Tetraponera nixa

Ward (2001) - At the type locality it was collected in open Eucalyptus tetradonta forest (Majer personal communication) and on revegetated bauxite mine-sites (Majer 1984; as 'Tetraponera sp. WE108').

Identification
Ward (2001) - Tetraponera nixa is evidently closely related to Tetraponera nitida and differs primarily by the much denser (and very short) pilosity on the head, mesosoma and appendages. Given that the amount of pilosity varies considerably in northern populations of T. nitida (see above) I was initially inclined to treat the hairy forms from Australia as conspecific as well. Several lines of evidence suggest, however, that T. nixa is a distinct species. (1) Among a reasonably extensive series of nitida-like specimens examined from northern Australia and New Guinea (about 240 workers and 35 queens, from 70 localities) the amount of standing pilosity falls into two discrete classes (CSC 0-4 and MSC 0-10, v. CSC 15-25 and MSC 30-56), without the intermediates that are seen in northern populations of T. nitida. Nevertheless, among this large number of specimens, only seven workers and one queen (from four localities) are referable to T. nixa, so additional samples are desirable. (2) From one locality, Cairncross West I. on the Great Barrier Reef, there are collections of both forms (one worker each) (ANIC), establishing their sympatric occurrence. (3) In T. nixa, standing pilosity is common on the dorsum of the head and on the sides, a feature not seen in any T. nitida workers, including hairy individuals (“setifera”) from northern localities. (4) There are additional slight morphological differences between T. nixa and T. nitida, in the shapes of the profemur and mesosoma (see description above), and bivariate plots of some measurement ratios separate the two taxa. The differences are accentuated when T. nixa workers are compared with just those T. nitida workers coming from the same region (Australia, New Guinea).

Distribution
Tetraponera nixa appears to be restricted to Cape York Peninsula and adjacent Torres Strait islands.

Distribution based on Regional Taxon Lists
Australasian Region: Australia.

Nomenclature

 *  nixa. Tetraponera nixa Ward, 2001: 638, figs. 74, 81 (w.) AUSTRALIA.

Worker
HW 0.69-0.75, HL 0.81-0.88, LHT 0.50-0.54, CI 0.84-0.88, FCI 0.12-0.14, REL 0.46-0.49, REL2 0.55-0.56, SI 0.53-0.55, SI3 0.95-1.01, FI 0.43-0.47, PLI 0.64--0.67, PWI 0.50-0.52, PDI 1.02-1.11, LHT/HW 0.70-0.75, CSC 15-25, MSC 30-56.

Similar to T. nitida (see above), except as follows: profemur slightly less robust: FI 0.43-0.47 and FW/PL 0.53-0.58 (v. 0.45-0.55 and 0.58-0.70, respectively, in T. nitida); mesosoma more slender, on average: PrWM/HW 0.56-0.58 and MTW/HW 0.46-0.47 (v. 0.58-0.65 and 0.47-0.52, respectively, in Australian and New Guinea samples of T. nitida); patch of dense punctures on anterior portion of pronotum less extensive, more confined to the anterior margin. Short standing hairs (0.03-0.05mm long) common and conspicuous on most of body, including the upper surface of head, sides of head, scapes and tibiae, as well as the mesosoma, petiole, postpetiole and gaster; CSC approximately 15-25, MSC ≥30; standing hairs tending to grade into pubescence (so that setal counts are approximate only). Black to dark brownish-black, appendages dark to medium brown, becoming lighter yellowish-brown on scape, first funicular segment, protibial and tarsi.