science Source

Smallest bird. Continuing with the bee theme, meet Mellisuga helenae, the bee hummingbird, which lives on Cuba and nearby islands. Weighing 0.056 to 0.071 of an ounce (less than 2 grams) and measuring 2.0 to 2.4 inches (5 to 6 centimeters) long, M. helenae has won the title of world’s smallest bird. Not only is it bee-size, M. helenae enjoys feeding on nectar like its namesake. Unlike a bee, however, M. helenae has bright, iridescent feathers.

A bee hummingbird perches on a twig in Cuba. Photograph by Steve Winter, National Geographic

Tell us—what small critters have you come across?

Researchers have known since the 1950s that Tetrahymena—a freshwater ciliate covered in hair-like projections—has seven sexes, Types I through VII, and each type can mate with every sex but its own (such that Type I can mate with individuals that have Types II through VII, and so on). But exactly how Tetrahymena determines its sexes remained a mystery—until now. (Get a genetics overview.)

The freshwater critter Tetrahymena is covered in hair-like projections. Image by Aaron J. Bell, Science Source

Scientists have discovered that a random process of DNA splicing and rearrangement during development determines which sexes Tetrahymena will become.

Tetrahymena mostly reproduces asexually, dividing into two identical daughter cells. When Tetrahymena reproduces, one of its two nuclei—known as the germline nucleus—doesn’t do anything, and only the genes on its other nucleus—called the somatic nucleus—are activated. (See “Synthetic DNA Created, Evolves on Its Own.”)

But when food is scarce, the organism can opt for sexual reproduction, which creates novel genetic combinations that may give daughter cells a better chance of surviving in a harsh environment.

Such tough conditions also drive the organisms to develop more sexes—and thus more mating options, said study leader Eduardo Orias, a biologist at the University of California, Santa Barbara.

“If you only have two sexes, there’s only a 50 percent chance that someone you meet will be of the right type,” Orias said. With seven different sexes, however, a ciliate’s chances of meeting Mr. or Mrs. Right increase to about 85 percent.

Seven Genes for Seven Sexes

But when scientists sequenced the Tetrahymena genome in 2006, they didn’t find any genes that jumped out at them as determining sex.

So in the lab, Orias and colleagues first deprived a strain of Tetrahymena of food to induce it to start mating sexually. To make things even more confusing, the strain used by the researchers had only six sexes, not seven.

Catching the ciliates in flagrante delicto, the researchers compared genes that were expressed during mating and those that were expressed during normal growth. The researchers identified one pair of genes that was active only during mating. When they inactivated this pair of genes, Tetrahymena no longer mated, making those genes good candidates for those that determine sex. (Also see “Heat Triggers Sex Change in Lizards by ‘Turning Off’ Key Gene.”)

The researchers then scoured the genome sequence of Tetrahymena, and they found six copies of these mating-type genes in the germline nucleus, one for each sex.

These six sexes were clustered together on a small segment of DNA, one right after the other. This array is bookended by the standard start and finish of a protein-coding gene. The next question the scientists had to answer was how Tetrahymena got from six or seven pairs of mating-type genes down to one.

Mating Roulette

In experiments, the team showed that, during mating, Tetrahymena randomly sort, snip, and rearrange the six or seven pairs of the mating-type genes until the organism is left with just one pair of genes on its somatic nucleus.

“It’s as if they had a roulette wheel with numbers on it and just gave it a spin,” Orias said.

Tetrahymena retains the full array of mating-type gene pairs on its germline nucleus for the next time it finds itself hungry and hears the soft sounds of Barry White playing in the background, so to speak.

What’s more, this one gene pair is likely expressed on the membrane of the cell. This makes sense, Orias explained, because Tetrahymena frequently touch before mating. It could be that this touch lets Tetrahymena determine the sex of the individual, not unlike how parents frequently dress their babies in either pink or blue to indicate gender. (See “Behind the Scenes at a NatGeo Baby Cover Shoot.”)

