Blogs / The Loom

Memo to Sci-Fi Movie Development Dept.

Re: Plant People Concept

Here are the specifics for the aliens in our next movie, VOYAGE TO THE PLANET OF THE PLANT PEOPLE. The people there are vegetarians, eating salads, seaweed drinks, etc. They are green, because when they digest their meals, their bodies move some of the plant matter to their skin. They use it to capture energy from the sun through photosynthesis. So the aliens sit outside in the sun a lot, getting lots of energy and growing to huge sizes, which is why they’re so hard to kill when Earthlings show up. I see the people from Blue Man Group–just add some yellow and we’re set. Or maybe William Dafoe?

Behold, Hollywood, the sea slug Elysia chlorotica. This emerald green slug grazes on algae. As it breaks down the algae, it preserves their photosynthetic structures, called plastids. The plastids are shipped to the surface of its body, where they can continue to photosynthesize. The slug thus makes a living as plants do. And it turns a beautiful shade of green along the way.

Recently, some scientists discovered that the sea slug is even more plantlike than previously thought thought. They wondered if some genes from the algae the slug ate had become incorporated into their own DNA. This movement of genes is called horizontal gene transfer. It’s common among bacteria, which swap genes for antibiotic resistance and such. It’s not as common among multicellular creatures, but it has happened a number of times. For example, our ancestors swallowed up bacteria that eventually became our mitochondria, the structures in our cells that use oxygen to generate energy. Mitochondria still have some of their own bacterial genes, and other bacterial genes have moved into our own DNA. The ancestors of green algae and plants swallowed up photosynthetic bacteria and harnessed their ability to photosynthesize. Those bacteria became plastids. The p of the genes from the plastids are now part of the DNA of plants.

Mary Rumpho of the University of Maine and her colleagues suspected that something like this had happened to the sea slugs. They were struck by the fact that the plastids continue to function in the slugs for months after they’ve been extracted from algae. But plastids normally can’t function on their own. They need help from proteins encoded by genes that are now carried in the algae’s DNA. It was possible that the slugs were making the proteins for their plastids.

So Rumpho’s group gathered up some sea slugs off the coast of Martha’s Vineyard and took a look at their DNA. They also took a look at the DNA of the one species of algae that the slugs put in their skin. As they suspected, the plasmids don’t have all the genes necessary for photosynthesis. The scientists discovered a crucial photosynthesis gene, called psbO, in the DNA of the slug. In fact, the sequence of the slug’s psbO gene is identical to the one in the species of algae that supplies them with their plastids.

Now that scientists can peer into genomes without too much difficulty, they’re probably going to find a lot of these gene transfers, and some of them are going to turn out to be big leaps–like the jump from the plant kingdom to the animal kingdom.  What I want to know is how a photosynthesis gene from the nucleus of algae got integrated into the DNA of the slug that eats it. I also want to know why other plant-eating animals didn’t merge with their food as well. Why aren’t sheep green? And finally, when will Voyage to the Planet of the Plant People wrap up?

Until then, you can enjoy Rumpho’s great web site dedicated to this symbiosis–complete with slug videos.

Just spoke today on New Hampshire Public Radio about my latest Discover column on the battle between the parents. Listen here.

Nature lies.

Organisms send signals to each other, and often those signals are honest–in other words, when another organism receives the signal, it can reliably use it to figure something out about the sender. Male fiddler crabs, like the one shown here, send a big, loud signal with their oversized claw. Often, that signal essentially says, “Do not mess with me.” And in many cases, that’s good advice.

Sometimes, though, it’s a major bluff.

(more…)

As I wrote in my story in the New York Times today, much of your DNA is shut down by molecules collectively known as epigenetic marks. Roughly 100 sites are notable exceptions to this rule: your mother’s copy of these stretches of DNA are silenced, while your father’s are free to make proteins and RNA–or vice versa. This imbalance, known as imprinting, is utterly fascinating, and when the imprinting system goes awry–when dad’s genes start becoming active when they shouldn’t, or when mom’s genes go quiet when they should be active–the effects can be catastrophic. I first became familiar with gene imprinting while writing an article for the Times a couple years ago about a scientist at Harvard named David Haig, who has a theory for how it had evolved. He argues that gene imprinting is the result of an evolutionary tug of war between mothers and fathers, because mammalian parents have an evolutionary conflict of interest.

