Rhopalomastix javana Wheeler, W.M., 1929

Wang, Wendy Y., Yong, Gordon W. J. & Jaitrong, Weeyawat, 2018, The ant genus Rhopalomastix (Hymenoptera: Formicidae: Myrmicinae) in Southeast Asia, with descriptions of four new species from Singapore based on morphology and DNA barcoding, Zootaxa 4532 (3), pp. 301-340 : 310-316

Rhopalomastix javana Wheeler, W.M., 1929 stat. n.

( Figs. 8–23 )

Rhopalomastix rothneyi subsp. javana Wheeler, W.M., 1929: 96 .

Types. Rhopalomastix rothneyi subsp. javana: Numerous workers, four females and three males from INDONESIA, Eastern Java, Besoeki, Bondowoso. Three syntype workers on 1 pin (USNM, cotype: MCZ.6.9.20783/ SNM.595.31) were examined. One worker (top on pin) is selected as the lectotype.

Diagnosis. Worker. Workers monomorphic with little size variation (lectotype and paralectotypes: HL 0.48– 0.52, HW 0.45–0.48). Head in full face view subrectangular, longer than wide, posterior margin with a shallow median concavity. In profile, clypeus broadly and weakly convex; entire dorsum finely striated; posterior half of head striate-reticulate and weakly shining; ventral surface of head largely superficially reticulate; outer surface of femora reticulate with shining interspaces; petiole bell-shaped, anterior face weakly concave. Head, mesosoma dorsum and gaster dark brown, rest of body yellowish brown.

Queen. Small-medium size (non-types: HL 0.48–0.49, HW 0.44–0.45), head slightly less rectangular than that of worker. In profile view, clypeus very weakly convex, almost flat; posterior half and ventral surface of head largely smooth and shiny, vertex feebly striated; outer surface of femora and gaster superficially reticulate; dorsum of mesosoma finely striate and shiny; anterior pronotal margin roundly convex; anterior face of petiole evenly concave, petiole distinctly narrower apically. Body colour generally uniformly dark brown; head, dorsum of mesosoma and gaster slightly darker brown, tibia and tarsus yellowish brown.

Male. Small size (non-types: HL 0.39–0.41, HW 0.38–0.4). Head almost entirely spherical in full face view, posterior margin broad and round; eye relatively smaller than other species, maximum diameter of eye only slightly exceeding midline of head; clypeus in profile roundly convex, strongly projecting form dorsum of head, rugulose with punctured interspaces and weakly shining; petiole short and sub-trapezoidal, apex smooth and blunt; entire head substriate-reticulate with smooth and shining interspaces, rest of body superficially reticulate; short standing hairs on entire dorsum including petiole and postpetiole.

Worker measurements. Lectotype and paralectotypes (n = 3): TL 1.83–1.98; HL 0.48–0.52; HW 0.45–0.48; SL 0.18–0.20; ML 0.48–0.50; PronW 0.28–0.32; EL 0.08; EW 0.04–0.06; CI 92–94; REL 17–18; SI 39–42.

Nine non-types (n = 9): TL 1.69–2.02; HL 0.46–0.48; HW 0.41–0.44; SL 0.17–0.19; ML 0.50–0.54; PronW 0.28–0.32; EL 0.08–0.1; EW 0.04–0.06; CI 89–93; REL 18–23; SI 40–44.

Queen measurements. Three non-types (n = 3; 1 alate and 2 dealate): TL 2.21–2.43; HL 0.48–0.49; HW 0.44–0.45; SL 0.18–0.20; ML 0.70–0.72; MsW 0.36–0.40; EL 0.15–0.16; EW 0.09–0.10; CI 92–94; REL 33–36; SI 40–45.

Male measurements. Two non-types (n = 2): TL 1.98–1.99; HL 0.39–0.41; HW 0.38–0.40; SL 0.06; ML 0.66–0.70; MsW 0.40–0.44; EL 0.18–0.20; EW 0.14; CI 97–98; REL 45–53; SI 15–16.

Redescription. Worker (lectotype, paralectotypes and non-types).Workers monomorphic with little variation in size. Head in full face view subrectangular, longer than wide, posterior margin with a shallow median concavity, posterolateral corners roundly convex, lateral margins of head broadly convex and weakly converging anteriorlyanterior clypeal margin less wide than posterior margin of head. Eye with 11–16 ommatidia. In profile view, outline of clypeus evenly and weakly convex, projecting slightly forward from dorsal margin of head. Mesosoma in profile box-shaped, subcylindrical, dorsal outline weakly convex and almost straight, propodeal declivity steep and shallowly concave. In dorsal view, mesosoma subrectangular, anterior pronotal margin broadly convex, sometimes angulate at its median point, humeral angles rounded, posterior propodeal margin weakly concave. In profile, petiole inclined posteriorly, slightly longer than high, apex distinctly narrower than base, anterior margin broadly concave; petiolar node bell-shaped, apex rounded and smooth, posterior face nearly straight and almost as steep as anterior face; petiole higher and longer than postpetiole, dorsal margin of postpetiole weakly convex and nearly flat. In dorsal view, petiole suboval, wider than long; postpetiole globular and larger than petiole.

