Melophorus potteri McAreavey

Heterick, Brian E., Castalanelli, Mark & Shattuck, Steve O., 2017, Revision of the ant genus Melophorus (Hymenoptera, Formicidae), ZooKeys 700, pp. 1-420 : 349-351

Melophorus potteri McAreavey

Melophorus potteri McAreavey 1947: 25, fig. 1.

Types. Syntype worker and queen: Patho, Victoria [MV] (examined: MV specimens T-11552, T-21872).

Other material examined.

New South Wales: 40 mi N Warren (Lowery, B.B.). Northern Territory: 15 km SE Alice Springs (Davidson, D. & Morton, S.), Lasseter Cave (Heatwole), Tanami (Greenslade, P.J. M. ). Queensland: ‘Gumbardo’ (Beutel, T.), ‘Merigol’ (Beutel, T.), Sandringham (Greenslade, P.J. M. ), St. George (Lowery, B.B.), Thallon (Lowery, B.B.). Victoria: Patho (Potter, H.A. [ANIC32-053439]), Patho (Potter, H.), Patho (Potter, H.A.), Patho (Potter, H.). Western Australia: 26 mi SSE Karonie (Taylor, R.W.), Pindar (Mercovich, C.). Western Australia: 12 km W of West Arthur (Jacobs, M. [JDM32-001571]), 18.5 km E Southern Cross (Heterick, B.E. [M135]), 19 km N Hines Hill (Heterick, B.E. [M07/M37/M38]), 74 km EbyN Cosmo Newberry (Feehan, J.E.), Eneabba (Bisevac, L. & Heterick, B.E. [JDM32-001572]), Ethel Creek (Varris, P.A. [JDM32-001573]), Rabbit Proof Fence Rd. (Heterick, B.E. [JDM32-004664]), Ravensthorpe (Lowery, B.B.).

Diagnosis.

Melophorus potteri is one of three members of the M. potteri species-group. Like the other two species, M. potteri has a large, oblique propodeal spiracle situated well before the declivitous face of propodeum, the spiracle bisecting much of the propodeum. This species is distinguished from the remaining members of the group by a combination of its glossy general appearance, its reduced palp formula (PF 3,4), its square or rectangular head capsule, the square protrusion of the anterior clypeal margin and the distally expanded basal margin of the mandible.

Minor worker description.

Head. Head rectangular; posterior margin of head planar to strongly convex; frons shining and smooth except for piliferous pits; 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 full-face view, eyes set at about 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 straight, divergent posteriad; frontal lobes straight in front of antennal insertion. Anteromedial clypeal margin narrowly protrusive anteromedially, the protrusion with a square border; clypeal psammophore set at or just above anterior clypeal margin; palp formula 3,4. Mandibular teeth in minor worker consisting of five teeth on the masticatory margin, with additional small denticles on the basal margin; mandibles securiform; third mandibular tooth distinctly shorter than apical tooth, but equivalent in length to remaining teeth; masticatory margin of mandibles approximately vertical 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; appearance of erect pronotal setae long (i.e., longest erect setae longer than length of eye) and unmodified; in profile, metanotal groove shallow, indicated mainly by an angle; propodeum matt or with a weak sheen and microreticulate; propodeum angulate, propodeal angle blunt; erect propodeal setae always absent; appressed propodeal setulae short, separated by more than own length and inconspicuous; propodeal spiracle situated nearer to midpoint of propodeum than to its declivitous face, and longer (length ≥ 0.50 × height of propodeum). Petiole. In profile, petiolar node squamiform; in full-face view, shape of petiolar node rectangular and variably concave medially; node shining and distinctly shagreenate-microreticulate. Gaster. Gaster shining, shagreenate ('LP record’ appearance); pilosity of first gastral tergite consisting of well-spaced short, inconspicuous, appressed setae only, erect setae always absent. General characters. Colour of foreparts orange to dark tan, legs yellowish, gaster chocolate.

Major worker description.

Head. Head square; posterior margin of head planar or weakly concave; cuticle of frons shining and smooth except for piliferous pits; 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 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 straight, divergent posteriad; frontal lobes straight in front of antennal insertion. Anterior clypeal margin narrowly protrusive anteromedially, the protrusion with a square border; clypeal psammophore set at or just above anterior clypeal margin; palp formula 3,4. Mandibular teeth in major worker consisting of five teeth on the masticatory margin with additional small denticles on the basal margin; mandibles securiform; 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 with weak to moderate sheen, shagreenate on pronotum and dorsum of mesonotum, otherwise microreticulate; anterior mesosoma in profile broadly convex; erect pronotal setae absent; in profile, metanotal groove shallow, indicated mainly by an angle and metathoracic spiracles; 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 absent; appressed propodeal setae short, separated by more than own length and in conspicuous; propodeal spiracle situated nearer to midpoint of propodeum than to its declivitous face, and longer (length ≥ 0.50 × height of propodeum). Petiole. In profile, petiolar node squamiform; in full-face view, shape of petiolar node rectangular and variably concave medially; node shining and faintly shagreenate-microreticulate. Gaster. Gaster shining, shagreenate ('LP record’ appearance); pilosity of first gastral tergite consisting of well-spaced short, inconspicuous, appressed setae only, erect setae always absent. General characters. Colour of foreparts orange to dark tan, legs yellowish, gaster brown.

Measurements.

Worker (n = 6): CI 83-100; EI 19-25; EL 0.22-0.25; HL 1.05-1.29; HW 0.87-1.30; ML 1.26-1.59; MTL 0.64-0.89; PpH 0.18-0.20; PpL 0.59-0.64; SI 80-82; SL 0.72-1.04.

Comments.

As with the closely related M. pelecygnathus , Melophorus potteri is a highly distinctive species that cannot be mistaken for any other Melophorus . The mandibles are securiform with the basal mandibular margin expanded, and the PF is 3,4. In addition, the ant shares the apomorphies of its group including the large, centrally placed and diagonal propodeal spiracle. The species, although not common, is widely distributed throughout Australia and has been recorded from all mainland states except the ACT and SA. In all likelihood, however, it also occurs in SA, at least. Several samples of the taxon have been available for sequencing, and on the five- and three-gene trees it appears as a sister to Melophorus pusillus . However, the two species have a very different appearance, and the placement of M. potteri as a sister to the M. aeneovirens complex on the highly conserved Wg tree seems more intuitively satisfying in view of the morphology.

Melophorus potteri is an obligate termitophage ( McAreavey 1947) and is unusual among ants with this lifeway in that the raiding is done on an individual basis. According to McAreavey’s source (Herbert Potter) the individual raiding ants break open the termite mounds and then back out, dragging the adult termite workers with them. The raids take place in temperatures of ‘90°F’ (around 32 degrees Celsius). Although not mentioned by McAreavey, it is tempting to think that the shape of each mandible (which resembles a blunt pair of forceps) may assist the ant’s grip on the soft termite body. Ecological notes suggest this species does not favour any particular habitat - it can be found in the far north and the far south of the continent and in deserts and in wet coastal areas and everywhere in between - and its occurrence may be determined more by the distribution of its favoured prey than climatic factors. Mallee woodland appears to be a common habitat, and savanna woodland and box pine scrub are also mentioned. In several instances, the ant was collected over red soil. Two workers were ‘swept’ (presumably by a butterfly net) at Karonie in the Western Australian goldfields, but the short, squat limbs of the ant do not appear suited to climbing, so the sweep of the net was probably over quite low vegetation in this case.