Case in point: fleas.
Scientists know very little about the vision of fleas. As insects, fleas have inherited the standard insect eye, which consists of slender
columns tightly packed together. But this standard insect eye has undergone drastic changes in fleas. Some fleas have what look like
simple eyespots. Others seem to lack any eye at all. To learn about this transformation, a team of biologists from Brigham Young
University have compared fleas to their relatives, which still have eyes.
This wouldn't have been possible even a few years ago, because scientists have only recently worked out the
"flea tree." Fleas evolved
from a group of insects with particularLY sharp vision. Their cousins include scorpionflies, which rely on their image-forming eyes to
help them scavenge dead insects. Their closest relatives are "snow fleas" (Boreidae). These wingless insects live in mountains, where
they feed on moss. They have small eyes, but can see well enough to jump away if you try to catch them. So it appears that fleas are
the product of a long-term evolution towards simpler eyes.
The scientists used this tree to track the evolution of some of the molecules that are essential for vision. Known as opsins, they respond
to light by triggering a chemical reaction that sends a signal from the eye to the brain. Opsins can be sensitive to different colors, depending
on their shape, which depends in turn on the DNA sequence in their genes. The scientists isolated the gene for green opsins from 11
species of scorpionflies, snow fleas, and true fleas.
The scientists then compared the DNA sequences for signs of change. A mutation to an opsin gene may have no effect on the opsin
molecule itself, or it may alter its structure dramatically. The difference depends on where in the DNA sequence that mutation strikes.
The scientists found that most changes that occurred during the evolution of fleas had no effect on the actual opsins. They confirmed
this by using the DNA sequence of the opsin genes to create computer models of the opsin molecules themselves. Even in fleas, the
green opsin molecule has basically the same structure as in scorpionflies--despite their radically different eyes.
Just because a gene hasn't changed for millions of years doesn't mean that it hasn't been experiencing natural selection. The scientists
found evidence that the opsin gene has been experience a special kind of natural selection in fleas and their relatives, known as purifying
selection. Purifying selection occurs if even the slightest change to the structure of a molecule puts a serious dent in the reproductive
success of an animal. The fact that fleas have experience purifying selection on their opsin gene means that it remains essential to their
survival. (The details of their work appear in a paper in press at the journal Molecular Biology and Evolution.)
So what on Earth are the fleas doing with their opsins? The scientists doubt that the fleas are using them in their eyes. They point out
that flea eyes are covered over in a tough layer of chitin, and they lack the lenses and other structures that would let them see. But in
many animals, ranging from pigeons to salmon to butterflies, opsins have also been found outside the eye. In some animals, they grow
inside the brain, while in others they grow on the abdomen or other parts of the body. Recent studies suggest that these opsins set the
pace for biological clocks by registering the change of light from day to night.
This brings us back around to the very origin of eyes, which I described in my first post. Long before full-fledged eyes evolved,
light-sensitive molecules may have existed in microbes, allowing them to change their movements during night and day. These molecules
may have been incorporated into early eyes, making it possible for animals to see. But this transition didn't mean that photoreceptors
could no longer serve their original function. Early insects may have used opsins both within their eyes to see and outside of their eyes
as biological clocks. Later, some lineages of insects lost their eyes. Some may have lost them in dark caves. Fleas, on the other hand,
lost their eyes as they became parasites. Instead of navigating through a complex landscape in search of a particular prey, they just
hopped from one host to the next. But they still relied on opsins to run their biological clocks. The authors point out that scientists have
also found opsins in other animals that have lost their eyes. The animals? None other than Astyanax.
What's particularly remarkable about the new study is how strongly the flea opsin resisted any evolutionary change--even after it was
no longer being used in the flea eye. The molecule need the same functional structure for both jobs. As I mentioned at the beginning
of my previous post, Charles Darwin recognized that the complexity of the eye might appear to pose a major challenge to his theory.
