Fergusobia rileyi, Davies & Giblin-Davis & Ye & Taylor & Thomas, 2012

Davies, Kerrie, Giblin-Davis, Robin, Ye, Weimin, Taylor, Gary & Thomas, Kelley, 2012, Nematodes from galls on Myrtaceae. II. Fergusobia / Fergusonina from small axillary bud (‘ stem’) and leaf (‘ pea’) galls in Australia, with descriptions of two new species, Zootaxa 3415 (1), pp. 1-22 : 12-17

Description of Fergusobia rileyi n. sp. Davies

( Figs 21–31 )

Measurements. Table 4.

Material examined. The description presented here is based on measurements of 8 parthenogenetic females, 21 males, and 3 pre-parasitic infective females from unilocular leaf ‘pea’ galls on a sapling of Corymbia sp. , growing in roadside vegetation by the Pacific Highway, Woodburn, near Grafton, New South Wales, Australia (29º 26.8’S, 153º 15.4’E), associated with an undescribed species of Fergusonina . Collected by K.A. Davies and G. Taylor, 21.vii.1999.

Holotype. One parthenogenetic female, with one infective female paratype and one male paratype on a slide deposited in the ANIC, Canberra , ACT, Australia, data as above.

Paratypes. Vouchers deposited at the WINC, The University of Adelaide, SA, Australia, 3 parthenogenetic ♀ s, 1 pre-parasitic infective ♀ s, 6 ♂ s; The Australian National Museum , Sydney, NSW, Australia, 3 parthenogenetic ♀ s, 1 pre-parasitic infective ♀, 10 ♂ s; and the USDA Nematode Collection , Beltsville MD, USA, 1 parthenogenetic ♀ and 4 ♂ s.

Description. Parthenogenetic female. Shape almost straight to arcuate, dorsally curved; body conoid behind vulva; usually smaller than amphimictic pre-parasitic female and males ( Fig. 22 ). Cuticle obscurely annulated, appearing longitudinally striated when viewed with light microscope; lateral fields obscure (not seen).

Cephalic region about 70 (56–73)% diameter of body at anterior end, offset, 1–2 µm long, unstriated; with rounded outline and flat circum-oral area in lateral view ( Fig. 25 ). Stylet 10–13 µm long, with conus about 40% of total length; basal knobs well defined, about 2µm wide at base, rounded and may be retrorse ( Fig. 25 ).

Orifice of dorsal oesophageal gland about 1–2 µm posterior to stylet knobs. Anterior fusiform part of digestive tract length 2.1 (1–2.8) times diameter, or 64 (55–75)% of body diameter. Oesophageal glands medium to large, occupying about 50% of body diameter, extending over 37 (32–50)% of total body length ( Fig. 22 ).

Secretory/excretory pore 68–126 µm from anterior end; duct refractile or not; secretory/excretory cell obscure (not seen). Hemizonid obscure (not seen).

Reproductive tract developing ventral to the oesophageal gland, in specimens with flexure at nerve ring it grows back towards tail on the dorsal side of the oesophageal gland; variable in length, extending part-way along gland with one flexure (in 2 of 7 specimens) or to nerve ring with 2 flexures (in remaining 5 specimens); oviduct with two oocytes per row; uterus extensile, up to about 60% of body length, eggs none (in 1 of 7 specimens), one (in 1 specimen), two (in 2 specimens), or three (in 4 specimens); vulva a depressed slit, flat, or with low broad protruding lips (in 4 of 7 specimens). Body narrowing gradually behind vulva. Tail conoid, length 1.0–2.7 times anal body diameter, with rounded tip ( Fig. 28 ).

Infective pre-parasitic female. Infecting mature larval or pupal stage of Fergusonina sp. Almost straight when relaxed by heat; maximum body diameter at mid-body length, tail region slender ( Fig. 23 ). Cuticle obscurely annulated, longitudinal striations visible when viewed with light microscope; lateral fields obscure (not seen). Large, inconspicuous, nuclei present in wall of intestine.

Cephalic region slightly offset, about 1–2 µm long, 68 (67–69)% diameter of body at anterior end. Circum-oral area flat or slightly elevated, with prominent stylet opening; stylet slender, 10–13 µm long, weakly sclerotised with retrorse basal knobs longer than wide; conus about 40% of length ( Fig. 26 ).

