No abstract

Darwin recognized that natural selection could not favor a trait in one species solely for the benefit of another species. The modern, selfish-gene view of the world suggests that cooperation between individuals, whether of the same species or different species, should be especially vulnerable to the evolution of noncooperators. Yet, cooperation is prevalent in nature both within and between species. What special circumstances or mechanisms thus favor cooperation? Currently, evolutionary biology offers a set of disparate explanations, and a general framework for this breadth of models has not emerged. Here, we offer a tripartite structure that links previously disconnected views of cooperation. We distinguish three general models by which cooperation can evolve and be maintained: (i) directed reciprocation--cooperation with individuals who give in return; (ii) shared genes--cooperation with relatives (e.g., kin selection); and (iii) byproduct benefits--cooperation as an incidental consequence of selfish action. Each general model is further subdivided. Several renowned examples of cooperation that have lacked explanation until recently--plant-rhizobium symbioses and bacteria-squid light organs--fit squarely within this framework. Natural systems of cooperation often involve more than one model, and a fruitful direction for future research is to understand how these models interact to maintain cooperation in the long term.

No abstract

No abstract

No abstract

No abstract

Following a sixty-year hiatus in western medicine, bacteriophages (phages) are again being advocated for treating and preventing bacterial infections. Are attempts to use phages for clinical and environmental applications more likely to succeed now than in the past? Will phage therapy and prophylaxis suffer the same fates as antibiotics--treatment failure due to acquired resistance and ever-increasing frequencies of resistant pathogens? Here, the population and evolutionary dynamics of bacterial-phage interactions that are relevant to phage therapy and prophylaxis are reviewed and illustrated with computer simulations.

The climatic and biotic conditions at any geographic location will change through time, for example, because of the advance of glaciers. If it is to avoid extinction, a species adapted to a moving habitat must either track its habitat spatially, or adapt genetically to the new environmental conditions. These processes of migration and evolution are important in determining continental biogeographic patterns. We develop a model to explore the relative contributions of adaptation and dispersal as alternative mechanisms whereby a population can respond to changing environmental conditions. In our model the environment to which the species is adapted moves across the landscape at a constant velocity, and a quantitative trait determines each individual's fitness as a function of the local environmental conditions. Local populations are allowed to adapt genetically to the environmental conditions at each point in space, so that a cline develops in the quantitative character. We find that if the rate of environmental movement is slow, the species will track its environment across space, otherwise it will go extinct. Additionally, the higher the genetic variance in the character, the easier it is for the species to maintain itself in a moving environment. Our results generalize previous models that predict a critical patch size of suitable habitat necessary for population persistence.