Some aspects of the taxonomy, biology, possible evolution and biogeography of nematodes of the spirurine genus Rhabdochona Railliet, 1916 (Rhabdochonidae, Thelazioidea)

Abstract

At present the nematode genus Rhabdochona Railliet, 1916 (Rhabdochonidae) comprises 92 possibly valid species, mostly intestinal parasites of freshwater fishes in all zoogeographical regions. Because of the absence of any phylogenetic studies using molecular methods in this nematode group, an attempt to evaluate affinities among these parasites and their zoogeography on the basis of morphological features and host-parasite relationships has been carried out. Only true definitive hosts should be considered for such evaluation. It appears that, during the evolution of Rhabdochona spp., there occur an increase in the number of anterior prostomal teeth, loss of lateral alae, the right spicule attains a boat-like shape and a dorsal barb develops on its distal tip, and the distal tip of the left spicule attains gradually a more complex structure; the eggs with a smooth surface are considered to be more primitive. Nematodes of this genus most probably originated in the region of present southern Asia at the beginning of Tertiary. Closest to the initial type appear to be members of the subgenus Globochona Moravec, 1972, from which lineages leading to the subgenera Globochonoides Moravec, 1975, Rhabdochona Railliet, 1916 and Sinonema Moravec, 1975 can be derived. The morphology of Rhabdochona spp. indicate a close relationship between the Palaearctic fauna of these nematodes with the Nearctic species, and the Oriental fauna with the Ethiopian fauna. The Neotropical species can be derived from Nearctic members of the subgenus Rhabdochona; the latter probably penetrated, along with leuciscine hosts into North America from Palaearctic Eurasia at the end of Tertiary. The distribution of Palaearctic species of Rhabdochona corresponds to faunistical complexes in the conception of ichthyologists.

Biogeographic Hierarchical Levels and Parasite Speciation

“…As siluriforms are considered the original hosts of Rhabdochona spp. (Moravec, 2010), the calibration point is taken to be 140 mya (Ferraris, 2007;Lundberg et al, 2007).…”

“…The form of this character is species specific to Rhabdochona spp. (Mejía-Madrid et al, 2007a;Moravec, 2010;Rasheed, 1965). Indeed, the first phylogenetic systematic analysis of this group recovered spicule form as a consistent character (Mejía-Madrid et al, 2007a).…”

“…from Asia, Europe, and America is increasing (Černotíková et al, 2011;Mejía-Madrid & Nadler unpublished data;Wijowá et al, 2007). In the present analysis 37 out of 92 (40%) valid species have been included, mainly because this set of species is fairly well described for their main discriminant character, the male left spicule, as well as for other key characters (Mejía-Madrid et al, 2007a;Moravec, 2010;Moravec et al, 2011). The American species are completely represented in the present analyses, but I include representative species distributed worldwide, with the exception of R. papuanensis Moravec, Ríha & Kuchta, 2008. The historical biogeographic analysis presented here is based on the updated matrix used for generating the phylogenetic framework of Rhabdochona spp.…”

“…The American species are completely represented in the present analyses, but I include representative species distributed worldwide, with the exception of R. papuanensis Moravec, Ríha & Kuchta, 2008. The historical biogeographic analysis presented here is based on the updated matrix used for generating the phylogenetic framework of Rhabdochona spp. presented in Mejía-Madrid et al (2007a) with additional character coding derived from recently redescribed species from the Americas and Asia (Moravec & Muzzall, 2007;Moravec, 2010;Moravec, et al, 2011; Figure 1). The results presented herein represent a new phylogenetic framework for Rhabdochona spp., with two outstanding characteristics: the phylogeny is fairly well resolved and the degree of resolution is higher than that previously recovered.…”

Rhabdochona (Rhabdochona) keralaensis sp. nov. (Rhabdochonidae) and some other nematodes in the Indian mottled eel Anguilla bengalensis bengalensis from India

“…Moravec (2010) (Kakar et al 2010, Aguilar-Aguilar et al 2010, Moravec and Yooyen 2011. However, R. gubernacula has subsequently been designated a species inquirenda by Moravec and Yooyen (2011) and R. ictaluri has been synonymized with R. kidderi Pearse, 1936 (see Moravec et al 2012).…”