Rates and patterns of chromosomal evolution in Drosophila pseudoobscura and D. miranda

¹ Universidade de Santiago de Compostela
² University of Edinburgh

^* To whom correspondence should be addressed. E-mail: cbhusson{at}usc.es.

Submitted on December 12, 2005
Revised on March 1, 2006
Accepted on 15 March 2006

	Abstract

Comparisons of gene orders between species permit estimation of the rate of chromosomal evolution since their divergence from a common ancestor. We have compared gene orders on three chromosomes of Drosophila pseudoobscura with its close relative, D. miranda, and the distant outgroup species, D. melanogaster, by using the public genome sequences of D. pseudoobscura and D. melanogaster and about 50 in situ hybridizations of gene probes in D. miranda. We find no evidence for extensive transfer of genes among chromosomes in D. miranda. The rates of chromosomal rearrangements between D. miranda and D. pseudoobscura are far higher than found before in Drosophila, and approach those for nematodes, the fastest rate among higher eukaryotes. In addition, we find that the D. pseudoobscura chromosome with the highest level of inversion polymorphism (Muller's element C) does not show an unusually fast rate of evolution with respect to chromosome structure, suggesting that this classic case of inversion polymorphism reflects selection rather than mutational processes. On the basis of our results, we propose possible ancestral arrangements for the D. pseudoobscura C chromosome, which are different from that current in the literature. We also describe a new method for correcting for rearrangements that are not detected with a limited set of markers.

Key Words: Drosophila miranda, Drosophila pseudoobscura, chromosomal evolution, chromosomal rearrangements, evolution rate

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