Austrostrongylus macropodis Chandler, 1924

Durette-Desset, M. C. & Beveridge, I., 2012, Redescriptions and descriptions of new species of Austrostrongylus Chandler, 1924 (Nematoda: Trichostrongylina), from Australian marsupials with a comparative study of features of the synlophe, Zootaxa 3512, pp. 1-41 : 13-18

Austrostrongylus macropodis Chandler, 1924

( Figs. 7–9)

Synonyms: Austrostrongylus paratypicus Mawson, 1973 . New synonymy.

Type material: holotype ♂ and allotype ♀, USNPC 26124; 2 ♂♂, 10 ♀♀, paratypes, Rice University, Dept of Biology HN 23049, currently in SAM 13720 .

Type host: Macropus rufogriseus (Desmarest) .

Site in host: small intestine

Material examined: From Macropus rufogriseus : New South Wales: 2 ♂♂ (holotype and paratype of A. paratypicus ), Bathurst ( SAM 41515, 5462 ) ; Victoria: 6 ♂♂, Laharum ( MNHN 584 MQ, SAM 45716) ; 7 ♂♂, Wartook ( SAM 45717) ; 3 ♂♂, Jimmy's Creek , Grampian Range ( SAM 45686) ; 1 ♂, Casterton ( SAM 33592) ; 1 ♂, Portland ( SAM 45609) ; South Australia: 1 ♂, Joanna ( SAM 45690) ; Tasmania: paratypes ( SAM 13720) ; 25 ♂♂, 5 ♀♀ Cape Barren Island ( SAM 45687) ; 5 ♂♂, Rushy Lagoon ( SAM 45688) ; 8 ♂♂, Waterhouse ( SAM 45689) ; 8 ♂♂, Blessington ( SAM 45691) ; 1 ♂, Sassafrass ( SAM 45747) .

Redescription: (based on specimens from Macropus rufogriseus ). Anterior part of body ( Fig. 7A–C): 6 tiny interno-labial papillae; excretory pore and deirids slightly anterior to oesophago-intestinal junction.

Male: (measurements of 5 specimens) length 3.96–4.62 (4.43) mm; maximum width 140–180 (170); length of cephalic vesicle 80–110 (90); length of oesophagus 390–450 (420); nerve ring, deirids and excretory pore 170–280 (230), 410–440 (430) and 370–480 (420) from anterior end respectively. Spicules 550–670 (610) long, calomus180–220 (200) long, lamina 370–450 (410); gubernaculum 50–90 (72) long. Bursa dissymmetrical with right lobe larger than left lobe ( Fig. 7I). Bursal pattern with right lobe of type 1–3–1, left lobe of type 1–4 with rays 3 and 6 diverging at same level from their common trunk; rays 4 thicker than other rays, particularly right ray; rays 8 arising from base of dorsal ray; rays 9 arising slightly asymmetrically on distal third of dorsal ray then dorsal ray dividing into 2 branchlets (rays 10) near its extremity; rays 10 shorter than rays 9. Genital cone not prominent ( Fig. 7I). Spicules slender, brown in colour; tips single ( Fig. 7F); spicule ala extends along almost entire length of spicule, with numerous transverse striations; ala greatly enlarged at distal extremity, forming complex folds on ventral surface of spicule tips ( Fig. 7H). Shaft of spicule simple anteriorly (calomus); transversely striated in midregion (lamina), supported by additional rod-like thickening ( Fig. 7G); striations disappear close to distal tip. Gubernaculum ( Fig. 7D) not visible in median views.

Female: (measurements from 5 specimens) length 6.8–7.6 (7.2) mm; maximum width 150–200 (170); length of cephalic vesicle 90–100 (95); length of oesophagus 410 (n=1); nerve ring and excretory pore 240 and 400 (n=1) from anterior end respectively. Vulva 835–900 (870) from posterior end ( Fig. 7J); didelphic; vagina vera short; vestibule 140–150 (145) long; anterior and posterior sphincters 39–60 (50) long, anterior infundibulum 130–380 (260) long; 4–14 (9) eggs in anterior uterus, 5–6 (5) in posterior uterus; eggs 85–90 (88) long, 40–45 (43) wide; tail 90–110 (100) long with attenuated extremity 20–35 (28) long ( Fig. 7J).

Synlophe: Studied in 1 male 8.0 mm long ( SAM 45716), 1 female 8.0 mm long ( SAM 45687) .

In both sexes, ridges arising between posterior margin of cephalic vesicle and anterior to excretory pore in male, posterior to oesophago-intestinal junction in female. Ridges disappearing in distal quarter of body, except ridge 1’ which disappears at beginning of distal third of body in male and from end of median third in female. Ridge 5’ lacking all along body.

At mid-body, right float with peduncle reduced and ridge 2 situated equidistant from ridges 1 and 6 ’ ( Figs. 8F, 9F). All along body, left float better developed than right float. In both sexes, size of right float increasing slightly to mid-body region then decreasing and disappearing 600 µm anterior to bursa ( Fig. 8I) and 50 µm posterior to vulva ( Fig. 9 J). In both sexes, size of left float increasing to distal quarter, then in male decreasing to level of bursa ( Fig. 8L) In female, size of left float decreasing to about 50 µm posterior to vulva then increasing to level of anus ( Fig. 9K). In distal quarter in male, left float directed ventrally ( Fig. 8I–K); remains orientated perpendicularly to body surface in female ( Fig. 9I, J).

