Melophorus purpureus

The principal author of this work has collected the dark form of this species near salt lakes (Kadji Lake) and the southern form in light soil in heathland (Sappers Rd). Based on its morphology and genetic affinities, this species may be granivorous. (Heterick et al. 2017)

Identification
Heterick et al. (2017) - Melophorus purpureus can be placed in the Melophorus biroi species-group on the basis of characters of the clypeus, propodeum, mandible and palps. The species is also placed in the Melophorus wheeleri species-complex because it agrees with the following apomorphies possessed by the complex: the minor worker often has more than five teeth, the largest major worker has a short, massive, elbowed mandible directed posteriad; in profile, the maxillary palps are short in the major and generally short in minor workers (in the minor worker, usually only attaining the neck sclerite at their maximum extent when the head is moderately inclined) and, in full-face view, the anterior margin of the clypeus in the large major worker is usually planar or weakly concave (variable in other subcastes but planar or narrowly protuberant anterior clypeal margins predominate). The combination of an evenly convex head capsule (when seen in full-face view), a clypeus that is not folded back, the absence of short, inconspicuous setae on the gaster and an evenly convex pronotum plus mesonotum when seen in profile serve to separate M. purpureus from most other members of the M. wheeleri complex. The minor worker bears a passing resemblance to that of Melophorus chauliodon but has a spheroidal, not elongate, eye and the minor and media workers often possess two or more bristly setae on the mesosoma (mainly on the pronotum), whereas the Melophorus chauliodon minor and media workers are invariably glabrous. The major and media workers of M. purpureus are readily separable from their counterparts in M. chauliodon in not having an offset tusk-like tooth on the mandible. Melophorus purpureus also resembles Melophorus hexidens, but that species seems to be endemic to NSW, and the clypeus is different.

This West Australian species needs additional material to be successfully delimited: currently, the populations included under this name show a lot of variation. Populations in the mid-west are black, with sparse erect setae in all workers, but material from the deep southwest and south coast tends to reddish and minor workers may be glabrous. Sequenced material from Sappers Road near Lancelin, WA reveals a sister or near sister relationship with M. wheeleri, which it closely resembles, in a five-gene tree, and it is sister to M. wheeleri and Melophorus marmar in a three-gene tree. The species, as currently constituted, can be separated from very similar ants by a combination of the conformation of the mandible (especially in the major worker), the shape of the eye and the appearance of the clypeus. In the field, minor workers, especially those of the paler southern form, may be mistaken for Melophorus turneri.

Distribution based on Regional Taxon Lists
Australasian Region: Australia.

Nomenclature

 *  purpureus. Melophorus purpureus Heterick, Castalanelli & Shattuck, 2017: 364, fig. 86 (w.) AUSTRALIA.

Worker
(n = 4): CI 113–126; EI 14–22; EL 0.21–0.38; HL 0.84–2.10; HW 0.95–2.65; ML 1.15–2.12; MTL 0.85–1.39; PpH 0.11–0.23; PpL 0.45–0.86; SI 51–100; SL 0.95–1.34.

Minor. Head. Head square; posterior margin of head planar or weakly convex; frons shining with superficial shagreenation or microreticulation only; pilosity of frons a mixture of a few well-spaced, erect setae interspersed with appressed setae only. Eye moderate (eye length 0.20–0.49 length of side of head capsule); in full-face view, eyes set above midpoint of head capsule; in profile, eye set anteriad of midline of head capsule; roughly ovoid, eye narrowed posteriad. In full-face view, frontal carinae distinctly concave; frontal lobes straight in front of antennal insertion. Anteromedial clypeal margin broadly emarginate with projecting anteromedial dimple; clypeal psammophore set at or above midpoint of clypeus; palp formula 6,4. Five to six 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 shining and microreticulate, microreticulation reduced on humeri; anterior mesosoma in profile convex anteriad, mesonotum often slightly overlapping pronotum, mesosoma planar or slightly sinuate posteriad; appearance of erect pronotal setae short and spinous; in profile, metanotal groove shallow, broadly V- or U-shaped; propodeum shining and microreticulate; propodeum smoothly rounded or with indistinct angle; propodeal dorsum and declivity confluent; 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 shorter (length < 0.50 × height of propodeum). Petiole. In profile, petiolar node squamiform; in full-face view, shape of petiolar node tapered with blunt vertex, or tapered with squared-off vertex; node shining and distinctly shagreenate-microreticulate. Gaster. Gaster shining, shagreenate (‘LP record’ appearance); pilosity of first gastral tergite consisting of well-spaced, erect and semi-erect setae interspersed with regularly placed appressed setae. General characters. Colour brownish-black, legs brown, tending yellowish distally.

Major. Head. Head horizontally rectangular, broader than wide; posterior margin of head weakly concave; cuticle of frons shining with superficial shagreenation or microreticulation only; 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, or set at about midpoint of head capsule; in profile, eye set anteriad of midline of head capsule; eyes elliptical, or roughly ovoid, eye narrowed posteriad. In full-face view, frontal carinae straight or weakly convex, or straight, divergent posteriad; frontal lobes straight in front of antennal insertion. Anterior clypeal margin broadly concave, or broadly emarginate; clypeal psammophore set at or above midpoint of clypeus; palp formula 6,4. Five mandibular teeth in major worker; mandibles strongly incurved, apical sector weakly carinate or incompletely carinate; third mandibular tooth distinctly shorter than apical tooth, but equivalent in length to remaining teeth; masticatory margin of mandibles approximately aligned vertically or weakly oblique. Mesosoma. Integument of pronotum, mesonotum and mesopleuron shining with indistinct microsculpture that is most pronounced on lower surfaces; anterior mesosoma in profile gently sinuous after initial steep pronotal incline; erect pronotal setae short, (i.e., shorter than length of eye) and unmodified; in profile, metanotal groove shallow, broadly V- or U-shaped; propodeum shining and shagreenate; propodeum angulate, propodeal angle blunt; length ratio of propodeal dorsum to its declivity between 1:1 and 1:2; erect propodeal setae variable in number, may be absent; appressed propodeal setae short, separated by more than own length and inconspicuous; propodeal spiracle situated at least twice its width from the declivitous face of propodeum, and shorter (length less than 0.50 × height of propodeum), or 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 tapered with blunt vertex, or tapered with squared-off vertex; node shining and faintly shagreenate-microreticulate. Gaster. Gaster shining, shagreenate (‘LP record’ appearance); pilosity of first gastral tergite consisting of well-spaced, erect and semi-erect setae interspersed with regularly spaced appressed setae. General characters. Colour body brownish-black, sometimes with dark reddish tints, legs variably brown and yellowish-brown.

Type Material
Holotype minor worker (middle ant) from Kadji Lake Rd, 29°07'S, 116°09'E, Western Australia, 28 January 1999, Heterick, B.E. Nest series 5 [JDM32-001885]. Paratypes: major and minor worker on same pin and with same details as holotype (WAM); 2 majors and a minor worker from Kadji Lake Rd, 29°07'S, 116°09'E, Western Australia, 28 January 1999, Heterick, B.E. Nest series 4 [ANIC32-001884] ; major and 2 minor workers from Kadji Lake Rd, 29°07'S, 116°09'E, Western Australia, 28 January 1999, Heterick, B.E. Nest series 3 [ANIC32-001883] (WAM).

Etymology
Latin purpureus (‘purple’); adjective in the nominative singular.