Sea snakes have some of the most potent venoms of any snake, but most of the 60 or so species are docile, rare, or sparing with their venom. The beaked sea snake (Enhydrina schistosa) is an exception. It lives throughout Asia and Australasia, has a reputation for being aggressive, and swims in estuaries and lagoons where it often gets entangled in fishing nets. Unwary fishermen get injected with venom that’s more potent than a cobra’s or a rattlesnake’s. It’s perhaps unsurprising that this one species accounts for the vast majority of injuries and deaths from sea snake bites.
But this deadliest of sea snakes has a secret: it’s actually two sea snakes.
By analysing the beaked sea snake’s genes, Kanishka Ukuwela from the University of Adelaide has shown that the Asian individuals belong to a completely different branch of the sea snake family tree than the Australian ones. They are two species, which have evolved to look so identical that until now, everyone thought they were the same. They’re a fantastic new example of convergent evolution, when different species turn up at life’s party wearing the same clothes.
As animals get bigger, so do their brains. But the human brain is seven times bigger than that of other similarly sized animals. Our close relative, the chimpanzee, has a brain that’s just twice as big as expected for its size. And the gorilla, which can grow to be three times bigger than us, has a smaller brain than we do.
Many scientists ask why our brains have become so big. But Karina Fonseca-Azevedo and Suzana Herculano-Houzel from the Federal University of Rio de Janeiro have turned that question on its head—they want to know why other apes haven’t evolved bigger brains. (Yes, humans are apes; for this piece, I am using “apes” to mean “apes other than us”).
Their argument is simple: brains demand exceptional amounts of energy. Each gram of brain uses up more energy than each gram of body. And bigger brains, which have more neurons, consume more fuel. On their typical diets of raw foods, great apes can’t afford to fuel more neurons than they already have. To do so, they would need to spend an implausible amount of time on foraging and feeding. An ape can’t evolve a brain as big as a human’s, while still eating like an ape. Their energy budget simply wouldn’t balance.
When you think about viruses, you might wonder how they infect, how they spread, and how they kill. These questions are of natural interest—you, after all, could play host to a grand variety of lethal viruses. But do remember: it’s not all about you.
A virus’ world contains not just potential hosts, but other viruses. It has competition. This simple fact is often ignored but it has profound implications. In a new study, Lisa Bono from the University of North Carolina has shown that competition between viruses can drive them to spill over into new hosts, imperilling creatures that they never used to infect.
In North America’s Sonoran desert, there’s a fly that depends on a cactus. Thanks to a handful of changes in a gene called Neverland, Drosophila pachea can no longer make chemicals that it needs to grow and reproduce. These genetic changes represent the evolution of subservience – they inextricably bound the fly to the senita cactus, the only species with the substances the fly needs.
The Neverland gene makes a protein of the same name, which converts cholesterol into 7-dehydrocholesterol. This chemical reaction is the first of many that leads to ecdysone – a hormone that all insects need to transform from a larva into an adult. Most species make their own ecdysone but D.pachea is ill-equipped. Because of its Neverland mutations, the manufacturing process fails at the very first step. Without intervention, the fly would be permanently stuck in larval mode. Hence the name, Neverland—fly genes are named after what happens to the insect when the gene is broken.
Fortunately, in the wild, D.pachea can compensate for its genetic problem by feeding on the senita cactus. The cactus produces lathosterol—a chemical related to cholesterol. D.pachea’s version of Neverland can still process this substitute, and uses it to kickstart the production of ecdysone.
The senita is the only plant in the Sonoran desert that makes lathosterol, the only one that lets the fly bypass the deficiency that would keep it forever young. It has become the fly’s dealer, pushing out chemicals that it cannot live without, and all because of changes to a single fly gene.
Here’s yet another reason why humans are weird: menopause. During our 40s, women permanently lose the ability to have children, but continue to live for decades. In doing this, we are virtually alone in the animal kingdom. From a cold evolutionary point of view, why would an animal continue to live past the point when it could pass on its genes to the next generation? Or put it another way: why don’t we keep on making babies till we die? Why does our reproductive lifespan cut out early?
One of the most popular explanations, first proposed in the 1966, involves helpful grandmothers. Even if older women are infertile, they can still ensure that their genes cascade through future generations by caring for their children, and helping to raise their grandchildren.* There’s evidence to support this “grandmother hypothesis” in humans: It seems that mothers can indeed boost their number of grandchildren by stepping out of the reproductive rat-race as soon as their daughters join it, becoming helpers rather than competitors.
Now, Emma Foster from the University of Exeter has found similar evidence among one of the only other animals that shows menopause: the killer whale.
Every whale and dolphin evolved from a deer-like animal with slender, hoofed legs, which lived between 53 and 56 million years ago. Over time, these ancestral creatures became more streamlined, and their tails widened into flukes. They lost their hind limbs, and their front ones became paddles. And they became smarter. Today, whales and dolphins – collectively known as cetaceans – are among the most intelligent of mammals, with smarts that rival our own primate relatives.