To some people, it still does; they argue that the components of the eye cannot function on their own, and so they could never have
existed on their own. By this reasoning, it would be impossible for one of these components--an opsin, for example--to do anything
useful if it wasn't inside an eye.The flea apparently sees things differently.Comments (9) + TrackBacks (0) Category: Evolution
The scientists used this tree to track the evolution of some of the molecules that are essential for vision. Known as opsins, they respond
to light by triggering a chemical reaction that sends a signal from the eye to the brain. Opsins can be sensitive to different colors, depending
on their shape, which depends in turn on the DNA sequence in their genes. The scientists isolated the gene for green opsins from 11
species of scorpionflies, snow fleas, and true fleas.
The scientists then compared the DNA sequences for signs of change. A mutation to an opsin gene may have no effect on the opsin
molecule itself, or it may alter its structure dramatically. The difference depends on where in the DNA sequence that mutation strikes.
The scientists found that most changes that occurred during the evolution of fleas had no effect on the actual opsins. They confirmed
this by using the DNA sequence of the opsin genes to create computer models of the opsin molecules themselves. Even in fleas, the
green opsin molecule has basically the same structure as in scorpionflies--despite their radically different eyes.
Just because a gene hasn't changed for millions of years doesn't mean that it hasn't been experiencing natural selection. The scientists
found evidence that the opsin gene has been experience a special kind of natural selection in fleas and their relatives, known as purifying
selection. Purifying selection occurs if even the slightest change to the structure of a molecule puts a serious dent in the reproductive
success of an animal. The fact that fleas have experience purifying selection on their opsin gene means that it remains essential to their
survival. (The details of their work appear in a paper in press at the journal Molecular Biology and Evolution.)
So what on Earth are the fleas doing with their opsins? The scientists doubt that the fleas are using them in their eyes. They point out
that flea eyes are covered over in a tough layer of chitin, and they lack the lenses and other structures that would let them see. But in
many animals, ranging from pigeons to salmon to butterflies, opsins have also been found outside the eye. In some animals, they grow
inside the brain, while in others they grow on the abdomen or other parts of the body. Recent studies suggest that these opsins set the
pace for biological clocks by registering the change of light from day to night.
This brings us back around to the very origin of eyes, which I described in my first post. Long before full-fledged eyes evolved,
light-sensitive molecules may have existed in microbes, allowing them to change their movements during night and day. These molecules
may have been incorporated into early eyes, making it possible for animals to see. But this transition didn't mean that photoreceptors
could no longer serve their original function. Early insects may have used opsins both within their eyes to see and outside of their eyes
as biological clocks. Later, some lineages of insects lost their eyes. Some may have lost them in dark caves. Fleas, on the other hand,
lost their eyes as they became parasites. Instead of navigating through a complex landscape in search of a particular prey, they just
hopped from one host to the next. But they still relied on opsins to run their biological clocks. The authors point out that scientists have
also found opsins in other animals that have lost their eyes. The animals? None other than Astyanax.
What's particularly remarkable about the new study is how strongly the flea opsin resisted any evolutionary change--even after it was
no longer being used in the flea eye. The molecule need the same functional structure for both jobs. As I mentioned at the beginning
of my previous post, Charles Darwin recognized that the complexity of the eye might appear to pose a major challenge to his theory.
To some people, it still does; they argue that the components of the eye cannot function on their own, and so they could never have
existed on their own. By this reasoning, it would be impossible for one of these components--an opsin, for example--to do anything
useful if it wasn't inside an eye.The flea apparently sees things differently.Comments (9) + TrackBacks (0) Category: Evolution
The scientists used this tree to track the evolution of some of the molecules that are essential for vision. Known as opsins, they respond
to light by triggering a chemical reaction that sends a signal from the eye to the brain. Opsins can be sensitive to different colors, depending
on their shape, which depends in turn on the DNA sequence in their genes. The scientists isolated the gene for green opsins from 11
species of scorpionflies, snow fleas, and true fleas.
