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Colloquium Papers
COLLOQUIUM PAPERS
Symbiosis as an adaptive process and source of phenotypic complexity
Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, AZ 85721
Genomics has revealed that inheritance systems of separate species are often not well segregated: genes and capabilities that evolve in one lineage are often stably acquired by another lineage. Although direct gene transfer between species has occurred at some level in all major groups, it appears to be far more frequent in prokaryotes than in multicellular eukaryotes. An alternative to incorporating novel genes into a recipient genome is acquiring a stable, possibly heritable, symbiotic association and thus enjoying benefits of complementary metabolic capabilities. These kinds of symbioses have arisen frequently in animals; for example, many insect groups have diversified on the basis of symbiotic associations acquired early in their evolutionary histories. The resulting associations are highly complex, often involving specialized cell types and organs, developmental mechanisms that ensure transfer of symbionts between generations, and mechanisms for controlling symbiont proliferation and location. The genomes of long-term obligate symbionts often undergo irreversible gene loss and deterioration even as hosts evolve dependence on them. In some cases, animal genomes may have acquired genes from symbionts, mirroring the gene uptake from mitochondrial and plastid genomes. Multiple symbionts often coexist in the same host, resulting in coadaptation among several phylogenetically distant genomes.
Baumannia cicadellinicola | genome degradation | horizontal gene transfer | insect | Sulcia muelleri
This paper results from the Arthur M. Sackler Colloquium of the National Academy of Sciences, "In the Light of Evolution I: Adaptation and Complex Design," held December 1–2, 2006, at the Arnold and Mabel Beckman Center of the National Academies of Sciences and Engineering in Irvine, CA. The complete program is available on the NAS web site at www.nasonline.org/adaptation_and_complex_design.
The authors declare no conflict of interest.
*To whom correspondence should be addressed at: Department of Ecology and Evolutionary Biology, University of Arizona, Biological Sciences West 310, 1040 Lowell Street, Tucson, AZ 85721. E-mail: nmoran{at}u.arizona.edu
© 2007 by The National Academy of Sciences of the USA
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