Journal of Molecular Evolution

, Volume 41, Issue 6, pp 727–731

Faster evolutionary rates in endosymbiotic bacteria than in cospeciating insect hosts


  • Nancy A. Moran
    • Department of Ecology and Evolutionary BiologyUniversity of Arizona
  • Carol D. von Dohlen
    • Department of Ecology and Evolutionary BiologyUniversity of Arizona
  • Paul Baumann
    • Microbiology SectionUniversity of California-Davis

DOI: 10.1007/BF00173152

Cite this article as:
Moran, N.A., von Dohlen, C.D. & Baumann, P. J Mol Evol (1995) 41: 727. doi:10.1007/BF00173152


The hypothesis of a universal molecular clock holds that divergent lineages exhibit approximately constant rates of nucleotide substitution over evolutionary time for a particular macromolecule. We compare divergences of ribosomal DNA for aphids (Insecta) and Buchnera, the maternally transmitted, endosymbiotic bacteria that have cospeciated with aphids since initially infecting them over 100 million years ago. Substitution rates average 36 times greater for Buchnera than for their aphid hosts for regions of small-subunit rDNA that are homologous for prokaryotes and eukaryotes. Aphids exhibit 18S rDNA substitution rates that are within the range observed in related insects. In contrast, 16S rDNA evolves about twice as fast in Buchnera as in related free-living bacterial lineages. Nonetheless, the difference between Buchnera and aphids is much greater, suggesting that rates may be generally higher in bacteria. This finding adds to evidence that molecular clocks are only locally rather than universally valid among taxonomic groups. It is consistent with the hypothesis that rates of sequence evolution depend on generation time.

Key words

AphidBacteriaBuchneraCospeciationEndosymbiosisEvolutionary ratesMolecular clockProkaryoteRibosomal DNA

Copyright information

© Springer-Verlag New York Inc 1995