Radial cleavage! Morula! Blastula! Gastrulation! The blastopore became the anus! Deuterostomy!
This video is amazing.
Thanks, A Blog Around the Clock!
Tuesday, October 28, 2008
Wednesday, September 17, 2008
Enhanced Partner Preference in a Promiscuous Species by Manipulating the Expression of a Single Gene
(http://images.livescience.com/images/monogamous_Prairie_Vole_03_10.jpg)
A team of scientists observed the arginine vasopressin receptor 1a gene in prairie voles (Microtus ochrogaster) who are socially monogamous animals. This is a largely unique behavior among rodents. Prairie voles form long-lasting pair bonds and both parents partake in raising their young. It is thought that two hormones, oxytocin and vasopressin, are essential in the development of monogamy. The scientists observed a gene that regulates vasopressin output in the brain to see if, when transplanted into a close promiscuous relative species, the meadow voles (Microtus pennsylvanicus), it would have the same effect in forming pair bonds. The scientists genetically modified meadow voles by transferring the viral vector V1aR gene into test subjects’ forebrain. Additionally, they isolated adult males for 24 hours with a receptive female and sought to find out whether the males preferred to return to the female with whom he had spent the previous day. After male meadow voles were given the opportunity to access new partners, would they prefer to return to the old one? They measured this empirically by timing how long affected males huddled with the female with whom they had previously been isolated. They also hoped to show that by changing a single gene they would be able to provide “a potential molecular mechanism for the rapid evolution of complex social behaviour.”
They found that males possessing the V1aR gene would go back to the females with whom they were isolated for 24-hours and huddle. Males who hadn't been genetically modified were found uniformly distributed among females after the 24-hour isolation with one female.
Monogamy is a rarely observed phenomenon in mammals. Unlike birds that lay eggs, parental investment can just as easily come from the mother as it can from the father. Female mammals, on the other hand, tend to have long gestation periods followed by long lactation periods before they can mate again. From a male perspective, if the objective is to pass your genes on to as many offspring as possible, it seems maladaptive to stay with one female when there are many other females you could potentially inseminate.
If females are the limiting factor, from an evolutionary perspective mammals should be largely polygynous. Polygyny is a mating system where one male mates with many females. From a female perspective, it may be in her best interest to be polygynous because “loser” females, or those with unattractive genetic material, would be able to mate with high quality males. Polygyny may also ensure superior habitat and resources supplied by the male.
Promiscuity is another viable option for mammals. It may be in males’ and females’ best interest to be promiscuous like the meadow voles and let sperm competition and cryptic female choice determine which males are successful in providing the gamete for the female’s egg. Given the severity of the many negative aspects of monogamy- and the advantages of other mating systems - why do certain species still engage in this behavior?
Polygyny and promiscuity favor few “winner” males, and the many “loser” males do not mate at all. This is not an argument for group selection, but if a loser male can hook a female into mating with him, it is in his best interest to invest all of his time and resources into her and not attempt to sequester many females. From a female perspective, monogamy may be the best choice because it provides ensured support for the female and her offspring. Gestation and lactation are incredibly energy-consuming and difficult if pursued solitarily.
Olivia Judson wrote about this paper in her blog, The Wild Side, and concluded with "it does raise the tantalizing prospect that, one day, it might really be possible to concoct love potions or pills that would alter brain chemistry and enhance the odds of a man forming a strong attachment to his lover." A tantalizing prospect, indeed!
Lim, M. M., Wang, Z., Olazabal, D. E., Ren, X., Terwillinger, E. F., Young, L. J. 2004. Enhanced Partner Preference in a Promiscuous Species by Manipulating the Expression of a Single Gene. Nature: 429.
Wednesday, August 27, 2008
Why do Giraffes have such long...
NECKS!?
Well, it appears to be for sexual selection. The standard story about why giraffes have evolved their incredibly long necks states that this trait has helped them in reaching to higher leaves. This story, however, is probably wrong. Observations of giraffes have shown that over 50 percent of the time, they feed with their necks horizontal and that during the food-scarce dry season, they feed in low bushes rather than in tall trees. The giraffes are obviously capable of feeding on higher leaves than other animals but this advantage doesn't seem to be sufficiently great to justify the costs of having such a long neck.
The giraffes' head is about 3 meters above the heart which makes it very difficult for the heart to pump blood to the brain. The giraffe has the highest blood pressure of all mammals and its heart weighs up to 10 kg. The largest giraffe on record was almost 6 meters tall and weighed about 2 tons. In spite of their size, the giraffe can run very fast, up to 60 km/h (aprox. 35 mph). Their heart seems to cope with such effort. Their front legs are 10 percent longer than the back legs which might also help them run.
