When you look at a kangaroo or a wallaby, it’s obvious the animal is well built for bouncing around the outback. What may be less obvious is that its arms are built for fighting—if it’s male, that is. Males of these species have disproportionately long arm bones. And the more brawling a species does, the more exaggerated the difference between the beefy-armed males and their normal-limbed mates.
To understand this evolutionary quirk, we’ll need to review the rules of fighting in wallabies and kangaroos. (Together, these animals are called macropodids.)
Males wrestle each other to show their dominance and to gain access to females. The first rule of macropodid fight club is not “don’t talk about macropodid fight club,” but “kick a lot.” Read More
This month has accidentally taken on a theme of “animals putting things outside their bodies that we think should stay inside” (starfish tags, sea squirt stomachs). So this post, which first appeared in April 2013, seemed like the right one to wrap up with.
She’s apparently a picky mater but not a picky eater. The female of a certain fly species, after mating with a male, dumps his ejaculate back out of her body and onto the ground. Then she gobbles it up. Despite new hints that this behavior may help the female choose which partner fertilizes her eggs, or keep her healthy in times of famine, scientists are still a little perplexed by it.
Various female insects, spiders, and birds are known to expel the male ejaculate from their bodies after the deed is done. In some cases, it seems to let them decide which male’s sperm reaches their eggs. Females don’t always choose who mates with them, but that doesn’t mean they have no choice in their progeny’s fatherhood. (This kind of female choosiness about sperm can lead to evolutionary arms races between males and females. The “copulatory plug” is a popular tool among male insects, spiders, reptiles, and even some mammals.)
Eating the ejaculate, as Euxesta bilimeki does, is less popular. Read More
We may call someone gutless who’s acting afraid. But certain coral-reef dwellers take gutless to a whole other level: they shoot their digestive tracts out of their bodies when they feel threatened. This seems to deter nearby fish from taking a bite. Even more amazing, though, is how quickly the gutless animals grow back their organs.
Polycarpa mytiligera is a little tube-shaped creature called an ascidian, or sea squirt. It resides in tropical waters of the Indian and Pacific oceans. With its base glued firmly to a coral reef or other surface, it feeds by filtering particles from the passing current. Some sea squirts look like colorful vases arranged together on a reef. But Polycarpa mytiligera lives alone and lets other bits of sea life grow all over its body for camouflage.
Scientists first noticed in the 19th century that some sea squirts have no guts. The animals are known for regenerating missing body parts, so it seemed that they must occasionally lose their digestive organs and grow them back. But how and why remained a mystery. Read More
There’s good news for scientists who study animals that are too small to carry a GPS monitor, or that spit ID tags back out through their arms. A setup using an off-the-shelf camera can precisely capture an animal’s path in three dimensions—without anyone touching the animal.
Emmanuel de Margerie, who studies animal behavior at the University of Rennes 1 in France, says there are several reasons to seek new animal-tracking technologies. To put a GPS or other kind of tag on an animal, you have to capture and handle it, which can be stressful for your study subject. The tags themselves can be expensive and unreliable, and sometimes get lost. And “small species cannot be tagged at all because the tag is too heavy for walking or flying normally,” he says.
So de Margerie thought up a way to track animals purely by sight. He and his coauthors have dubbed it “rotational stereo videography” (RSV). It works like this: Read More
Scientists already knew starfish have superpowers. They can regenerate entire lost limbs or organs; some can even regrow a whole body from one arm. And these animals have just revealed another bizarre ability. To two Danish students, it first appeared as the power to really wreck an experiment.
At the University of Southern Denmark, students Frederik Ekholm Gaardsted Christensen and Trine Bottos Olsen were asked to tag some starfish. The task was simple: inject the Asterias rubens with microchips, the same kind that veterinarians implant in pet dogs. This would let researchers easily identify individual starfish later on. The technique had already been used successfully in sea urchins.