Understanding Tetrahymena‘s strange sexual behaviors has a larger impact than just figuring out how one particular group of species finds a mate, the team added. The research also can help researchers better understand how DNA is spliced and recombined in other species, which is important in the development of immune function and even potentially cancer cells.

If Tetrahymena ever needed a dating service, however, these seven-sexed critters would likely pay a fortune.

Female Ulidiid flies (Euxesta bilimeki) expel and eat ejaculate because it allows them to decide who will be the best father of their offspring, a new study says. (Also see “Female Flies Put Up a Fight to Keep Sex Short.”)

Just as lovers, partners, and spouses frequently exchange gifts and share meals during courtship and beyond, so do many animal species.

Usually, the male builds a nest or provides a food gift for the female, in order to help convince her that his genes are high quality and that he would make a good father. In these cases, the female is directly choosing her mate, and the offspring benefit both from the good genes of the parents and from the food or housing provided by the male. (Read about weird mating and courtship rituals.)

But for some species of mammals, birds, and insects—in which fertilization is internal—the effects of female choice are less obvious to the male. In a process called cryptic female choice, a female can exert control over her baby daddy by expelling a male’s sperm after copulation.

This method is especially effective in species like E. bilimeki, in which the female can store the male’s sperm before using it to fertilize her eggs, according to the study authors.

The Mating Game

Researchers knew that female E. bilimeki would expel and eat sperm, but didn’t know why.

To find out, Christian Luis Rodriguez-Enriquez and colleagues at the Institute for Ecology in Vera Cruz, Mexico, watched 74 pairs of E. bilimeki court and mate. They found that all of the females expelled and ate at least some of the ejaculate that they’d stored in specialized sperm-storage organs. (See “Sperm Tracked in 3-D—A First.”)

When the team looked closer, they found that one-quarter of the females purged all of the ejaculate from their bodies. This meant that the males with whom they recently mated would have no chance of fathering their offspring, according to the study, published recently in the journal Behavioral Ecology and Sociology.

Since females mate multiple times, the amount of ejaculate she expels can help increase or decrease the likelihood that a male will be the father of her offspring. The more sperm she expels, the less likely the male will pass on his genes.

So what makes an undesirable suitor? A male fly that’s too aggressive, the study found: The longer a male pursued a female before mating made the female more likely to expel and consume the ejaculate.

Rodriguez-Enriquez and colleagues hypothesize that this may be because the female grows tired of evading the male and copulates simply to avoid his amorous pursuits. Expelling the sperm means that she doesn’t have to worry about making babies with males who don’t know the meaning of “back off!”

Plus, she just might get some nutritious liquid in exchange for her hassle.

Sperm: It’s Not What’s For Dinner

Ulidiid flies live in the deserts of Mexico and the U.S. Southwest, where water and food are scarce. That made researchers initially suspect that the female flies might be eating the ejaculate for sustenance. (Also see “Beetles Are Thirsty for Sex.”)

To test this theory, the team raised females on one of several different diets: a very high-quality diet containing protein, sugar, and water; a high-quality diet containing sugar and water; water only; and neither water nor food.

The females that were given no food or water for two days did live longer if they consumed expelled sperm after mating, but this consumption had no effect on the survival or longevity of the well-fed flies.

But the starved and thirsty flies were no more likely than the well-fed flies to consume the ejaculate—showing that they don’t eat it for food.

Although mysteries remain about the sperm-eating flies, the results show that females continue to play a crucial role in selecting the father of their offspring—even after mating.

Discarded food atop a compost pile at an organic farm. Photograph by Hannele Lahti, National Geographic

People have been using manure as fertilizer for millennia. But scientists now believe they can turn human urine into liquid gold—as composting material. 

The premise is simple: Pee is rich in nitrogen, which plants desperately need. Commercial fertilizers boost plant growth and yield by providing abundant nitrogen to the plant’s roots.

