I dedicate this blog post to all animal lovers, to those of us perpetually fascinated by the animal kingdom, especially other fellow vertebrates, and even more specially mammals and birds. This blog is a critter edition: we have necking giraffes, killer cats, co-evolving dogs, blind mole rats showcasing evolution in action, pigeon DNA, smart dolphins, and more! Sorry enthusiasts of other science fields, today you get only zoology mixed with evolution and some neuroscience.
Let’s start with something adorable:
Specialized sensory neurons that make caresses feel good. There is something that social mammals
all have in common: we love to be caressed, petted, cuddled. It makes sense for social bonds to derive pleasure from the touch of our friends. Grooming is very often a component of social bonding. Given how important this behavior is for social animals, it is not entirely surprising that we have evolved specialized sensory cells to relay a sensation of pleasure when they are activated. A few years ago, neurobiologists at Caltech (California) found a specialized type of cell in mice: it was found only in areas of the skin with hair, and very spread out distribution of nerve endings. To find out what these neurons did, the scientists first try to study them in isolated patches of skin, but they could never get them to fire. They needed the animal itself. They then introduced a gene into mouse embryos, to mark these neurons. In other words, in the genetically engineered mice, the neurons will light up when activated. But in order to see them light up, they had to open a small hole in the mouse’s spine, and use a microscope to look at the end projections of these specialized neurons. They saw that these neurons lit up only in response to massage, stroking, basically cuddling, but not to pinching or poking. The researchers then made other engineered mice so that these mechanosensory (touch-sensitive) neurons would fire when the mice were given a drug. These mice learned to recognize a specific chamber out of three chambers, where they were given the drug, and if allowed to choose, they always went to that preferred chamber. The scientists concluded that the mice feel pleasure; they feel comforted, when these neurons are activated, and speculate that a drug may be developed in the future to impart a feeling of calmness and wellbeing in people, exactly when we feel caressed and comforted by our friends and family. Given the choice, I prefer the touch of my loved ones, or cuddling up with my dogs, to be given a drug to feel cuddled. But I can see how such a drug would help some people.
Your adorable kitty is a ruthless killer of wildlife. A recent meta-analysis of 21 different studies of feral and domestic cats shows that previous estimates of how many birds and small mammals cats kill were lower than they really are, by 2 to 4 times. Your cute cuddly kitty is an adorable efficient killer: in the United States alone cats kill approximately 2.4 billion birds and 12.3 billion small mammals (mice, rats, voles, squirrels, chipmunks, shrews and rabbits). One could of course argue that cats do a very good job of killing mice and rats and since these are considered pests and not wildlife, that is a good thing. But most of the small mammals they kill are wildlife and not mice and rats, according to the study. Environmentalists have long seen free-roaming domestic cats as an invasive species, a big threat to conservation efforts. The solution would be, of course, to keep all cats indoors but many people argue it is not fair to keep cats always inside. Dogs are already not allowed to be free-roaming and the same rule should apply to cats. Cats can get killed by traffic and other outdoor hazards as well too. For dogs it is different because dogs get to go out for walks, get to go to the dog park, etc. I'm of course not trying to tell cat owners what to do, bit this in t=interesting data and it should be taken into consideration.
Dogs evolved to eat pizza and pasta! No, it's not my dog Lola who says that, although she vehemently agrees, pizza, pasta, bagels and bread being some of her favorite treats. A new genomic study by Swedish researchers, comparing the DNA of dogs of 14 different breeds to the DNA of wolves, have identified some genomic regions that are common to all these dog breeds, but are not present in the wolves. Many of these regions contain genes involved in brain development and function, probably related to dog's friendliness towards humans as well as their uncanny ability to read our moods, understand our language and body language, follow our fingers pointing to stuff, etc. But they also found 10 genes that help dogs digest starches. Since we humans also evolved the capacity to better digest starches (and fats), around the time agriculture started, this is a great example of co-evolution. I think it's a beautiful story: best friends sharing meals evolved together. Tonight I'm cooking pasta and will give my dogs some too. So all those ultra-expensive dog foods claiming to mimic exactly the wolf diet and be the best for dogs, are probably a waste of money.
A smart dolphin asks for help? I’m sure you guys have seen this video that is all over the internet this week (it was posted on our site by a couple of us previously). The video is astonishing because it shows an adult male wild bottlenose dolphin with a fishing line wrapped around one its fins who swims up to a diver, seemingly asking for help, and remains calm while the diver disentangles the fishing line by cutting it.
