I just spent over a month hibernating out west this winter, hanging out with some very excellent dogs. Which reminds me, dogs. Batrachoseps attenuatus, Procyon lotor, Sceloporus occidentalis — hell, I just said Phalacrocoracidae to my roommate today. Our IB 104 field trip friends are amazing… but what about dogs? Sure, they’ve been busying sniffing out cancer, protecting penguins, and helping us understand human conditions, from allergies and OCD to a rare genetic disease called centronuclear myopathy. But does science know every thing there is to know about our best friends? No, of course not! So, here’s a roundup of some recent dog studies.
How we understand each other
The human brain has a “voice area” that helps us picture our friends and gauge their moods just by hearing them. To see if dog brains have dedicated voice areas, researchers trained 11 dogs to lie still in an fMRI while wearing headphones that deliver sounds: 200 dog and human noises like whining, barking, and laughing. (Please check out this picture of a happy bunch of dogs posing with a brain scanner, and this video of the doggy subjects.) After doing the same with 22 humans, they found that dog brains can process voices in the same way that human brains do, by picking up on the emotional content in voices. Happy sounds, like a baby’s giggle, made the primary auditory cortex of both human and dog participants light up more than with unhappy sounds, like a man’s hacking cough. And since these voice areas are in similar locations in us and dogs, the researchers think they likely evolved 100 million years ago, when we shared our last common ancestor. [Current Biology via Science, New Scientist]
We’re pretty good at telling the difference between lonely or angry barks and happy barks (scientists confirmed this years ago). But what exactly are we listening for? To find out, researchers devised an online survey to assess how we perceive emotions in vocalizations. Shorter calls (from humans or dogs) were regarded as more emotionally positive than longer calls, according to 39 human volunteers. And higher pitched samples were rated as more emotionally intense than lower pitched sounds. [Biology Letters via Science]
Love, it’s all in the left eyebrow. Researchers used high-speed video cameras to capture the facial expressions of 12 dogs wearing blue tape on their heads to pinpoint subtle facial tics. Each were led into a room divided by partitions, and when the curtains would part for 800 milliseconds, the dog might see its owner, an unfamiliar person, its favorite squeaky ball, or an object it feared, like nail clippers. When the dogs saw their owners, they lifted their eyebrows way up high (watch this video of a poodle). Strangers caused them to move their left ears back slightly, a sign of caution. Nail clippers caused them to twitch their right ears — perhaps a sign of a learned response, which is governed by the left side of the brain. [Behavioural Processes via Science]
Did we take wolf pups from the wild, or did wolves start hanging around human settlements to eat scraps? No one really knows (or rather, agrees on) when and where the first domestication took place. Fossils place the earliest dogs at 33,000 years ago in Siberia, whereas DNA studies of modern dogs put domestication 10,000 years ago in Southeast Asia or the Middle East.
According to a recent study — the largest collection of ancient dog and wolf DNA sequences ever published — European hunter-gatherers domesticated dogs from wolves around 20,000 to 30,000 years ago. After sequencing the complete genomes of mitochondria from 18 ancient dogs and wolves, researchers found that nearly all modern dogs share a close kinship with ancient dogs or wolves from Europe. The common ancestor of domestic dogs, they found, lived in Europe 18,800–32,100 years ago. [Science via Nature News]
Another study focusing on North American dogs found that a least one indigenous breed has genetic roots in this continent dating back 1,000 years or more. When humans first came to the Americas from Asia, they likely brought dogs with them but most of their descendants were eradicated when Columbus and Europeans arrived in America. Dogs who survived were thought to have interbred with European dogs over time. A team of researchers looked at the mitochondrial DNA of modern breeds with indigenous origins: the Inuit sled dog, Alaskan malamute, Greenland dog, Chihuahua, Xoloitzcuintli (Mexican hairless dog), and Perro Sín Pelo del Peru (Peruvian hairless dog). All but the malamute had very little influence of European dogs. A portion of Chihuahua DNA was an exact match to an ancient dog found in the two American continents — suggesting that it descended from original canine inhabitants who haven’t mixed with European breeds. Additionally, most breeds in the study had a lot in common with modern East Asian dogs, which makes sense if indigenous American breeds descended from the first dogs that traveled from Asia to the Americas. [Proceedings of the Royal Society B via NPR]
