Melophorus biroi

Melophorus biroi is the most abundant and widespread of all the small Melophorus species. The ant is a ground forager and almost certainly a generalist in its habits.

Identification
Heterick et al. (2017) - Melophorus biroi can be placed in the Melophoprus biroi species-group on the basis of characters of the clypeus, propodeum, mandible and palps. The species is placed in the Melophoprus biroi species-complex on the basis of a further suite of characters (viz, metatibia of major worker with only one preapical spur [except rarely in the mjobergi clade]; clypeal psammophore placed anteriorly at or just above anterior margin of clypeus in the minor worker and often in the major worker; head dorsoventrally compressed to varying degrees in the minor worker of most species with the eyes placed high on the sides; compact legs, and small body size [(excluding mjobergi clade) HW of smallest minor 0.36 mm, average HW of smallest minors 0.46 mm; HW of largest known major 1.29 mm, average HW of largest majors (where known) 1.05 mm]). Melophorus biroi is very similar to several other small or very small Melophorus. The minor worker can be distinguished from similar forms by its almost invariably glabrous mesosoma, the lack of erect setae, especially marginal setae, on the gaster, the weakly impressed metanotal groove, the truncate propodeum, the thin, widened petiolar node and the lack of heavy sculpture on the mesopleuron. Since the major worker of many M. biroi complex species is not known, the M. biroi major worker cannot be diagnosed with high definition, and is best identified from nest series in which minor workers are also included. However, this subcaste has a weakly convex pronotum and mesonotum and a weakly ot moderately impressed metanotal groove enabling it to be separated from the very similar Melophorus castanopus (flattened pronotum and mesonotum) and Melophorus dicyrtos (strongly convex pronotum and mesonotum and deeply impressed metanotal groove), and the posterior clypeal margin is arched. The anterior clypeal margin often has a small dimple (as in many members of the Melophoprus fieldi complex). Melophorus biroi shows a lot of morphological variation, and there is substantial molecular evidence that this is a species complex of at least several species. Further investigation into Melophorus biroi is needed.

The glabrous mesosoma in the minor worker, lack of erect non-marginal setae on the first gastral tergite and the straight appearance of the mesosoma in profile differentiate this ant from others in its clade. The taxon exhibits a variety of colours and morphologies: most southwestern populations have tawny orange foreparts and a dark gaster, while populations in the northern part of the Swan Coastal plain are uniformly large and dark. Melophorus biroi specimens in northern Australian and in arid parts may be rather rugose and brownish in colour, often with darker heads and gasters, while M. biroi from the eastern NSW tend to be dark coloured, quite gracile, and with longer heads (although not as long or compressed as seen in Melophorus longiceps).

Distribution
Found in all mainland Australian states and in Tasmania.

Distribution based on Regional Taxon Lists
Australasian Region: Australia.

Habitat
Known habitats include Eucalyptus woodland, inland dunes, ‘dry sclerophyll’, ‘coastal scrub’, sandstone scrub, mallee, mallee heath, burned mallee, grazed eucalyptus dieback area, box-pine scrub, twig litter, scattered shrubs and spinifex over red sand, relict Kwongan bushland, mulga bushland, remnant brigalow, closed forest, semi-arid red clay soil, white sand over leaves, and paddock. This species also occurs in suburban areas, particularly those with some remnant vegetation.

Nomenclature

 *  biroi. Melophorus biroi Forel, 1907a: 29 (s.) AUSTRALIA.
 * Combination in M. (Erimelophorus): Wheeler, W.M. 1935c: 71.
 * Status as species: Emery, 1925b: 12; Taylor & Brown, 1985: 123; Bolton, 1995b: 250; Heterick, et al. 2017: 161 (redescription).
 * Senior synonym of marius, propinqua: Heterick, et al. 2017: 162.
 * propinquus. Melophorus fieldi var. propinqua Viehmeyer, 1925a: 36 (w.) AUSTRALIA.
 * Subspecies of fieldi: Taylor & Brown, 1985: 123; Bolton, 1995b: 250.
 * Junior synonym of biroi: Heterick, et al. 2017: 162.
 * marius. Melophorus marius Forel, 1910b: 66 (s.) AUSTRALIA.
 * Combination in M. (Erimelophorus): Wheeler, W.M. 1935c: 71.
 * Status as species: Emery, 1925b: 12; Taylor & Brown, 1985: 124; Bolton, 1995b: 250.
 * Junior synonym of biroi: Heterick, et al. 2017: 162.

Heterick et al. (2017) - At present, the species diagnosis is the best that can be managed, but there are undeniably questions regarding the monophyly of M. biroi, and the possibility that, on further investigation, M. biroi, M. fieldi propinqua and Melophorus marius may prove to constitute more than one species. In fact, the wide genetic divergence makes this putative taxon polyphyletic on a three-gene tree, and more material – especially from the Kimberley region and from the eastern states – is needed to untangle the currently confusing picture, in which phenetics and genetics are in conflict.

