Trends in Genetics
OpinionCauses and evolutionary significance of genetic convergence
Section snippets
Evolutionary convergence provides outstanding study systems
During the billions of years of evolution, similar selective pressures have occasionally led to the independent evolution of identical or similar traits in distantly related species, a phenomenon referred to as phenotypic convergence 1, 2. The recent wide use of genetic and/or phylogenetic approaches has uncovered diverse examples of repeated evolution of adaptive traits including the multiple appearances of eyes 3, 4, echolocation in bats and dolphins 5, 6, pigmentation modifications in
When phenotypic convergence is caused by mutations in the same gene
In the numerous reports of phenotypic convergence the responsible genetic mechanisms remain largely unknown because their identification is often complicated by the involvement of complex biochemical cascades as well as epistatic interactions 19, 23, 24. In some cases it has been shown that different loci are involved in phenotypic convergence (e.g. Refs 8, 25, 26), demonstrating that similar phenotypes can be reached through alterations of distinct enzymes. However, other studies have traced
Evolutionary significance of convergent recruitment
Convergent recruitment indicates that genes suitable for creating a given phenotype are rare 20, 28, 29. Whereas the absence of appropriate genes in some lineages can hamper the acquisition of specific phenotypes, the presence of genes that are able to acquire a given function can enhance the probability that a given group of organisms evolves a new trait. During evolution coding sequences have reached different areas of protein space (Box 1) through the accumulation of amino acid replacements.
When phenotypic convergence is caused by identical substitutions
In addition to convergent recruitment, several studies have traced phenotypic convergence to identical genetic substitutions in different lineages 5, 6, 37, 38, 39. Whereas convergent substitutions can theoretically occur in coding and non-coding regions, most reports concern replacement of the same protein residue by an identical amino acid in independent lineages. After careful statistical consideration 37, 40 or experimental demonstration 27, 41, the adaptive value of repeated substitutions
Concluding remarks
Whereas convergent recruitment suggest that only a few genes have the potential to create a specific phenotypic change, the occurrence of convergent adaptive substitutions at diverse taxonomic scales tells us that some substitutions are more likely to be involved in the emergence of a novel adaptation. Studies of natural selection at the genetic level can benefit greatly from the information provided by convergent adaptive substitutions because these provide naturally occurring genetic points
Acknowledgements
Funding for this work was provided by the Swiss National Science Foundation grant PBLAP3-129423 to P.A.C. and the Intra-European fellowship PIEF-GA-2008-220813 to G.B. The authors thank Kaya Schmandt and three anonymous reviewers for helpful comments on earlier versions of the manuscript.
Glossary
- Convergence
- independent appearance of the same trait in different lineages.
- Convergent recruitment
- the process of homologous gene becoming recurrently responsible for a novel function.
- Convergent substitution
- replacement of the same ancestral character (e.g. amino acid) by an identical character.
- Epistatic interaction
- influence of one gene on the expression of another gene.
- Gene family
- a group of homologous genes which are generally responsible for similar catalytic reactions. Multigene families contain
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