Thursday, September 27, 2007

Evolution of Cooperation

Ford Denison at This Week in Evolution posted today on two interesting new papers dealing with the evolution of cooperation.

The original view of evolution was epitomized by the phrase "Nature, red in tooth and claw." (I'm not sure how popular it was with scientists, but it was undoubtedly popular with the public). This view dovetailed nicely with the concepts of "survival of the fittest" and "natural selection."

In the 30s, 40s and 50s, old-school ecologists, such as W.C. Allee and Alfred Emerson, sort of rebelled against this paradigm, claiming that animals often behaved altruistically, particularly to their peers. This period marked the apex of the Group Selectionist school of ecological thinking.

The pendulum swung back the other way in the 60s, when a young post-doctoral associate at the University of Chicago, G.C. Williams, left lecture by Emerson muttering "Something must be done...." (Perhaps apocryphal, from Sober & Wilson's Unto Others). The result was Adaptation and Natural Selection (1966). This marked the rise of the Selfish Gene movement in evolutionary biology, culminating with Richard Dawkins classic, The Selfish Gene. This is not to say that the concept of cooperation was totally abandoned. Actually, it was placed on a more substantial theoretical foundation, particularly by W.D. Hamilton, who developed the notion of kin selection and Hamilton's Rule. Nonetheless the emphasis was definitely on selfish behavior.

More recently cooperation has been making a comeback. Many papers are being published in the field and there are quite a few labs devoted to the subject. To Ford's two papers, I'd like to add one of my own, reporting on work from the Currie Lab at UW: Madison. The paper has just appeared in PLoS One so all can access. Here Poulson et al. (2007) look at the evolution of cooperation using a really neat study system: the fungus-farming ants.

The attine ants are really Earth's first farmers because they began to cultivate fungus by providing it food and protection over 50 million years ago, with the domestication of a fungus in the family Lepiotaceae. As any farmer knows, it's hard work to keep your crop free of pests and disease. This is true too for the ants; their fungal crop often suffers infestation from the parasitic microfungi, Escovopsis.

Fortunately for the ants, they have help, from the actinomycetous bacteria, Pseudonocardia no less. (For more on actinomycetes, check out Twisted Bacteria; he also posted on this system earlier). Specifically, the Pseudonocardia are the third partners in the mutualism; they produce antibiotics that inhibit Escovopsis growth. Poulson et al. (2007) write "The antibiotic-producing bacteria are typically housed in elaborate structures on the cuticle of workers, connected to exocrine glands that appear to provide nutrients to support the growth of Pseudonocardia." So, in other words, these ants maintain little bottles of pest spray on their backs. How cool is that?

Educational materials can be found here and here.

Incidentally, the phrase, "Nature, red in tooth and claw" derives from canto 56 in the poem, In Memoriam A.H.H., by the English poet Alfred, Lord Tennyson. It's a wonder anyone found it; the poem is quite long :P

Photo: Bridge forming ants from Mark Ridley's Evolution.


  1. A recent paper related to collaboration, selfishness and communication among bacteria: Social cheating in Pseudomonas aeruginosa quorum sensing. But read first the press release, which explains it in a readable (and entertaining) way: Bacteria join ranks of lazy cheaters. The topic yields nice headlines ("cheating" and the like), so the article has appeared in many sites on the web.

  2. Thanks for citing my blog and for alerting me to this interesting new paper from Currie's lab. The antagonism they report between the antibiotic-producing bacteria is reminiscent of that between the fungi the ants grow, which I've discussed earlier. In each case, it prevents the ants from getting the (presumed) benefits of biodiversity.