Dorsum and lateral surface of head finely striated and shining, posterolateral corners also feebly reticulate, interspaces smooth and shining; posterior-most portion of vertex of head just above occiput in posterodorsal view largely unsculptured, smooth and shiny. Ventral surface of posterior half of head mostly superficially reticulate with smooth and shining interspaces. Mandible mostly smooth and shining, area close to masticatory margin punctate. Lateral surface of mesosoma striate-reticulate and shining; dorsum of mesosoma striated. Petiole, postpetiole and gaster superficially reticulate with smooth and shining interspaces.

Dorsal and ventral surfaces of head with abundant short standing and suberect hairs interspersed by sparse longer erect hairs, gena with abundant short appressed hairs. Mesosoma dorsum with sparse, scattered short standing hairs and sparse longer erect hairs close to dorsolateral margin. Anterior rising face of petiole with uniformly short appressed hairs, posterior declivity covered with short erect and subdecumbent hairs; apex of petiolar node with short erect hairs and 1–2 pairs of much longer erect hairs. Postpetiole with abundant short erect and suberect hairs, and 1 pair of long erect hairs. Gaster very pilose, all surfaces covered with abundant short suberect and erect hairs, interspersed by sparse longer erect hairs.

Head, dorsum of mesosoma and gaster generally darker brown in colour, rest of body more yellowish brown, tips of antennae and legs pale in tone.

Queen (non-types). Small-medium size. Head in full face view subrectangular, slightly less rectangular than that of worker, longer than wide; lateral margins almost entirely straight and parallel to each other, posterolateral corners smooth and rounded, posterior margin nearly straight with a shallow median concavity. Eye large (>100 ommatidia); posterior margin of eye located slightly below midline of head in full face view. In profile, clypeus very weakly convex, almost entirely flat. Scape short, not exceeding midline of head when lain back. In profile, mesosoma sub-cylindrical, more elongate than that of worker, dorsal outline weakly and broadly convex, propodeal junction rounded and smooth, posterior face of propodeum steep and almost vertical, shallowly concave. In dorsal view, mesosoma sub-cylindrical, anterior pronotal margin roundly convex, humeral angles distinctly obtuse though rounded and smooth, mesoscutum wider than long. In profile view, petiole inclined posteriorly, longer than high, anterior margin weakly concave; petiolar node bell-shaped, apex roundly convex, posterior face steeper than anterior face; dorsal margin of postpetiole weakly convex, not as long as postpetiole, dorsal margin weakly convex. In dorsal view, petiole suboval, less than twice as wide as long; postpetiole globular, much larger and wider than petiole.

Posterior half of head mostly smooth and shining, feeble striations on frons and venter, anterior half of head finely striated and shiny, clypeus striated but with a median spot that is smooth and shining. Mandible mostly smooth and shining, area next to masticatory margin slightly striate-punctate Lateral surface of mesosoma weakly substriate-reticulate, interspaces smooth and shining. Dorsum of mesosoma mostly striated and shining, median section of pronotum superficially reticulate with smooth and shining interspaces. Lateral surfaces of petiole and postpetiole reticulate, interspaces smooth and shining; apices of petiole and postpetiole feebly and superficially reticulate, mostly smooth and shining. Gaster largely smooth and shining, partly superficially and weakly reticulate.

Dorsum and ventral surface of head covered with abundant short erect and suberect hairs, with sparse longer erect hairs. Dorsum of mesosoma with sparse short standing hairs and sparser long erect hairs, mainly along dorsolateral margin. Anterior face of petiole with short appressed and/or decumbent hairs, posterior face with multiple short erect hairs, apex with short erect hairs, 1–2 pairs of longer erect hairs; postpetiole with multiple short standing hairs and a pair of longer erect hairs. Gaster pilose, with abundant short appressed hairs, scattered short standing hairs and sparse long erect hairs.

Entire body generally uniform dark brown; head, dorsum of mesosoma and gaster slightly darker brown; tibia and tarsus paler and more yellowish brown.