This video was uploaded by a Hawaiian ecotourism company that does manta ray tours in off the coast of Kailua-Kona. Everything occurs with such calmness and deliberation, that I confess that my first thought was that it was staged and the dolphin was a trained animal. Incredibly, at one point, the dolphin returns to the surface for a breath before re-approaching the divers. It sure seems like the animal is asking for help. A dolphin scientist, Justin Gregg, thought this event was remarkable because wild dolphins are scared of scuba divers bubbles, and the animal in the video is very relaxed. He speculates that the animal could have been weak or sick, therefore appears calm. He also suggests that perhaps the dolphin, who was seeing rubbing against mooring lines to try to disentangle itself, saw the divers are simply another thing to rub himself against. This seems far-fetched to me, but it is always difficult to know for sure what is going on in the head of animals. It is very tempting to say the dolphin was asking for help. That’s what it looks like. The explanation I like best is that the dolphins in the area off the coast are used to seeing humans and have been fed by humans, so they already view humans as “helpful.” It is illegal to feed wild dolphins therefore nobody is going to asmit to the behavior, but it seems the best explanation to me.
Evolution in action in blind mole rats. Evolutionary biologists love to fight about speciation. Speciation is the process that allows two species to arise from one. Speciation happens when the members of what was once one species can no longer interbreed. There are two types: allopatric speciation and sympatric speciation. Allopatric speciation occurs when a physical barrier, such as a river, mountain chain, etc., separate two populations and after a long time, if they met again, they would not be able to interbreed because by then, the two populations would be genetically distinct. There are evolutionary biologists that say the speciation can be sympatric, that is, occur in the same place, without obvious physical barriers, due to natural variation. Sympatric speciation is controversial. Now Israeli scientists caught two populations of the Middle East blind mole rat in the act of sympatric speciation. They found that two blind mole rat (Spalax galili) populations, even though separated by a few feet of easily excavated soil, are very different based on their mitochondrial DNA, showing they are not interbreeding much. In this area, igneous basalt rock has been pushed against the chalk bedrock by past geological activity. The plants that grow above each area are different, because the soil is different, so it creates a sort of barrier even though the two populations could easily meet in their underground tunnels. The researchers have preliminary evidence that female and male mole rats taken from one soil type prefer to mate with each other even in the presence of mole rats from the other soil type. The scientists think that given enough time, these would evolve into separate species, and claims this as an example of sympatric speciation. Not so fast, says Jerry Coyne. Definitive proof would be if the animals were no longer capable of interbreeding. The Israeli scientists are expanding their observation and if they confirm that the mating preferences have changed, this could be clearly considered an example of sympatric speciation. Observable sympatric speciation events are rare, so evolutionary biologists get very excited when they can see this type of evolution in action.
Sexual selection is not responsible for the giraffe’s long neck. Observations about giraffe biology and behavior led many zoologists to propose that the giraffe’s impossibly long neck was the result of sexual selection. Male giraffes battle each other using their necks as sledgehammers, thus, sexual selection would favor those with the most powerful neck, which would win more battles and thus leave more offspring. Before sexual selection was proposed, most zoologists thought that the long neck resulted from competition for food: giraffes with longer necks would be able to reach higher into the trees and thus have access to more resources. A new study about how giraffes’ heads and necks grow points back in the direction of food competition. They examined 65 male and 71 female giraffes from two different populations, and found very small differences between male and female giraffes in terms of skull and neck mass. This goes against the sexual selection explanation, because in that case males would have ended up having longer, heavier necks than females (similar to the antlers of some male deer). In addition, the “necking” battles occur mostly in younger males, and they are contests of dominance and not really to directly gain access to females. The researchers also found no correlation between dominance and neck morphology. Ultimately more data from the fossil record will be needed to give us more clues as to why giraffes ended up with such a long neck. And no, it was not so that they could look out for land on Noah’s arc.
The genome of the domestic pigeon: Darwin was right once again. Charles Darwin was a pigeon fancier, and he maintained that all fancy domestic pigeon breeds derived from the wild rock dove (Columba livia), which is the animal that we mostly call simply "pigeon" (see photo to the left). The traits of fancy domestic pigeon breeds are sometimes so remarkable (see photos below) that many people have argued that other Columba species, in particular Columba rupestris. Scientists have just published in Science a big study sequencing the genomes of street pigeons from the US, and of 36 different fancy breeds. They are al more closely related to each other than to C. rupestris. Basically they are all C. livia. Another interesting discovery from this genetic study is that the head crests (basically feathers that grow in the reverse direction), from the smallest to some outrageously big ones, are all caused by the same recessive mutation, suggesting that the mutation evolved just once within the species.