Now a couple scientists are extending this conflict theory to explain why so many imprinted genes are turning up in psychiatric disorders, ranging from autism to schizophrenia. They argue that the conflict between our parents plays out in our brains, too. This morning you can read about this provocative idea in my latest Discover column on the brain, or in this article by Benedict Carey in the Times.

These articles ought to come with a disclaimer: when we write about conflicts between parents, we are speaking metaphorically. We are actually referring to the rise and fall of different genes over millions of years, as natural selection acts on populations of thousands or millions of individuals. Just because you inherited imprinted genes from your mother or father doesn’t mean they sat down and drew up plans for using to maximize their own reproductive success (unless your father was Dr. Evil, I suppose…) Nevertheless, this new research does add an extra dimension to Philip Larkin’s ode to all miserable kids, which Larkin recites in this video (if you haven’t heard it before, just be warned that there’s some old-time Anglosaxon profanity along the way):

Hah!

Last month I wrote in the New York Times about Spore, a highly anticipated game that let you follow life from microbe to intergalactic civilization. I had a couple evolutionary biologists play around with it to get their reaction, and contact a couple others who had had a chance to play the game. They gave it positive–though decidely mixed–marks. In today’s issue of Science, John Bohanon describes the reactions of a number of other biologists, and they really don’t like it at all. Here’s what Ryan Gregory has to say:

“The problem is that the game features virtually none of the key ingredients of evolution as we understand it,” says Gregory. “There’s no shared common descent between species, since every single creature in Spore can trace its lineage back to a different single-celled organism that arrives from space.” Spore also lacks biological variation. “When you run into other members of your species, they are always identical clones of you.” Nor does it have natural selection. “There are no consequences for dying, since you just reappear at your nest.” Your organism does evolve, says Gregory, “in the sense that it changes over time, but it really has no bearing on how things evolve in the real world.”

I believe the article is behind a subscription wall, but you can check out a wiki Bohanan set up for an in-depth report card.

…because you weren’t quite slaked by my post yesterday on this creature, check out Darren Naish’s typically fascinating and inforomation-dense post today at Tetrapod Zoology.

In recent years, dinosaurs have gotten awfully cute. They’re no longer Victorian lumps of saggy muscle. A lot of them are not even frightening. They’re fuzzy, feathery little critters. But, as I’ve written before, cuteness is not what drives paleontologists to hunt for these fossils and spend years poring over them in laboratories.

Today brings another case in point. Chinese paleontologists published a report in Nature about a new fossil they’ve named Epidexipteryx hui. The fossil comes from rocks that are somewhere between 152 and 168 million years old. Much of its skeleton was preserved on a slab, along with impressions on the surface of its body that the scientists conclude were feathers. At this point, the discovery of yet another feathered dinosaur is not big news. But Epidexipteryx looks to be important for several reasons.

One is its kinship to birds.  The researchers compared 363 traits on Epidexipteryx and 19 other dinosaurs and birds. Along with its feathers, Epidexipteryx has many traits that link it closely to birds, such as a humerus that’s as long as its femur. In fact, the analysis reveals this dinosaur was one of the closest relatives to Archaeopteryx and all other birds capable of flight.

Obviously, Epidexipteryx was no flier itself. It didn’t have the right feathers on its arms to give it enough lift. Nor did the many other feathered dinosaurs scientists have unearthed over the past 15 years. To understand what function feathers served before flight, paleontologists have looked to living birds. Flight feathers are just one of many different kinds found on them. Fuzzy feathers help insulate birds, and many paleontologists have proposed that insulation was one of the early adaptations of feathers on dinosaurs.