Another reason why it is unlikely that the giraffe's neck has evolved due to feeding habits is that its closest relatives, although big, had short necks. The discovered fossils reveal large animals with long legs rather than long necks. The largest giraffe relative discovered insofar had legs almost twice as long than those of modern giraffes but a short neck. Other giraffe relatives have had impressive horns - while the giraffes have only two small horns. The giraffe evolved around 1 million year ago in the African savannah at the time when our ancestor Homo Erectus had already spread from Africa throughout Asia. The giraffe ancestor was significantly smaller in size and had a shorter neck than today's giraffes. So, what favored the growth of that incredible neck in a relatively short time?
One proposal is that the neck helped the giraffe spot predators from the distance, but most biologists reject this explanation as being much too ad hoc. Instead, the most widely accepted hypothesis is that the neck evolved under the pressure of sexual selection. Thus, the giraffe's neck is similar to the peacock's tail or to the moose's horns.
This explanation is in no way obvious, especially because the female giraffes also have long necks, while sexual selection usually favors such "wild" traits only in males. Nonetheless, observations of giraffes' behavior seem to support this view.
The first clue is quite direct: male giraffes, unlike female giraffes, use their necks to fight each other. Moreover, before an actual fight, they point their noses upwards as if they are trying to create the impression that their necks are higher. Researchers have discovered that this is indeed a sign of domination as some males run away from a dominant bull that does such a sign.
"An average male giraffe's neck weighs 90.72 kg. and can stretch 1.83 meters long. Giraffes fight over females by swinging their necks and heads like a medieval ball and chain. The longer and heavier the neck, the more momentum behind the often bone-shattering head slams," Kathy Wollard remarked.
A study in the 1980s by Pratt and Anderson had shown that the main criterion that determines the dominance among bulls is neck size. They classified the giraffes in three classes, A, B, C according to neck size and horns lengths and discovered that neck length is what counted. "The larger-necked A bulls were consistently dominant over B and C bulls, and they courted females significantly more often than B or C did. Ranking also appeared to be important in female mate choice: females allowed themselves to be urine tested (a test of their sexual receptiveness) by A bulls more often than B bulls, and they refused to be urine tested by C bulls in two-thirds of all encounters," wrote Robert Simmons and Lue Scheepers who first argued in favor of the sexual selection theory in the 1990s.
But why do female giraffes also have long necks? Simmons and Scheepers argued that the neck, unlike the tails or the horns, is a trait much too heavily integrated in the organism to be controlled only by a small number of genes. Therefore, the females necessarily inherit the same "neck genes" as the males.
There are however differences between males and females - exactly as one would expect from the theory of sexual selection. Female giraffes do have smaller necks than the males because their necks stop growing in their "adolescence", when they are around 6 years old. This probably happens because females have a gene that silences the neck-growing genes. The males' necks on the other hand grow constantly throughout their lives (giraffes live about 20 years). The largest males are about 53 percent heavier than the largest females.
The fact that the neck is a hindrance and has a large survival cost has been demonstrated by other studies, conducted since the late 1960s, which have shown that male giraffes were about twice as likely as females to be killed by a predator - mostly lions. This kind of difference, again, is a hallmark of sexual selection.
Finally, there is another interesting fact that can explain the long necks of female giraffes. The male giraffes are among the most homosexual mammals. Bruce Bagemihl has discovered that in some areas, 94% of mounting incidents were between two males. Males don't just fight with their necks - in one in 20 cases they engage in affectionate behavior. On the other hand, female giraffes engage in homosexual behavior only in one percent of the time. It thus seems that female giraffes have sexually selected males with longer and longer necks, but the males themselves find long necks sexy. So, in order to still get males, females also had to grow long necks.
Well, it appears to be for sexual selection. The standard story about why giraffes have evolved their incredibly long necks states that this trait has helped them in reaching to higher leaves. This story, however, is probably wrong. Observations of giraffes have shown that over 50 percent of the time, they feed with their necks horizontal and that during the food-scarce dry season, they feed in low bushes rather than in tall trees. The giraffes are obviously capable of feeding on higher leaves than other animals but this advantage doesn't seem to be sufficiently great to justify the costs of having such a long neck.
The giraffes' head is about 3 meters above the heart which makes it very difficult for the heart to pump blood to the brain. The giraffe has the highest blood pressure of all mammals and its heart weighs up to 10 kg. The largest giraffe on record was almost 6 meters tall and weighed about 2 tons. In spite of their size, the giraffe can run very fast, up to 60 km/h (aprox. 35 mph). Their heart seems to cope with such effort. Their front legs are 10 percent longer than the back legs which might also help them run.
