Eggs, Sperms, Bones and Brains

Here are links to some not so "Just So Stories" about animals - dead and alive.

A Supersized Chicken: [link] The original Nature article requires subscription for full access.

One of the world's top fossil hunters has unveiled a previously unknown gigantic, chicken-like dinosaur that may change evolutionary theory on prehistoric animals.

The remains of the animal, thought to have weighed 1400 kilograms, was discovered by Professor Xing Xu, from Chinese Academy of Sciences, Mongolia's Erlian basin, an area rich with fossils. The new species, named Gigantoraptor erlianensis, is the biggest bird-like dinosaur ever found and at a height of 5 metres is about the size of the famous Tyrannosaurus rex, Xing says.

The 85 million-year-old creature was 35 times heavier than other known similar species, and is thought to have had a beak and sporadic patches of feathers, according to a paper in today's issue of the journal Nature. Through analysing its skeleton, the researchers believe the Gigantoraptor shared the same ancestor and belonged to the same family as the Oviraptor.

With a beak and feathers, the Oviraptor is also bird-like and flightless, but weighed a mere 1-2 kilograms.
The largest known feathered animal before the Chinese discovery was the half-tonne Stirton's Thunder Bird, which lived in Australia more than 6 million years ago.

"If you saw a mouse as big as a pig you would be very surprised; it is the same when we found the Gigantoraptor," Xing says.

DNA Restores The Cuckold's Nest: [link] Okay, we have known this for ever - men's anxiety over fatherhood. DNA testing for paternity has put many a man's mind to rest. But paternity tests are beyond the financial reach of the majority of men in the world. So, absent any concrete proof, men will go on wondering about the biological origin of their offspring. What came as a bit of a surprise to me in the linked article, is that this innate suspicion is reflected even in men's considerations for adoption - they tend to gravitate towards children who bear some resemblance to themselves. Women on the other hand, simply look for healthy babies.

High-profile paternity suits point to a trendy obsession for the ultimate proof of biological fatherhood. But to evolutionary psychologists, they're just a recent and hi-tech twist on age-old anxieties.

Since hunter-gatherer times, men have relied not on DNA swabs but on a little-understood calculus of physical resemblance to decide whether to invest in little Emma or Ethan. In the infant's upper face and eyes, the skeptical pater familias looks for clues.

The latest study, done early this year by Brock University psychology professor Anthony Volk, show cues of genetic relatedness are more important to men than women. He showed photos of infants' faces to male and female subjects, and asked them to make hypothetical adoption choices. In the journal Evolutionary Psychology, Volk reported that men reacted more positively to children with facial traits resembling them, while women's decisions were influenced more by healthy looks.

The three studies determined infanticide and spousal murder are often committed by men who learn a child isn't theirs, or who come to believe it.

Males may have acquired their skill at discerning resemblance to deal with "extra-pair paternity" – sex outside of a monogamous relationship – explains Steven Platek, the author of several studies in this field and a lecturer in evolutionary psychology at the University of Liverpool, in Britain. The extra-curricular coupling, particularly among animals, helps females ensure "good gene" acquisition.

Birds, Bees, Reptiles and Sharks - Parenthood Minus Daddy: [link]  Can this happen in humans? Apparently, further down the long road of bio-technology, it is a possibility even without divine intervention.

Well, you know how it is with the stories we tell kids. We leave a few things out. The truth about babies is that sometimes, there's no sperm. There's just an egg, but a baby hatches anyway. Many bees don't have daddies. Neither do some birds. It's called parthenogenesis—literally, virgin birth. We're finding more and more animals that can reproduce this way, and we're learning how to engineer it in others. We're even tinkering with mommy-daddy procreation in humans. If you think sex is kinky, wait till you see the alternatives.

In bees, fertilized eggs become females. Unfertilized eggs become males. Even without a queen, some female honeybees can keep a colony going by laying eggs that fertilize themselves.

Birds do it, too. Up to 30 percent of unfertilized turkey eggs can spontaneously begin to develop. In one study, selective breeding boosted the rate above 40 percent. A 1975 U.S. government report documented more than 50 mature turkeys that were never fathered.

Lately, parthenogenesis has been verified in various snakes and lizards, extending the list to about 70 vertebrate species, including fish, frogs, and chickens. But the beasts at the top of the food chain—lions, sharks, Komodo dragons—seemed impervious.

Then, in December, Nature delivered the first shock: "Parthenogenesis in Komodo dragons." Tests showed that seven juvenile dragons in European zoos were unfertilized offspring, known as parthenogens.

Still, the process hadn't been proved in sharks or mammals. And there seemed to be a good reason why. An egg that fertilizes itself makes two identical sets of chromosomes, including sex chromosomes. In birds, snakes, and most lizards, two identical sex chromosomes make a male. That allows parthenogenesis to function as a DNA survival mechanism, since an isolated female—close your ears, kids—can produce a son and mate with him. But in sharks or mammals, this wouldn't work, since two identical sex chromosomes—XX—make a female.

Or so we thought. Three weeks ago, Biology Letters delivered the second surprise: "Virgin birth in a hammerhead shark." A perfectly formed baby shark had appeared in a tank in Nebraska. Tests proved she, too, was a parthenogen.

Cross posted from Accidental Blogger.

Comments

[Usha]

I'd just happened to have seen these articles right before you published this digest on this blog. Ain't nature amazing?

Can parthenogensis happen in humans? Hmmm... don't we have an entire global religious movement hinged on the belief that it already has?

[Ruchira Paul]

".. don't we have an entire global religious movement hinged on the belief that it already has?

We do, we do! That's what I referred to in the following sentence in my intro to the parthenogenesis portion of the post.

..it is a possibility even without divine intervention.

[Usha]

Or perhaps it always happens only with divine intervention... ;^)