Iridomyrmex conifer

Identification
The greatly enlarged and triangular-shaped propodeum will separate this species from the majority of other Iridomyrmex species. Separation of I. conifer from the otherwise similar Iridomyrmex setoconus and Iridomyrmex turbineus is based on the presence of at most a few short and stout setae on the dorsum of the mesosoma, while in I. turbineus the setae are long and flexuous and in I. setoconus they are short and stout but very abundant.

Distribution based on Regional Taxon Lists
Australasian Region: Australia.

Shattuck & McMillan (1998) discuss the unique nest construction to be observed for I. conifer. In winter, nests are constructed with an above ground thatched mound consisting of vegetation such as small twigs, grass, grass and cladodes of Casuarina, while summer nests are subterranean without an above ground mound. Underground nests are constructed within easy foraging distance (i.e., no greater than one metre from a food source), whereas winter mound nests may be up to 12 metres from food sources. The latter are always situated within a sunny position. The diet of the adult ants is mainly nectar and honeydew, with nectar being preferred when available. The ants will also scavenge arthropods, earthworms and small, dead vertebrates (Shattuck & McMillan, 1998).

Nomenclature

 *  conifer. Iridomyrmex conifer Forel, 1902h: 463 (w.) AUSTRALIA. Forel, 1907h: 297 (q.); Crawley, 1922c: 26 (m.); Wheeler, G.C. & Wheeler, J. 1974b: 398 (l.). See also: Shattuck, 1994: 103; Shattuck & McMillan, 1998: 303; Heterick & Shattuck, 2011: 64.

Taxonomic Notes
The I. conifer species-group (minus Iridomyrmex alpinus) was revised by Shattuck & McMillan in 1998. The separation of I. conifer and Iridomyrmex turbineus based on morphology is open to some debate, the character being used in the key proposed by the above authors (namely, erect mesosomal setae) exhibiting a variable pattern. The erect setae have two different characters, those found in I. turbineus being long and flexuous, whereas the erect setae found in ants here referred to I. conifer—where they occur at all—are short and stout. Worker samples held in the Curtin Ant Collection exhibit this variable pilosity: e.g., a worker of I. conifer, collected in Banksia sandplain just north of Perth, possesses more than six short, stout setae on the pronotum, while other workers from locations on the Swan Coastal Plain often possess a couple to half-a-dozen stout, erect mesonotal setae with or without accompanying pronotal setae. Ants collected at localities in the Darling Scarp or near the south coast tend to have a completely glabrous mesosoma. There also appear to be subtle differences in the appressed pilosity, although this feature has to be balanced against the often poor mounting and preservation of pinned workers, especially of older specimens: the Swan Coastal Plain ants have mainly smooth, straight setulae, whilst those from the uplands and south coast often have these setulae linked together in small skeins, giving the ant a more woolly appearance. The much more extensive holdings reveal the same pattern: pins of workers from Jurien Bay and Perth possess one or a few short to very short, stout, erect setae on the pronotum and/or mesonotum, whereas ants from the Darling Scarp and the south coast region have a completely glabrous mesosoma. A pin of three workers from Yallingup, near the extreme southern portion of the Swan Coastal Plain shows an intermediate pilosity pattern; in this case the many erect pronotal setae are short and rather stout, and less than the maximum diameter of the antennal scape, whereas the longest flexuous setae in I. turbineus are longer than the maximum antennal scape diameter.

The overall picture suggests the presence of three, possibly four separate or largely separate populations of south-western members of the I. conifer complex. Iridomyrmex setoconus has unique features, and is easily recognisable. Iridomyrmex turbineus can be identified by the flexuous pronotal setae, which are usually numerous. Within I. conifer, there is a weaker signal of two populations, one found on or largely on the Swan Coastal Plain, and the other with a more extensive distribution in the Darling Range and along the south coast and in the southwest corner of Western Australia. In their revision of the I. conifer group, Shattuck and McMillan (1998) discuss the presence of two disjunct populations of I. conifer, but these only partially correspond to the biogeography implied here. The two authors also examined apparently variable traits within the taxon, namely the angle of the propodeum and the appearance of the erect and suberect gula setae, but were unable to find strong correlation consistent with genetic separation. Heterick & Shattuck (2011) consider it highly desirable to examine the above mentioned variability in a future taxonomic project that selectively targets nest samples of I. turbineus and the two populations of I. conifer mentioned here (i.e., the hairy form and the glabrous form), using both morphological and molecular techniques.

Description
Worker Description. Head. Posterior margin of head strongly concave; erect setae on posterior margin in full- face view set in a row, or present in small aggregations on one or both sides of posterior margin of head, or present singly or as a couple of setae on either side of posterior margin of head, or absent; sides of head noticeably convex; erect genal setae absent from sides of head in full-face view (one to a few small setae may be present near mandibular insertion). Ocelli absent; in full-face view, eyes set at about midpoint of head capsule; in profile, eye set anteriad of head capsule; eye semi-circular, or asymmetrical, curvature of inner eye margin more pronounced than that of its outer margin. Frontal carinae convex; antennal scape surpassing posterior margin of head by 0.2-0.5 x its length. Erect setae on scape absent, except at tip; prominence on anteromedial clypeal margin projecting as blunt but distinct protuberance; mandible elongate triangular with oblique basal margin; long, curved setae on venter of head capsule absent. Mesosoma. Pronotum moderately and evenly curved over its length, or weakly undulant or almost straight. Erect pronotal setae moderate in number (6-12), short and bristly, or sparse (6 or fewer) and bristly, or lacking or very minute (one or two tiny setae may be present). Mesonotum sinuous. Erect mesonotal setae sparse (6 or fewer) and bristly, or sparse to absent. Mesothoracic spiracles always inconspicuous; propodeal dorsum protuberant; placement of propodeal spiracle mesad, more than its diameter away from propodeal declivity; propodeal angle present as a bluntly defined acute angle, the propodeal dorsum conical in shape. Erect propodeal setae sparse to absent. Petiole. Dorsum of node acuminate, or convex; node thin, scale-like, orientation more-or-less vertical. Gaster. Non-marginal erect setae of gaster present or absent on first gastral tergite; marginal erect setae of gaster present on first tergite, or absent on first tergite. General characters. Allometric differences between workers of same nest absent. Colour reddish-brown to reddish black. Colour of erect setae pale yellowish.

Measurements. Worker (n = 21)—CI 95–105; EI 20–25; EL 0.23–0.29; EW 0.13–0.18; HL 1.08–1.35; HW 1.05–1.38; ML 0.53–0.77; PpH 0.27–0.44; PpL 0.63–0.85; SI 95–110; SL 1.13–1.35.

References based on Global Ant Biodiversity Informatics

 * Heterick B. E. 2009. A guide to the ants of south-western Australia. Records of the Western Australian Museum Supplement 76: 1-206.
 * Heterick B. E., and S. Shattuck. 2011. Revision of the ant genus Iridomyrmex (Hymenoptera: Formicidae). Zootaxa 2845: 1-174.
 * Shattuck S. O., and P. McMillan. 1998. Revision of the species of the Iridomyrmex conifer group (Hymenoptera: Formicidae), with notes on their biology. Australian Journal of Zoology 46: 301-315.