Monomorium rothsteini

Sparks et al. (2015) have split what was once thought to be a variable, widespread species into many species. Under this new taxonomic hypothesis past distribution data reported for Monomorium rothsteini and any studies involving this ant need to be reevaluated to determine what species they include.

Identification
Sparks et al. (2015) - A member of the M. rothsteini species group. Small amber species with a concave clypeal margin. The dorsal surface of the propodeum lack longitudinal strigae and the longitudinal depression is very shallow or absent giving the propodeum and rounded appearance.

Distribution
This species is known from the coastal and inland regions of central and northern Queensland.

Distribution based on Regional Taxon Lists
Australasian Region: Australia.

Biology
Heterick (2001) - M. rothsteini group appears to found colonies both by claustra! colony foundation and by fission. Founding queens of claustral colonies in the study area were fully alate, whereas queens starting colonies by budding were brachypterous. Though the colour of the alate and the brachypterous queens was different they were otherwise indistinguishable. Moreover, under laboratory conditions a brachypterous queen changed to the colour of the alate after three weeks. Briese hypothesised that food stress was the determining factor in the type of colony formation.

Monomorium rothsteini is predominantly a seed harvester, taking the seeds of forbs, grasses and plants such as saltbush (Atriplex spp.). A small amount (10% <) of animal material is also eaten (Briese and Macauley 1980). The venom of M. rothsteini and another Australian Monomorium (“sp. 1066”) has recently been analysed (Andersen et al. 1991 ). The findings suggest that these species belong to a separate radiation from that of Monomorium species found elsewhere in the world, though one constituent in M. rothsteini links it with known North American Monomorium.

Genetics
COI sequences. Genbank accession numbers for this species are KC572911–KCC572920 and KC572923.

Nomenclature

 *  rothsteini. Monomorium rothsteini Forel, 1902h: 444 (w.) AUSTRALIA. Imai, Crozier & Taylor, 1977: 348 (k.); Heterick, 2001: 409 (q.m.). Combination in M. (Parholcomyrmex): Santschi, 1919a: 328; in Chelaner: Ettershank, 1966: 97; in Monomorium: Taylor, 1987b: 3. Senior synonym of doddi: Heterick, 2001: 408; Sparks, Andersen & Austin, 2015: 517.
 * doddi. Monomorium (Parholcomyrmex) rothsteini st. doddi Santschi, 1919a: 328 (w.) AUSTRALIA. Combination in Chelaner: Ettershank, 1966: 96; in Monomorium: Taylor, 1987b: 3. Junior synonym of rothsteini: Heterick, 2001: 408; Sparks, Andersen & Austin, 2015: 517.

Worker
Sparks et al. (2015) - (n=9). HW 0.70–0.96, HL 0.74–0.96, EL 0.16–0.18, PMH 0.29–0.37, PH 0.25–0.33, PNH 0.18–0.23, LHW 0.45–0.59, EW 0.10–0.12, PML 0.47–0.64, ML 0.80–1.05, PL 0.37–0.43, PNWdv 0.20–0.27.

Small species with a medium sized, rectangular head which narrows from immediately behind eyes to vertex; posterior cephalic margin shallowly depressed medially. Anterodorsal margin of the clypeus concave with frontolateral carinae forming rounded ridges that extend just beyond anteroventral clypeal margin, anterolateral angles are bluntly rounded; anteroventral margin without a small median projection, margin appears straight. Sculpture on frons variable: strigate, extending well above antennal lobes or restricted to antennal lobes and area in between or rarely limited to a few strigae only present on antennal lobes; coarse lateral cephalic strigae not reaching eye margin or rarely with one or two strigae reaching eye margin. Eyes medium, EW 0.20–0.23 x LHW, 10 ommatidia in longest vertical axis, 8 in longest horizontal axis.

Mesonotum with coarse strigae extending from metanotal groove onto posterior region only, rugulose between strigae, remainder smooth and shining; posterior mesonotum generally flat and contiguous with surrounding surface of mesonotum or rarely raised with a faint horseshoe shaped margin. Mesopleuron alveolate with strigulae spanning area between metanotal groove and promesonotal suture on dorsal half. Propodeum in lateral view with dorsolateral angles clearly forming an obtuse angle; laterally alveolate with 3–4 strigae over the metapleural gland bulla; dorsally with anterodorsal transverse carina present, a few weak transverse strigae present on some specimens, longitudinal carinae absent, longitudinal depression very shallow or absent, propodeum appears flat or slightly rounded dorsally; posterolateral corners rounded above metapleural lobes and dorsolateral angles rounded. Petiole node of medium breadth: between 2 and 2.5 x eye width when viewed from above; shape in posterior view oval, in lateral view anterior and posterior faces converging, apex narrowly rounded from higher anterior face to lower posterior face; posterior surface of petiole node finely reticulate laterally and basally but not extending more than half way to dorsal surface or may appear to be without sculpture, smooth and shining, postpetiole faintly reticulate on posterior surface.T1 completely smooth and without sculpture.

Head and mesosoma dark amber orange to orange brown, legs brown, petiole and postpetiole dorsally infuscated, metasomal tergites dark brown.

Queen
Heterick (2001) - HML 4.10-6.00; HL 1.24-1.51; HW 1.38-1.72; Cel 105-121; SL 0.79-1.10; SI 56-64; PW 1.17-1.59 (16 measured).

As for the queen of Monomorium sordidum, but with the following apomorphies.

Head. Vertex planar, or convex; frons longitudinally striate with erect and suberect setae. (Viewed from front) compound eyes set in posterior half of head capsule, or set in anterior half of head capsule; (viewed laterally) compound eyes set posterior of the midline of head capsule, or set at midline of head capsule.

Alitrunk. Mesoscutal pilosity consisting of decumbent and subdecumbent setulae anteriad and erect and suberect setae posteriad; dorsal appearance of mesoscutum smooth and shining with a few scattered piliferous pits, or striolate and microreticulate. Propodeal sculpture present as uniform rugosity, with well defined costulae on declivitous face of propodeum. Metapleural lobes absent or indistinct. Propodeal spiracle lateral and nearer metanotal groove than declivitous face of propodeum.

Petiole and postpetiole. Propodeal sculpture present; petiolar node rugose. Ratio of greatest node breadth (viewed from front) to greatest node width (viewed in profile) near 4:3. Height ratio of petiole to postpetiole near 1: 1; height-length ratio of postpetiole near 2:1. Sculpture present in form of microreticulation; ventral process absent or vestigial.

General characters. Colour variable: brown, orange or red, alone or in combination, head, appendages and gaster often lighter than alitrunk. Brachypterous alates seen and examined. Ergatoid or worker-female intercastes not seen.

Male
Heterick (2001) - HML 3.86-4.62; HL 0.97-1.10; HW 1.17-1.41; Cel 121-128; SL 0.26-0.34; SI 24-29; PW 1.38-1.66 (7 measured).

As for the male of Monomorium sordidum, but with the following apomorphies.

Alitrunk. Axillae separated by distance of about half greatest width of scutellum.

Petiole and postpetiole. Sculpture present in form of microreticulation, or present; petiolar node rugose. Heightlength ratio of postpetiole near 2: 1.

General characters. Colour brown to black.