Of course, commercial fertilizers can harm the environment if they get into lakes and streams. As well, not all farmers in the developing world can afford to buy fertilizer for their crops. Enter pee. (Related: “Human Pee With Ash Is a Natural Fertilizer.“)

Debendra Shrestha, a researcher at Tribhuvan University in Kathmandu, Nepal, noted that Nepalese farmers have been applying human urine to their crops for centuries.

Unlike commercial fertilizers, urine is free and abundantly available. Plus, it doesn’t seem to have any harmful environmental effects. The main question that remained was whether it actually worked: Would plants grow better when their soil was treated with human urine?

Pee Power

To answer this question, Shrestha and colleagues grew sweet peppers (Capsicum annum) in soil that had various combinations of human urine, compost, and urea—the main nitrogen-containing chemical in human urine. The urine was collected from communal toilets in Kathmandu, whereas the compost was sourced from cow manure. (Also see “Urine Battery Turns Pee Into Power.”)

The plants grown in soil that had a combination of human urine and compost grew the tallest, yielded the most peppers, and had the most total fruit weight per plant, according to the study, published recently in the journal Scientia Horticulturae.

The scientists say the pee was so effective because of several factors working together. For instance, the mix of compost and urine decreased the amount of nitrogen lost in the soil while making more carbon available to the plants.

“We need to start moving toward the application of urine in combination with compost,” Shrestha said in an interview with <a ” href=”http://www.scidev.net/en/south-asia/news/crop-thrives-on-urine-compost-mix.html” target=”_blank”>SciDev.Net.

To Pee or Not to Pee?

Still, not everyone is convinced. Other studies in Africa that used a combination of human urine, human manure, and poultry manure found that these substances did not yield more crops than commercial fertilizers did. (See “Human Waste to Revive Haitian Farmland?”)

The use of human urine, noted Surendra Pradhan, a researcher at the International Water Management Institute who is based in Ghana, has major problems, according to SciDev.Net.

For one, although urine is freely available, not all cultures might take to the idea of using it on their crops. What’s more, it needs to be used along with compost for it to be effective, since urine alone doesn’t have enough nutrients to sustain plant growth over several years. (Read more about sustainable agriculture.)

Last, although commercially available fertilizers aren’t free, many governments do subsidize their availability, which may decrease the overall appeal of urine-based fertilizers.

Surviving such a long time between meals takes a lot of guts—literally. New research shows that a trout can change the size of its intestinal tract based on the availability of salmon eggs, its favorite food. (Also see “Bulging Mutant Trout Created: More Muscle, More Meat.”)

University of Washington biologists Jonny Armstrong and Morgan Bond were studying the Dolly Varden’s migration patterns when they came upon a mystery.

The Dolly Varden trout during spawning season. Photograph by Morgan Bond, University of Washington

For the first four or five years of life, Dolly Varden trout travel to the northern Pacific to feed during the spring and summer, then return to freshwater streams and lakes during winter. After that, the fish stay in fresh water, never returning to the sea for the rest of their 12-year life span. (Watch a video of trout spawning.)

But the Dolly Varden population that Bond and Armstrong were studying lived in Alaska‘s Chignik Lake (map), where there’s very little food in the lake and surrounding streams for part of the year.

The trout get one opportunity to feed: When salmon arrive in these waters to spawn. The researchers couldn’t identify any other food source for the trout. (Read more about Pacific salmon.)

When the researchers calculated how much energy the fish likely obtained from the annual surplus of salmon eggs and compared this with the estimated number of calories the fish would need to survive for an entire year, they found a thousand-calorie deficit.

“We were stumped. How could these large fish—the most [fertile] in the whole [Chignik Lake] population—get enough energy to survive and reproduce in these barren waters?” Armstrong said.

“Blown Away”

But the team had a breakthrough when they thought about similar predators that sit and wait for their prey, like pythons. These animals can go for long periods of time without eating. (Related: “Python Hearts Double in Size—Now We Know Why.”)

What’s more, migrating birds can expand their guts as they gorge to put on weight and then shrink them back down to make their long journeys easier.

