Fergusobia robustae Davies, 2018

Davies, Kerrie A., Ye, Weimin, Taylor, Gary S., Scheffer, Sonja, Bartholomaeus, F. & Giblin-Davis, Robin M., 2018, Nematodes from galls on Myrtaceae. XI. Descriptions of five new species of Fergusobia from Australia, Zootaxa 4399 (1), pp. 1-31 : 7-12

Fergusobia robustae Davies n. sp. apud MSp 74 ( Davies et al. 2012a)

( Fig. 2 )

Measurements. Table 3.

Material examined. Holotype: Parthenogenetic female Beverley Park Golf Club , Cogarah Bay, Sydney NSW, Australia (33°97.84’ S 151°13.14’ E). From multilocular terminal bud galls on Eucalyptus robusta Smith , collected by Kerrie Davies and Elizabeth Cameron on 13.iv.2002. On a slide with an infective female and a male, deposited in the ANIC, Canberra, ACT, Australia .

Paratypes: Vouchers (collection data as above) deposited at the WINC, The University of Adelaide, SA, Australia, 5 parthenogenetic females, 5 infective females and 8 males on slides numbered WINC 0 63692 ( WNC 2386 ) ; at the Australian Museum , Sydney, NSW, Australia, 5 parthenogenetic females, 5 infective females and 10 males on slides; and at the USDA Nematode Collection, Beltsville, MD, USA 1 parthenogenetic female, 1 infective female and 1 male on a slide. The description presented here is based on measurements of 14 parthenogenetic ♀ s, 11 infective ♀ s and 20 ♂ s.

Description. Parthenogenetic female. Body C-shaped, dorsally curved with ventral side convex, most curvature in posterior half of body; relatively small; relatively broad (a = 7–10); smaller in size than infective females and males; body narrows behind vulva to form a cylindroid tail. With light microscope, cuticle appears smooth, sub-cuticle with strong longitudinal striae. Lateral fields ribbon-like, with edges apparently raised, but no internal incisures apparent. With SEM, fields have two bands of faint broken striae, separated by a band of smooth cuticle ( Fig. 2I ).

Cephalic region ~ 80–90% diameter of body at anterior end, slightly off-set, 1.4–2 µm high, unstriated; rounded outline in lateral view, circum-oral area barely raised ( Fig 2D ). Stylet short, with cone ~ 40–50% length, basal knobs small, rounded, <2 µm wide.

Orifice of dorsal pharyngeal gland ~1 µm posterior to stylet knobs. Anterior fusiform part of digestive tract occupying 44 (37–48)% body diameter, length 1.9–2.9 times diameter; lumen of tract broadens at distal end of dorsal pharyngeal gland. Pharyngeal glands enormous, extending over intestine, occupying 72 (67–78)% of body diameter, distance from head to posterior end of glands being 50 (33–67)% of total body length. Gland nucleus large, with large nucleolus. Lumen of intestinal tract broadens near distal end of gland; in 3 of 4 specimens examined the narrow lining of intestine protrudes some distance into expanded area.

Secretory/excretory pore opens anterior to level of nucleus of pharyngeal gland; duct surrounded by prominent duct cell, secretory/excretory cell not seen. Hemizonid 3 or 4 annules anterior to pore ( Fig. 2A ).

Reproductive tract variable in length, outstretched, extending part-way along pharyngeal gland or to nerve ring; oviduct usually with two oocytes for the first few rows behind the cap cell followed by a length where oocytes are not regularly arranged, followed by rows with two and finally rows with one; quadricolumella rough, uterus with 1 egg in about half specimens examined; vulva a simple transverse slit with rounded protruding lips in some specimens; no vulval plate. Anus pore-like, opens in cuticular depression. Tail relatively short, sub-cylindrical, convex on ventral side; length 1–2 times anal body diameter; tip broadly rounded ( Fig. 2K ).

Infective pre-parasitic female. Infects mature larval stage of Fergusonina sp. or pupa. Open C shape when relaxed by heat with most curvature in posterior half ( Fig. 2B, H ); maximum body diameter at mid-body length or at vulva; body tapers gradually posterior to anus to a tip that is almost hemispherical. Cuticle obscurely annulated, <1 µm wide; longitudinal striae apparent with light microscope; lateral fields not seen. Large nuclei present in body wall.

