Pristionchus undetermined

Ragsdale, Erik J., Kanzaki, Natsumi, Röseler, Waltraud, Herrmann, Matthias & Sommer, Ralf J., 2013, Three new species of Pristionchus (Nematoda: Diplogastridae) show morphological divergence through evolutionary intermediates of a novel feeding-structure polymorphism, Zoological Journal of the Linnean Society (Zool. J. Linn. Soc.) 168 (4), pp. 671-698 : 686-690

PRISTIONCHUS HOPLOSTOMUS SP. NOV.

= Pristionchus sp. 17 apud Mayer et al. (2009)

Description

Measurements: See Table 2. Adults: Species gonochoristic (i.e. dioecious), with males and females.

Stenostomatous form: Metastegostom bearing: crescent-shaped right subventral ridge, with two or three minute denticles, the denticle at the apex of the ridge being the most conspicuous ( Fig. 7E ); in the left subventral sector, three or four blunt or weakly pointed left subventral denticles, apparently projecting from a common cuticular plate ( Fig. 7D ).

Twelve-plated stenostomatous form: Only one individual observed, presumed rare. Cheilostom divided into 12 complete, distinct per- and interradial plates ( Fig 7E ), some of which may be fused at bases ( Fig. 4E). Anterior end of each plate rounded and elongated to stick out from stomatal opening and form a small flap ( Figs 4E, 7F ). Anterior margin of pro- and mesostegostom, smooth or irregular ( Fig. 7F ). Metastegostom bearing: a large, flint-shaped dorsal tooth ( Fig. 7F ); a crescent-shaped right subventral ridge, with three minute denticles, the denticle at the apex of the ridge being the most conspicuous; three large, triangular left subventral denticles ( Figs 4E, 7F ).

Eurystomatous form: Cheilostom divided into six distinct per- and interradial plates, some plates incompletely split into two longitudinal strips, usually for about two-thirds the length of plate, division of plate often asymmetrical ( Fig. 4F, I), incisions between strips sometimes difficult to observe by LM ( Fig. 4I), resulting in between six and 12 strips in total ( Figs 4F, G, I, 7G, H ). Anterior end of each strip rounded and elongated to stick out from stomatal opening and form a small flap, i.e. constituting between six and 12 flaps in total ( Figs 5A , 7G, H ), although plates that are not split sometimes end in two flaps ( Figs 4F, G, 5A ). Metastegostom bearing: a large and strongly sclerotized claw-like dorsal tooth; a large, claw-like or pointed right subventral tooth ( Fig. 7G, H ); in the left subventral sector, a ridge of large denticles of varying shape, size, and number, i.e. between six and eight, arising from a split cuticular plate, in addition to an adventitious denticle and a separate plate with two or three denticles ( Figs 4G, H, 7G ).

All measurements are in Mm, and are presented as mean ± SD (range), except for the single male specimen, for which all measurements are given. L, total body length; L′, total body length to tail; a, body length/maximum body diameter; b, neck length/body length; c, body length/tail length; c′, tail length/anal body width; T, testis length/body length; V, vulva from anterior end/body length.

All measurements are in Mm, and are presented as mean ± SD (range)

Male: Oval manubrium at anterior end of spicule ( Fig. 8G ). Gubernaculum conspicuous, about one-third spicule length, slightly broader anteriorly such that dorsal wall is recurved, and that dorsal and ventral walls separate at a 15° angle at posterior end ( Fig. 8G ). In lateral view, anterior half of gubernaculum with two serial curves separated by anteriorly directed process and with highly concave terminal curvature about one-quarter of gubernaculum length and proximal curvature about one-third of gubernaculum length; posterior half forming a tube-like process enveloping spicules ( Fig. 8G ). Nine pairs of genital papillae and a pair of phasmids present, and arranged as <P1 (P2d, P3), C, P4, P5d, Ph, (P6, P7, P8), P9d> [= <v1 (v2d, v3), C, v4, ad, Ph (5, v6, v7), pd> in the nomenclature of Sudhaus & Fürst von Lieven, 2003] ( Figs 8E, F , 12B ). Positions of P1 papillae located more than one cloacal body diameter posterior to cloacal slit, P2d and P3 closer to P4 than to P1, P2d at same level or slightly anterior to P3, P4 only slightly posterior to (i.e. within one-quarter of cloacal body diameter of) C, and closer to P2d than to P5d, P5d equidistant between P4 and P6, Ph clearly anterior to P6 and equidistant between P5d and P6, P6–P8 linearly arranged, and P9d clearly posterior to P7–P8 ( Figs 8E, F , 12B ).