The scientists then compared the DNA sequences for signs of change. A mutation to an opsin gene may have no effect on the opsin
molecule itself, or it may alter its structure dramatically. The difference depends on where in the DNA sequence that mutation strikes.
The scientists found that most changes that occurred during the evolution of fleas had no effect on the actual opsins. They confirmed
this by using the DNA sequence of the opsin genes to create computer models of the opsin molecules themselves. Even in fleas, the
green opsin molecule has basically the same structure as in scorpionflies--despite their radically different eyes.
Just because a gene hasn't changed for millions of years doesn't mean that it hasn't been experiencing natural selection. The scientists
found evidence that the opsin gene has been experience a special kind of natural selection in fleas and their relatives, known as purifying
selection. Purifying selection occurs if even the slightest change to the structure of a molecule puts a serious dent in the reproductive
success of an animal. The fact that fleas have experience purifying selection on their opsin gene means that it remains essential to their
survival. (The details of their work appear in a paper in press at the journal Molecular Biology and Evolution.)
So what on Earth are the fleas doing with their opsins? The scientists doubt that the fleas are using them in their eyes. They point out
that flea eyes are covered over in a tough layer of chitin, and they lack the lenses and other structures that would let them see. But in
many animals, ranging from pigeons to salmon to butterflies, opsins have also been found outside the eye. In some animals, they grow
inside the brain, while in others they grow on the abdomen or other parts of the body. Recent studies suggest that these opsins set the
pace for biological clocks by registering the change of light from day to night.
This brings us back around to the very origin of eyes, which I described in my first post. Long before full-fledged eyes evolved,
light-sensitive molecules may have existed in microbes, allowing them to change their movements during night and day. These molecules
may have been incorporated into early eyes, making it possible for animals to see. But this transition didn't mean that photoreceptors
could no longer serve their original function. Early insects may have used opsins both within their eyes to see and outside of their eyes
as biological clocks. Later, some lineages of insects lost their eyes. Some may have lost them in dark caves. Fleas, on the other hand,
lost their eyes as they became parasites. Instead of navigating through a complex landscape in search of a particular prey, they just
hopped from one host to the next. But they still relied on opsins to run their biological clocks. The authors point out that scientists have
also found opsins in other animals that have lost their eyes. The animals? None other than Astyanax.
What's particularly remarkable about the new study is how strongly the flea opsin resisted any evolutionary change--even after it was
no longer being used in the flea eye. The molecule need the same functional structure for both jobs. As I mentioned at the beginning
of my previous post, Charles Darwin recognized that the complexity of the eye might appear to pose a major challenge to his theory.
To some people, it still does; they argue that the components of the eye cannot function on their own, and so they could never have
existed on their own. By this reasoning, it would be impossible for one of these components--an opsin, for example--to do anything
useful if it wasn't inside an eye.The flea apparently sees things differently.Comments (9) + TrackBacks (0) Category: Evolution
The scientists used this tree to track the evolution of some of the molecules that are essential for vision. Known as opsins, they respond
to light by triggering a chemical reaction that sends a signal from the eye to the brain. Opsins can be sensitive to different colors, depending
on their shape, which depends in turn on the DNA sequence in their genes. The scientists isolated the gene for green opsins from 11
species of scorpionflies, snow fleas, and true fleas.
The scientists then compared the DNA sequences for signs of change. A mutation to an opsin gene may have no effect on the opsin
molecule itself, or it may alter its structure dramatically. The difference depends on where in the DNA sequence that mutation strikes.
The scientists found that most changes that occurred during the evolution of fleas had no effect on the actual opsins. They confirmed
this by using the DNA sequence of the opsin genes to create computer models of the opsin molecules themselves. Even in fleas, the
green opsin molecule has basically the same structure as in scorpionflies--despite their radically different eyes.