Starfish came to the university from local fishers who had caught them by accident. The students injected the tags into the animals as directed. But within days, those same tags showed up at the bottom of the tank. Somehow, the starfish were expelling the foreign objects from their bodies. Read More
How long could you survive as a tortoise? Sure, the basic rules are easy: Eat plants. Hide in your shell. Slow and steady wins the race. But a tortoise in danger has to make some quick decisions. Especially if it’s been flipped onto its back, slow and steady isn’t good enough. The tortoise’s best strategy, in fact, depends on its age.
Ana Golubović, a biologist at the University of Belgrade in Serbia, is interested in how the behavior of turtles and tortoises changes over their lifetimes. Baby tortoises are small and fairly soft. As they age, their shells harden and the reptiles grow—and grow, and grow. The older the tortoise, the bigger it is. (You can even estimate a tortoise’s age by counting rings on its shell, like a tree trunk.)
This means an adult tortoise can rely on its shell in ways that a younger one can’t. Golubović notes that not only do juveniles have softer shells, but they get no protection from their parents, and they’re bite-sized to some predators. So a young tortoise that gets attacked and flipped is more vulnerable than its better-armored elders are. Read More
You snooze, you lose paternity. That’s the message of a new study on wild birds in Germany. Males that wake up the earliest are able to sneakily mate with other birds’ partners. Males that sleep in, meanwhile, get stuck raising young that aren’t their own.
Great tits (Parus major) appear monogamous at first glance. They stick with one partner and cooperate to raise their young. But, like many other birds that scientists call “socially monogamous,” they sleep around. Great tit nests often contain eggs from more than one father.
North Dakota State University biologist Timothy Greives knew from previous studies that songbirds often use the early morning for their trysts. This could mean that males who are true early birds have a better chance of finding extra partners—and guarding their own partners from other males. Supporting this idea, a study in blue tits showed that males have greater mating success outside their home nests if they start singing earlier in the morning. Read More
What’s a scientist to do with 1.2 million photos, most of grass but some containing valuable data about endangered animals? Turn the whole thing over to the public, if you’re the creators of Snapshot Serengeti. This project caught the attention of tens of thousands of volunteers. Now their work has produced a massive dataset that’s already helping scientists in a range of fields.
Amputees often feel eerie sensations from their missing limbs. These “phantom limb” feelings can include pain, itching, tingling, or even a sense of trying to pick something up. Patients who lose an eye may have similar symptoms—with the addition of actual phantoms.
Phantom eye syndrome (PES) had been studied in the past, but University of Liverpool psychologist Laura Hope-Stone and her colleagues recently conducted the largest study of PES specifically in patients who’d lost an eye to cancer.
The researchers sent surveys to 239 patients who’d been treated for uveal melanoma at the Liverpool Ocular Oncology Centre. All of these patients had had one eye surgically removed. Some of their surgeries were only 4 months in the past; others had taken place almost 4 and a half years earlier. Three-quarters of the patients returned the surveys, sharing details about how they were doing in their new monocular lives. Read More
Let’s say you’re clever enough to build and use tools, but your species hasn’t learned how to manufacture pants. So you can’t store your hard-won tools in your pocket, or in a belt or box. What to do? One species of crow is showing scientists how it answers that question—and how it changes its strategy based on how likely its tools are to go missing.
New Caledonian crows, native to islands in the southwest Pacific Ocean, are renowned tool makers and users. They prey on bugs that live inside branches and plants. To fish out their prey, the birds use sticks or leaves, which they may trim and tweak to fashion into hooks.
Humans have sometimes noticed these birds trapping their tools under one foot while they munch on a bug, or stashing tools in convenient holes. It makes sense—after going to the trouble to MacGyver a fishing hook out of a plant, you wouldn’t want to lose it either. And when the birds do lose their tools, they can look distinctly peeved. Watch the bird at the beginning of this video drop its stick and fly off in a huff: Read More