Number of ridges: at oesophago-intestinal junction in male: 7 (2 dorsal, 5 ventral); same number just posterior to this junction in female ( Figs. 8D, 9E) and at mid-body ( Figs. 8F, 9F). At mid-body, single axis of orientation inclined at 65° to sagittal axis in male, 75° in female.

Sequence of origin of ridges: from posterior margin of vesicle cephalic to 60 µm anterior to excretory pore in male: ridge 3’ ( Fig. 8A), then 2’, 4’, 1 ( Fig. 8B), then 2, ( Fig. 8C), then 1’, 6’ ( Fig. 8D); from posterior margin of cephalic vesicle to 40 µm posterior to oesophago-intestinal junction in female: ridges 2’, 3’, then 1’, 1 ( Fig. 9A), then 2 ( Fig. 9B), then 6’ ( Fig. 9C), then 4’ ( Fig. 9E).

Sequence of disappearance of ridges: ridge 1’at beginning of distal third of body in male, at end of median third in female ( Figs. 8G, 9G); in male, then 2’, 2, at beginning of distal third of body ( Fig. 8H), then between 500 µm anterior to bursa (650 µm anterior to caudal extremity) and 470 µm anterior to bursa, ridges 1, 6’ ( Fig. 8I), then 4’ ( Fig. 8J), then 3’ ( Fig. 8K); in female, between 800 µm anterior to vulva (2.0 mm anterior to distal extremity) and 700 µm posterior to vulva, ridges 2 ( Fig. 9H), then 6’, 1 ( Fig. 9I), then 2’ ( Fig. 9J), then 3’, 4’ ( Fig. 9K).

Position of left ridge 1’: ridge 1’ arising in sub-dorsal position ( Figs. 8D, 9A) then migrating ventrally. At mid-body, situated in front of left lateral cord ( Figs. 8F, 9F); in same position until disappearing.

Remarks. This species was first described by Chandler (1924) based on specimens obtained from a specimen of M. rufogriseus rufogriseus which died in an American zoo. The only previous record under this name from a wild animal, that of Spratt et al. (1991) (SAM 14839) is not of this species but rather A. wallabiae and therefore, this is the first series of records of the species from wild hosts in Australia.

The species has been identified here based on the excellent illustrations of the spicules and bursa by Chandler (1924) and by comparison with the paratypes in SAM. The spicules of this species are quite characteristic and are readily recognisable. Mawson (1973) examined the holotype, allotype and paratypes but noted that the holotype and allotype were extremely dark and contracted and that few internal details were visible. She illustrated the posterior ends of the male and the female based on the paratypes but noted that details were not discernable. The paratypes are in a poor state of preservation having evidently dessicated at some stage and many of the specimens are broken. The collection apparently also includes a female of A. wallabiae . However, two males are present and the spicules of these two paratypes are identical with those found in the newer material except for the fact that they are shorter (412, 420 µm) conforming with the measurements provided in the description of Chandler (1924).

Examining the type specimens of A. paratypicus , it was evident that the holotype male was identical with the description of A. macropodis given by Chandler (1924). Among the paratypes of A. paratypicus (SAM 5462) were two males, one of which was clearly identifiable as A. macropodis and the other was A. smalesae sp. n., described below. Both were in the collection of nematodes from which A. wallabiae had originally been described by Johnston & Mawson (1939). Mawson (1973) however chose to describe these specimens as a new species, noting a very close relationship with A. macropodis , but commenting on differences in spicule length (520–700 µm in A. paratypicus ; 375–500 µm in A. macropodis ) and 'apparent' differences in the branching of the dorsal ray. She also noted that they came from different host sub-species, A. macropodis from M. rufogriseus rufogriseus from Tasmania and A. paratypicus from M. rufogriseus banksianus (Quoy & Gaimard) on the Australian mainland.

However, apart from the highly characteristic appearance of the spicules and the dissymmetry of the bursa which is not seen in any of the related species occurring in M. rufogriseus , no differences were noted between specimens from the two subspecies of hosts. Spicule lengths from three different populations of nematodes from M.r. rufogriseus collected on Cape Barren Island (508–616 µm) and from two localities in Tasmania (Waterhouse: 500–628 µm and Rushy Lagoon: 454–585µm) did not differ from measurements obtained from nematodes from M. r. banksianus on the mainland (550–670 µm). No explanation can be provided as to why the spicules of the paratype specimens are shorter. Mawson (1973) also noted that the dorsal ray might differ between these two species; however, no differences were noted in the material examined. For these reasons, A. paratypicus is considered to be a synonym of A.macropodis .

The number of ridges in the synlophe reaches its maximum of 7 (2 dorsal, 5 ventral), in the male anterior to the level of the excretory pore ( Fig. 8D) and just posterior to the oesophago-intestinal junction in the female ( Fig. 9E); at mid-body there are 7 ridges (2 dorsal, 5 ventral) in both sexes ( Figs. 8F, 9F). Ridge 5’ is entirely absent.

Ridges disappear in the posterior third of the body except for ridge 1’ which disappears at the end of the median third of the body. In the male, ridges terminate anterior to the bursa, at which level, the right float has disappeared but the left float is present ( Fig. 8L). In the female, ridges are present anterior and posterior to the vulva ( Figs. 9I, J) at which level, the right float is reduced and the left float is present.

This species is prevalent in M. rufogriseus in New South Wales, Victoria and Tasmania. Aussavy et al. (2011) reported a prevalence of 38% in M. rufogriseus in Victoria, as well as a single infection in M. fuliginosus , but did not find the species in sympatric M. giganteus and W. bicolor . Apparently, no specimens from M. fuliginosus were retained and as a consequence, this record has not been included in the present revision.