Fergusobia brittenae Davies, 2010

Taylor, Gary S. & Davies, Kerrie A., 2010, The gall fly, Fergusonina lockharti Tonnoir (Diptera: Fergusoninidae) and description of its associated nematode, Fergusobia brittenae sp. nov. (Tylenchida: Neotylenchidae), Journal of Natural History 44 (15 - 16), pp. 927-957 : 940-948

Fergusobia brittenae Davies sp. nov.

( Figures 4 , 5 ; Table 8)

Holotype

South Australia. Parthenogenetic female, Goolwa , (35°31′ S, 138°46′ E), February 1995, C. Britten, collected from an apical leaf bud gall on a young ornamental E. camaldulensis (ANIC) .

Paratypes

South Australia. Slides 1–16, including 16 parthenogenetic females, 14 preparasitic infective females and 27 males, 18 juveniles, collected from apical leaf bud galls on E. camaldulensis , and 20 parasitic females dissected from female flies and pupae, at

Goolwa in February and March, 1995, C. Britten and KAD [WINC 004340; Waite Nematode Collection, The University of Adelaide (WNC) 936].

Other material examined

All from apical leaf bud galls on E. camaldulensis .

South Australia. Eleven parthenogenetic females, two preparasitic infective females, 14 males, Melrose, KAD and GST, 31 October 1998 ( WINC 004753–4 , WNC 2007– 8); one preparasitic infective female, two males, from creek bed 50 km south of Marla , KAD and B Kranz, 11 March 1999 ( WINC 004390 , WNC 2016); 31 parthenogenetic females, four preparasitic infective females, six males, Brachina Gorge, Flinders Ranges, KAD and B Kranz , 11 March 1999 ( WINC 004391–2 , 004258 , 004514 , WNC 2017); 16 females, 14 preparasitic infective females, 27 males, Strathalbyn, KAD and V Kempster, 4 March 2003 ( WINC 063858 , WNC 2324) .

New South Wales. Three preparasitic infective females, five males, Dubbo , KAD, 13 December 1998 ( WINC 004512 , WNC 2012) .

Western Australia. Ten females, 11 males, Kununurra, KAD and J Done, 15 July 1996 ( WINC 004800 , WNC 963); nine parthenogenetic females, five preparasitic infective females, 15 males, Westonia, KAD, 20 October 2000 ( WINC 004715 , 004283–5 , WNC 2205); 24 parthenogenetic females, one parasitic female, 21 males, Kellerberrin, KAD, 21 October 2000 ( WINC 004716 , 004286–7 , WNC 2206); three females, 11 males, Halls Creek , KAD, 6 July 2001 ( WINC 004721 , 004279–80 , WNC 2221) .

Description

Parthenogenetic female. ( Figures 4A , 5A,B ). Measurements as in Table 8. Occurs in terminal leaf bud gall. Dorsally curved when relaxed by heat, with ventral side convex, to form strong C-shape ( Figure 4A ); smaller than amphimictic preparasitic female; cuticle weakly annulated, apparently striated when viewed with the light microscope; lateral fields arising about one body width behind cephalic region, about 3 µm wide at mid-body length, with SEM delineated by two weak ridges with area between containing small, weak, broken striae less than 2 µm long ( Figure 5A ). Cephalic region small relative to width of body at anterior end, off-set, unstriated; in lateral view has rounded outline and little or no central elevation around stylet opening. With SEM, cephalic region circular ( Figure 5B ), with two groups of three equal rounded sectors, separated by narrower less rounded lateral sectors; openings of labial sensillae pore-like, near the centre of the rounded sectors; amphidial openings pore-like, situated closer to stylet opening on the lateral sectors. Stylet with conus at 40–50% of length, basal knobs well-defined, rounded.

Orifice of dorsal oesophageal gland approximately 2 µm posterior to stylet knobs; digestive tract with anterior non-muscular fusiform-shaped part, twice as long as wide, occupying about 75% of body width, followed by short narrow “isthmus” which widens abruptly to broader part associated with the oesophageal glands; oesophago–intestinal junction obscure; lumen of tract widens slightly to enclose a valve-like structure at about 30% length of anterior fusiform part, broadens at about 50% length of dorsal oesophageal gland. Oesophageal glands large to enormous (occupying 75–80% of body width, extending over intestine to about 50% of total body length), with anterior dorsal diverticulum; dorsal gland with large nucleus with very large nucleolus.

Secretory–excretory pore 78–151 µm from anterior end with prominent duct leading to large ovoid cell 10–15 µm long, which “pushes aside” the oesophageal gland. Nerve ring around “isthmus”; hemizonid extending over two annules, eight or nine annules in front of secretory–excretory pore.