Cephalic region not offset, domed shape; circum-oral area flat; stylet slender, weakly sclerotised with tiny round basal knobs ~1µm wide; cone ~ 40% of length.

Orifice of dorsal pharyngeal gland often obscure, less than height of a stylet knob posterior to knobs. Anterior fusiform part of digestive tract little expanded, occupying 46 (33-73)% of body diameter, length 4.2 (3.5–5.2) times diameter. Pharyngeal glands extending over intestine, occupying 53 (32–84)% body diameter, distance from head to posterior end of glands being 23 (19–26%) of total body length.

Secretory/excretory pore opens near distal end of pharyngeal glands, opposite or posterior to gland nucleus; duct obscure; secretory/excretory cell not seen. Hemizonid immediately anterior to pore ( Fig. 2B ).

Uterus packed with sperm in inseminated females; vagina perpendicular to body axis; reproductive tract extending to nerve ring. Vulva a transverse slit, vulval lips small but clearly raised ~ 1 µm, no vulval plate present. Anus an obscure pore. Tail straight, short; length 1–2 times diameter at anus, tip almost hemispherical ( Fig. 2L ).

Male. Body arcuate in shape when relaxed by heat, short tail region curved ventrally ( Fig. 2C ). Cuticular annules ~1µm wide; strong longitudinal striae in sub-cuticle apparent with light microscope; lateral fields faint, lines not discernible.

Cephalic region occupying 80–90% anterior body diameter, clearly offset ( Fig. 2F ), ~ 1.5–3 µm high; circumoral area flat or raised, with lightly sclerotised framework; sturdy stylet with cone 40% of length, knobs round, 2 µm wide. Orifice of dorsal pharyngeal gland ~ 1 µm behind knobs. Anterior fusiform part of digestive tract occupying 67 (37–82)% of body diameter, length 2.1 (1.5–2.7) times diameter. Pharyngeal glands extending over intestine, occupying 72 (67–78)% of body diameter, distance from head to posterior end of glands being 27 (23– 31)% of total body length.

Secretory/excretory pore opens posterior to nucleus of pharyngeal gland; duct non-refractile; secretory/ excretory cell not seen. Hemizonid extending over two annules, immediately or up to 6 annules anterior to pore.

Reproductive tract with single testis, usually extending part-way along pharyngeal gland and may reach nerve ring, flexed in some specimens; testis, seminal vesicle and vas deferens not clearly differentiated. Bursa smooth; not prominent; arises 20 – 30% along length of body; apparently terminates just anterior to tail tip ( Fig. 2C ). Spicules paired, stocky, angular at ~40% length; relatively strongly sclerotised; manubrium similar to or wider than shaft, not offset; blade narrows gradually to bluntly rounded tip with concavity on distal edge; spicular nerve opening terminal ( Fig. 2N ). Inconspicuous muscles associated with cloaca. Tail arcuate, ventrally concave, subconoid; length 1.2–1.9 times diameter at cloaca; broadly rounded tip ( Fig. 2J ).