Orifice of dorsal oesophageal gland about 2µm posterior to stylet knobs. Anterior fusiform part of digestive tract length 3.3 (2.3– 4.5) times diameter, or 51 (40–57)% of body diameter. Oesophageal glands occupying 47–56% body diameter, extending over intestine for an average 25 (21–31)% of total body length ( Fig. 23 ).

Secretory/excretory pore opening 90–94 µm behind anterior end; secretory/excretory cell obscure (not seen). Hemizonid extending over 2 or 3 annules, immediately in front of secretory/excretory pore or three annules in front.

Reproductive tract extending to nerve ring, sometimes hypertrophied with many reflexes; uterus filled with sperm in inseminated females; vagina at right angle to body axis, sometimes with small posterior diverticulum, plugged with refractive material. Vulva surrounded by small cuticular plate ( Fig. 31 ), lips small, about 1 µm high.

Tail conoid, length 2.2–3.1 times diameter at anus, tip bluntly rounded ( Fig. 29 ).

Parasitic female. Not seen.

Male. Body almost straight or arcuate when relaxed by heat, curved with ventral side concave ( Fig. 21 ). Cuticle with obscure annules about 1.2 µm wide, longitudinal striations apparent with light microscope; lateral fields obscure (not seen).

Cephalic region 73 (60–78)% diameter of body at anterior end, offset, 2–3 µm long, circum-oral area flat or slightly raised, with prominent opening for stylet; framework lightly sclerotised. Stylet 11–13 µm long, with conus about 40% of length, knobs round, about 2 µm wide ( Fig. 24 ). Anterior fusiform part of digestive tract length 2.6 (2.3–3) times diameter, or 50–68% of body diameter. Orifice of dorsal oesophageal gland about 2 µm behind stylet knobs. Oesophageal glands occupying 40–74% of body diameter, extending over intestine for an average of 28 (26–33)% of total body length.

Secretory/excretory pore opening 81–121 µm from anterior end, opposite nucleus of oesophageal gland; secretory/excretory cell obscure (not seen). Hemizonid extending over two or three annules, one or two annules in front of secretory/excretory pore.

Reproductive tract with single testis, variable in length, extending to nerve ring (10 of 21 specimens) or overlapping dorsal oesophageal gland; straight or sometimes reflexed (3 of 21 specimens); testis, seminal vesicle and vas deferens clearly not differentiated but cap cell usually clearly offset. Bursa smooth, peloderan; arising about 90–95% of body length from posterior, sometimes near level of stylet knobs. Spicules paired, arcuate, weakly sclerotised; manubrium not or just offset, wider than shaft, with rounded head; blade narrowing gradually to bluntly rounded tip; opening obscure (may be terminal or sub-terminal) ( Fig. 30 ). Large muscles associated with cloaca. Tail length 2.7–4.2 times diameter at cloaca; arcuate, slender in comparison to rest of body; tail tip rounded ( Fig. 27 ).

Diagnosis and Relationships. Fergusobia rileyi n. sp. is characterized by the following combination of morphological features: an almost straight to arcuate parthenogenetic female with a conoid tail, an arcuate infective female with relatively narrow tail with a pointed tip, and arcuate males with arcuate spicules, a relatively slender tail, and long peloderan bursa. It is also distinguished by its biogeography and host range, being collected from Corymbia sp. in subcoastal north-eastern New South Wales, associated with an undescribed species of fergusoninid fly having larvae lacking a dorsal shield, and collected from characteristic unilocular leaf ‘pea’ galls. Its status as a distinct species is corroborated by molecular data from sequencing of 28S D2/D3 ( Fig. 1 ) (see also Ye et al. 2007; Davies et al. 2010a).

In having cuticle that does not swell on fixation, the parthenogenetic female of F. rileyi n. sp. differs from F. jambophila , F. pohutukawa and F. viridiflorae . The body shape of F. rileyi n. sp. parthenogenetic females is almost straight, differing from the C-shape of F. ptychocarpae , F. brevicauda , F. philippinensis , F. indica , F. magna , F. dealbata , and F. tumifaciens . The tail shape (elongate, conoid, slightly arcuate) differs from that of parthenogenetic females of F. quinquenerviae , F, cajuputiae , F. leucadendrae , F. fisheri , F. nervosae and F. camaldulensae n. sp. (broad, with broadly rounded tip); and F. curriei (short, broad, with an angular tip).