Reproductive tract with single outstretched gonad, prodelphic, variable in length, extending part-way along intestine in some specimens, to posterior end of dorsal oesophageal gland in others, and to nerve ring in some; uterus with quadricolumellar, may contain single egg, curves to join vagina, which is directed forward; vulva with protruding lips in some specimens, a depressed slit in others. Rectum a simple tube, without obvious musculature, anus an inconspicuous pore. Vulva and anus usually with plugs of refractile material. Body narrows behind vulva, abruptly in some specimens. Tail narrow, length one and a half to two times body width at anus, tip bluntly rounded. Phasmids not seen.

Infective preparasitic female ( Figure 4B ). Measurements as in Table 8. Occurs in terminal leaf bud gall, infects mature larval stage of fly or puparium. Open C-shape when relaxed by heat; maximum body width at mid-body length; cuticle with inconspicuous annulations, apparently striated when viewed with light microscope; lateral fields arise about one body width behind cephalic region, plain, ribbon-like, with strong irregular striae. Large nuclei with prominent nucleoli in epidermis, scattered along length of nematode.

Cephalic region continuous with body, weakly sclerotized, outer edges of sectors higher than stylet opening; stylet slender, weakly sclerotized with inconspicuous pyriform basal knobs; conus at about 40% of length; amphids not seen.

Orifice of dorsal oesophageal gland 2–3 µm posterior to stylet knobs; oesophageal glands occupying about two-thirds body width, extending over intestine to about 30% body length. Anterior part of digestive tract swollen, non-muscular, with valvelike structure; cells of intestinal wall with prominent nuclei.

Secretory–excretory pore opens opposite distal end of oesophageal glands; secretory–excretory cell large, about 7 µm long with large nucleus. Nerve ring around “isthmus”; hemizonid five annules in front of secretory–excretory pore.

Uterus more than half length of reproductive tract, packed with sperm in inseminated females, clearly separated from oviduct; no postvulval sac but a small diverticulum packed with sperm present in some specimens; vagina directed anteriorly, plugged with refractile material; oviduct short with flexure; reproductive tract extending to nerve ring; some hypertrophy of tract in some specimens. Vulva a transverse slit; lips may be raised. Anus pore-like, often plugged with refractile material; rectum very small, non-muscular. Tail slightly longer than wide, tip bluntly rounded. Phasmids not seen.

Parasitic female ( Figure 4C ). Measurements as in Table 8. Occurs in haemocoele of abdomen of fly. Epidermis thickened, contains many scattered large nuclei. Cephalic region may or may not be offset, more so in specimens with less development of the reproductive system. Body arcuate in shape, obese, with hypertrophied reproductive organs, and broadly rounded at both head and tail. Cuticle and stylet absent.

Oesophagus and intestine degenerate; anus not seen. Ovary convoluted; vulva a depressed transverse slit.

Male ( Figure 4D ). Measurements as in Table 8. Occurs in terminal leaf bud gall. Body J-shaped when relaxed by heat, tail region curved ventrally. Cuticle with longitudinal striations apparent when viewed with light microscope, no apparent annulations; lateral fields about 10 µm wide at mid-body, with central ribbon-like band which appears raised with fine, obscure striae.

Cephalic region off-set, with lightly sclerotized framework; amphids not seen; stylet and oesophagus as for parthenogenetic females. Oesophageal glands occupy 50–70% of body width, extend over intestine to about 20% of total body length. Lumen of intestinal tract broadens sharply under dorsal oesophageal gland.

Secretory–excretory pore opens near distal end of oesophageal gland, duct broadens and runs to mid-line; large ovoid secretory–excretory cell about 7 µm long with large nucleus. Nerve ring around “isthmus”; hemizonid in front of pore, opposite large nucleus in dorsal oesophageal gland.

Reproductive tract with single testis, variable length, may extend to distal end of dorsal oesophageal gland and overlaps it in some specimens; extensive vas deferens, containing amoeboid sperm, length apparently dependent on amount of sperm produced. Bursa membranous, smooth, may be difficult to see; peloderan; arises about 2.5 tail lengths anterior to cloaca. Genital papillae absent. Spicules strongly sclerotized, robust, paired, angular near their middle; manubrium large but not off-set, unclear if opening is terminal or subterminal; spicule tips usually protruded in fixed specimens, covered with refractile material. No gubernaculum. Tail curved ventrally, about 1.5 times as long as width at cloaca, tip bluntly rounded. Phasmids not seen.

Etymology

Named after Miss Caitlin Britten, who located the Goolwa field site.