Epidexipteryx means “display wing,” and the name is apt. Its remarkable tail feathers could not have helped it fly, nor could they have kept it warm. Instead, they bear a striking resemblance to the extravagant feathers of some living species of birds, like the widowbird. Male birds use long tail feathers to attract females, possibly by advertising their good genes. The tails evolve to great lengths, even though the males have to pay a cost–either in the energy to grow them, or in the drag they create during flight.

Epidexipteryx is compelling evidence that feathers had already evolved for display before birds used them to fly. It should not be surprising that other feathered dinosaur fossils discovered so far don’t show signs of long tail feathers. Only a small number of living bird species have evolved to widowbird-like extremes, for reasons scientists don’t yet understand. Sexual selection must have been at work in Jurassic dinosaurs, just as it is at work in their living cousins, the birds. And just as birds have evolved many different ways to show off–from rooster combs to red patches on red-winged blackbirds–it makes sense that dinosaurs evolved their own courtships too.

Source: Zhang et al, A bizarre Jurassic maniraptoran from China with elongate ribbon-like feathers, Nature 23 October 2008 doi:10.1038/nature07447

Evolution: Education and Outreach is a relatively new journal that helps teachers, students, and scientists teach evolutionary biology. I’ve just contributed a piece to a special issue on the evolution of the eye. I take a look at a couple examples of eyes evolving in weird ways. One example may be familiar to readers of this blog–the flatfish. The other example, illustrated here, is the stalk-eyed fly. The point I try to make in the piece is that these examples are not just a couple exhibits at a freak show. They tell us something important about the forces at work in evolution. Thankfully, the editors have made the journal open-access, so you can go read it for yourself.

One of Darwin’s lesser known obsessions was with faces–how we make different faces, and what they say about us. Today, psychologists and neuroscientists are discovering the hidden conversation between brain and face, with a lot of tools Darwin never had–MRI scanners, subcutaneous eletrodes, and Botox.

Botox?

Indeed. In fact, some recent studies with Botox raise the weird possibility that our national love affair with that face-freezing drug may be subtly altering the emotions of millions of people.

For more, check out my new column on the brain in the November issue of Discover.

[Illustration from Darwin’s The Expression of Emotions via Darwin Online]

[10/16/08 Correction appended: see end of post]

When our ancestors moved ashore some 360 million years ago, they underwent a lot of changes as they evolved from ocean-swimming fish to land-walking tetrapods. For one thing, they needed feet instead of fins. Paleontologists have discovered a series of fossils that document the early evolution of limb bones in our aquatic ancestors, showing how long bones first evolved, then parts of the wrist and digit-like bones, and finally full-blown feet. But lots of other changes happened at the same time, producing traits in tetrapods not found in other animals. Tetrapods, for example, are good at hearing airborne sounds, thanks to small bones that can vibrate in their ears. The earliest of those bones to have evolved was the stapes. But the stapes did not come from nowhere.

New clues to the origin of our ears  were published today in the journal Nature. They come from a fossil known as Tiktaalik, a 370-million-year old fish with a lot of tetrapod features, such as neck and a very leg-like fin. (See this Loom post on Tiktaalik for details.) Tiktaalik’s discoverers first published a description of the beast back in 2006, but there was only space for a tiny portion of the details they uncovered in its skeleton. Today they report on Tiktaalik’s skull. (more…)

I just got back from a pretty remarkable lecture by the husband-and-wife team of Peter and Rosemary Grant. The Grants started studying Darwin’s finches on the Galapagos Islands in 1973, and they made some of the most detailed studies of evolution in the wild ever carried out. Their adventures were chronicled 14 years ago by Jonathan Weiner in the Beak of the Finch, which won the Pulitzer Prize. But the Grants did not stop. They continued to observe the birds evolve, and make fascinating new discoveries. In 2002, I wrote an article on what they’d learned after some three decades of research. Six years have passed since then, and at today’s lecture I learned that they retired from Princeton just last month. But apparently they’re still going back to the Galapagos. So their lecture today was not a summing up, but yet another status report.

(more…)