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The complex hybrid origins of the root knot nematodes revealed through comparative genomics

Lunt, David H.; Kumar, Sujai; Koutsovoulos, Georgios; Blaxter, Mark L.


Sujai Kumar

Georgios Koutsovoulos

Mark L. Blaxter


Root knot nematodes (RKN) can infect most of the world’s agricultural crop species and are among the most important of all plant pathogens. As yet however we have little understanding of their origins or the genomic basis of their extreme polyphagy. The most damaging pathogens reproduce by obligatory mitotic parthenogenesis and it has been suggested that these species originated from interspecific hybridizations between unknown parental taxa. We have sequenced the genome of the diploid meiotic parthenogen Meloidogyne floridensis, and use a comparative genomic approach to test the hypothesis that this species was involved in the hybrid origin of the tropical mitotic parthenogen Meloidogyne incognita. Phylogenomic analysis of gene families from M. floridensis, M. incognita and an outgroup species Meloidogyne hapla was carried out to trace the evolutionary history of these species’ genomes, and we demonstrate that M. floridensis was one of the parental species in the hybrid origins of M. incognita. Analysis of the M. floridensis genome itself revealed many gene loci present in divergent copies, as they are in M. incognita, indicating that it too had a hybrid origin. The triploid M. incognita is shown to be a complex double-hybrid between M. floridensis and a third, unidentified, parent. The agriculturally important RKN have very complex origins involving the mixing of several parental genomes by hybridization and their extreme polyphagy and success in agricultural environments may be related to this hybridization, producing transgressive variation on which natural selection can act. It is now clear that studying RKN variation via individual marker loci may fail due to the species’ convoluted origins, and multi-species population genomics is essential to understand the hybrid diversity and adaptive variation of this important species complex. This comparative genomic analysis provides a compelling example of the importance and complexity of hybridization in generating animal species diversity more generally.


Lunt, D. H., Kumar, S., Koutsovoulos, G., & Blaxter, M. L. (2014). The complex hybrid origins of the root knot nematodes revealed through comparative genomics. PeerJ, 2014(1), Article e356.

Journal Article Type Article
Acceptance Date Mar 31, 2014
Online Publication Date May 6, 2014
Publication Date May 6, 2014
Electronic ISSN 2167-8359
Publisher PeerJ
Peer Reviewed Peer Reviewed
Volume 2014
Issue 1
Article Number e356
Keywords genome sequencing; phylogenomics; Meloidogyne incognita; Meloidogyne hapla; Meloidogyne floridensis; comparative genomics; hybrid speciation
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