Just because a gene hasn't changed for millions of years doesn't mean that it hasn't been experiencing natural selection. The scientists
found evidence that the opsin gene has been experience a special kind of natural selection in fleas and their relatives, known as purifying
selection. Purifying selection occurs if even the slightest change to the structure of a molecule puts a serious dent in the reproductive
success of an animal. The fact that fleas have experience purifying selection on their opsin gene means that it remains essential to their
survival. (The details of their work appear in a paper in press at the journal Molecular Biology and Evolution.)
So what on Earth are the fleas doing with their opsins? The scientists doubt that the fleas are using them in their eyes. They point out
that flea eyes are covered over in a tough layer of chitin, and they lack the lenses and other structures that would let them see. But in
many animals, ranging from pigeons to salmon to butterflies, opsins have also been found outside the eye. In some animals, they grow
inside the brain, while in others they grow on the abdomen or other parts of the body. Recent studies suggest that these opsins set the
pace for biological clocks by registering the change of light from day to night.
This brings us back around to the very origin of eyes, which I described in my first post. Long before full-fledged eyes evolved,
light-sensitive molecules may have existed in microbes, allowing them to change their movements during night and day. These molecules
may have been incorporated into early eyes, making it possible for animals to see. But this transition didn't mean that photoreceptors
could no longer serve their original function. Early insects may have used opsins both within their eyes to see and outside of their eyes
as biological clocks. Later, some lineages of insects lost their eyes. Some may have lost them in dark caves. Fleas, on the other hand,
lost their eyes as they became parasites. Instead of navigating through a complex landscape in search of a particular prey, they just
hopped from one host to the next. But they still relied on opsins to run their biological clocks. The authors point out that scientists have
also found opsins in other animals that have lost their eyes. The animals? None other than Astyanax.
What's particularly remarkable about the new study is how strongly the flea opsin resisted any evolutionary change--even after it was
no longer being used in the flea eye. The molecule need the same functional structure for both jobs. As I mentioned at the beginning
of my previous post, Charles Darwin recognized that the complexity of the eye might appear to pose a major challenge to his theory.
To some people, it still does; they argue that the components of the eye cannot function on their own, and so they could never have
existed on their own. By this reasoning, it would be impossible for one of these components--an opsin, for example--to do anything
useful if it wasn't inside an eye.The flea apparently sees things differently.Comments (9) + TrackBacks (0) Category: Evolution
The scientists used this tree to track the evolution of some of the molecules that are essential for vision. Known as opsins, they respond
to light by triggering a chemical reaction that sends a signal from the eye to the brain. Opsins can be sensitive to different colors, depending
on their shape, which depends in turn on the DNA sequence in their genes. The scientists isolated the gene for green opsins from 11
species of scorpionflies, snow fleas, and true fleas.
The scientists then compared the DNA sequences for signs of change. A mutation to an opsin gene may have no effect on the opsin
molecule itself, or it may alter its structure dramatically. The difference depends on where in the DNA sequence that mutation strikes.
The scientists found that most changes that occurred during the evolution of fleas had no effect on the actual opsins. They confirmed
this by using the DNA sequence of the opsin genes to create computer models of the opsin molecules themselves. Even in fleas, the
green opsin molecule has basically the same structure as in scorpionflies--despite their radically different eyes.
Just because a gene hasn't changed for millions of years doesn't mean that it hasn't been experiencing natural selection. The scientists
found evidence that the opsin gene has been experience a special kind of natural selection in fleas and their relatives, known as purifying
selection. Purifying selection occurs if even the slightest change to the structure of a molecule puts a serious dent in the reproductive
success of an animal. The fact that fleas have experience purifying selection on their opsin gene means that it remains essential to their
survival. (The details of their work appear in a paper in press at the journal Molecular Biology and Evolution.)