Diagnosis and relationships. Fergusobia robustae n. sp. is morphologically characterized by the combination of a small, C-shaped parthenogenetic female with a short cylindroid tail with a broadly rounded tip; an arcuate to C-shaped, relatively broad infective female with a tail tip that is almost hemispherical; and an arcuate male with a strong angular spicule and a bursa arising at 30–40% of body length. Morphologically, F. robustae n. sp. is similar to F. brittenae , F. cosmophyllae , F. floribundae , and F. minimus , and all were collected from TLBGs. Fergusobia floribundae was collected from Angophora , but the other close species were collected from host plants classified as Eucalyptus subgenus Symphyomyrtus , as was E. robusta . While third instar larvae of flies associated with F. floribundae lack a dorsal shield, those associated with F. robustae n. sp. and the other species mentioned above have a dorsal shield with teeth. Molecular sequences for F. robustae n. sp. are not available, but morphological differences between them and nematodes from similar gall forms, related host plants and flies with similar dorsal shields suggest that they are separate species. They are separated from F. brittenae in lacking the enormous secretory/excretory cell present in the latter, and by the form of the lateral fields. In F. brittenae , the fields comprise a ribbon of broken striae, but in F. robustae n. sp. they comprise two separated bands of striae. The parthenogenetic female of F. cosmophyllae (354–406 µm) is larger than that of F. robustae n. sp. (249–358 µm). Further, spicule length of F. robustae n. sp. (17–21 µm) is larger than in F. cosmophyllae (12–15 µm). Fergusobia robustae n. sp. was collected from E. robusta , from Section Latoangulatae, i.e., its host was genetically dissimilar to that of the morphometrically similar F. minimus , collected from E. tereticornis , from Section Exsertaria. The morphometrics of the two Fergusobia spp. generally overlap, but the structure of the excretory system appears to differ between them, with F. robustae n. sp. lacking the large cells surrounding the duct that occur in F. minimus . The morphology of the infective female differs, with that of F. robustae n. sp. having a more anterior vulva (V 71 –78 vs 80–82% in F. minimus ), more slender bodies (diameter 21–29 vs 35–44 µm respectively), and a larger stylet (6.5–9 vs 4–5.5 µm long respectively). Spicule morphology differs between the two species, being angular at 40% of length in F. robustae n. sp. vs 50% in F. minimus . Fergusobia robustae n. sp. and F. colbrani are similar, but collected from hosts of different genera ( Eucalyptus vs Angophora ) and from different gall forms (TLBG vs spheroid leaf galls). The parthenogenetic female of F. robustae n. sp. cannot be clearly separated from that of F. colbrani , but is more curved in shape when heat-killed, and has a smaller tail volume.

In shape, the parthenogenetic female of F. robustae n. sp. is similar to F. brevicauda , F. brittenae , F. cajuputiae , F. curriei , F. cosmophyllae , F. delegatensae , F. diversifoliae , F. fasciculosae , F. floribundae , F. gomphocephalae , F. indica , F. leucoxylonae , F. magna , F. microcarpae , F. minimus , F. morrisae , F. nervosae , F. pimpamensis , F. planchonianae , F. porosae , F. ptychocarpae , F. tumifaciens , F. viminalisae , and F. viridiflorae (Cshape) . However, it differs from F. armillarisae , F. camaldulensae , F. dealbatae , F. decorae , F. eugenioidae , F. janetae n. sp., F. leptospermum , F. leucadendrae , F. linariifoliae , F. obliquae n. sp., F. pruinosa e n. sp., F. rileyi , F. rosettae , F, schmidti , and F. sporangae , which have straighter bodies. In length (249–358 µm), the parthenogenetic female of F. robustae n. sp. is smaller than that of F. indica (525–626 µm), F. janetae n. sp. (514–723 µm), and F. magna (418–689 µm), and tends to be smaller than that of F. delegatensae (345–427 µm) and F. floribundae (352– 466 µm). In having cuticle which does not swell when fixed with hot formalin, the female differs from F. jambophila , F. linariifoliae and F. pohutukawa , in which it does. The stylet (6.5–9 µm) of the parthenogenetic female is shorter than in F. camaldulensae (11–13 µm), F. leucoxylonae (9–11 µm) and F. schmidti (11–14 µm). In having enormous oesophageal glands (b’ 1.7–2.7), the female is similar to F. quinquenerviae but lacks the extra lobe or flex found in glands of the latter. In having a body that narrows gradually behind the vulva, is curved and cylindroid in shape, with a bluntly to broadly rounded tail tip, the parthenogenetic female of F. robustae n. sp. differs from that of F. brevicauda , F. cajuputiae , F. curriei , F. dealbatae , F. fisheri , F. gomphocephalae , F. microcarpae , F. nervosae , F. obliquae n. sp., F. porosae , F. pohutukawa , and F. tumifaciens (tail more slender, shape arcuate to straight; or smaller in volume); from F. fasciculosae (tail broader, c’= 1 (0.8–1.3) vs 1.5 (1.1–2.1) in F. robustae n. sp.), and F. philippinensis (truncate tip). In length (12.5–27 µm, mean 18 µm), the tail of female F. robustae n. sp. is usually shorter than in F. tolgaensis (mean 22 µm, range 18–25 µm). The parthenogenetic female lacks the broad opening of the stylet aperture present in F. sporangae . The female is separated from F. juliae in lacking a plate of cuticle that surrounds the vulva in the latter. The female of F. robustae n. sp. is separated from F. diversifolia , F. pauciflorae n. sp. and F. viminalisae on the form of the vulva—being raised or protruding in F. robustae n. sp. vs flat or depressed in the latter species. The circum-oral area of the parthenogenetic female of F. robustae n. sp. is flat, but peaked in F. viminalisae , and the hemizonid is immediately anterior to the pore vs 2–4 annules anterior to it in the latter females. The hemizonid is immediately anterior to the pore in F. robustae n. sp., but 4–5 annules anterior in F. pimpamensis . Using morphological characters only, the parthenogenetic female of F. robustae n. sp. cannot be separated from F. morrisae , F. planchonianae , F. ptychocarpae , or F. viridiflorae .

