Phylogeny of dracunculoid nematodes (Chromadorea: Rhabditida: Spirurina: Dracunculoidea) from some Eurasian freshwater fishes

Abstract

Sets of small ribosomal DNA (SSU rDNA) and large ribosomal DNA (LSU rDNA) sequences were obtained for Philometroides moraveci Vismanis & Yunchis, 1994, Philometra kotlani (Molnár, 1969), Philometra rischta Skrjabin, 1923, Philometra cf. obturans (Prenant, 1886) (Philometridae), Sinoichthyonema amuri (Garkavi, 1972), Agrachanus scardinii (Molnár, 1966), Kalmanmolnaria intestinalis (Dogiel & Bychowsky, 1934) and Skrjabillanus tincae Shigin & Shigina, 1958 (Skrjabillanidae). Phylogenetic analysis of SSU rDNA data shows that dracunculoid nematodes are divided into two well-supported clades designated as Clade I and Clade II, respectively. Clade I includes the type species of the genus Philonema Kuitunen-Ekbaum, 1933, some species from the family Daniconematidae Moravec & Køie, 1987 and two subfamilies of skrjabillanids, Skrjabillaninae Shigin & Shigina, 1958 and Esocineminae Moravec, 2006. Clade II unites species from the families Dracunculidae Stiles, 1907, Micropleuridae Baylis & Daubney, 1926 and Philometridae Baylis & Daubney, 1926. Within the Philometridae, there are several well-supported groups of species, one of which unites freshwater Philometra spp. from the Palearctic cyprinids, identified as P. kotlani, P rischta, P. ovata (Zeder, 1803) and P. cyprinirutili (Creplin, 1825). However, the phylogenetic relationships of most philometrids are unresolved. An analysis of partial SSU and LSU rDNA sequences indicates that there is no direct phylogenetic relationship between Agrachanus Tikhomirova, 1971 (type species Skrjabillanus scardinii Molnár, 1966) and Skrjabillanus Shigin & Shigina, 1958 (type species Sk. tincae), which means that the genus Agrachanus can be resurrected. Our study confirms that Philonematinae Ivashkin, Sobolev & Khromova, 1971 should be elevated to the family rank. We formally establish the family Philonematidae Ivashkin, Sobolev & Khromova, 1971 stat. nov. We also suggest combining the superfamilies Dracunculoidea Stiles, 1907 and Camallanoidea Railliet & Henry, 1915 into the infraorder Camallanomorpha Roberts, Janovy & Nadler, 2013.

On the Evolutionary History of Philometridae (Nematoda: Dracunculoidea): Integrative Taxonomy Reveals Evidence of Character Diversification and Host–Parasite Cophylogenetic Patterns

“…Even though the current database has few 28S sequences of philometrids and the phylogenetic reconstruction generated from these sequences was limited to 11 species belonging to three genera (Philometra, Philometroides and Buckleyella), some important results could be observed. Similar to the phylogenies of 18S [4,14,15,17], that of 28S showed no monophyly of Philometra and Philometroides, the basal position of Ps. acreanensis, the monophyly of components of Clade B (Ph.…”

“…Philometroides seriolae, the type species of the genus, is a sister lineage of Ph. gymnosardae forming a strongly supported relationship, documented in several phylogenetic reconstructions from 18S sequences [4,14,15,17]. Some authors suggest that the isolation source of the 18S sequence identified as Ps.…”

“…tunisiensis Moravec, Chaabane, Neifar Gey et Justine, 2016 was not considered due to some taxonomic problems (see the discussion of this paper). The dracunculoid Philonema onchorynchi Kuitunen-Ekbaum, 1933 (Philonematidae) was used as outgroup, based on previous phylogenies of Philometridae/Dracunculoidea showing that this nematode, which is also parasitic in fish, represents a closely related basal lineage to Philometridae [4,[12][13][14][15]17]. Information on these sequences associated with parasite and host taxa, habitat, geographic origin, site of infection of gravid females, GenBank ID and reference is given in Table 1.…”

“…Several genetic characterizations of philometrid nematodes have been published in the last two decades [4,[12][13][14][15][16][17], which were important for the advancement of knowledge about their diversity [1,4]. However, despite this progress, most species are yet to be genetically characterized and need morphological revaluation [4].…”

“…Therefore, the evolutionary history and systematics of Philometridae remain blurry. For example, the largest genera within the family, namely, Philometra Costa, 1845 and Philometroides Yamaguti, 1935, have been polyphyletic in molecular phylogenies, suggesting their artificiality and the necessity of a revaluation of their generic diagnosis [4,[14][15][16][17].…”