Differential diagnosis: Pristionchus hoplostomus sp. nov. is diagnosed from all other species of Pristionchus and Diplogastridae , except P. fukushimae sp. nov., by a eurystomatous form with cheilostomatal plates variably and incompletely split versus being completely divided into six or 12 plates. It is further distinguished from all other species of Pristionchus , except P. triformis sp. nov. and P. fukushimae sp. nov., by an anteriorly serrated versus smooth stegostomatal ring in the eurystomatous form and by a finely serrated versus smooth anterior gymnostomatal ring of the eurystomatous form. It is distinguished from all other Pristionchus species , except P. triformis sp. nov. and P. fukushimae sp. nov., by a serrated versus smooth anterior gymnostomatal ring in the eurystomatous form. The species is distinguished from P. triformis sp. nov. and P. fukushimae sp. nov. by the presence versus absence of a distinct, additional left subventral plate with multiple denticles. Pristionchus hoplostomus sp. nov. is separated from P. fukushimae sp. nov. by reproductive isolation, namely by the inability to produce viable hybrid F 1 offspring. It is further distinguished from P. fukushimae sp. nov. by: male papilla P4 being closer to P3 than to P5d versus equidistant between P3 and P5d; the anterior curvature of gubernaculum being shallow versus deeply concave; the proximal curvature of gubernaculum being one-third versus one-half of gubernaculum length. It is tentatively also distinguished from P. triformis sp. nov. by: P2d slightly anterior to or overlap- ping versus clearly anterior to P3; P4 being closer to P3 than to P5d versus equidistant between P3 and P5d; P5d being closer to Ph than to P4 versus equidistant between P4 and Ph; P9d being clearly posterior to, versus overlapping, P7–P8. Pristionchus hoplostomus sp. nov. is distinguished from all other species by its unique SSU rRNA sequence, an 830-bp fragment of which differs from each of the phylogenetically close species P. triformis sp. nov. and P. fukushimae sp. nov. by five nucleotides. Finally, P. hoplostomus sp. nov. is distinguished from P. triformis sp. nov. by a gonochoristic versus hermaphroditic mode of reproduction.

Type locality: The culture from which the type specimens were obtained was originally isolated by Marie-Anne Félix from soil from a botanical garden in Tokyo, Japan .

Type material and strain: Holotype stenostomatous male, two paratype stenostomatous males, and three paratype six-plated eurystomatous females are deposited in the UCRNC, CA, USA. Two paratypes each of stenostomatous males and eurystomatous females are deposited in the Swedish Natural History Museum , Stockholm, Sweden. Two paratypes each of stenostomatous males and eurystomatous females are deposited in the Natural History Museum , Karlsruhe, Germany. The type strain is available under culture code JU1090.

Etymology: The species epithet is derived from the Greek o˝ plON (‘armor, tool’) + ƠT ó MA (‘mouth’), and refers to the stacked rows of left subventral denticles in the eurystomatous form.

Figures

Figure 5. Scanning electron micrographs of the cheilostom plasticity of Pristionchus hoplostomus sp. nov. and Pristionchus triformis sp. nov. Scale bars: 5 Mm. A, stoma of P. hoplostomus sp. nov., showing an irregular number of cheilostomatal flaps (eight), including one flap split only at the tip (star); en face view; top, dorsal. B, megastomatous form of P. triformis sp. nov., showing 12 completely divided cheilostomatal plates and flaps; en face view; left, subdorsal.

Figure 7. Adults of Pristionchus hoplostomus sp. nov. A, whole body of stenostomatous female, right lateral view. B, whole body of stenostomatous male, right lateral view. C, lip region of stenostomatous male, lateral view. D–H, stomatal region of female. D, stenostomatous form, left lateral view, showing left subventral ridge (below, left) and dorsal tooth (below, right). E, stenostomatous form, right lateral view, showing dorsal tooth (below, left) and right subventral ridge (below, right). F, 12-plated stenostomatous form, showing left subventral denticles (below, left) and dorsal tooth (below, right). G, eurystomatous form, showing two variants of left subventral metastegostom (below, left) and one variant of dorsal tooth (below, right). H, eurystomatous form, exhibiting a variation of stoma width, right lateral view, showing 11-plate variant of cheilostom dissected from body (below, far left), dorsal tooth (below, center), and right subventral tooth (below, right).

Figure 8. Adults of Pristionchus hoplostomus sp. nov. A–D, female; E–G, male. A, neck region of stenostomatous individual, right lateral view. B, anterior gonad branch, right lateral view. C, tail region, left lateral view. D, anus, ventral view. E, tail region, ventral view. F, tail region, right lateral view, including close-up (not to scale) of papilla P6–P8 in left

Figure 12. Comparative tail morphology of males of Pristionchus triformis sp. nov., Pristionchus hoplostomus sp. nov., and Pristionchus fukushimae sp. nov. Views are ventral. A, line drawings of the male tail: the relative positions of the papillae, cloaca, and phasmid are indicated by the arrowheads on the vertical bars. Papilla characters in P. triformis sp. nov. males are considered tentative (N = 1), and were interpreted from lateral view. Although the papillae arrangement is similar in the three species, the distinguishing characters are: P2d clearly separated from, versus overlapping, P3; P4 equidistant between P3 and P5d (P. triformis sp. nov. and P. fukushimae sp. nov.) versus closer to P3 than to P5d (P. hoplostomus sp. nov.); P5d equidistant between P4 and Ph (P. hoplostomus sp. nov. and P. fukushimae sp. nov.) versus closer to Ph than to P4 (P. triformis sp. nov.); position of P9d clearly posterior to (P. hoplostomus sp. nov.), slightly posterior to (P. fukushimae sp. nov.), or overlapping (P. triformis sp. nov.) P7–P8. B, scanning electron micrograph of the male tail of P. hoplostomus sp. nov.