The infective female of F. robustae n. sp. is similar in shape to those of F. fasciculosae , F. gomphocephalae and F. nervosae (open C-shape). It differs from F. eugenioidae , F. juliae , F. morrisae , F. pruinosae n. sp., F. ptychocarpae , F. tumifaciens , and F. viminalisae (J-shape); F. janetae n. sp., F. linariifoliae , F. porosae and F. rileyi (straight); F. armillarisae , F. brevicauda , F. camaldulensae , F. colbrani , F. cosmophyllae , F. cajuputiae , F. decorae , F. fisheri , F. leucoxylonae , F. microcarpae , and F. quinquenerviae (arcuate); and F. magna (less slender; a = 12.2 (10.0–13.3) vs 15.9 (13.8–17.7)). In length (412–521 µm), it is larger than the infective female of F. armillarisae (279–291 µm), F. brevicauda (370 µm), F. cajuputiae (239–309 µm), F. colbrani (369–405 µm), F. dealbatae (307–347 µm), F. decorae (207–256 µm), F. fasciculosae (268–332 µm), F. fisheri (241–395 µm), F. gomphocephalae (222–298 µm), F. leptospermum (376–382 µm), F. leucadendrae (270–291 µm), F. leucoxylonae (252–358 µm), F. linariifoliae (347–384 µm), F. microcarpae (302–341 µm), F. morrisae (322–395 µm), F. nervosae (282 µm), F. philippinensis (290-370 µm), F. planchonianae (303–339 µm), F. porosae (277–300 µm), F. quinquenerviae (259–325 µm), F. rosettae (249–267 µm), F. schmidti (252–395 µm), F. sporangae (289–353 µm), F. tolgaensis (223–272 µm), and F. viridiflorae (321 µm). The infective female of F. robustae n. sp. has a tail 25– 54 µm long, with an almost hemispherical tip, differing from F. magna in which the tail is longer (78–131 µm), from F. pauciflorae n. sp. which has a narrower tip, from F. pruinosae n. sp. which has a notched tip, and from F. obliquae n. sp. which has a sub-cylindroid tail. The female of F. robustae n. sp. lacks the post-anal intestinal sac that is present in F. delegatensae and F. planchonianae . The infective female has a larger stylet than that of F. floribundae and F. minimus (respectively, 7–9 vs 5–8 and 4–5.5 µm), and the stylet tends to be smaller than in F. diversifoliae (9–11 µm). The female differs from F. curriei and F. pimpamensis in tending to have a more anterior vulval opening (V% = 71–78 vs 76–82 and 76–85). The infective female of F. robustae n. sp. is separated from F. brittenae and F. diversifoliae on the position of the hemizonid: 3–4 annules anterior to the excretory pore vs 5 in F. brittenae and 9–11 in F. diversifoliae .

