Introduction
Evolution occurring over ecological time scales can potentially affect community functions both directly and indirectly; the latter via changes in composition . Community composition and function in turn shapes evolution . Disentangling the effect of evolution from purely ecological dynamics on community function therefore requires manipulation of evolutionary changes independently of ecological changes. In simple laboratory communities of readily culturable taxa, this can be achieved by evolving taxa within communities, and then comparing the function of evolved and ancestral communities reassembled to have the same starting taxonomic composition . This approach is however impractical for most natural communities, where there is extensive diversity and many taxa are hard to culture in isolation. An alternative approach involves a degree of separation of evolutionary and ecological processes in time. Community members can be pre-adapted for different amounts of time, added back into a community and the compositional and functional consequences determined (14). The pre-adaptation step will likely result in changes in community composition, which might then influence the composition of ancestral community to which it is returned. The impact of this can be greatly minimised by the addition of only very small amounts of the pre-adapted community.
We used this approach to determine the importance of rapid evolution on the composition and function of a methanogenic community. Methane production, which is of both major environmental and biotechnological significance, is the result of interactions between many different community members, with the breakdown of complex polymers to methane involving a number of biochemical steps carried out by different taxa. This diversity makes it a parsimonious system to investigate the potential role of rapid evolution, as large amounts of ecological trait variation are predicted to impede rapid evolutionary change . Furthermore, methane production typically increases rapidly during propagation on a novel feedstock , providing an unambiguous community level phenotype for which the role of rapid evolution can be determined. We initiated 12 replicate laboratory fermenters using a methanogenic community isolated from an industrial anaerobic digestor. These communities were “pre-adapted” for 6 weeks, while the ancestral community was kept at 4°C to minimise any compositional and evolutionary changes. The pre-adapted communities were then inoculated at a low frequency (1%) into new reactors set up from the ancestral community (“adaptation” treatment), and gas production and composition over 6 weeks compared with “control” reactors initiated with the ancestral community only (Fig. 1).