So what on Earth are the fleas doing with their opsins? The scientists doubt that the fleas are using them in their eyes. They point out
that flea eyes are covered over in a tough layer of chitin, and they lack the lenses and other structures that would let them see. But in
many animals, ranging from pigeons to salmon to butterflies, opsins have also been found outside the eye. In some animals, they grow
inside the brain, while in others they grow on the abdomen or other parts of the body. Recent studies suggest that these opsins set the
pace for biological clocks by registering the change of light from day to night.
This brings us back around to the very origin of eyes, which I described in my first post. Long before full-fledged eyes evolved,
light-sensitive molecules may have existed in microbes, allowing them to change their movements during night and day. These molecules
may have been incorporated into early eyes, making it possible for animals to see. But this transition didn't mean that photoreceptors
could no longer serve their original function. Early insects may have used opsins both within their eyes to see and outside of their eyes
as biological clocks. Later, some lineages of insects lost their eyes. Some may have lost them in dark caves. Fleas, on the other hand,
lost their eyes as they became parasites. Instead of navigating through a complex landscape in search of a particular prey, they just
hopped from one host to the next. But they still relied on opsins to run their biological clocks. The authors point out that scientists have
also found opsins in other animals that have lost their eyes. The animals? None other than Astyanax.
What's particularly remarkable about the new study is how strongly the flea opsin resisted any evolutionary change--even after it was
no longer being used in the flea eye. The molecule need the same functional structure for both jobs. As I mentioned at the beginning
of my previous post, Charles Darwin recognized that the complexity of the eye might appear to pose a major challenge to his theory.
To some people, it still does; they argue that the components of the eye cannot function on their own, and so they could never have
existed on their own. By this reasoning, it would be impossible for one of these components--an opsin, for example--to do anything
useful if it wasn't inside an eye.The flea apparently sees things differently.Comments (9) + TrackBacks (0) Category: Evolution
The scientists used this tree to track the evolution of some of the molecules that are essential for vision. Known as opsins, they respond
to light by triggering a chemical reaction that sends a signal from the eye to the brain. Opsins can be sensitive to different colors, depending
on their shape, which depends in turn on the DNA sequence in their genes. The scientists isolated the gene for green opsins from 11
species of scorpionflies, snow fleas, and true fleas.
The scientists then compared the DNA sequences for signs of change. A mutation to an opsin gene may have no effect on the opsin
molecule itself, or it may alter its structure dramatically. The difference depends on where in the DNA sequence that mutation strikes.
The scientists found that most changes that occurred during the evolution of fleas had no effect on the actual opsins. They confirmed
this by using the DNA sequence of the opsin genes to create computer models of the opsin molecules themselves. Even in fleas, the
green opsin molecule has basically the same structure as in scorpionflies--despite their radically different eyes.
Just because a gene hasn't changed for millions of years doesn't mean that it hasn't been experiencing natural selection. The scientists
found evidence that the opsin gene has been experience a special kind of natural selection in fleas and their relatives, known as purifying
selection. Purifying selection occurs if even the slightest change to the structure of a molecule puts a serious dent in the reproductive
success of an animal. The fact that fleas have experience purifying selection on their opsin gene means that it remains essential to their
survival. (The details of their work appear in a paper in press at the journal Molecular Biology and Evolution.)
So what on Earth are the fleas doing with their opsins? The scientists doubt that the fleas are using them in their eyes. They point out
that flea eyes are covered over in a tough layer of chitin, and they lack the lenses and other structures that would let them see. But in
many animals, ranging from pigeons to salmon to butterflies, opsins have also been found outside the eye. In some animals, they grow
inside the brain, while in others they grow on the abdomen or other parts of the body. Recent studies suggest that these opsins set the
pace for biological clocks by registering the change of light from day to night.
