Biologists zero in on role of plasticity in evolution

Mar 10, 2014 by Peter Reuell
Grad student Delbert André Green II (left) and Associate Professor Cassandra Extavour have been able to show how phenotypic plasticity may be connected to evolution in a single mechanism — insulin signaling in fruit flies. “This is the first example, to my knowledge, that shows this link — between heritability and plasticity — being controlled by the same mechanism,” Extavour said. Credit: Kris Snibbe/Harvard Staff Photographer

For more than a century, scientists have suggested that the best way to settle the debate about how phenotypic plasticity—the way an organism changes in response to environment—may be connected to evolution would be to identify a single mechanism that controls both. Harvard researchers say they have discovered just such a mechanism in insulin signaling in fruit flies.

Cassandra Extavour, an associate professor of organismic and evolutionary biology, and grad student Delbert André Green II were able to show that a single molecular pathway plays a role in both heritable changes in the flies' number of ovarioles—egg-producing compartments in the ovaries—and in how they react to their environments by shutting down some ovarioles. The study is described in a paper published this month in the Proceedings of the Royal Society B.

"This is the first example, to my knowledge, that shows this link—between heritability and plasticity—being controlled by the same mechanism," Extavour said. "What we've done with this paper is show that an important trait that controls how many offspring a fruit fly will have exhibits both heritable variation and phenotypic plasticity, and that both are controlled by insulin signaling."

While the study offers the first evidence of a link, it also addresses larger questions that have long lingered in .

"More broadly, the question this work is looking at is: What is the contribution of phenotypic plasticity to evolution?" Extavour said. "There is a great deal of variation that is caused by phenotypic plasticity—like butterfly eyespots or the size of frog tadpoles or whether an organism will reproduce asexually or sexually. All those things seem like they could have a large impact on fitness, but if none of those changes are heritable, they may not be relevant to evolution. These are questions that have occupied the scientific community for decades."

Scientists have long understood that different insects, including different species of , have different numbers of ovarioles. More recently, a number of studies have shown that that those differences, at least in fruit flies, were tied to variation in insulin signaling.

For Extavour and Green, the first hint that a heritable trait—differences in ovariole number—might be linked with phenotypic plasticity came when they put flies on a starvation diet.

Extavour explained that ovariole number is among the traits that flies can alter through phenotypic plasticity. When food is abundant, the flies ramp up their reproduction to take advantage of the situation. When they are starved, however, the flies make fewer ovarioles in an effort to conserve resources. The surprise for researchers, Extavour said, was that some flies seemed to notice the change in their food supply virtually overnight, while others responded far more slowly.

The mechanism behind those phenotypic changes is insulin signaling.

"We found a difference in the operation of this molecular pathway between species," Extavour said. "The reason that's exciting is because it explains two things about their reproduction—the first is why they have different ovariole numbers overall, and the second is why they respond differently to being starved. Or in other words, why they have different levels of phenotypic plasticity in ovariole number."

Importantly, Extavour said, the trait researchers used to explore the connection between plasticity and heritability has a clear link to evolutionary fitness.

"This is a trait … where the potential impact on fitness is pretty clear," she said. "Flies that have few ovarioles aren't going to lay as many eggs, and they'll have fewer offspring than flies with more ovarioles."

In addition to uncovering the first molecular links between heritability and plasticity, Extavour and Green were able to demonstrate that the differences in insulin signaling—with some species showing high levels and others showing lower levels—could be tied to local ecological conditions.

To get at that question, they compared fruit fly species found only in the Seychelles, in the Indian Ocean, with species found around the world.

What they found, Extavour said, was striking: Flies from the Seychelles, which typically lived in restricted habitats and specialized in a single diet, had significantly lower levels of insulin signaling, and significantly fewer ovarioles, than flies that ate a more general diet.

"We're hypothesizing that the type of niche the flies occupy might have an influence on whether they have high or low levels of , and that in turn is going to have an effect on whether they have high or low numbers of ovarioles," Extavour said. "One way to summarize that is to say that flies with very limited and restricted diets don't need to have a particularly finely tuned response to changes in nutrition, because they largely don't experience any changes in their diet. For the that live catch-as-catch-can, however, if food supplies are good at the moment, they need to be able to sense that quickly and ramp up reproduction quickly, or if food is bad, they need a mechanism to know that so they can turn it down and not waste their resources."

The research is an important step, Extavour added, but "doesn't end the debate about heritability and phenotypic plasticity. What it does it give us a concrete example of something that had been theorized—it's saying, 'Yes, this is possible.' "

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HenisDov
1 / 5 (1) Mar 10, 2014
איך נברא היקום יש מאין
Origin And Nature of the Universe
New Science 2013 versus classical science
Classical Science Is Replaced By 2013 Gravity Comprehension !!!
http://universe-l...gravity/
Attn classical science hierarchy, including Darwin and Einstein…
"I hope that now you understand what gravity is and why it is the monotheism of the universe…DH"
=================================
Gravity is the natural selection of self-attraction by the elementary particles of an evolving system on their cyclic course towards the self-replication of the system. Period
( Gravitons are the elementary particles of the universe. RNA nucleotides genes and serotonin are the elementary particles of Earth life)
כח המשיכה
כח המשיכה הוא הבחירה הטבעית להיצמדות הדדית של חלקיקי היסוד של מערכת מתפתחת במהלך התפתחותה המחזורית לעבר שיכפולה. נקודה
( הגרוויטון הוא חלקיק היסוד של היקום. הגנים, הנוקלאוטידים של חומצה ריבונוקלאית והסרוטונין הם החלקיקים היסודיים של חיי כדור הארץ) Dov Henis (comments from 22nd century)
http://universe-l...science/
http://universe-l...-theory/
JVK
1 / 5 (2) Mar 11, 2014
Nutrient-dependent/pheromone-controlled adaptive evolution: a model
http://www.socioa...53/27989

Excerpt: "Clearly, however, the epigenetic effects of food odors and pheromones are involved in neurogenic niche construction as exemplified in nematodes (Bumbarger, Riebesell, Rödelsperger, & Sommer, 2013), and in flies (Swarup et al., 2013)."

Excerpt: "In flies, ecological and social niche construction can be linked to molecular-level cause and effect at the cellular and organismal levels via nutrient-dependent changes in mitochondrial tRNA and a nuclear-encoded tRNA synthetase. The enzyme enables attachment of an appropriate amino acid, which facilitates the reaction required for efficient and accurate protein synthesis (Meiklejohn et al., 2013).

The conserved molecular mechanisms that enable ecological adaptations are detailed in my 2013 review, which includes other across-species examples of cause and effect sans mutations.
JVK
1 / 5 (2) Mar 11, 2014
Classical Science Is Replaced By 2013 Gravity Comprehension !!!


http://universe-l...-theory/

Singularity is attained only ONCE per circa 20 billion years when ALL the gravitons of the universe are together at zero inter-gravitons space because it takes the totality of their combined low inter-attraction force to form the universal singularity.


Can anyone else make sense of that statement and link what they think it means to the singularities of mathematics, geometry, complex analysis, natural sciences or technology and economics, and/or the singularity of Creation that leads from olfactory receptor genes to nutrient-dependent pheromone-controlled ecological adaptations in species from microbes to man?

It seems clear that all singularities make sense only in the context of a Creator God.

If that doesn't make sense to you, keep asking "Where did gravity come from?" Tell me when you figure that out.