No abstract

No abstract

2A and 3). Nevertheless, in both environments there was no relation between ability to diversify and time spent evolving in the original high-nutrient media (Fig. 3) (sign tests of correlations between number of genotypes and transfer number for the six lines: P Ͼ 0.2 in both cases). Adaptation can limit the ability of bacterial genotypes to diversify genetically. This was not the result of generalist evolution or the evolution of an intrinsic reduction in evolvability, but was caused by environment-specific adaptation. Given the strong empirical support for both the importance of environmental heterogeneity in diversification (7-14) and epistasis (6, 24), it is likely that rugged fitness landscapes, a requirement for the observed effects, are common. These results are therefore likely to be generally relevant and may help to explain patterns of diversity over both micro-and macroevolutionary time scales. Consistent with recent interpretations of macroevolutionary adaptive radiations (25), we predict that in environments that can potentially support similar levels of diversity, diversification is more likely to occur immediately following colonization of the environment than through expansion into new niches within the environment after an extinction event. 25. D. Schluter, The Ecology of Adaptive Radiations (Oxford Univ. Press, Oxford, 2000). 26. We thank L. Hurst and three anonymous referees for comments on the manuscript. This work was funded by the Royal Society and Natural Environment Research Council (UK).

No abstract