This brings us back around to the very origin of eyes, which I described in my first post. Long before full-fledged eyes evolved,
light-sensitive molecules may have existed in microbes, allowing them to change their movements during night and day. These molecules
may have been incorporated into early eyes, making it possible for animals to see. But this transition didn't mean that photoreceptors
could no longer serve their original function. Early insects may have used opsins both within their eyes to see and outside of their eyes
as biological clocks. Later, some lineages of insects lost their eyes. Some may have lost them in dark caves. Fleas, on the other hand,
lost their eyes as they became parasites. Instead of navigating through a complex landscape in search of a particular prey, they just
hopped from one host to the next. But they still relied on opsins to run their biological clocks. The authors point out that scientists have
also found opsins in other animals that have lost their eyes. The animals? None other than Astyanax.
What's particularly remarkable about the new study is how strongly the flea opsin resisted any evolutionary change--even after it was
no longer being used in the flea eye. The molecule need the same functional structure for both jobs. As I mentioned at the beginning
of my previous post, Charles Darwin recognized that the complexity of the eye might appear to pose a major challenge to his theory.
To some people, it still does; they argue that the components of the eye cannot function on their own, and so they could never have
existed on their own. By this reasoning, it would be impossible for one of these components--an opsin, for example--to do anything
useful if it wasn't inside an eye.The flea apparently sees things differently.Comments (9) + TrackBacks (0) Category: Evolution
The scientists used this tree to track the evolution of some of the molecules that are essential for vision. Known as opsins, they respond
to light by triggering a chemical reaction that sends a signal from the eye to the brain. Opsins can be sensitive to different colors, depending
on their shape, which depends in turn on the DNA sequence in their genes. The scientists isolated the gene for green opsins from 11
species of scorpionflies, snow fleas, and true fleas.
The scientists then compared the DNA sequences for signs of change. A mutation to an opsin gene may have no effect on the opsin
molecule itself, or it may alter its structure dramatically. The difference depends on where in the DNA sequence that mutation strikes.
The scientists found that most changes that occurred during the evolution of fleas had no effect on the actual opsins. They confirmed
this by using the DNA sequence of the opsin genes to create computer models of the opsin molecules themselves. Even in fleas, the
green opsin molecule has basically the same structure as in scorpionflies--despite their radically different eyes.
Just because a gene hasn't changed for millions of years doesn't mean that it hasn't been experiencing natural selection. The scientists
found evidence that the opsin gene has been experience a special kind of natural selection in fleas and their relatives, known as purifying
selection. Purifying selection occurs if even the slightest change to the structure of a molecule puts a serious dent in the reproductive
success of an animal. The fact that fleas have experience purifying selection on their opsin gene means that it remains essential to their
survival. (The details of their work appear in a paper in press at the journal Molecular Biology and Evolution.)
So what on Earth are the fleas doing with their opsins? The scientists doubt that the fleas are using them in their eyes. They point out
that flea eyes are covered over in a tough layer of chitin, and they lack the lenses and other structures that would let them see. But in
many animals, ranging from pigeons to salmon to butterflies, opsins have also been found outside the eye. In some animals, they grow
inside the brain, while in others they grow on the abdomen or other parts of the body. Recent studies suggest that these opsins set the
pace for biological clocks by registering the change of light from day to night.
This brings us back around to the very origin of eyes, which I described in my first post. Long before full-fledged eyes evolved,
light-sensitive molecules may have existed in microbes, allowing them to change their movements during night and day. These molecules
may have been incorporated into early eyes, making it possible for animals to see. But this transition didn't mean that photoreceptors
could no longer serve their original function. Early insects may have used opsins both within their eyes to see and outside of their eyes
as biological clocks. Later, some lineages of insects lost their eyes. Some may have lost them in dark caves. Fleas, on the other hand,
lost their eyes as they became parasites. Instead of navigating through a complex landscape in search of a particular prey, they just
hopped from one host to the next. But they still relied on opsins to run their biological clocks. The authors point out that scientists have
also found opsins in other animals that have lost their eyes. The animals? None other than Astyanax.