Infective females of F. rileyi n. sp. are almost straight in shape, which separates them from every other described species of Fergusobia for which this stage has been described. Fergusobia brevicauda , F. brittenae , F. cajuputiae , F. curriei , F. dealbatae , F. fisheri , F. leucadendrae , F. nervosa , F. magna , F. philippinensis , F. ptychocarpae , F. quinquenerviae , and F. viridiflorae all have infective pre-parasitic females with more curved body shapes.

The shape (slender, conoid, arcuate) of the tail of males of F. rileyi n. sp. differs from that of all described males of Fergusobia except for F. magna . The arcuate shape of the spicule differs from that of F. magna (in which it is more angular), and the bursa of F. rileyi n. sp. (90–95% body length) is much longer than that of F. magna (30–50% body length).

Fergusobia rileyi n. sp. is morphologically similar to MSp 40, 41, and 59, respectively from leaf ‘pea’ galls on E. marginata ( Fig. 15 ), E. pauciflora ( Fig. 13 ), and E. obliqua L’Herit. 1788 ( Fig. 17 ), and MSp 61 from small leaf bud galls on E. delegatensis ( Fig. 16 ). In all these cases, the parthenogenetic females are arcuate in shape, and the males have long bursa. Fergusobiid nematodes (MSp 82) have been collected from leaf pea galls on C. maculata (Hook.) K.D. Hill & L.A.S. Johnson 1995 ( Fig. 14 ), which is genetically close to the host for F. rileyi n. sp., and these nematodes are morphologically similar to F. rileyi n. sp., but also to F. magna and F. pohutukawa (K.A. Davies, unpub. data). Like F. rileyi n. sp. and F. magna , parthenogenetic females from C. maculata have an extensile uterus. However, like F. pohutukawa , parthenogenetic females from C. maculata have a swollen cuticle and a pointed tail tip—characteristics absent in F. rileyi n. sp.

From phylogenetic analyses based on sequences of D2/D3, F. rileyi n. sp. is genetically similar to Fergusobia MSp 34 from shoot bud galls on E. near nitida (V 286), and MSp 40 and 41 from leaf pea galls on E. marginata (V 64) and E. pauciflora (V 280) ( Fig 1 ; also Ye et al. 2007; Davies et al. 2010a).

Etymology. Named for Dr. Ian Riley, The University of Adelaide; Adelaide, South Australia; in recognition of his contributions to the study of Plant Nematology.

Figures

FIGURE 1. The 10001st Bayesian tree inferred from D2/3 under TVM+I+G model (lnL=3666.3835; freqA=0.2858; freqC=0.1462; freqG=0.2398; freqT=0.3281; R(a)=0.9646; R(b)=4.53; R(c)=2.4724; R(d)=0.3335; R(e)=4.53; R(f)=1; Pinva=0.5461; Shape=0.5601). Posterior probability values exceeding 50% are given on appropriate clades. The legend on the tree has the format: Nematode species, Australia state name, voucher number, gall type and host.

FIGURES 21–31. Fergusobia rileyi n. sp. ex Corymbia sp. (all bar 31 in lateral view): 21, whole male and habitus; 22, whole parthenogenetic female and habitus; 23, whole infective female and habitus; 24, head of male; 25, head of parthenogenetic female; 26, head of infective female; 27, tails of males; 28, tails of parthenogenetic females; 29, tails of infective females; 30, spicule; 31, sub-ventral view of posterior region of infective female showing vulval plate. Scale bars: 21, 22, 23 = 50 µm; 24, 25, 26, 31 = 10 µm; 30 =5 µm.

FIGURES 13–20. Habitus drawings of mostly undescribed Fergusobia nematodes collected from ‘stem’ or ‘pea’ galls: 13, male and parthenogenetic female from E. pauciflora (MSp 41); 14, parthenogenetic female from C. maculata (MSp 82); 15, male and parthenogenetic female from E. marginata (MSp 40); 16, male and parthenogenetic female from E. delegatensis (MSp 61); 17, male and parthenogenetic female from E. obliqua (MSp 59); 18, female from E. amygdalina (MSp 55); 19, male, parthenogenetic and infective female of F.camaldulensae n. sp.; 20, male, parthenogenetic and infective female of F. rileyi n. sp. Scale bars = 50 µm.