With this in mind, the researchers measured the gut sizes of Dolly Varden trout in Chignik Lake before and after the annual salmon run—and found that the trouts’ guts were 2.6 times larger immediately after the salmon run.

“We were blown away that animals could rapidly and reversibly change their organ size—not just stretch the tissue out, but actually build bigger organs,” said Armstrong. Their study appeared March 19 in the Journal of Animal Ecology.

Feast and Famine

The extra intestinal tissue allows the trout to take advantage of the food surplus, eating a lot and obtaining as much energy as possible. When the salmon eggs run out, however, the fish economize. Smaller guts might not allow the fish to eat as much, but they also require much less energy to maintain. (See pictures of the world’s largest trout in the wild.)

“It’s like trying to choose a car—a sports car can go the fastest, but it also burns up the most gas. Digestive flexibility is a valuable tactic for life in a world of feast and famine—it allows animals to eat more when food is plentiful and to burn less energy when food is scarce,” Armstrong noted.

Dolly Varden trout caught in August (top), after spawning season, are bigger than fish caught in June (below). Photograph by Morgan Bond, University of Washington

“What was neat is that this was really just a serendipitous side project. We were both actively pursuing our other projects and snuck in this field sampling on the side,” he added.

“Morgan and some other field researchers basically just went fishing while they were taking a break from other sampling. They brought the fish back to the lab, and when Morgan and when I needed a break from our dissertation projects, we’d squeeze in some time for lab work,” Armstrong said.

Trout Not Harmed by Salmon Fishing

Besides helping us understand the extreme flexibility of the fish digestive system, Armstrong and Bond’s research also provides insight into the current management of salmon fisheries. (Also see “Alaska’s Clash Over Salmon and Gold Goes National.”)

Since up to half of all salmon in an individual population are harvested for commercial fisheries, scientists have wondered whether removing the salmon harms their predators.

At least Dolly Varden trout populations appear unharmed by current salmon harvesting levels—perhaps due to their extraordinary ability to wait a year for their next meal.

So the next time you find yourself counting the seconds until lunch, take solace in the fact that you won’t have to wait nearly as long as this trout.

But when it comes to the creepy factor, Osedax worms—nicknamed “zombie worms”—beat out even the goriest movies.

A recent study reveals that these faceless, mouthless worms enjoy making sweet, sweet love inside decomposing whale skeletons that have fallen to the bottom of the ocean floor.

An adult female bone-eating worm. Photograph courtesy Norio Miyamoto/Naturwissenschaften.

Originally discovered off the coast of California in 2002, Osedax—whose name is derived from the Latin for “bone eating”—got its name for its peculiar living quarters: the bones of a decomposing gray whale. These deep-dwelling worms secrete acid to bore through the hard outer bones of whales and other large vertebrate skeletons to reach the nutritious oils within. (See “New Worms Eat (and Eat and Eat) Only on Dead Whales.”)

The weirdness doesn’t stop there. Unlike many species of animals, female Osedax worms are much larger than the males—so much larger, in fact, that 50 to 100 males can live inside the female in one of nature’s most bizarre harems.

The males’ sole purpose, as far as researchers have been able to figure out, are as sperm providers. But scientists still didn’t know exactly how these worms developed and reproduced.

The Bare Bones 

To study the worms’ mating process, Norio Miyamoto and colleagues at the Japan Agency for Marine-Earth Science and Technology obtained a set of whale bones from off the coast of Cape Noma, Japan. (See more pictures of bone-eating worms.)

The researchers added pieces of these bones to the petri dishes containing O. japonicus larvae of both genders. Six weeks after the female larvae moved into their new whale-bone homes, they began to pump out eggs, which were then fertilized by the dwarf males.

“This rapid sexual maturation of females, alongside the male dwarfism which was observed, enables the worms to reproduce effectively in the food-rich but highly isolated habitat of whale bones,” according to the study, published recently in the journal Naturwissenschaften.

