This Week in Evolution

Experimental populations of hermaphroditic plants evolved a significant increase in male function in only three generations.

Many plant species are hermaphrodites, with each individual producing both pollen and seeds. Others species have separate sexes, as mammals and birds do, while still others have mixtures of unisexuals and hermaphrodites. Based on the distribution of these traits in the family tree of life, evolutionary transitions among these "lifestyles" appear to have been fairly common. This week's paper shows how hermaphrodites can evolve to be more female or, in this case, more male. Hermaphroditic Sex Allocation Evolves When Mating Opportunities Change was just published in Current Biology by Marcel Dorken and John Pannell.

Continue reading "How fast can sexual traits evolve?" »

Posted by R. Ford Denison at 03:24 AM | Permalink | Comments (0)

How did the first life on Earth arise? We may never know for sure, but can we at least demonstrate one or more mechanisms that could have led to life as we know it? Not yet, but this week’s paper seems like a significant step towards that goal. “Self-sustained replication of an RNA enzyme” was published in Science by Tracey Lincoln and Gerald Joyce.

Most species have protein-based enzymes (running the biochemical reactions needed for growth and reproduction) and DNA-based heredity (passing genetic information to the next generation), with RNA serving various other functions. Under the “RNA-world” hypothesis, however, RNA molecules once served both as enzymes and for heredity. Some viruses use RNA as their hereditary material and some RNA molecules still act as enzymes, with a key role in protein synthesis, for example.

Can we recreate the early RNA world in a laboratory? What is the simplest system that could evolve by natural selection, eventually leading to something that would be universally recognized as alive?

Continue reading "Experimental evolution of an RNA world" »

Posted by R. Ford Denison at 08:04 PM | Permalink | Comments (0)

Fossils and DNA-sequence comparisons among species are like fingerprints and other clues found at crime scenes. We can often draw reliable conclusions about past events (evolutionary or criminal) from such physical evidence, but some people prefer eyewitness accounts. So evolutionary biologists are increasingly doing experiments that let us see evolution in action. Evolution is a change over generations, so the short generation times of microbes make them especially useful for experimental evolution.

Two recent examples, both published in Proceedings of the Royal Society, are "Experimental evolution of a microbial predator's ability to find prey", by Kristina Hillesland, Greg Velicer, and Richard Lenski, and "Experimental evolution of a sexually selected display in yeast", by David Rogers and Duncan Grieg.

Continue reading "Experimental evolution of predation and sexual attractiveness" »

Posted by R. Ford Denison at 08:18 PM | Permalink | Comments (0)

I’m done with two grant proposals, revising a book chapter, and checking the final version of a review article. I still have a pile of interesting reading and writing to do before I can get back into the lab – actually, I did help Ryoko set up an experiment yesterday – but no more looming deadlines for awhile. So, here are two more summaries of talks from Evolution 2008.

Do I know you?

The ability to tell other individuals apart by their faces is presumably maintained by natural selection, so you can recognize and avoid bad guys. But is there also selection for looking different enough to be recognizable? Or is it better to blend in with the crowd, so you can get away with stuff?

Michael Sheehan and Elizabeth Tibbetts are studying individual recognition in wasps (Tibbetts and Dale, 2007). Their hypothesis is that distinctive-looking individuals benefit, because they get in fewer fights over dominance.

Continue reading "More talks from Evolution 2008" »

Posted by R. Ford Denison at 09:37 PM | Permalink | Comments (0)

About 1500 scientists attended Evolution 2008 here last week. The four-day meeting was filled with 15-minute talks (usually ten at once, in different rooms), plus two evening poster sessions (like a science fair, for grownups, with discussions rather than judging), scenically located on a pedestrian bridge over the Mississippi. Reports that “scientists are abandoning evolution�? appear to be exaggerated.

Here are summaries of some of the talks I enjoyed.

Continue reading "Evolution 2008: sexy plants, battling bacteria, durable cooperation" »

Posted by R. Ford Denison at 08:36 PM | Permalink | Comments (3)

This week’s paper is Facultative cheater mutants reveal the genetic complexity of cooperation in social amoebae published in Nature by Lorenzo Santorelli and colleagues at Rice University and Baylor College of Medicine, both in Texas.

The evolution of cooperation is a central problem in the history of life. Darwin explained how sophisticated adaptations -- “the structure of the beetle which dives through the water… the plumed seed which is wafted by the gentlest breeze�? -- can evolve in a series of small improvements over generations. But some of the major transitions in evolution are harder to explain, because It seems that they should have been opposed, rather than supported, by natural selection. The origin of multicellular life is a good example. It’s not that hard to imagine independent cells working together in loose groups for mutual benefit – huddling together for defense, say – but why would a cell give up the ability to reproduce, as most of the cells in our bodies have done?