Worker
(n = 8): CI 92–113; EI 22–37; EL 0.18–0.24; HL 0.53–0.97; HW 0.49–1.10; ML 0.69–1.24; MTL 0.36–0.66; PpH 0.09–0.12; PpL 0.29–0.51; SI 69–105; SL 0.51–0.76.

Minor. Head. Head square, or approximately oval with straight sides; posterior margin of head planar to strongly convex; frons shining with superficial shagreenation or microreticulation only; frons consisting exclusively or almost exclusively of well-spaced, appressed setae only (small, erect setae, if present, usually confined to ocular triangle or posterior margin of head). Eye moderate (eye length 0.20–0.49 length of side of head capsule); in profile, eye set at about midpoint of head capsule; in profile, eye set around midline of head capsule; eyes elliptical or slightly reniform. In full-face view, frontal carinae straight or weakly convex; frontal lobes straight in front of antennal insertion. Anteromedial clypeal margin broadly and evenly convex; clypeal psammophore set at or just above anterior clypeal margin; palp formula 6,4. Five mandibular teeth in minor worker; mandibles triangular, weakly incurved; third mandibular tooth distinctly shorter than apical tooth and teeth numbers two and four; masticatory margin of mandibles approximately vertical or weakly oblique. Mesosoma. Integument of pronotum, mesonotum and mesopleuron with weak to moderate sheen and superficial microreticulation (more pronounced on mesopleuron); anterior mesosoma in profile broadly convex, or smoothly rounded anteriad, thereafter pronotum and whole of mesonotum flattened and on same plane as propodeum, or weakly elevated anteriad, thereafter gently sinuate, pronotum and mesonotum on same plane; erect pronotal setae absent; in profile, metanotal groove shallow, broadly V or U-shaped, or a weak or vestigial furrow; propodeum shining and microreticulate; propodeum angulate, propodeal angle blunt; length ratio of propodeal dorsum to its declivity between 1:1 and 1:2; erect propodeal setae always absent; appressed propodeal setulae short, separated by more than own length and inconspicuous; propodeal spiracle situated on or beside declivitous face of propodeum, and longer (length ≥ 0.50 × height of propodeum). Petiole. In profile, petiolar node squamiform; in fullface view, shape of petiolar node uniformly rounded; node shining and smooth with vestigial sculpture. Gaster. Gaster shining with superficial microreticulation; pilosity of first gastral tergite consisting of well-spaced short, inconspicuous, appressed setae only, erect setae always absent. General characters. Colour variable, often orange-and-brown or concolorous brown; if foreparts light-coloured, gaster always brown to black.

Major. Head square; posterior margin of head weakly concave; cuticle of frons shining and smooth except for piliferous pits and a few striolae around antennal insertions and frontal carinae; pilosity of frons a mixture of a few well-spaced, erect setae interspersed with appressed setae only. Eye small (eye length less than 0.2 × length of head capsule); in full-face view, eyes set above midpoint of head capsule; in profile, eye set anteriad of midline of head capsule; eyes elliptical. In full-face view, frontal carinae concave; frontal lobes straight in front of antennal insertion. Anterior clypeal margin broadly and evenly convex; clypeal psammophore set at or just above anterior clypeal margin; palp formula 6,4. Five mandibular teeth in major worker; mandibles triangular, weakly incurved; third mandibular tooth distinctly shorter than apical tooth and teeth numbers two and 4; masticatory margin of mandibles approximately aligned vertically or weakly oblique. Mesosoma. Integument of pronotum, mesonotum and mesopleuron with weak to moderate sheen, shagreenate on pronotum and dorsum of mesonotum, otherwise microreticulate; anterior mesosoma in profile broadly convex, or pronotum smoothly rounded anteriad and flattened posteriad, mesonotum narrowly convex; erect pronotal setae short and unmodified, or weakly expanded distally; in profile, metanotal groove shallow, broadly V- or U-shaped; propodeum shining and finely striolate and microreticulate; propodeum smoothly rounded or with indistinct angle, or angulate, propodeal angle blunt; length ratio of propodeal dorsum to its declivity greater than 1:2; erect propodeal setae absent; appressed propodeal setae sparse or absent, if present then not regularly spaced; propodeal spiracle situated on or beside declivitous face of propodeum, and shorter (length less than 0.50 × height of propodeum). Petiole. In profile, petiolar node squamiform; in full-face view, shape of petiolar node uniformly rounded, or square with rounded angles; node shining and smooth with vestigial microreticulation anteriad. Gaster. Gaster shining, shagreenate (‘LP record’ appearance); pilosity of first gastral tergite consisting of short, bristly, erect setae over well-spaced, short, appressed setae. General characters. Colour mostly orange with brown gaster, head may be brown with yellow pronotum and mesonotum and brown propodeum and metasoma, or head and gaster may be brown with tan mesosoma.

Type Material
Heterick et al. (2017) - Holotype (probable) major worker, Mt Victoria, Blue Mountains, New South Wales [] (examined: images of HNHM specimen provided by Zoltan Vas).