Now, Shixia Xu from Nanjing Normal University has found that a gene called ASPM seems to have played an important role in the evolution of cetacean brains. The gene shows clear signatures of adaptive change at two points in history, when the brains of some cetaceans ballooned in size. But ASPM has also been linked to the evolution of bigger brains in another branch of the mammal family tree – ours. It went through similar bursts of accelerated evolution in the great apes, and especially in our own ancestors after they split away from chimpanzees.
It seems that both primates and cetaceans—the intellectual heavyweights of the animal world—could owe our bulging brains to changes in the same gene. “It’s a significant result,” says Michael McGowen, who studies the genetic evolution of whales at Wayne State University. “The work on ASPM shows clear evidence of adaptive evolution, and adds to the growing evidence of convergence between primates and cetaceans from a molecular perspective.”
If you only looked at mammals, you could reasonably believe that the chisellers have inherited the earth. Of all the various species of mammals, forty percent are rodents. Rats, mice, squirrels, guinea pigs… all of them have the same modus operandi. They gnaw their way into their food with self-sharpening chisel-like teeth.
Whether tiny gerbil or huge capybara, rodents eat with the same special teeth. The upper and lower jaws each have a single pair of incisors that grow continuously through their lives. The front of each tooth is made from hard enamel, while the back is made of soft dentine. As the rodent gnaws, the incisors scrape at each other, and the dentine wears away faster than the enamel. This creates a permanently sharp edge, useful for cracking into wood, nuts and flesh alike. Once gnawed, the rodent passes its food to the back of their mouths to be chewed by grinding molars.
But on the Indonesian island of Sulawesi, Jacob Esselstyn has discovered a new species of rodent that radically departs from this universal body plan: a “shrew-rat” that he calls Paucidentomys vermidax.Its name –a mash-up of Latin and Greek—gives a clue to its lifestyle. It means “worm-devouring, few-toothed mouse”.
Words like “individual” are hard to use when it comes to the black cottonwood tree. Each tree can sprout a new one that’s a clone of the original, and still connected by the same root system. This “offspring” is arguably the same tree – the same “individual” – as the “parent”. This semantic difficulty gets even worse when you consider their genes. Even though the parent and offspring are clones, it turns out that they have stark genetic differences between them.
It gets worse: when Brett Olds sequenced tissues from different parts of the same black cottonwood, he found differences in thousands of genes between the topmost bud, the lowermost branch, and the roots. In fact, the variation within a single tree can be greater than that across different trees.
As Olds told me, “This could change the classic paradigm that evolution only happens in a population rather than at an individual level.” There are uncanny parallels here to a story about cancer that I wrote last year, in which British scientists showed that a single tumour can contain a world of diversity, with different parts evolving individually from one another.
I learned about Olds’ study at the Ecological Society of America Annual Meeting and wrote about it for Nature. Head over there for the details.
Photo by Born1945
Cheetahs have two problems: their numbers are low because their habitats have disappeared over time, and they have very low genetic diversity. Neither factor bodes well for their future, but which presents them with the greatest risk of extinction? This isn’t just an academic question. It’s one with real consequences for conservation, and affects whether breeding programmes should just focus on raising more cheetahs, or should carefully mix and match parents to produce genetically diverse young.
Really, what you want is an experiment that tinkers with population size and genetic diversity independently to see which matters most. And obviously, you cannot do that with cheetahs since they are rare and hard to work with. And, you know, endangered.
Tim Wootton from the University of Chicago recognised this problem. As he told the audience at the 2012 Ecological Society of America Annual Meeting: “We needed an alternative charismatic organism.” To chuckles, he unveiled his choice: the sea palm. It’s a brown frond-like seaweed that grows on the western coast of North America. Wootton calls it “probably the world’s coolest algae”.
Twelve years ago, he and his wife Cathy Pfister bred sea palms to varying degrees of genetic diversity and transplanted them onto rocky shores in clumps of different size. Yesterday, he presented the results of the experiment. I wrote about the study for Nature News, so head over there to see what happened.
Image by Eric in SF
In Nicole King’s lab, a bacterium is making a group of tiny cells stick together. That might seem a little humdrum for a group whose members can build electric grids, create snow, and cripple nations. But King’s bacteria should not be overlooked, for they are recapping one of the most important events in the history of life: the move from one cell to many.
The cells in question are choanoflagellates – the closest living relatives of all animals. They’re not our direct ancestors, but they give us clues about what those ancestors were like when they were still swimming around as single cells. Choanoflagellates normally live in solitude, moving about with sperm-like tails and voraciously eating bacteria. But they can also form big colonies. If we can understand why this happens, we might get hints as to why our single-celled ancestors did the same.
King has now found the answer, and it’s a tantalising one. The solitary cells become sociable after being exposed a molecule called RIF-1 that’s produced by some of the bacteria that they eat. When they divide in two, the daughters normally go their separate ways; add a splash of RIF-1, and they stick together instead.
This raises an obvious question: did bacteria also help the single-celled ancestors of animals to band together? Did they contribute to the evolutionary foundation of every ant and elephant, every fish and finch? “That’s my favourite hypothesis,” says Rosie Alegado, the lead author on the new study. “Animals evolved in seas teaming with bacteria and have been passively exposed to bacterial chemical cues, intended and unintended.” But she cautions that this is still an open question.