MBE Advance Access published online on April 2, 2003
Molecular Biology and Evolution, doi:10.1093/molbev/msg081
Molecular Biology and Evolution © Society for Molecular Biology and Evolution 2003; all rights reserved
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1 Dipartimento di Scienze Ambientali, Università degli Studi di Parma, Parco Area delle Scienze, 43100 Parma, Italy
* To whom correspondence should be addressed. E-mail: andrea{at}dsa.unipr.it.
Ancient asexuals have been considered to be a contradiction of the basic tenets of evolutionary theory. Barred from rearranging genetic variation by recombination, their reduced number of gene arrangements is thought to hamper their response to changing environments. For the same reason, it should be difficult for them to avoid the build-up of deleterious mutations. Several groups of taxonomically diverse organisms are thought to be ancient asexuals, although clear evidence for or against the existence of recombination events is scarce. Several methods have recently been developed for predicting recombination events by analyzing aligned sequences of a given region of DNA that all originate from one species. The methods are based on phylogenetic, substitution and compatibility analyses. Here we present the results of analyses of sequence data from different loci studied in several groups of evolutionarily distant species that are considered to be ancient asexuals, using seven different types of analysis. The groups of organisms were the arbuscular mycorrhizal fungi (Glomales), Darwinula stevensoni (Darwinuloidea crustacean ostracods) and the bdelloid rotifers (Bdelloidea), which are thought to have been asexual for the last 400, 25-100 and 35-40 million years, respectively. The seven different analytical methods evaluated the evolutionary relationships among haplotypes and these methods had previously been shown to be reliable for predicting the occurrence of recombination events. Despite the different degree of genetic variation among the different groups of organisms, at least some evidence for recombination was found in all species groups. In particular, predictions of recombination events in the arbuscular mycorrhizal fungi were frequent. Predictions of recombination were also found for sequence data that has previously been used to infer the absence of recombination in bdelloid rotifers. Although our results have to be taken with some caution since they could signal very ancient recombination events or possibly other genetic variation of non-recombinant origin, they suggest that some cryptic recombination events may exist in these organisms. Key Words:
Ancient asexuals, recombination, gene conversion, mosaic sequences
© 2003 Society for Molecular Biology and Evolution
Original Articles
Evidence of Recombination in Putative Ancient Asexuals
2 Institute of Ecology, University of Lausanne, Biology Building, 1015 Lausanne, Switzerland
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