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November 24, 2010

Darwinian agriculture book, plant breeding meeting, grant on evolution of multicellularity...

Princeton University Press sent the third review of the draft for my book, "Darwinian agriculture: where does Nature's wisdom lie?" and needed my responses to all three reviews, so that's kept me too busy to blog this week. Sorry about that. Two of three reviews were enthusiastic, so I'm guessing the book will actually be published.

Next week, I'll be in Paris, talking to plant breeders interested in "organic and low-input" farming. I'm going to talk about evolutionary tradeoffs and associated opportunities, including our ideas for improving symbiotic nitrogen fixation and Jacob Weiner's ideas for crops that cooperate to suppress weeds. Someone emailed me saying the meeting (EUCARPIA) had more people wanting to attend than they could accommodate.

Mike Travisano, Will Ratcliff, Mark Borrello, and I got an NSF grant for experimental evolution of multicellularity. We already have some cool results, which I'll write about as soon as our first paper is published.

November 15, 2010

Lengthy comment on group selection

Someone left a comment on an old post about group selection, here. Its length and use of an apparent pseudonym make me suspect cut-and-paste, in which case I'll delete it. IT WAS SO I DID.

See also this recent post.

November 12, 2010

So many papers, so little time

Here are the papers I'm considering this week. Any requests? Otherwise, I'll probably discuss one of my own recent papers, on the implications of evolutionary tradeoffs for agriculture and human health.
Why genes overlap in viruses

Identification of an ant queen pheromone regulating worker sterility

DDS, 4,4′-diaminodiphenylsulfone, extends organismic lifespan

Evolutionary history of partible paternity in lowland South America

The evolution of cultural adaptations: Fijian food taboos protect against dangerous marine toxins

Conditional Cooperation and Costly Monitoring Explain Success in Forest Commons Management

Periodic climate cooling enhanced natural disasters and wars in China during AD 10-1900

A climate for contemporary evolution

The evolution of menopause in cetaceans and humans: the role of demography

Prosocial behaviour emerges independent of reciprocity in cottontop tamarins

Fossilized glycolipids reveal past oceanic N2 fixation by heterocystous cyanobacteria

November 6, 2010

Do more-durable public goods select for or against cheating?

"I don't think taxpayers should have to pay for the bailout; let the government pay for it!" -- An irate taxpayer, interviewed after an earlier corporate bailout
This week's paper is "Molecular and regulatory properties of a public good shape the evolution of cooperation", recently published by Rolf Kummerli and Sam Brown in the Proceedings of the National Academy of Sciences. The full paper is freely available on-line, making it an example of a public good.

Public goods are benefits that are widely available, rather than available only to those that produce them. A school, a bridge, or a medical treatment developed in a government lab may be used by someone who didn't contribute to its cost, such as a child, a tourist, or a wealthy tax-cheat. All three of these examples are durable, continuing to providing benefits for many years, although the school won't be much use unless we continue paying teachers. How does the durability of public goods affect the prevalence of "free-riders", who take the benefit without contributing to the cost?

This week's paper discusses a public good used by bacteria, namely, pyoverdin, which picks up scarce iron from the environment and releases it to iron-hungry bacteria. Iron is often scarce inside the hosts infected by these bacteria, because hosts actively limit iron levels to prevent infection. Starving humans may have low enough iron levels that we shut down the iron-reducing system, but then relief supplies arrive, including iron pills....

Pyoverdin is a public good because it can be used by bacterial "cheaters" that don't release any of it into the environment. Making pyoverdin has a cost, so you might expect "cheaters" to proliferate. That does tend to happen, but it depends on how durable pyoverdin is (that is, how many times each molecule can transfer iron before it breaks down) and on the production options available to the bacteria.

Bacterial neighborhoods where everyone makes pyoverdin tend to get invaded by cheats that never make pyoverdin. If pyoverdin breaks down quickly, though, those neighborhoods fall apart, killing off the cheats, while more-cooperative neighborhoods survive longer. So durability undermines cooperation. ("We already have a bridge -- no more taxes!")

But things are different if the "cooperators" make pyoverdin only when it's in short supply. Then the cost of cooperation is lower, so cheaters don't invade as easily. ("Let's inspect the bridge yearly, but make costly repairs only if needed.")

The "results" just described are actually predictions from their computer model. But Kummerli and Brown also looked at real bacteria that differ in pyoverdin production. Although different pyoverdins differ in durability, they simulated increased durability mainly by adding pyoverdin. Consistent with the computer model, cheaters that never make pyoverdin out-competed cooperators, but only when pyoverdin levels were low. With more "durable" bioverdin, cooperators stopped making bioverdin, eliminating their competitive disadvantage. So increasing the durability of public goods can actually favor cooperation, so long as cooperators don't over-invest in public goods.

A large fraction of fundamental scientific research is currently supported as a public good. When people started dying in large numbers from AIDS, we didn't know what caused it. Some people thought it was caused by "being gay." In theory, individual drug companies could all have tried to find the cause and kept their results secret, each hoping to gain a monopoly on effective AIDS treatments. But probably no company would have invested enough money to make much progress, knowing that another company might be doing similar work and further along. So the task of finding the cause fell mainly to government researchers and government-funded university researchers, who then published their results. Drug companies then stepped in and used that information to develop a variety of effective treatments.

So scientific knowledge is mainly a public good and a relatively durable one. Today's technology is based on scientific knowledge generated over many decades. How much do we want to invest today in generating new knowledge, only some of which will be used immediately?

November 5, 2010

This week's picks

Three recent papers that look interesting:

Molecular and regulatory properties of a public good shape the evolution of cooperation

Multiple mating and its relationship to alternative modes of gestation in male-pregnant versus female-pregnant fish species

Evolution of Yeast Noncoding RNAs Reveals an Alternative Mechanism for Widespread Intron Loss

November 3, 2010

Is it really bet-hedging?

Before the ink is even dry on our Current Biology paper on bet-hedging in rhizobia (actually, before it's even printed), Xue-Xian Zhang and Paul B Rainey have critiqued it in Genome Biology. They summarize Will Ratcliff's results, then ask "whether it is an evolutionary response to fluctuating selection shaped by natural selection." Experimental evolution, an approach Rainey and colleagues have used successfully, would be a good way to answer this question.

But is it really even bet-hedging? To qualify as bet-hedging, you need to sacrifice arithmetic-average fitness to gain greater geometric-average fitness. That would obviously depend on the environment, but it seems reasonable to assume that having half your progeny go dormant would sacrifice fitness when food is abundant, while increasing the chances of having at least one surviving progeny under starvation.

Zhang and Rainey seem to think there's an additional requirement to qualify as bet-hedging, namely, "switching rates to suit prevailing conditions." I disagree. Isn't a 50:50 mix of stocks and bonds (rather than 100% stocks, which have higher average return but are riskier) considered bet-hedging, even if you never change that ratio? But I do agree that it's important to know whether the ratio of dormant to growing cells changes in response to conditions, which I would call phenotypic plasticity. We are working on that.

November 1, 2010

Carnival of Evolution

Lots of people are blogging about evolution now. Byte-size Biology has a good selection of recent posts.