Submitted to: Molecular Phylogenetics and Evolution
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/15/2007
Publication Date: 3/12/2007
Citation: Weimin, Y., Giblin-Davis, R.M., Davies, K.A., Purcell, M.F., Scheffer, S.J., Taylor, G.S., Center, T.D., Morris, K., Thomas, K. 2007. Molecular phylogenetics and the evolution of host plant associations in the nematode genus Fergusobia (Tylenchida: Fergusobiinae). Molecular Phylogenetics and Evolution. 45(1):123-141. 2007. Interpretive Summary: Diversion of water flow from the Everglades during the 1950s allowed exotic species to invade previously undisturbed, pristine habitats. Foremost amongst these invaders was the Australian melaleuca tree which usurped a half million acres. Biological control is being implemented to assist effort to control this plant by hampering the trees ability to re-establish in areas where it has been removed. Plant-feeding insects imported from Australia are being released after long-term testing ensures that they will not harm other plants. Most recently, a fly that carries a nematode in its body cavity was released to compliment the earlier release of a weevil. The nematode is deposited in the plant tissue with the fly eggs where it causes the plant tissue to form a tumor-like growth called a gall which the fly larvae eats. As part of the effort to ensure that these organisms would not attack anything other than melaleuca, it was necessary to determine how they were related to other similar species from related plants. It was found that the insect and nematode lineages tracked the plant lineages suggesting a long co-evolutionary history of the plant-fly-nematode association so that each plant species hosted its own unique fly and nematode.
Technical Abstract: Fergusobia nematodes (Tylenchida: Fergusobiinae) and Fergusonina flies (Diptera: Fergusoninidae) are mutualists that develop together in galls formed in meristematic tissues of many species of the plant family Myrtaceae in Australasia. Evolutionary relationships of Fergusobia species were inferred from phylogenetic analyses of the DNA sequences of the nuclear ribosomal DNA near-full length small subunit (up to1689 bp), partial large subunit D2/D3 domain (up to 889 bp), and partial mitochondrial cytochrome oxidase subunit I (618 bp). The analyses included 21 SSU, 87 D2/D3, and 82 mtCOI sequences from Fergusobia isolates sampled from a variety of myrtaceous hosts and gall types in Australia and New Zealand between 1999 and 2006. The SSU data supported a monophyletic Fergusobia genus within a paraphyletic Howardula. A clade of Drosophila-associated Howardula, including H. aoronymphium, was the closest sequenced sister group. Sequence data of LSU and mtCOI supplied significant phylogenetic information across this broadly divergent genus. Phylogenetic analysis revealed a many monophyletic clades within Fergusobia. The relationships inferred by D2/D3 and mtCOI were congruent with some exceptions. Well-supported clades were generally consistent with host plant species and gall type. However, phylogenetic analysis suggested host switching or putative hybridization events in many groups, except the lineage of shoot bud gallers on the broad-leaved Melaleucas.