Wednesday, December 24, 2008

Small and Blue and Beautiful

Yesterday I blogged about something very small.

Today I'd like to call your attention to some articles that talk about something very big.

Forty years ago today, astronauts took this historic photo, "Earthrise". I didn't remember that until reading the editorials in the Times, of course, since I wasn't around yet. Some say that this image helped jump-start the environmental movement.

Anyway, the articles from today and from 1968 are worth checking out. Here is today's editorial reflecting on 1968 and now; this op-ed piece observes that while *we* may be fragile, life on earth has endured worse than humans and survived. From the first editorial, click on the "Related Articles" links to download some of the original articles from 1968, which are not available as web pages. This photograph is also so famous that it has its own Wikipedia page.

From the 1968 editorial:
To see the earth as it truly is, small and blue and beautiful in that eternal silence where it floats, is to see ourselves as riders on the earth together, brothers on that bright loveliness in the eternal cold — brothers who know now they are truly brothers.

PS: For more on "Earthrise" and a short video clip from the Apollo 8 mission, visit this Dot Earth post from today.

Tuesday, December 23, 2008

The 40 Million Year Old Virgins

Imagine, on this cold near-solstice day, that in the spring you go out to a nearby pond and collect a sample of water. You bring it home, put a drop on a microscope slide, and take a look at the pond's microcosm. Zooming around your sample are a wide variety of "wee beasties" -- you might see a blobby amoeba, a diflagellate like Chlamydomonas, and many other single-cell organisms.

Then a large, mostly transparent creature comes into focus. It doesn't look like all the others. It's far more complex, like a mechanical sea creature in miniature. Something like this:

Beautiful, isn't it?

This is a rotifer, a tiny aquatic animal in the phylum Rotifera. It may be small, but it is bilaterally symmetric and has a distinct head. It pulls in food particles with the wheel-like structure (hence "rotifer" or "wheel-bearer") around its mouth.

The rotifer pictured above is, however, special for another reason. This is a bdelloid rotifer (the b is silent). You are looking at a species that has not mated in at least 40 million years.

All bdelloid rotifers are female, and they reproduce by parthenogenesis. (Olivia Judson talks about them at length in her excellent book, Dr. Tatiana's Sex Advice to All Creation, and wrote a column about them in June.) This is highly unusual, since it is generally thought that gene exchange is an important mechanism for evolution. Yet with no sexual reproduction, how could the bdelloids have speciated so intensely (there are estimated to be 350 species) and persisted for so long?

Researchers at Harvard and Woods Hole may have the answer. In a paper published in Nature in May, geneticists found that when they analyzed rotifer DNA, they found genes known to occur in plants, fungi, and bacteria. This evidence suggests that rotifers have been engaging in horizontal gene transfer (HGT).

HGT is a well-known phenomenon, but it was primarily known from single-celled organisms. For example, many bacteria are known to incorporate novel genes from other members of the population, or even from other species. When you only have one cell, it's not too hard to get a novel gene into that cell. Most animals, which are by definition multicellular, can't do this; most of us pass our genes to our offspring via specialized reproductive cells, which are typically hidden away inside gonads. Unless novel genes make it to the sex cells and can therefore be passed on to the next generation, HGT has not taken place. (Passing genes to your offspring is vertical inheritance.)

Bdelloids, however, appear to be capable of massive horizontal gene transfer. Gladyshev et al. point out that this is not a case of rotifers simply retaining genes that are common to all life; that case is both extremely unlikely and not supported by the data. Instead, they suggest,

It may be that HGT is facilitated by membrane disruption and DNA fragmentation and repair associated with the repeated desiccation and recovery experienced in typical bdelloid habitats, allowing DNA in ingested or other environmental material to enter bdelloid genomes.

With their proclivity for moist habitats, bdelloids also run the risk of dessication. They are able to withstand repeated dessication; in fact, it might be necessary for the continued success of the entire class, since this appears to be the mechanism by which they gain new genetic material. The authors conclude,

Although the adaptive importance of such massive HGT remains to be elucidated, it is evident that such events have frequently occurred in the genomes of bdelloid rotifers, probably mediated by their unusual lifestyle.