Another reason why it is unlikely that the giraffe's neck has evolved due to feeding habits is that its closest relatives, although big, had short necks. The discovered fossils reveal large animals with long legs rather than long necks. The largest giraffe relative discovered insofar had legs almost twice as long than those of modern giraffes but a short neck. Other giraffe relatives have had impressive horns - while the giraffes have only two small horns. The giraffe evolved around 1 million year ago in the African savannah at the time when our ancestor Homo Erectus had already spread from Africa throughout Asia. The giraffe ancestor was significantly smaller in size and had a shorter neck than today's giraffes. So, what favored the growth of that incredible neck in a relatively short time?
One proposal is that the neck helped the giraffe spot predators from the distance, but most biologists reject this explanation as being much too ad hoc. Instead, the most widely accepted hypothesis is that the neck evolved under the pressure of sexual selection. Thus, the giraffe's neck is similar to the peacock's tail or to the moose's horns.
This explanation is in no way obvious, especially because the female giraffes also have long necks, while sexual selection usually favors such "wild" traits only in males. Nonetheless, observations of giraffes' behavior seem to support this view.
The first clue is quite direct: male giraffes, unlike female giraffes, use their necks to fight each other. Moreover, before an actual fight, they point their noses upwards as if they are trying to create the impression that their necks are higher. Researchers have discovered that this is indeed a sign of domination as some males run away from a dominant bull that does such a sign.
"An average male giraffe's neck weighs 90.72 kg. and can stretch 1.83 meters long. Giraffes fight over females by swinging their necks and heads like a medieval ball and chain. The longer and heavier the neck, the more momentum behind the often bone-shattering head slams," Kathy Wollard remarked.
A study in the 1980s by Pratt and Anderson had shown that the main criterion that determines the dominance among bulls is neck size. They classified the giraffes in three classes, A, B, C according to neck size and horns lengths and discovered that neck length is what counted. "The larger-necked A bulls were consistently dominant over B and C bulls, and they courted females significantly more often than B or C did. Ranking also appeared to be important in female mate choice: females allowed themselves to be urine tested (a test of their sexual receptiveness) by A bulls more often than B bulls, and they refused to be urine tested by C bulls in two-thirds of all encounters," wrote Robert Simmons and Lue Scheepers who first argued in favor of the sexual selection theory in the 1990s.
But why do female giraffes also have long necks? Simmons and Scheepers argued that the neck, unlike the tails or the horns, is a trait much too heavily integrated in the organism to be controlled only by a small number of genes. Therefore, the females necessarily inherit the same "neck genes" as the males.
There are however differences between males and females - exactly as one would expect from the theory of sexual selection. Female giraffes do have smaller necks than the males because their necks stop growing in their "adolescence", when they are around 6 years old. This probably happens because females have a gene that silences the neck-growing genes. The males' necks on the other hand grow constantly throughout their lives (giraffes live about 20 years). The largest males are about 53 percent heavier than the largest females.
The fact that the neck is a hindrance and has a large survival cost has been demonstrated by other studies, conducted since the late 1960s, which have shown that male giraffes were about twice as likely as females to be killed by a predator - mostly lions. This kind of difference, again, is a hallmark of sexual selection.
Finally, there is another interesting fact that can explain the long necks of female giraffes. The male giraffes are among the most homosexual mammals. Bruce Bagemihl has discovered that in some areas, 94% of mounting incidents were between two males. Males don't just fight with their necks - in one in 20 cases they engage in affectionate behavior. On the other hand, female giraffes engage in homosexual behavior only in one percent of the time. It thus seems that female giraffes have sexually selected males with longer and longer necks, but the males themselves find long necks sexy. So, in order to still get males, females also had to grow long necks.
Friday, August 1, 2008
Everyone is Narcissistic
Here's Looking at Me, Kid
This article generated some question marks for me. I tend to see the world and observe human behavior from a evolutionary perspective, so the content of this article seemed obvious. Of course we are narcissists!
Within the spheres of ethics that exist in individuals, the very first is that of self-love. How are we to pass our genes on to subsequent generations (arguably the purpose of life) if we are more concerned about others? Does altruism exist in nature? Not likely. Most cases in which one could argue selflessness as a motive for an organism to act in the interest of another have been proved wrong. Ultimately, these "altruistic" behaviors benefit the seemingly thoughtful animal in the long run, as opposed to the alternative route that would appear to benefit it in the short-term.
An obvious example of misdiagnosed altruism can be found in male anubis baboons (Papio anubis) who may willingly assist other males in copulating with sexually receptive females. And does this really surprise you? I have heard countless laments from our own male species about a "friend," or one with whom he has formed an alliance, who exploits friendships only to bolster his own chances of mating with the opposite sex.
While the helper baboon appears to willingly eliminate his own chances of mating with the female of interest, the act is not necessarily altruistic. This mating strategy can subvert the normal age and size sexual dominance hierarchy. As males patiently scale the hierarchy, they heighten their own chances of mating successfully by using this behavior. The assumption is that the helper baboon will eventually become the helpee. By assisting another with whom he has formed an alliance, he will in the long run be rewarded with a better chance of mating successfully than had he not helped at all.
