Archive for the ‘Biology’ Category

On the left is the African Clawed Frog (Xenopus laevis), while its cousin (the Western Clawed Frog, Xenopus tropicalis), sits on the right. Image provided courtesy of Robert Grainger.

Platannas are 18 species of clawed frogs native to sub-Saharan Africa. Their genus name, Xenopus, means “strange foot,” in reference to the curved claws present on each hind foot. Two members of this genus, Xenopus laevis (the African Clawed Frog) and Xenopus tropicalis (the Western Clawed Frog), are also model organisms studied by biologists to understand the basics of vertebrate development and vertebrate genetics. Yesterday, scientists announced that one of these species, the Western Clawed Frog, became the first amphibian to have its genome sequenced.

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The threespine stickleback made a brief appearance in yesterday’s New York Times. I pay attention to such things (albeit one day late) because I study threespine sticklebacks and their close relatives for my thesis research on the evolution of sex chromosomes.

However, the stickleback’s appearance yesterday had nothing to do with my research. But, a team from the University of Bonn, led by Marion Mehlis, looked at the threespine stickleback to address a very specific question: cannibalism. Many animals, for one reason or another, eat their young. Sticklebacks are no exception. Male sticklebacks guard nests of fertilized eggs during the breeding season (female sticklebacks play no part in parenting). But, sometimes, a male will eat some or all of the eggs in his nest. Why? What triggers this behavior?

It certainly seems counterproductive. Male sticklebacks do all the work in the breeding season: defending a territory, building a nest, courting female after female, chasing a female away once she lays her eggs in the nest, fertilizing the nest, and caring for the eggs until they hatch. Why would any male in his right mind go to all the effort of building a nest a courting a female when he’s just going to devour his kids before they hatch? Well, as it turns out, he might do that when those aren’t his kids in the nest.

In the stickleback field (as in other fields), there is another group of males — the sneaker males. These males don’t typically build nests and defend territories. They lurk near a courting couple, waiting until a female has laid her eggs in another male’s nest. Then, the sneaker male enters the nest (usually while the hard-working male is busy chasing away the female) and fertilizes the eggs. Sneaker male (now sneaker dad) swims away, leaving the hapless hard-working male to tend his offspring.

Mehlis and colleagues wondered: do stickleback males eat the eggs in their nest when those eggs were fertilized by another male? They conducted trials to test this, switching batches of eggs (we call them “clutches”) in a nest tended by one male with eggs that were fertilized by another male. As it turns out, a male stickleback is much more likely to consume eggs if those eggs weren’t fertilized by him — if he wasn’t the dad. Mehlis and colleagues aren’t exactly sure what kind of signal the male is sensing that indicates paternity, but it’s likely some sort of olfactory (“smell”) cue.

The study sheds some light on the puzzle of male stickleback cannibalism. As for the type of signal at work in these fish, stay tuned!

Image of female (upper) and male (lower) threespine sticklebacks provided courtesy of Dr. Joseph Ross.

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One of the fascinating puzzles of evolutionary biology is how old structures change over time to acquire new functions or features. We can ask the “how” on multiple levels:

  • What genetic changes occurred?
  • What physiological changes occurred?
  • Did ecological factors contribute?
  • How quickly did the new function or feature arise?

The list of questions can go on and on.  However, scientists don’t always have tools at their disposal to answer everything.  For extinct organisms, we have only the fossil record.  Molecular biologists like me don’t get DNA to play with in those cases (usually). Physiologists don’t get muscle and bone samples. Thus, we can’t fully answer how whale fins developed from an ancestor who walked on solid ground. Though we have whales here today, all those walking ancestors died millions of years ago.

But, even with these limitations, we can still learn something about how older structures can change to acquire new functions. Recently, two biologists published an account of a “new” feature derived from an “old” structure: the cobra’s hood. In cobras and several other groups of snakes, the ribs, muscles, and skin near the head and neck (as much as snakes have a neck) can spread out away from the body’s core, forming an elaborate display hood when the animal is startled or threatened.

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In 2007, a reindeer herder and his two sons found this remarkably well-preserved baby woolly mammoth frozen solid in the Yamal-Nenets Autonomous Okrug (District) in northern Russia. The herder named her (for it is indeed a she) Lyuba, after his wife. The International Mammoth Committee, a consortium of scientists dedicated to the preservation and study of mammoth remains, has safeguarded and studied Lyuba ever since. Usually quartered at the Shemanovsky Yamal-Nenets Museum and Exhibition Centre in Salekhard, Russia, she is beginning a tour across the United States. Her first stop is Chicago’s Field Museum of Natural History.

Scientists report that Lyuba lived a tragically short life. Yet, the unique circumstances of her death have permitted us to learn a great deal about her mammoth kin, who roamed the planet as recently as ten millennia ago. Some 42,000 years ago, when Lyuba was just one month old and still nursing on her mother’s milk, fell into a muddy river bank. Struggling in vain to free herself, she sank and suffocated in the muck. Her remains froze in the permafrost, slowing decay and preserving soft tissue, skin, hair, and even stomach contents.

