Published by Oxford University Press [2008] on behalf of the Society for Experimental Biology
Preface
Despite an increased recognition of the multifunctional roles of symbioses both in lineage creation (endosymbiosis) and ecological adaptation, the past importance and continued involvement of symbioses in evolutionary processes has received less attention. Partnership formation can be seen as a ‘quick fix’ on an evolutionary timescale, providing innovative solutions to situations that were outside the capability of the genome of one or more of the partners, resulting in enhanced metabolic capabilities and greater environmental flexibility. Rather surprisingly, however, the significance of this in terms of evolutionary fitness is still somewhat speculative, as are the evolutionary drivers behind partnership formation. That ancient prokaryotes were often crucial to the formation of these partnerships is perhaps not surprising given their remarkable ability to tolerate a wide range of environmental extremes.
Classic views about symbioses involving mutual co-operation are often difficult to reconcile with the experimental evidence that often shows one partner benefits significantly more than the other. In the case of the chloroplast and mitochondrial symbionts considerable reductions in their genomes have occurred during the course of evolution, so that much of the metabolic control has shifted to the nucleus. What were the initial advantages associated with these associations? Could a reduced genome size have been an advantage in these ancestral partnerships? Of particular interest is the recognition that similar signalling networks may be present in a range of plant symbioses that were, in turn, based on common developmental pathways. Do all symbioses have a similar basal plan? Clearly, classical views about symbioses may fall short of the experimental facts and often fail to account for any evolutionary benefits. At the ecosystem scale there is still much to understand about the role that symbioses may have in inter-plant interactions and the shaping of communities. New insights and approaches to understanding symbioses are, however, attempting to reconcile some of the uncertainties that underpin the establishment and maintenance of partnership formation in plant symbioses and their ecological significance.
It was against this background that a special session on symbioses was organized as part of the Annual Meeting of the Society for Experimental Biology held in Glasgow, UK, in April 2007. This was also the first time for 20 years that there had been a session on symbioses at the Annual Meeting. The presentations at the meeting encompassed a diverse range of animal, microbe, and plant symbioses. Although only papers based on plant associations are included in this Special Issue they represent a diverse collection of reviews and experimental studies that provide new insights or alternative perspectives on symbioses and symbiotic interactions.
I would like to acknowledge the Society for Experimental Biology, The Journal of Experimental Botany, The International Symbiosis Society, and the British Ecological Society for financial support. In addition, I thank my meeting co-organizers, Angela Douglas, Derek Mitchell, Julie Scholes, and Tom Wilkinson, for their support.
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