Male (non-types). Small size. Head in full face view almost entirely spherical, posterior margin broad and round; eye relatively smaller as compared to other species, maximum diameter of eye only slightly exceeding midline of head, outline of eye exceeding lateral margin of head by a little. In profile, head broad-ovate, lateral corners smooth and rounded, ventral and posterior margins forming a continuous curved outline; clypeus roundly convex and strongly projecting from dorsum of head. In profile, mesosoma sub-oblong, dorsal margin almost completely straight, propodeal junction roundly convex, posterior face of propodeum steep and almost entirely vertical. In dorsal view, mesosoma obovate, notauli absent. In profile view, petiole inclined posteriorly, short and subtrapezoidal, longer than high, anterior margin weakly concave, apex smooth and blunt, weakly convex and sloping downwards gently, posterior margin very short; anteroventral extension of subpetiolar process shallow and subtriangular, longer at base than apex. Dorsal outline of postpetiole weakly convex, differentiated from gaster by a weak but distinct cinctus.

Entire head mostly substriate-reticulate, with smooth and shining interspaces and scattered punctures; clypeus rugulose with punctured interspaces and weakly shining. Lateral surface of mesosoma weakly striate-reticulate, interspaces smooth and shining; dorsum largely striated and shining, propodeum superficially reticulate with smooth and shiny interspaces. Petiole, postpetiole and gaster superficially reticulate with smooth and shiny interspaces.

Dorsum of head with abundant short standing hairs, lateral and ventral surfaces with numerous short decumbent and appressed hairs. Dorsal surfaces of mesosoma, petiole, postpetiole and gaster mostly with abundant short standing hairs, propodeum with visibly much sparser standing hairs.

Generally dark greyish-brown; head, dorsum of mesosoma and gaster darker blackish-brown; funiculi of antennae light brown; joints of legs, tarsus pale brownish-yellow.

Distribution. Indonesia (eastern Java), Singapore, Thailand ( Fig. 76 ).

Habitat. Non-type specimens from Singapore were collected from bark of common native trees, e.g. Campnosperma auriculatum (Blume) Hook. f., in secondary forests and nature reserves which used to be abandoned plantations; specimens from Thailand were collected from bark of mango trees. Nests do not appear to occupy large expanses of tree bark.

Remarks. We compared the queen specimens of R. javana from Singapore with the holotype queen (head missing) of Rhopalomastix rothneyi from India. We found the Singapore queen specimens of R. javana (SQJV) to be quite different from the holotype queen of R. rothneyi (QR): 1) in SQJV, pronotal length in dorsal view is more than half of propodeal length; in QR, the pronotal length is less than half of propodeal length; 2) mesoscutellar disc of SQJV less than twice as wide as long; in QR, mesoscutellar disc more than twice as wide as long; 3) SQJV propodeum in dorsal view more than twice as wide as long, with broadly concave posterior margin; in QR, propodeum less than twice as wide as long, with roundly convex posterior margin; 4) anterior margin of petiole of SQJV broadly concave, posterior margin steep and nearly flat; in QR, anterior margin not distinctly concave, as steep and flat as posterior margin; 5) SQJV is generally smaller (MsW 0.36–0.40 in SQJV, MsW 0.42 in QR)

Three workers, two males on two pins each with ‘typus’ labels (MHNG) and 23 workers on pins with ‘cotypus’ labels of R. rothneyi (MHNG) from Peradineya [sic], Sri Lanka were also examined. Although labeled as such, they are not type specimens of R. rothneyi . We compared workers of the Sri Lankan specimens (SLW) with the lectotype and paralectotypes of R. javana from Java (JVW). We found the following differences between SLW and JVW: 1) for SLW, straight-line distance of eye to mandibular insertion in profile view ± maximum diameter of eye; in JVW, distance of eye to mandibular insertion> maximum diameter of eye; 2) in JVW, mesosoma relatively short in proportion to head length (HL/ML 89–91); in SLW, mesosoma slightly more elongate (HL/ML 83–87); 3) in JVW, slope of the propodeal declivity is more deeply concave, with a distinctly concave posterior propodeal margin in dorsal view; for SLW, slope of the propodeal declivity is steep and mostly flat.

The male of R. javana from Singapore (SMJV) differs from the Sri Lankan male (SLM) by the following traits: 1) SMJV has a more orbicular head, broadly and evenly rounded posteriorly in full face view; SLM has a more longitudinally oval head, with posterior margin more elongate; 2) SMJV is smaller (SMJV HL 0.39–0.41, HW 0.38–0.40, MsW 0.4–0.44; SLM HL 0.44, HW 0.40–0.42, MsW 0.48–0.5); 3) mesoscutum of SMJV in profile view roughly as high as pronotum; in SLM, mesoscutum distinctly much higher than pronotum, with a roundly convex anterior margin.

Given the character differences between R. rothneyi and both the types and the Singapore populations of R. javana , especially those between the holotype queen of R. rothneyi and SQJV, we thereby choose to raise the subspecies javana to species status. There remains the strong possibility of future revision of R. rothneyi and its previous subspecies, when fresh material from across the species range is available for DNA/molecular investigation.