In short, Lyuba (pronounced Lee-OO-bah) is a rare and Earth-shattering find. As far as mammoth remains go, we’re used to finding skeletons, occasionally clumps of hair or tissue, or one or two mummified remains. A whole frozen animal can (and in this case, has) revealed a lot. CAT and MRI scans of her soft tissues have shown us how her innards are arranged. Stomach contents revealed that she’d still been nursing when she died. Hair and skin samples have even given molecular biologists like me something to drool over: a rare specimen of intact mammoth DNA!

Lyuba’s tour of the United States will hopefully draw attention to the problems faced by the International Mammoth Committee. Most woolly mammoth specimens (skeletal or otherwise) that have been recovered frozen and relatively well-preserved in permafrost. However, as Siberian permafrost melts for good, no one knows how many undiscovered mammoth specimens there are that will begin to thaw and decay. The International Mammoth Committee is racing against time to unearth mammoth remains and preserve them for study. Otherwise, we’ll only have a handful of samples like Lyuba to help us understand these elephant relatives that roamed the northern latitudes with our ancestors.

If you find yourself in Chicago up through 6 September 2010, head on over to the Field Museum and see Lyuba for yourself. The exhibit will also go to Boston, Jersey City, Saint Louis, Denver, San Diego, and Anchorage.

Image of Lyuba, a one-month old female woolly mammoth (Mammuthus primigenius) preserved by Siberian permafrost, is provided courtesy of the International Mammoth Committee and Francis Latreille.

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I’ve been so busy this past week that I completely missed the exciting news from the world of biology: a second bird genome has been sequenced. A genome is the sum of all the genetic material in an individual or organism — all the genes, all the regulatory sequences that control when and where genes are turned on, and all the other DNA sequences that might have a purpose we don’t yet know about. While a good number of genomes of vertebrates (backboned animals) have been sequenced1, up until now the chicken had been the sole bird to have its genome sequenced.

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The New York Times Magazine has a wonderful article out on the phenomenon of homosexuality among animals. Ignored by many biologists for over a century thanks to human taboos on the subject, same-sex pairing is now acknowledged among many different types of animals, including birds, mammals, and even insects. Now, peer-reviewed literature cites instances of homosexuality in nearly 500 different species, including the fish I study, the stickleback.

Not all of these published accounts include lifelong same-sex pairing, or even sex between two members of the same sex. Homosexual behavior in different animal species is very dependent on the typical sexual and breeding behaviors of that species. For example, among stickleback fishes, males mate with multiple females during the breeding season, and vice versa. Typically, breeding males establish and defend a territory against other fish, and build a nest. When the nest is ready, they court passing females in a complex courtship display that has been studied by ethologists for a century. An enamored female will enter the nest just long enough to lay her eggs, then the male will quickly fertilize the eggs and chase the female away. He cares for the fertilized eggs and newly-hatched larvae, until the larvae grow large enough to swim away on their own. In a species like the stickleback, the sexes already have a minimal interaction with one another: court and breed. There is no sex for pleasure, and there is no lifelong bonding. Thus, reports of homosexual behavior among the sticklebacks is similarly limited: accounts of one male attempting to court another male to enter his nest. No homosexual sex, and no homosexual parenting.

The New York Times Magazine article takes similar care to parse the accounts of homosexuality in the animal kingdom: each instance must be viewed through the lens of the animal’s unique life history. But, with these mounting accounts of homosexuality among animals, how do we now view human homosexuality? One interpretation would simply see same-sex attraction in humans as just another natural occurrence of homosexuality among animals (after all, humans are animals). Given the universal observation of homosexuality among all known human cultures and societies, this would seem to fit that model: among all humans everywhere, homosexuality occurs at a small rate (3-5%). Our rate is lower than homosexuality other animals, and perhaps larger than others. But, homosexuality remains most controversial in us.

I could go on and on. The first paper I wrote in college defended the theory that homosexuality in human males is biological in nature: gay men have no more control over their sexuality than their straight or bisexual counterparts. However, lucky for you, I am meeting with my thesis committee today. Thus, I have to stop here, and let the New York Times Magazine take over.

Regardless of your views, the New York Times Magazine article is definitely worth a read:
“Can Animals Be Gay?”

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This must be earthquake awareness week. Yesterday, I was browsing science news reports, and found a nice summary from the BBC News on an interesting and entirely unintended collision between herpetology and seismology.

Last year, a powerful 6.3-magnitude earthquake struck L’Aquila, Italy, killing over 300 and devastating local towns. As it just so happened, British ecologists about 50 miles from the quake’s epicenter were studying mating behavior of the common toad (Bufo bufo). Five days before the earthquake, the toads fled their colony for no apparent reason. The earthquake struck, and then several days later the toads returned and resumed their normal lives. Did the toads somehow sense the approaching disaster, days before it struck? Did they flee to more secure ground? Was their departure a simple coincidence? The ecology team has now published their data and findings in the Journal of Zoology. They conclude that the toads did specifically flee their breeding site due to the approaching earthquake, and only came back after the cessation of major seismic activity.

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