Tetraponera rotula

When foraging workers of T. rotula are disturbed they exhibit a distinctive behavior: they run rapidly with the gaster turned at right angles to the long axis of the body.

Identification
Ward (2001) - Workers of T. rotula can be distinguished from those of the related species, Tetraponera punctulata, by the shiny, puncticulate integument (punctures about 0.005 mm in diameter); sparse pubescence, especially on the pronotum; and large globose petiolar node, with steep anterior and posterior faces. Tetraponera rotula workers are also smaller on average, with proportionally larger eyes, differences that are diagnostic in the queen caste (see key to queens).

Distribution
Tetraponera rotula is known from northern Australia (Queensland, Northern Territory) and New Guinea.

Distribution based on Regional Taxon Lists
Australasian Region: Australia. Indo-Australian Region: New Guinea.

Biology
Ward (2001) - The type series was taken from a dead twig of Clerodendrum inerme, at edge of mangrove, in north Queensland. A second nest series was collected from a dead twig of Pometia pinnata in rainforest near Madang, Papua New Guinea. Other habitat records include “rainforest edge”, “semi-dry littoral forest”, “riparian monsoon forest” and “dry, rocky Eucalyptus woodland”. The species has also been reported nesting in hollow stems of lianas and visiting extrafloral nectaries of malvaceous bushes (Braekman et al. 1987). These data suggest that the species is somewhat generalised with respect to habitat and nest-site usage, although with a tendency to occur in wetter sites than T. punctulata.

Braekman et al. (1987) isolated venom gland compounds from workers of a New Guinea population of T. rotula-the ant was identified only as a species of Tetraponera related to T. punctulata-and discovered a series of novel alkaloidal contact poisons, which they termed tetraponerines (see also Merlin et al. 1988; Renson et al. 1994; Devijver et al. 1995). These are released from the tip of the sting apparatus and applied to adversaries by smearing rather than stinging. This defense mechanism was observed to be effective in deterring attack by workers of the aggressive ant, Anoplolepis gracilipes. Braekman et al. (1987) noted that the lancets of the sting apparatus of T. rotula are enlarged and splayed at the tip, make the sting more suited to depositing the venom than injecting it.

Comparative studies of other members of the nigra-group are needed to determine the extent to which tetraponerines and modified sting morphology are uniquely characteristic of T. rotula. Certainly the gaster-turning behavior does not appear to occur in workers of related species, based on field observations of T. punctulata, Tetraponera tucurua, Tetraponera laeviceps, and Tetraponera atra (Ward personal observation).

Nomenclature

 *  rotula. Tetraponera rotula Ward, 2001: 644, figs. 89, 95, 151, 165, 177 (w.m.) AUSTRALIA.

Worker
HW 0.73-0.81, HL 0.86-1.01, LHT 0.62-0.73, CI 0.81-0.88, FCI 0.13-0.17, REL 0.36-0.41, REL2 0.44-0.48, SI 0.54-0.57, SI3 1.14-1.29, FI 0.42-0.47, PLI 0.70-0.81, PWI 0.56--0.67, PDI 1.06-1.14, LHT/HW 0.83-0.90, CSC 1-2, MSC 0-8.

Relatively small species, with moderately broad head (CI >0.80); clypeus short, its anteromedial portion even with, or protruding only slightly beyond, the anterolateral clypeal margin; distance between frontal carinae subequal to, or slightly exceeding, maximum scape width; eye of moderate size (see REL and REL2 values), scape length always markedly greater than eye length (SI3 > 1.12); profemur not notably robust (FI <0.48); pronotum relatively slender (PrWM/MTW 1.04-1.17), with well defined lateral margins; mesopropodeal impression with a pit-shaped depression, flanked by lateral ridges; propodeum slightly higher than wide, its dorsal face somewhat flattened in profile (weakly convex) and rounding into the steep declivitous face; petiole with a short anterior peduncle and a large globular node, with steep anterior and posterior faces and a broadly rounded summit; posterior half of petiolar sternite with prominent ventral protrusion; postpetiole appearing spherical in dorsal view and about as wide as long; metabasitarsal sulcus well developed, lying in a darkened patch of cuticle adjacent to a slight carina and occupying about 0.5-0.6x the length of the basitarsus. Integument smooth and shiny, with numerous very fine punctures, about 0.005 mm in diameter, and separated by several diameters; malar area with coarser and more elongate punctures. Standing pilosity generally uncommon (see CSC and MSC values), absent from mesonotum; petiole and postpetiole with 0-2 and 0-4 short standing hairs, respectively; appressed pubescence present but rather sparse on most of body (hairs separated by about their lengths), becoming moderately dense on abdominal tergite IV Black to dark brownish-black, mandibles, antennae and tarsi medium-brown.

Type Material
Holotype. Worker, 4 km ENE Cairns, Queensland, Australia, <5 m, l6°55'S 145°48'E, 17.i.1989 (P. S. Ward #10002). Paratypes. Series of workers and males, same data as holotype.