In shape (arcuate to J-shaped), the male of F. robustae n. sp. is similar to those of F. brittenae , F. curriei , and F. fasciculosae , and differs from F. pimpamensis (J or C-shape), F. juliae , F. magna , F. planchonianae , F. ptychocarpae , and F. viridiflorae (with strongly curved posterior). With a body length of 348–448 µm, the male is smaller than that of F. magna (446–588 µm) and F. janetae n. sp. (639–750 µm), and larger than that of F. decorae (205–287 µm), F. fasciculosae (274–336 µm), F. gomphocephalae (228–283 µm), F. leucadendrae (254–350 µm), F. leucoxylonae (251–293 µm), F. nervosae (277–312 µm), F. porosae (270–326 µm), F. quinquenerviae (256–329 µm), F. rosettae (246–319 µm), and F. tolgaensis (268–349 µm). In length (6.5–9 µm), the stylet of the male is shorter than in F. camaldulensae (10–13 µm), F. leucoxylonae (10–13 µm), F. pohutukawa (10–11 µm), and F. rileyi (11–13 µm). The male of F. robustae n. sp. has a flattened circum-oral area, differing from that of F. jambophila , F. rosettae , F. sporangae , and F. tolgaensis , in which it is raised. The shape of the tail (arcuate, conoid, with a broadly rounded tip) differs from that of F. philippinensis (truncate tip) and from F. leucadendrae (bluntly rounded tip). The tail of male F. robustae n. sp. tends to be shorter than that of F. dealbatae (23–36 vs 32–50 µm long), and the ratio c’ differs (1.5 (1.2–1.9) vs 2.2 (2–2.7)). Spicule length (17–21 µm) is larger than in F. leucadendrae , F. porosae , and F. viminalisae (respectively, 14–17, 11–16, and 10–15 µm); and smaller than in F. brevicauda (21–27 µm). The shape of the spicule is angular, differing from that of F. pimpamensis and F. rosettae , in which it is arcuate. The bursa arises at ~ 20–30% of body length, differing from F. armillarisae , F. cajuputiae , F. camaldulensae , F. colbrani , F. diversifoliae , F. floribundae , F. jambophila , F. janetae n. sp., F. leptospermum , F. linariifoliae , F. magna , F. morrisae , F. nervosae , F, obliquae n. sp., F. pauciflorae n. sp., F. planchonianae , F. pruinosae n. sp., F. pohutukawa , F. ptychocarpae , F. rileyi , F. rosettae , F. schmidti , and F. viridiflorae in which it is longer (>50%); and from F. tumifaciens , in which it is shorter (9–16%). In having a smooth bursa, it differs from F. delegatensae , F. gomphocephalae , and F. pimpamensis in which it is crenate. Morphologically, it is difficult to separate the male of F. robustae n. sp. and F. minimus. However, F. robustae n. sp. tends to have a broader body (respectively, a = 7.9–11.8 vs 11–15.7). The male of F. robustae n. sp. differs from that of F. brittenae in lacking the large excretory cell of the latter. The position of the hemizonid separates the male of F. robustae n. sp. (3–5 annules anterior to excretory pore) from that of F. eugenioides (immediately anterior to pore) and F. microcarpae (1–2 annules anterior). Morphologically, the male cannot be separated from that of F. curriei and F. fisheri , but is collected from a different gall form (TLBG vs FBG and FLG) and a different host species.

Etymology. Named after Eucalyptus robusta , the plant species from which the nematodes were collected.

Figures

FIGURE2. Fergusobia robustaen. sp.ex E.robusta(all inlateral view): A,Entire parthenogenetic female;B, Entireinfective female;C, Entire male; D, Anteriorend of parthenogeneticfemale; E, Anteriorend of infectivefemale; F, Anteriorend ofmale; G; Habitus of parthenogenetic female; H, Habitus of infectivefemales; I, Lateral lines (drawn from SEM); J,Tails of males; K, Tailsof parthenogeneticfemale;L,Tails of infectivefemales; M, Habitus ofmales; N,spicules.Scalebars:A,B, C= 50 µm; D, E, F = 10 µm; N = 5 µm; I = 2 µm.Tails not drawn to scale.