Comments

Diagnosis and relationships. Fergusobia brittenae sp. nov. is characterized by having a parthenogenetic female with a tight C-shaped body when relaxed, large oesophageal glands, a small cephalic region relative to body width, a large secretory–excretory cell, and a narrow tail one and a half to twice as long as wide. The infective female is arcuate in shape, with relatively small oesophageal glands, and a bluntly rounded tail tip. The J-shaped male is larger than the parthenogenetic female, with a short bursa and angular spicules with a large manubrium. All adult forms found in the plant gall have large, prominent secretory–excretory cells. Stylets of infective and parthenogenetic females and males are shown in Figure 4E , outlines of head shape in Figure 4F , and shape of male spicules in Figure 4G .

Parthenogenetic females of Fb. brittenae sp. nov. (328–418 µm) are larger than those of Fb. fisheri , Fb. jambophila Siddiqi , Fb. brevicauda Siddiqi , Fb. philippinensis Siddiqi , Fb. quinquenerviae , Fb. cajuputiae , Fb. leucadendrae , and Fb. nervosae [respectively, 228–305 µm ( Davies and Lloyd 1996), 195–300 µm ( Siddiqi 1986), 260– 390 µm ( Siddiqi 1994), 229–310 µm ( Siddiqi 1994), 224–324 µm (Davies and Giblin- Davis 2004), 221–273 µm ( Davies and Giblin-Davis 2004), 205–303 µm ( Davies and Giblin-Davis 2004), and 245–309 µm ( Davies and Giblin-Davis 2004)], but smaller than Fb. magna ( Siddiqi 1986) and Fb. indica (Jairajpuri, 1962) Siddiqi, 1986 [respectively, 500–780 µm ( Siddiqi 1986) and 525–626 µm ( Siddiqi 1986)]. The strong C-shape when heat-relaxed separates it from Fb. jambophila ( Siddiqi 1986) , Fb. tumifaciens Currie ( Currie 1937) , Fb. curriei ( Fisher and Nickle 1968) , Fb. fisheri ( Davies and Lloyd 1996) , Fb. brevicauda ( Siddiqi 1994) , Fb. pohutukawa Davies ( Taylor et al. 2007) and the parthenogenetic females of the Melaleuca leucadendra complex ( Davies and Giblin-Davis 2004), which have an arcuate to open C-shape. The cuticle of Fb. brittenae sp. nov. does not swell when fixed, as it does in Fb. pohutukawa ( Taylor et al. 2007) and Fb. jambophila ( Siddiqi 1986) . The females have a smaller a ratio than female Fb. indica [respectively, 8.4–11.9 and 13.4–19 ( Siddiqi 1986)]. Parthenogenetic females of Fb. brittenae sp. nov. have larger oesophageal glands (b ’ 2–3.5) than parthenogenetic female Fb. magna (4.2–8.8) ( Siddiqi 1986) and Fb. indica (4–5) ( Siddiqi 1986), but smaller than those of F. viridiflorae (1.4–1.9) ( Davies and Giblin-Davis 2004) and Fb. quinquenerviae (1.6–2.2) ( Davies and Giblin-Davis 2004), which have reflexed glands or additional lobes not seen in Fb. brittenae sp. nov. The tail (23–37 µm) is longer than in Fb. fisheri , Fb. jambophila and Fb. cajuputiae [respectively, 13–16 µm ( Davies and Lloyd 1996), 20 µm ( Siddiqi 1986) and 9–20 µm ( Davies and Lloyd 1996)], but shorter than in Fb. magna and Fb. indica [respectively, 60–95 µm and 50–65 µm ( Siddiqi 1986)]. The position of the vulva (%V) overlaps that of all other described species of Fergusobia . The value of ratio c in parthenogenetic females of Fb. brittenae sp. nov. overlaps those of other described species, but the ratio c ’ (1.5–2.1) is smaller than in Fb. magna (3.6–4.8) ( Siddiqi 1986) and larger than in Fb. fisheri (0.9–1.3) ( Davies and Lloyd 1996) and Fb. cajuputiae (0.8–1.4) ( Davies and Lloyd 1996). In size and shape, Fb. brittenae sp. nov. is morphologically close to Fb. ptychocarpae ( Taylor and Davies 2008) , but is separated from it by having a larger excretory–secretory cell and by the position of the hemizonid (respectively, eight or nine annules in front vs. at the level of the excretory–secretory pore).

