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).