This article generated some question marks for me. I tend to see the world and observe human behavior from a evolutionary perspective, so the content of this article seemed obvious. Of course we are narcissists!
Within the spheres of ethics that exist in individuals, the very first is that of self-love. How are we to pass our genes on to subsequent generations (arguably the purpose of life) if we are more concerned about others? Does altruism exist in nature? Not likely. Most cases in which one could argue selflessness as a motive for an organism to act in the interest of another have been proved wrong. Ultimately, these "altruistic" behaviors benefit the seemingly thoughtful animal in the long run, as opposed to the alternative route that would appear to benefit it in the short-term.
An obvious example of misdiagnosed altruism can be found in male anubis baboons (Papio anubis) who may willingly assist other males in copulating with sexually receptive females. And does this really surprise you? I have heard countless laments from our own male species about a "friend," or one with whom he has formed an alliance, who exploits friendships only to bolster his own chances of mating with the opposite sex.
While the helper baboon appears to willingly eliminate his own chances of mating with the female of interest, the act is not necessarily altruistic. This mating strategy can subvert the normal age and size sexual dominance hierarchy. As males patiently scale the hierarchy, they heighten their own chances of mating successfully by using this behavior. The assumption is that the helper baboon will eventually become the helpee. By assisting another with whom he has formed an alliance, he will in the long run be rewarded with a better chance of mating successfully than had he not helped at all.
Thursday, May 8, 2008
Male Anglerfish can be 'Clingy'
Anglerfish, a deep sea fish named for the spiny appendage on its head that it uses as bait to "fish" its prey, has an unusual mating habit. As it spends its time in the bottom of the ocean, finding a mate is a problem - but the species solved this evolutionary challenge beautifully.
At first, scientists were perplexed because they’ve never caught a male anglerfish. Also, all female anglerfish have a lump on their body that looks like a parasite. Only later did scientists discover that the lump is the remain of the male fish.
The tiny male anglerfish are born without any digestive system, so once they hatch, they have to find a female quickly. When a male finds a female, he quickly bites her body and releases an enzyme that digests his skin and her body to fuse the two in an eternal embrace. The male then wastes away, becoming nothing but a lump on the female anglerfish’s body!
When the female is ready to spawn, her "male appendage" is there, ready to release sperms to fertilize her egg.
Taken from Journal of Ichthyological Research
Monday, April 21, 2008
Evolutionary Oddity: Lungless Frog Found on Island of Borneo
The first recorded species of frog that breathes without lungs has been found in a clear, cold-water stream on the island of Borneo in Indonesia. The frog, named Barbourula kalimantanensis, gets all its oxygen through its skin.
(Article from National Geographic Website)
Previously the only four-limbed creatures known to lack lungs were salamanders.
A species of earthwormlike, limbless amphibian called a caecilian is also lungless.
Tetrapods, or four-limbed creatures, that develop without lungs are rare evolutionary events, Bickford and colleagues write.
The researchers suggest lunglessness in B. kalimantanensis may be an adaptation to the higher oxygen content in fast-flowing, cold water."Cold water can hold more dissolved oxygen than warm water," Bickford explained.
The frog also has a low metabolic rate, which means it needs less oxygen.
What's more, the species is severely flat compared to other frogs, which increases the surface area of the skin.
"Along with the fact that having lungs makes you more likely to be swept away in a fast-flowing stream—because you would float—this [is] a very strong context for the evolution of loss of lungs," Bickford said.
(Article from National Geographic Website)
Thursday, April 3, 2008
New Flat-Faced Fish Sighted Off Indonesia
Divers have spotted a new type of fish off Ambon Island in Indonesian waters. The striped fish, which is about the size of a human fist, is believed to be an anglerfish because it crawls along the ground and into crevices using leglike pectoral fins. But unlike most anglerfish, this species does not have a "lure" dangling from its head to attract prey, so it probably represents a family of fish previously unknown to science, says Ted Pietsch, a professor of aquatic and fishery sciences at the University of Washington.
Three scuba divers first spotted and photographed one of the fish in late January. In search of international experts to identify the fish, they found Pietsch, who says the fish is unmistakably an anglerfish because of the leglike fins on its sides. Anglerfish are also known as frogfishes and toadfishes.
The new fish appears to be fleshy with tough skin, because it is able to squeeze itself into very small cracks in coral reefs without getting scratched. That may be how it has escaped human attention for so long.
The divers who discovered the fish kept quiet about it for a while. But now that another adult, two juveniles, and a mass of eggs have been seen, the word is out.
(Article from PopularScience)
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