Molecular characterisation and phylogenetic relationships of cystoid nematodes of the family Heteroderidae (Nematoda: Tylenchida)

Abstract

The cystoid sedentary nematodes of the Heteroderidae include more than 30 recognised species belonging to from nine to 11 genera, depending on the opinion of the authority. In the present study, we collected nematode populations of species belonging to some of these genera, as well as other cyst-forming species from different locations in the USA, Vietnam, Germany and Russia. The populations of cystoid nematodes represent seven valid species, Atalodera carolynae, Cryphodera sinensis, Meloidodera astonei, M. floridensis, M. mexicana, M. sikhotealiniensis, Rhizonemella sequoiae, two unidentified species of Atalodera, six unidentified species of Cryphodera, and three putative new species of Rhizonemella. We also obtained samples of cyst-forming nematodes that include an unidentified species of Betulodera from California, and Heterodera guangdongensis from Vietnam. A population of Rotylenchulus sp. from Arizona, intercepted in Florida, and a population of an unidentified species of Verutus from Germany were also added to this study. All of these populations were characterised using sequences of the D2-D3 of 28S rRNA, ITS rRNA or mitochondrial COI genes. A total of 89 new sequences were obtained from these analyses. Phylogenetic relationships within the family Heteroderidae were reconstructed based on the D2-D3 of 28S rRNA, ITS rRNA and mitochondrial COI gene sequences. Results revealed that the subfamily Ataloderinae was paraphyletic. Ekphymatodera thomasoni, a non-cyst-forming species, clustered with the cyst-forming nematodes. Representatives of the subfamily Verutinae formed clades within Heteroderidae. The genus Meloidodera was non-monophyletic and distributed within two clades: i) M. sikhotealiniensis and Cryphodera spp. from Asia and Europe; and ii) M. astonei, M. floridensis and M. mexicana from North America. Based on comparative molecular analysis Meloidodera alni syn. n. is proposed as a junior synonym of M. sikhotealiniensis. Problems of taxonomy and phylogeography of cystoid nematodes are also discussed.