Whale skeletons are often separated by huge distances, which would make finding mates difficult—hence, the females carry a lot of little males with them. (Related: “Dead Whale Contains a Bounty of Life.”)

The team also found that the newborn larvae could survive for ten days in the water without eating—allowing the young animals to drift until they find other promising corpses.

These findings help explain not only the function of the worms’ odd sexual behaviors, but also their success at rapidly colonizing dead whales around the world.

Kinky gets the job done—at least for these zombie worms.

One species of sea cucumber, however, didn’t appear to get the memo: Scientists have discovered that the giant California sea cucumber (Parastichopus californicus) actually uses its anus as a second mouth.

A giant sea cucumber in the Pacific Ocean. Photograph by Gerald and Buff Corsi, Visuals Unlimited

Scientists already knew that the marine invertebrate, which lives in the shallow ocean waters off the Pacific coast of North America, breathes with its butt.

Because they don’t have lungs, sea cucumbers rely on respiratory trees, a set of long tubes running down either side of the body with a lot of different branches. P. californicus is shaped like a hollow tube, with a mouth at one end and its anus at the other.

The respiratory trees receive oxygen when water is pumped through their anus using the muscles of their cloaca, an opening at the end of the intestinal tract. (Watch a video of sea cucumbers fighting with their guts—literally.)

The 20-inch-long (50-centimeter-long) animal is no slouch: It can pump 3.5 to 4 cups of water per hour through its anus, transferring the oxygen from the water into its respiratory trees, which then oxygenates its cells.

A diver holds a sea cucumber off Ft. Lauderdale, Florida. Photograph by Lois Booth, My Shot

The sheer amount of water flowing into the anus got two invertebrate biologists thinking—since P. californicus sifts plankton and other small particles from water using its tentacles, could it do something similar using its anus?

Though “an animal is not expected to ingest food through its anus”—as William Jaeckle and Richard Strathmann note at the beginning of their study in the March issue of Invertebrate Biology—it turns out the answer is yes.

Multipurpose Anus

Their first hint that the sea cucumber anus was doing triple duty came from a structure called the rete mirabile, a set of blood vessels that connect the sea cucumber’s respiratory trees with its gut.

Initially, Jaeckle, of Illinois Wesleyan University, and Strathmann, of the University of Washington, thought that the rete mirabile was used to transfer oxygen from the respiratory trees to the gut. But if P. californicus were obtaining food via its anus, it would likely use the rete mirabile to transfer the food to the gut. (Watch a video of a hairy sea cucumber.)

A sea cucumber in Okinawa, Japan. Photograph by Gary Hughes, Your Shot

To test their idea, the team fed several sea cucumbers radioactive algae, which also contained iron particles. The iron and radioactivity proved an easy way to trace the food as it traveled through the sea cucumber’s body. For instance, areas of the body with the highest concentrations of radioactivity would provide clues about which orifices the animal was using to eat.

Not surprisingly, the results showed that the sea cucumbers ate the algae through their actual mouths, which then traveled through their gut. (See pictures of colorful sea creatures.)

However, the researchers also found a high level of radioactivity when they looked at the rete mirabile. The only way that those blood vessels could have such a high concentration of radioactivity is if the animal was transferring food from the respiratory trees to the gut via the rete mirabile.

Bottom Feeders

When the scientists looked at tissue samples from the sea cucumber under the microscope, they found even more hints that P. californicus was using its anus as a second mouth: They found small pieces of algae and iron in the respiratory trees near the anus.  (Also see “Why Sea Slugs Dispose of Their Own Penises.”)

In addition, the sea cucumber’s respiratory trees had small, finger-like projections known as microvilli that are normally found in the gut and aid with nutrient absorption. This also indicated that P. californicus was absorbing food using its anus and respiratory trees.

The authors conclude that although they looked only for evidence of bipolar feeding—the more formal and perhaps polite term for eating with your butt—in one species of sea cucumber, many other species are likely to use this method of feeding.

Bottom line? Eating with your butt may not be all that unusual.

