Morphological, morphometrical, and molecular characterization of Metarhabditis amsactae (Ali, Pervez, Andrabi, Sharma and Verma, 2011) Sudhaus, 2011 (Rhabditida, Rhabditidae) from India and proposal of Metarhabditis longicaudata as a junior synonym of M. amsactae

Abstract

A new population of Metarhabditis amsactae from India is morphologically, morphometrically, and molecularly characterized. This material is characterized by having 0.65 to 1.14 mm length, lips rounded, and grouped in pairs, stoma with metastegostoma bearing setose denticles, pharynx with metacorpus slightly swollen and fusiform, nerve ring, and excretory pore located at isthmus level, female reproductive system didelphic-amphidelphic with vulva equatorial, female tail conical-elongate with acute tip, male tail conical with large and robust posterior filiform part, spicules free with hooked manubrium slightly bent ventrad, gubernaculum with narrow corpus, bursa open leptoderan with eight genital papillae and phasmids posterior to the GP8. Molecular studies based on 18S and 28S rDNA genes are provided for the first time for the species. In addition, integrated morphological, morphometrical, and molecular characters are compared with other previous records of the species. According to our analysis, Metarhabditis longicaudata and other material described as different species are proposed as new junior synonyms of M. amsactae.

Keywords: 18S rDNA; 28S rDNA; ITS rDNA; Metarhabditis amsactae; Metarhabditis longicaudata n. syn.; Molecular analysis; Morphology; New synonym; Taxonomy.

Figure 1:

Metarhabditis amsactae (Ali, Pervez, Andrabi, Sharma and Verma, 2011) Sudhaus, 2011 (line drawing). A: Anterior region; B: Cephalic region; C: Anterior branch of the female reproductive system; D: Entire female; E: Entire male; F: Female posterior region; G: Male posterior region.

Figure 2:

Metarhabditis amsactae (Ali, Pervez, Andrabi, Sharma and Verma, 2011) Sudhaus, 2011 (light microscopy). A: Anterior region (arrow pointing to the excretory pore); B: Cephalic region; C: Vagina region; D: Female posterior region (black arrow pointing to the anus, white arrow pointing to the phasmid); E: Anterior branch of the female reproductive system (black arrow pointing to the spermatheca); F-J: Male posterior region in lateral (F-I) and ventral (J) views, at spicules (F, H) and bursa (G, I) level (black arrows pointing to the genital papillae, white arrows pointing to the phasmids).

Figure 3:

Metarhabditis amsactae (Ali, Pervez, Andrabi, Sharma and Verma, 2011) Sudhaus, 2011 (scanning electron microscopy). A, B: Cephalic and lip region in sublateral and frontal views, respectively; C, F: Lateral field (arrows pointing to the longitudinal incisures); D, E: Excretory pore (arrow) at ventral and lateral views, respectively; G, H: Vulva in ventral and lateral views, respectively; I: Female anus; J, K: Female posterior region in right lateral and ventral views, respectively (white arrows pointing to the phasmid); L, M; Male posterior region in ventral and lateral views (black arrows pointing to the genital papillae, white arrows pointing to the phasmids).

Figure 4:

Bayesian Inference tree from previously and the newly sequenced Metarhabditis amsactae (bold) and other closely related species based on sequences of the Internal Transcribed Spacer (ITS1-5.8S-ITS2) rDNA region. Bayesian posterior probabilities (%) are given for each clade. The scale bar shows the number of substitutions per site.

Figure 5:

Bayesian Inference tree from the newly sequenced Metarhabditis amsactae (bold) and other closely related species based on sequences of the small subunit (18S) of rDNA region. Bayesian posterior probabilities (%) are given for each clade. The scale bar shows the number of substitutions per site.

Figure 6:

Bayesian Inference tree from the newly sequenced Metarhabditis amsactae (bold) and other closely related species based on sequences of the D2/D3 domain of large subunit (28S) of rDNA region. Bayesian posterior probabilities (%) are given for each clade. The scale bar shows the number of substitutions per site.