Friday, September 05, 2014

the extended phenotype: indirect genetic effects on ecosystems

thescientist |  The relationship between an individual’s phenotype and genotype has been fundamental to the genetic analysis of traits and to models of evolutionary change for decades. Of course, scientists have long recognized that phenotype responds to nongenetic factors, such as environmental variation in nutrient availability or the presence of other, competing species. But by assuming that the genetic component of a particular trait is confined to your genes and only yours, scientists overlooked another important input: the genes of your neighbors.
Take field crickets as an example. To identify potential mates, female crickets listen with ears on their forelegs to the males’ songs, produced by the rubbing together of their forewings. Some males emit series of long, trill-like chirps, an advertisement of their fitness that females find very attractive. Songs dominated by short chirps have less pull. But female crickets don’t evaluate songs on their absolute merits; instead, their preferences are influenced by the songs they’ve heard in the past. Female crickets previously exposed only to songs with long chirps are less likely to respond to short-chirp songs than females that have been exposed to the songs of less-fit males already. The insects appear to be retaining information about available males and then using that information to assess the attractiveness of suitors.1
Choosing mates amidst competition is ubiquitous among animals, but the logistics of how such choice evolved is less straightforward: because male song type is largely determined by genetics, female mating behavior is under the influence of male genes. In other words, the females’ decision-making behaviors evolved based on the genetic composition of the entire social group. Such indirect genetic effects (IGEs), also called associative effects or extended phenotypes, are common and have profound implications for evolution. Beyond learning and behavior in social species, IGEs affect how organisms develop, how productive plants are, and whether individuals are attacked by predators, herbivores, and disease.
In some sense, examples of IGEs are intuitively obvious. No individual exists in a vacuum, isolated from the influences of others it encounters. Yet for decades, many prominent evolutionary theories assumed that all of the genetic influences on an individual’s phenotype came from genes within itself. What the field needs now is a clear framework that recognizes IGEs as additional factors in a population’s evolution, allowing for more-accurate predictions about how biological systems will change in the future. The genetic makeup of an individual not only influences phenotypes of individuals in its own species, but can have far-reaching effects on organisms at different trophic levels within its food web, impacting the dynamics of entire ecosystems. The role of commensal microbes in human health is a prime example of how IGEs can transcend species boundaries.
How IGEs affect evolutionary dynamics remains very much an open question. Recent theoretical strides in this area show how IGEs can greatly accelerate evolutionary change and hint at their hitherto unsuspected roles in such varied phenomena as animal mating rituals, the development of human agricultural systems, species range shifts in response to climate change, and even altruism. The influences of IGEs on diverse evolutionary processes are undoubtedly more complicated than most models can capture, and biologists must think creatively about new phenomena that IGEs may drive.


BigDonOne said...

[ BD unearthed this little essay for your weekend perusal... ]
FUTURE TIME ORIENTATION by Andy MacDonald at May 16, 2006
Along with many of our readers, I was confused by the term "future time orientation" as used in the Seattle Public School's definition of cultural racism. (Mentioned in this SP article) So I did some Googling.

It turns out, judging by the number of hits, "time orientation" is a big topic in education and psychology, but hard
definitions are not easy to find. The best I've seen is "how people compare the present to the future [or the past]." Even
that definition is sketchy, so I'll summarize my impressions from reading a number of pages relating to the subject.

The time orientation of a person or culture can be past, present or future. (There are other dimensions, such as
monochronic and polychronic, which we don't need to go into here.) Past-oriented cultures tend to believe all the great decisions were made in the past, and present society is a degenerate version of some past golden age. They
don't value innovation highly, preferring to preserve what already exists. Tibet is a good example of such a culture, and fundamentalist Islam fits the definition, too. Future-oriented people, in contrast, believe in setting goals, planning how to reach them and innovating when necessary to accomplish their aims. Western society is the prime example of a future-oriented culture, and even for us it is a relatively recent invention, really only arising during the Renaissance. Present-oriented folks think only about the here and now, not considering how their acts relate to tradition or will effect their happiness in the future. They are impulsive and will not delay immediate gratification
for some greater future reward.

Which of these orientations is best? According to the Seattle Public Schools, even asking the question is racist. However, free academic inquiry still exists as an idea, even if it is dying in the academy, so I will attempt an answer.

Future time oriented cultures have higher standards of living and healthier populations than others, because they produce innovations to create a better life. Future-oriented individuals are more likely to sacrifice in the present (such as studying for exams rather than playing) for reward in the future. They are also more likely to plan ahead for career and retirement, and so be less dependent as they get older. Past-oriented people are more passive but at least have strong tradition to fall back on. If that tradition includes saving for a rainy day or being part of an extended family that helps in old age, a person can do rather well. Present-orientation doesn't provide any safeguards. Too many of our citizens fall in this category, spending themselves into debt, having unprotected sex, and engaging in other risky
behaviors without thought of the consequences.

Future time orientation provides more benefits than the other two, and the schools should promote that outlook. "Be prepared," as the Boy Scouts say, and beyond that teach children to know what they want out of life and how to plan and sacrifice to achieve their goals. To do less is to condemn them to a life of sloth and ignorance.