Molecular Biology and Evolution, Vol 16, 157-164, Copyright © 1999 by Society for Molecular Biology and Evolution
A Hugall, J Stanton and C Moritz
Among root knot nematodes of the genus Meloidogyne, the polyploid obligate
mitotic parthenogens M. arenaria, M. javanica, and M. incognita are
widespread and common agricultural pests. Although these named forms are
distinguishable by closely related mitochondrial DNA (mtDNA) haplotypes,
detailed sequence analyses of internal transcribed spacers (ITSs) of
nuclear ribosomal genes reveal extremely high diversity, even within
individual nematodes. This ITS diversity is broadly structured into two
very different groups that are 12%-18% divergent: one with low diversity
(< 1.0%) and one with high diversity (6%-7%). In both of these groups,
identical sequences can be found within individual nematodes of different
mtDNA haplotypes (i.e., among species). Analysis of genetic variance
indicates that more than 90% of ITS diversity can be found within an
individual nematode, with small but statistically significant (5%-10%; P
< 0.05) variance distributed among mtDNA lineages. The evolutionarily
distinct parthenogen M. hapla shows a similar pattern of ITS diversity,
with two divergent groups of ITSs within each individual. In contrast, two
diploid amphimictic species have only one lineage of ITSs with low
diversity (< 0.2%). The presence of divergent lineages of rDNA in the
apomictic taxa is unlikely to be due to differences among pseudogenes.
Instead, we suggest that the diversity of ITSs in M. arenaria, M. javanica,
and M. incognita is due to hybrid origins from closely related females (as
inferred from mtDNA) and combinations of more diverse paternal lineages.
ORIGINAL ARTICLE
Reticulate evolution and the origins of ribosomal internal transcribed spacer diversity in apomictic Meloidogyne
Co-operative Research Centre for Tropical Plant Pathology, Queensland, Australia. ahugall@zoology.uq.edu.au
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