So, in conclusion, bdelloids have done away with sex as we know it, but periodically get turned into rotifer jerky, incorporate new genes while their cells are cracked open, and when reconstituted and repaired produce more copies of themselves, thus passing new genes to the next generation.

Lots of questions remain; for example, what are rotifers doing with all these new genes? (One example is a bacterial gene for cell walls; no one knows how an animal might make use of a cell wall.) I will keep you posted on all rotifer-related news updates. Stay tuned!

Gladyshev, E. et al. "Massive Horizontal Gene Transfer in Bdelloid Rotifers." Science 30 May 2008: Vol. 320. no. 5880, pp. 1210 - 1213

Judson, O. "The Weird Sisters" The New York Times, June 3, 2008.

Monday, December 15, 2008

Plants Fighting Back

On Tuesday I reached into the container of cilantro from the grocery store and quickly pulled my hand back in surprise. Something had hurt me! But what?

My thoughts went to some alarming places. Bits of metal? Shards of glass? I felt like I had been pricked by something sharp, but there were no marks on my fingertips. No blood was drawn.

I dumped all of the cilantro into a colander and moved it around with a fork. There in the middle was the culprit. Initially its camouflage had concealed it from sight, but on closer inspection it stood out from its surroundings.

Clearly, those are not cilantro leaves. Any guesses?

It turned out my instinct was correct, because the first page I pulled up on Wikipedia was stinging nettle, where I saw the above picture. The plant mixed with my cilantro was the spitting image.

What makes a stinging nettle sting? The sting is caused by a combination of chemicals, not just by the hairs alone which, although sharp, are tiny. Tiny and hollow, and filled with a combination of chemicals that give a noticeable irritation: acetylcholine, serotonin, and perhaps most importantly, histamine and possibly formic acid. Yikes.

Surprisingly, nettles are easily tamed, and can be made into tea or even eaten when young ( and cooked). They're also good for your hair, feature prominently in hippie-dippie shampoos, and are mixed into cattle feed to give the bovines shiny coats. My nettle, however, was transferred by fork to the trash bin, as I was in no mood to attempt to tame it. (And my hair is already quite shiny, thank you.) I do admire it for fighting back, though. As a vegetarian, I'm not really used to food that puts up much of a struggle, so this was an interesting interaction between me and a plant.

But I think I'll stick with cilantro just the same.

Thursday, December 4, 2008

Wild Edibles Seafood Market, or, What Not to Buy

Over the long weekend, I visited Grand Central Station to check out the holiday marketplace. While we were there, our group also visited the food markets . I love the temple of dairy that is Murray's Cheeses, and Penzey's Spices is always a treat.

And then I was face to face with a red snapper.

I don't often spend time near the seafood counter at the grocery store, nor do I actively seek out fishmongers on a regular basis. But I can recognize a red snapper, and I was mildly perturbed to see one on display at Wild Edibles Fish Market. I decided to leave one of my Seafood Watch seafood guides with whoever was on duty and send an email to the company when I got home.

Then I looked closer. There was a sign near the snapper with a bright red fish symbol and a description of why red snapper is not a recommended seafood choice. I surveyed the rest of the catch of the day; every fish was marked with a sign, and a not insignificant number carried the red "Avoid" tag. A sign hanging over the counter informed me that Wild Edibles was working with the Blue Ocean Institute to help people decide which seafood to buy.

They even had wallet-sized seafood guides available at the counter.

I was horrified. They were actually selling the fish that their own signs declared threatened or endangered. I asked the woman working the counter, "How can you sell this when you know that it's endangered?" Her response: "Well, we want the customers to decide. If they tell us to stop selling it, we'll stop selling it."

Let's tell them.

Tell them that they ought to know better. Tell them that they do know better. Let them know you don't want to see fish on the menu that, by any account, would be better described as "Endangered Species" than "Catch of the Day". And while you're at it, tell your local fish seller too. Go to your grocery store and see if they're selling red snapper, orange roughy, Chilean seabass, or any other endangered fish. Give them a seafood guide, or two, or ten.

While you're at it, you might want to let the Blue Ocean Institute know what you think of their endorsement, as well. Shame on them for lending their name to an irresponsible fish merchant.