The lectotype and paralectotypes of R. javana (JVW) are morphologically similar to the Singapore (SWJV) and Thai (TWJV) specimens, except for a few minor differences: 1) JVW is overall uniformly yellowish brown with pale yellow antennal tips, but SWJV and TWJV are in general not uniform in colour, with head and mesosoma usually darker brown than rest of body, antennal tips and legs paler yellowish brown; 2) eye size of JVW relatively smaller in proportion to head width compared to SWJV and TWJV (JVW: REL 17–18; SWJV, TWJV: REL 18– 23). On the other hand, the heads of JVW and TWJV are generally larger than that of SWJV (JVW, TWJV: HL 0.48–0.52, HW 0.45–0.48; SWJV: HL 0.46–0.48; HW 0.41–0.44). These minor differences may simply be morphological variation or polyphenism among geographically distant allopatric populations. For now, given the lack of DNA/molecular evidence and the minor morphological differences, we here choose to treat the Singapore and Thai populations as R. javana , until fresh specimens of R. javana can be obtained from its type locality (Java), and more compelling DNA information from different genetic markers (nuclear and mitochondrial) is available for comparison with the Singapore and Thai specimens.

Workers of R. javana are similar to small workers of R. johorensis , but may be differentiated from the latter based on characters indicated in couplet (5) of the species key. Workers of R. javana are also similar to small workers of R. tenebra , but can be distinguished from the latter based on characters as explained in “Remarks” under the latter description.

Non-type material examined. SINGAPORE: 18 workers, 1 queen, 1 male, Mandai Track (1.40337°N, 103.77824° E), 4 Jan 2017, G.W. Yong leg. , colony no. GY-SG17-RhoN, ZRC _ HYM000576 ( THNHM, ZRC); 12 workers, 2 queens, Bukit Timah Nature Reserve (1.35449°N, 103.78211°E), nest in bark of Campnosperma auriculatum , 21 Jun 2017, C. Peeters leg., colony no. WW-SG17-015, ZRC _HYM_0001732 (ZRC). THAILAND: W. Thailand, Kanchanaburi Prov., Sai Yok Dist., Ban Tha Sao , 280 m a.s.l. (14.33389° N, 98.98° E), collected from a mango tree, 11 Mar 2018, W. Jaitrong leg. , colony no.WJT 110318 -1 ( THNHM, ZRC); same locality, date and collector, colony no.WJT 110318 -2 ( THNHM, ZRC); Central Thailand, Saraburi Prov., Phu Kae Botanical Garden , 89 m a.s.l. (14.67056°N, 100.88500°E), 18 Mar 2018, W. Jaitrong leg., colony no.WJT 180318 -2 ( THNHM, ZRC) .

DNA Barcoding. SINGAPORE: 16 workers were successfully barcoded, 8 each from a colony in Mandai (ZRC_HYM_0000576) and another colony in BTNR (ZRC_HYM_0001732). THAILAND: 14 workers were successfully barcoded, 5 each from 2 colonies in West Thailand (WJT 110318 -1, WJT 110318 -2), and 4 from a colony in Central Thailand (WJT 180318 -2). Based on the combined cluster dendrogram ( Fig. 1 ), barcode divergences from other species are as follows: R. murphyi , 19.2%, R. glabricephala , 17%; R. johorensis , 13.8%; R. striata , 13.8%; R. tenebra , 7.1%.

Figures

FIGURE 1. Cluster dendrogram of COI (313 bp) barcodes of Rhopalomastix from Singapore and Thailand. Objective clustering of barcodes was performed based on uncorrected p-distances using the ‘best close match’ criteria; the number at each ‘node’ represents the percentage divergence or pairwise distance threshold at which clusters split or lump together. Each cluster identified as a species is highlighted in one colour per respective species. Sequences of Thai Rhopalomastix are outlined in red.

FIGURE 76. Distribution of R. javana and R. johorensis in Southeast Asia.

FIGURES 8–11. Lectotype worker of R. javana stat. n. 8, habitus in profile; 9, head in full-face view; 10, closeup of head in profile view; 11, body in dorsal view.

FIGURES 12–15. Non-type worker of R. javana stat. n. from Singapore, Mandai Track, ZRC_HYM_0000576; 12, habitus in profile; 13, head in full face view; 14, closeup of head in profile view; 15, body in dorsal view.

FIGURES 16–19. Non-type queen of R. javana from Singapore, Bukit Timah Nature Reserve, ZRC_HYM_0001732; 16, habitus in profile; 17, head in full face view; 18, body in dorsal view; 19, closeup of mesosoma in dorsal view.

FIGURES 20–23. Non-type male of R. javana from Singapore, Mandai track, ZRC_HYM_0000576; 20, habitus in profile; 21, head in full face view; 22, body in dorsal view; 23, closeup of mesosoma in dorsal view.