Preparasitic, infective females of Fb. brittenae sp. nov. are larger (375–550 µm) than those of Fb. philippinensis (290–370 µm) ( Siddiqi 1994), and have a more conical tail with a rounded rather than a subtruncate tip. They are also larger than the infective females of the M. leucadendra complex: Fb. quinquenerviae , Fb. cajuputiae , Fb. dealbatae , Fb. leucadendrae , Fb. nervosae and Fb. viridiflorae [respectively, 259–325 µm, 239–309 µm, 307–347 µm, 227–291 µm, 282 µm and 321 µm long ( Davies and Giblin-Davis 2004)]. In shape, the infective females of Fb. brittenae sp. nov. lack the ventrally curled tail of Fb. ptychocarpae ( Taylor and Davies 2008) . The infective females have relatively smaller oesophageal glands (b ’ 3.2–6.4) than those of Fb. cajuputiae (2.2–3.1) and Fb. leucadendrae (1.8–2.6) ( Davies and Giblin-Davis 2004). The ratio a (8.8–13.6) of these females overlaps that in other described species. The position of the vulva (72–77% of body length) is more anterior in infective females of Fb. brittenae sp. nov. than in Fb. quinquenerviae , Fb. cajuputiae , Fb. dealbatae , Fb. leucadendrae , Fb. nervosae and Fb. viridiflorae respectively (where it ranges from 79 to 87%) ( Davies and Giblin-Davis 2004). The range of tail lengths (20–44 m) for Fb. brittenae sp. nov. overlaps those of other described species, as does ratio c ’ (1–1.5). Ratio c (13–22) of Fb. brittenae sp. nov. of infective females is larger than in Fb. leucadendrae (9–12) ( Davies and Giblin-Davis 2004), and overlaps that of other described Fergusobia .

The J-shape of the male of Fb. brittenae sp. nov. is similar to that of Fb. tumifaciens ( Currie 1937) , Fb. curriei , Fb. quinquenerviae , Fb. cajuputiae , Fb. leucadendrae and Fb. nervosa ( Davies and Giblin-Davis 2004) , but its body is less arcuate than in Fb. dealbatae , Fb. viridiflorae ( Davies and Giblin-Davis 2004) and Fb. ptychocarpae ( Taylor and Davies 2008) , and the tails of Fb. fisheri ( Davies and Lloyd 1996) , Fb. brevicauda and Fb. philippinensis ( Siddiqi 1994) are less ventrally curved. In general, the ranges of body length, tail length, spicule length and ratios a and b ’ of males of Fb. brittenae sp. nov. overlap those of other described species of Fergusobia . However, males are larger (339–519 µm) than those of Fb. nervosae (277–312 µm) ( Davies and Giblin-Davis 2004), and have a larger c ratio (9.5–21.7) than male Fb. nervosae (8.2–9.2) ( Davies and Giblin-Davis 2004). In having a short, broad tail, i.e. a small c ’ ratio (0.7–1.4), males of F. brittenae sp. nov. are distinguished from those with more slender tails [ Fb. philippinensis (1.7–2.4) ( Siddiqi 1994), Fb. jambophila (1.7–2.5) ( Siddiqi 1986), Fb. cajuputiae (2–3.1), Fb. dealbatae (2–2.7), F. nervosae (1.5–2.1) and Fb. viridiflorae (1.8–2.8) ( Davies and Giblin-Davis 2004), Fb. pohutukawa (2.1–2.8) ( Taylor et al. 2007) and Fb. ptychocarpae (1.5–3) ( Taylor and Davies 2008)]. The spicule of Fb. brittenae sp. nov. is longer (19–25 µm) than that of Fb. leucadendrae (14–17 µm) ( Davies and Giblin-Davis 2004), and lacks the offset manubrium of Fb. pohutukawa ( Taylor et al. 2007) .

Comparison of specimens of Fb. brittenae sp. nov. collected from Goolwa, South Australia, with those collected from geographically remote sites in Western Australia and New South Wales showed that the nematodes were morphologically similar. Molecular analyses ( Ye et al. 2007) support that Fb. brittenae sp. nov. is a valid species, sister to an undescribed species from similar terminal leaf bud galls on Eucalyptus tereticornis .

Figures

Figure 4. Fergusobia brittenae sp. nov.: (A) entire parthenogenetic female, with habitus outlines; (B) entire infective preparasitic female; (C) entire parasitic female; (D) entire male; (E) stylets of infective female (left), parthenogenetic female (middle), male (right); (F) outlines of heads of male (top row), infective female (middle), parthenogenetic female (bottom row); (G) spicules. Scale bars: A, E–G, 10 µm; B–D, 50 µm.

Figure 5. Fergusobia brittenae sp. nov., scanning electron micrographs: (A) vulva and lateral field of parthenogenetic female; (B) head of parthenogenetic female. Black arrows indicate position of openings of two (of six) labial sensillae; white arrow indicates position of one (of two) amphids. Scale bar: 10 µm.