Ribosomal DNA in the Grasshopper Podisma pedestris: Escape From Concerted Evolution

Author:

Keller Irene1,Chintauan-Marquier Ioana C12,Veltsos Paris1,Nichols Richard A1

Affiliation:

1. School of Biological and Chemical Sciences, Queen Mary, University of London, London E1 4NS, United Kingdom and

2. Laboratoire d'Ecologie Alpine, Université Joseph Fourier, 38041 Grenoble Cedex 09, France

Abstract

Abstract Eukaryote nuclear ribosomal DNA (rDNA) typically exhibits strong concerted evolution: a pattern in which several hundred rDNA sequences within any one species show little or no genetic diversity, whereas the sequences of different species diverge. We report a markedly different pattern in the genome of the grasshopper Podisma pedestris. Single individuals contain several highly divergent ribosomal DNA groups. Analysis of the magnitude of divergence indicates that these groups have coexisted in the Podisma lineage for at least 11 million years. There are two putatively functional groups, each estimated to be at least 4 million years old, and several pseudogene groups, many of which are transcribed. Southern hybridization and real-time PCR experiments show that only one of the putatively functional types occurs at high copy number. However, this group is scarcely amplified under standard PCR conditions, which means that phylogenetic inference on the basis of standard PCR would be severely distorted. The analysis suggests that concerted evolution has been remarkably ineffective in P. pedestris. We propose that this outcome may be related to the species' exceptionally large genome and the associated low rate of deletion per base pair, which may allow pseudogenes to persist.

Publisher

Oxford University Press (OUP)

Subject

Genetics

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