One ancient Asian breed in particular, the Tibetan mastiff (bred from the Chinese native dog), can presently be found living comfortably on the Tibetan Plateau, which averages an elevation of 4,500 meters. To find out what mutations created this altitude-loving dog, a team gathered DNA from 32 Tibetan mastiffs, 20 Chinese native dogs, and 14 wolves. They found that the mutations were in 11 genes, including 9 genes with clear relevance to living that high: energy metabolism for efficiently turning food into energy where the air is thin, hemoglobin building to help chaperone oxygen through the bloodstream, and new blood vessel construction. One other mutation — for a molecule that builds up oxygen-starved cells — has also turned up in studies of Tibetan people. [Molecular Biology and Evolution via Discover]
Researchers looking for differences between the genomes of 12 wolves and 60 dogs identified 36 regions of the genome that set dogs apart from wolves. (These aren’t the differences responsible for variation between breeds.) They found that, unlike wolves, dogs possess 10 genes for digesting starches and breaking down fats — suggesting that domestication may have adapted dogs to thrive on the foods we eat. [Nature via Nature News]
What’s in a wag? Six years ago, scientists showed us how a swing to the right means dogs are happy, while a swing to the left means they’re anxious. But can dogs distinguish between the wags of other dogs? Researchers monitored the heart rates and reactions of 43 dogs while showing them videos of other dogs wagging their tails. (Like in this video.) Turns out, every dog understands the meaning in a left or right tail wag. When the video dog wagged to the left — an activation of the right side of the brain, linked with flight from danger — the test dogs looked anxious and their heart rates increased. But when the video dog swung its tail to the right — activating the left hemisphere, linked with social approachability — the test dogs stayed calm and relaxed. [Current Biology via Los Angeles Times, Science]
Wolf packs are typically made up of a nuclear family led by a single breeding pair, whereas dogs often live with unrelated (and often fixed) dogs. To see if dogs have a social hierarchy similar to wolves, researchers outfitted 6 dogs with GPS harnesses to track their paths while they traveled off-leash through an open grassy field with their owner 14 times (watch this video of them romping). They found that dogs who consistently took the lead were older, more aggressive, and more trainable than the dogs who followed. These most dominant dogs were followed in nearly 75% of their interactions with another dog. The main leader is a spayed female, which suggests that dogs organize themselves into a hierarchy even without a breeding pair to direct them. [PLoS Computation Biology via Science, New Scientist]
Do dogs present themselves differently when they’re protecting their food versus when they’re goofing around? Researchers let dogs choose between photos of two other dogs, while simultaneously playing a recording of either a food or a play growl: One photo is of a dog whose size matched the growl (which reflects the length of a dog’s vocal tract), and the other is of a dog either larger or smaller than the growler. When the listening dogs heard the food growl, they focused on the image of the dog who’s the size of the growling dog. But when they heard the play growl, they fixed their eyes on the photo of the bigger dog — even though the growl was made by a smaller one. This suggests that dogs give an honest growl when guarding their food. But a small dog making a big-dog growl during play probably knows that the other dog can see its size and recognizes that it’s just making a joke. (Ha!) [Applied Animal Behaviour Science via Science]
And of course, physics and poop!
Ah, the familiar wet dog shake. Do all furry mammals dry themselves this way? Using high-speed video equipment, researchers studied 16 sopping wet species, including dogs, rats tigers, and bears. They found that each tunes its shaking speed to get as dry as possible without wasting that much energy. Small animals have to shake the fastest to generate the force required to overcome the surface tension that holds water to fur. With large animals, their size makes it easier to generate sufficient force, so they don’t have to move as fast to reach a similar degree of dryness. Additionally, loose skin whips fluids much faster, generating forces up to 70 times that of gravity! Make sure to watch this amazing pan-taxonomic video to the tune of Blue Danube. [Journal of the Royal Society Interface via Nature News]
Migratory animals like birds and whales have been known to use the orientation of Earth’s magnetic field for navigation. Turns out, dogs align themselves to Earth’s magnetic field when they’re pooping. Researchers spent two years observing 5,582 pee breaks and 1,893 defecation stops. When the field was stable, dogs preferred to squat along the North-South axis and actively avoided the East-West axis. (That’s without the influence of leashes, fire hydrants, or fences.) During periods of instability — when the sun’s magnetic field and solar winds vary its orientation — the dogs didn’t show any preference for the North-South axis. Speaking of poo, in at least one Italian city, every dog will be given a blood test to create a DNA database of pet dogs; when poop is cleaned off the streets, they can be tested to see if they match any dog on file. [Frontiers in Zoology via Discover]
Update March 6: I just noticed a “doggy science” hot topics link in Science.
Images: J. Fang