What's particularly remarkable about the new study is how strongly the flea opsin resisted any evolutionary change--even after it was
no longer being used in the flea eye. The molecule need the same functional structure for both jobs. As I mentioned at the beginning
of my previous post, Charles Darwin recognized that the complexity of the eye might appear to pose a major challenge to his theory.
To some people, it still does; they argue that the components of the eye cannot function on their own, and so they could never have
existed on their own. By this reasoning, it would be impossible for one of these components--an opsin, for example--to do anything
useful if it wasn't inside an eye.The flea apparently sees things differently.Comments (9) + TrackBacks (0) Category: Evolution
The scientists used this tree to track the evolution of some of the molecules that are essential for vision. Known as opsins, they respond
to light by triggering a chemical reaction that sends a signal from the eye to the brain. Opsins can be sensitive to different colors, depending
on their shape, which depends in turn on the DNA sequence in their genes. The scientists isolated the gene for green opsins from 11
species of scorpionflies, snow fleas, and true fleas.
The scientists then compared the DNA sequences for signs of change. A mutation to an opsin gene may have no effect on the opsin
molecule itself, or it may alter its structure dramatically. The difference depends on where in the DNA sequence that mutation strikes.
The scientists found that most changes that occurred during the evolution of fleas had no effect on the actual opsins. They confirmed
this by using the DNA sequence of the opsin genes to create computer models of the opsin molecules themselves. Even in fleas, the
green opsin molecule has basically the same structure as in scorpionflies--despite their radically different eyes.
Just because a gene hasn't changed for millions of years doesn't mean that it hasn't been experiencing natural selection. The scientists
found evidence that the opsin gene has been experience a special kind of natural selection in fleas and their relatives, known as purifying
selection. Purifying selection occurs if even the slightest change to the structure of a molecule puts a serious dent in the reproductive
success of an animal. The fact that fleas have experience purifying selection on their opsin gene means that it remains essential to their
survival. (The details of their work appear in a paper in press at the journal Molecular Biology and Evolution.)
So what on Earth are the fleas doing with their opsins? The scientists doubt that the fleas are using them in their eyes. They point out
that flea eyes are covered over in a tough layer of chitin, and they lack the lenses and other structures that would let them see. But in
many animals, ranging from pigeons to salmon to butterflies, opsins have also been found outside the eye. In some animals, they grow
inside the brain, while in others they grow on the abdomen or other parts of the body. Recent studies suggest that these opsins set the
pace for biological clocks by registering the change of light from day to night.
This brings us back around to the very origin of eyes, which I described in my first post. Long before full-fledged eyes evolved,
light-sensitive molecules may have existed in microbes, allowing them to change their movements during night and day. These molecules
may have been incorporated into early eyes, making it possible for animals to see. But this transition didn't mean that photoreceptors
could no longer serve their original function. Early insects may have used opsins both within their eyes to see and outside of their eyes
as biological clocks. Later, some lineages of insects lost their eyes. Some may have lost them in dark caves. Fleas, on the other hand,
lost their eyes as they became parasites. Instead of navigating through a complex landscape in search of a particular prey, they just
hopped from one host to the next. But they still relied on opsins to run their biological clocks. The authors point out that scientists have
also found opsins in other animals that have lost their eyes. The animals? None other than Astyanax.
What's particularly remarkable about the new study is how strongly the flea opsin resisted any evolutionary change--even after it was
no longer being used in the flea eye. The molecule need the same functional structure for both jobs. As I mentioned at the beginning
of my previous post, Charles Darwin recognized that the complexity of the eye might appear to pose a major challenge to his theory.
To some people, it still does; they argue that the components of the eye cannot function on their own, and so they could never have
existed on their own. By this reasoning, it would be impossible for one of these components--an opsin, for example--to do anything
useful if it wasn't inside an eye.The flea apparently sees things differently.Comments (9) + TrackBacks (0) Category: Evolution