Continue reading "Knowing when not to cheat" »

Posted by R. Ford Denison at 09:41 PM | Permalink | Comments (0)

There are enough examples of ‘‘cheating’’ in bacteria ... that mindless obedience to such [quorum-sensing] chemical signals cannot be assumed. Mindlessness can be assumed, but not obedience. -- Denison et al. (2003) Ecology 84:838-845

Quorum sensing, an exchange of chemical signals among bacteria, can solve the coordination problem. But this week's paper Cooperation and conflict in quorum-sensing bacterial populations shows that quorum sensing doesn't automatically solve the problem of cheaters. The paper is by Stephen Diggle, Ashleigh Griffin, Genevieve Campbell, and Stuart West and published in Nature.

Continue reading "Communication doesn't automatically prevent cheating" »

Posted by R. Ford Denison at 11:08 PM | Permalink | Comments (0)

Two papers on cooperation this week. If you were trying to help someone, but end up causing problems for them, were you being cooperative? I have no idea, so I like to study cooperation in microbes. Microbes don't have brains, so "intent" isn't a factor. And the only definition of "benefit" that makes sense is an increase in Darwinian fitness or reproductive success, which is often easy to measure in microbes; just count them.
I like these definitions:

Cooperation: a behaviour which provides a benefit to another individual (recipient), and which is selected for because of its beneficial effect on the recipient. [Exhaling CO2 isn't cooperation; it evolved as a side-effect of breathing oxygen, not to benefit plants.]
Cheaters: individuals who do not cooperate (or cooperate less than their fair share), but are potentially able to gain the benefit of others cooperating. ["Equal share" might be less ambiguous.]

Continue reading "Cooperation and cheating in microbes: quorum sensing and persisters" »

Posted by R. Ford Denison at 05:27 PM | Permalink | Comments (0)

Yesterday, my wife asked, "why are there so many theoretical papers in evolutionary biology?" I suggested one reason may be that evolutionary theory is better developed, in the sense of making accurate predictions, than theory in much of biology. This week's paper, comparing results from an evolution experiment to predictions of a mathematical model, is a good example.

The paper is about the evolution of cooperation. This is a hot topic and also my own area of research. Humans enforce cooperation, to varying extents. For example, we often punish cheaters, those who try to benefit from cooperative activities of others without contributing anything themselves. Human cheaters are mostly pretty stupid -- don't even think about plagiarizing this blog for a term paper! -- but what about cheaters with no brains at all?

Continue reading "How disturbed are most cheaters, really?" »

Posted by R. Ford Denison at 10:16 PM | Permalink | Comments (4)

A reader asked an interesting question about the difficulty of coordinated evolution of groups of genes. Although I welcome comments and questions, I won't usually have time for detailed responses. and I'd already discussed one paper this week. But then Huxley brought in a recent issue of Nature he'd been chewing on, and there it was: "Empirical fitness landscapes reveal accessible evolutionary paths" (Nature 445: 383-386). So I guess I should take this dog-given opportunity to talk about the evolution of multiple interacting genes. The Nature paper is a review article with no original data, so isn't eligible for my regular weekly paper discussion, but maybe it's OK as a bonus paper, especially since the most interesting papers it discusses were published within the last year and they do contain original data.

The exciting thing about these papers is that people are starting to use molecular methods in experiments that solve "you can't get there from here" problems in evolutionary biology.

Continue reading "Experiments with "fitness landscapes" explain evolution of interacting genes" »

Posted by R. Ford Denison at 03:57 PM | Permalink | Comments (9)

Last week's paper discussed trade-offs between seed size and seed number. Many such trade-offs (growth vs. reproduction, more seeds vs. taller stem, etc.) follow directly from conservation of matter or energy, but what about other sorts of trade-offs? It has been suggested, for example, that there is a trade-off between competitiveness and dispersal ability. Why should this be? For seeds, at least, a larger seed gives the seedling a head-start against competitors, but smaller seeds travel farther on the wind.

This week's paper proposes another trade-off, for which the mechanism is less obvious. "Drop or fly? Negative genetic correlation between death-feigning ability and flying ability as alternative anti-predator strategies", was written by Tatunori Ohno and Takahisa Miyatake and published in Proceedings of the Royal Society B (vol. 274, p. 555-560).

Continue reading "Experimental evolution: play dead or fly away?" »

Posted by R. Ford Denison at 07:05 PM | Permalink | Comments (3)