title: Invasion and persistence of a selfish gene in the Cnidaria.
abstract: BACKGROUND
  Homing endonuclease genes (HEGs) are superfluous, but are capable of invading populations that mix alleles by biasing their inheritance patterns through gene conversion. One model suggests that their long-term persistence is achieved through recurrent invasion. This circumvents evolutionary degeneration, but requires reasonable rates of transfer between species to maintain purifying selection. Although HEGs are found in a variety of microbes, we found the previous discovery of this type of selfish genetic element in the mitochondria of a sea anemone surprising.
  
  
  RESULTS
  We surveyed 29 species of Cnidaria for the presence of the COXI HEG. Statistical analyses provided evidence for HEG invasion. We also found that 96 individuals of Metridium senile, from five different locations in the UK, had identical HEG sequences. This lack of sequence divergence illustrates the stable nature of Anthozoan mitochondria. Our data suggests this HEG conforms to the recurrent invasion model of evolution.
  
  
  CONCLUSIONS
  Ordinarily such low rates of HEG transfer would likely be insufficient to enable major invasion. However, the slow rate of Anthozoan mitochondrial change lengthens greatly the time to HEG degeneration: this significantly extends the periodicity of the HEG life-cycle. We suggest that a combination of very low substitution rates and rare transfers facilitated metazoan HEG invasion.
authors.affiliation: School of Biological Sciences, University of Auckland, New Zealand; National Environment Research Council Centre for Population Biology, Imperial College, London, United Kingdom. m.goddard@auckland.ac.nz
authors.forename: Matthew R
authors.initials: MR
authors.lastname: Goddard
authors.forename: Jessica
authors.initials: J
authors.lastname: Leigh
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Roger
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Pemberton
mesh_terms: D000818:Animals; D001499:Bayes Theorem; D003063:Cnidaria / Q000145:classification / Q000201:enzymology* / Q000235:genetics*; D004262:DNA Restriction Enzymes / Q000235:genetics*; D004272:DNA, Mitochondrial / Q000235:genetics; D003576:Electron Transport Complex IV / Q000235:genetics*; D019143:Evolution, Molecular; D005785:Gene Conversion; D022761:Gene Transfer, Horizontal; D050259:Genes, Mitochondrial; D005828:Genetics, Population; D008957:Models, Genetic; D010802:Phylogeny; D012615:Sea Anemones / Q000201:enzymology / Q000235:genetics; D013045:Species Specificity; D006113:United Kingdom
chemical_list: D004272:DNA, Mitochondrial; D003576:Electron Transport Complex IV; D004262:DNA Restriction Enzymes