A 520-million-year-old fossil arthropod known as a fuxianhuiid literally shoveled food in its mouth. Photograph courtesy Jie Yang.

For most animals, the rules of anatomy are pretty straightforward: head and brain at the very top and legs at the bottom. But a 520 million-year-old fossil animal recently discovered in southern China breaks both of these rules.

Called a fuxianhuiid, this common ancestor of modern arthropods—insects, spiders, and sea creatures like lobsters—has some pretty bizarre traits—its legs are under its mouth, and its spine extends far above its brain.

The find, published earlier this week in the journal Nature, is one of the oldest animal fossils ever discovered, said lead researcher Javier Ortega-Hernandez, of the University of Cambridge in the U.K. (Also see “Biggest Fossil Spider Found.”)

“Fuxianhuiids have been crucial for understanding the origin of the arthropod head, which provides a lot of information that allows biologists to reconstruct the evolutionary history of arthropods,” Ortega-Hernandez said.

For instance, the head “allows us to reconstruct what the common ancestor looked like, which is of great importance for fleshing out the evolutionary relationships of the group.”

Scientists knew that fuxianhuiids (pronounced foo-see-an-who-eeds) existed from previous excavations in China’s Yunnan Province (map). However, the creatures’ hard outer shells, or carapaces, that hindered attacks from predators also prevented researchers from seeing the full array of their body parts. What’s more, their softer antennae and legs generally decay before they have a chance to fossilize, unlike the carapace.

The newfound fuxianhuiid specimens, however, were fossilized in an unusual position that preserved the arrangement of their soft bodies.

Stuffing Its Face

A closer examination of the fossils revealed that the fuxianhuiids had legs directly under their mouths that they used to literally shovel food into their mouths on their seafloor habitat.

Ortega-Hernandez said that these legs are quite possibly the earliest examples of limbs used for eating—though their existence has been controversial, since previous fuxianhuiid fossils did not clearly show these limbs. (Also see “New Genitalia-Headed Fish Is Evolutionary Mystery.”)

“These structures have been subject of a heated debate for almost a decade,” he said.

Another unusual find from the fuxianhuiid fossils is that a small piece of neural cord protruded from their brains—making the species the oldest example of a nervous system that stretches out above the head. Only a few types of modern animals still have this anatomy.

Getting a clear look at the fuxianhuiid head is important, since evolutionary biologists frequently use the head to determine the closest relative of an unknown arthropod species.

If you look at modern insects and crustaceans, it seems like fuxianhuiid features have disappeared over the course of 520 million years. Look more closely, however, and Ortega-Hernandez said that the forces of natural selection have simply altered these structures, not eliminated them.

Take spiders, for instance. The fuxianhuiids’ antennae have become the spider’s fangs, and the legs under their mouths have become pedipalps—a pair of specialized appendages that the spider uses to get food into its mouth.

A reconstruction of what one species of fuxianhuiid may have looked like when alive. Illustration courtesy Javier Ortega-Hernandez

“Very Strange Animals”

Fuxianhuiids flourished during the Cambrian period, from 540 to 485 million years ago, which was when life first became very complex—and very weird. (See a prehistoric time line.)

It was the planet’s experimental period, like a teenager flitting between fashion fads, trying to find himself. Some of the best Cambrian fossils have been found in the Yunnan Province and Canada‘s Burgess Shale. (Read about a 3-foot (0.9-meter) “shrimp” that dominated the Cambrian seas.)

That’s why fuxianhuiids, in all of their weirdness, provide valuable insights into the ancestors of not just of arthropods, but of all animals, Ortega-Hernandez said. He and his team, which includes scientists from Yunnan University in China, are currently analyzing other finds from the area, hoping to tease out more of what Cambrian life was like as a whole.

“Fuxianhuiids in general are very strange animals,” he said—so don’t be surprised if the other finds are equally bizarre.

Another species of fossil fuxianhuiid. Photograph courtesy Jie Yang.