Amblyoponini

Ward, P. S., 1994, Adetomyrma, an enigmatic new ant genus from Madagascar (Hymenoptera: Formicidae), and its implications for ant phylogeny., Systematic Entomology 19, pp. 159-175 : 167-171

Redefinition of the Amblyoponini

Long considered a rather primitive group of ants, possibly reflective of an early stage in ant evolution (Wilson, 1971; Hoelldobler & Wilson, 1990), the Amblyoponini were well characterized by Brown (1960; see also Brown, 1974 a, b; Gotwald & Levieux, 1972) but they have not heretofore been defined explicitly in terms of derived characters that would signify their monophyly. The characterization given below refers to all currently recognized, extant amblyoponine genera for which the worker caste is known (i. e. Amblyopone , Concoctio , Mystrium , Myopopone , Onychomyrmex and Prionopelta ). These were compared to a representative range of taxa in other ponerine tribes ( Ectatommini. Platythyreini , Ponerini , Typhlomyrmecini ) as well as to Apomyrma and the principal leptanilline and doryline section genera. In the diagnosis below, apparent apomorphic conditions are marked with an asterisk. Some of these are unique, others have appeared convergently in other ant groups, as discussed below. A comparison with Adetomyrma appears after the diagnosis.

Tribe Amblyoponini Forel, 1893

1. * Worker, queen. Anterior clypeal margin with a row of specialized, stout setae which give it a denticulate appearance (Figs 8 - 11, 14, 15); this may be accentuated by the setae arising from cuticular projections ( Mystrium , some Amblyopone ). The setae are secondarily reduced in some species, lost in Amblyopone mutica (Santschi) .

2. *? Worker, queen. Mandibles overlapping at their tips when closed and typically, but not always, without distinct

basal and masticatory borders. Differentiated borders can be seen in Concoctio and some Amblyopone , however, so the groundplan for the tribe is uncertain.

3. * Worker, queen. Palp formula 5,3, with reductions therefrom (Brown, 1960).

4. Worker, queen. Twelve antennal segments, with uncommon secondary reduction to as few as 9 and 7.

5. Worker, queen. Antennal sclerite (torulus) raised medially and fusing with the overlapping frontal lobes.

6. * Worker. Compound eyes reduced or, less commonly, absent.

7. * Worker, queen. Eyes, when present, situated behind the middle of the sides of the head.

8. Worker. Promesonotal suture unfused.

9. * Worker. Mesonotum short and transverse, on a flattened mesosoma, shorter than the basal (= dorsal) face of the propodeum, usually much so.

10. * Worker, queen, male. Metacoxal cavities encircled by cuticle, the endpoints meeting broadly but not fused (Figs 19, 20). Fusion occurs as a secondary development within the tribe, in Onychomyrmex and possibly others.

11. * Worker, queen. Metapleural gland orifice directed predominantly dorsally and posteriorly, on a curved surface mesad of a posterolateral swelling or plate; orifice plainly visible, as a thin crescentic cavity, in posterior view; no guard hairs arising from the posterolateral swelling (Figs 25, 26, 31, 32). The metapleural gland orifice of Myopopone is somewhat divergent, opening laterally as well as posterodorsally.

12. * Worker, queen. Petiole (abdominal segment 2) shape characteristic: essentially apedunculate, with a steep, broad anterior face and a flat dorsal face that extends to the posterodorsal margin without descending into a distinct posterior face.

13. * Worker, queen, male. Abdominal sternum 2 with distinctive configuration: fused anteriorly with the tergum, but not fully fused posteriorly, i. e. with some free play between the sternite and adjacent tergite; posterior portion of sternum 2, i. e. section posterior to the region of definitive fusion, typically triangular or pyriform in shape (ventral view), its anterior apex occurring at a ' pinch point' marked by the approximate convergence of three structures: the laterotergite (see 14 below), the anterior termination of the (usually well developed and antero-dorsally undercut) ventral petiolar tooth, and the lower margins of the collar-like peduncular flange that encircles the tergum anteriorly (Fig. 37); very rarely (e. g. A. mutica ) the petiolar tooth and peduncular flange absent.

14. *? Worker, queen, male. Abdominal tergum 2 with a distinct laterotergite which parallels the posterior portion of the sternum, forming a hinge joint with it; laterotergite broad posteriorly, narrowing anteriorly and terminating at the ' pinch point' near the lower margins of the collar-like peduncular flange (Fig. 37). Laterotergite reduced / lost in Prionopelta (Fig. 38) and in most Onychomyrmex .

15. *? Worker, queen, male. Petiole broadly attached to upper margins of abdominal segment 3 and helcial sternite broad. A significant narrowing of the broad dorsal attachment occurs only in the aberrant Amblyopone mutica .

16. Worker, queen, male. Abdominal segment 3: ter-gosternal fusion of presclerites and postsclerites,

17. Worker, queen. Abdominal segment 4: differen-tiation of presclerites and tergosternal fusion of the entire segment.

18. * 7 Worker, queen, male. Absence of stridulatory file on abdominal tergum 4.

19. Worker. queen. Pygidium simple.

20. Worker, queen. Sting apparatus well developed, furcula present.

21. Worker, queen, male. Tibial spurs 1.2.2. with reductions therefrom.

22. * Worker, queen. Posterior metatibial spur stout subtriangular and curved (Hashimoto, 1991 b), its lower margin pectinate and upper margin barbulate.

23. Worker, queen, male. Tarsal claws simple.

Some of the starred features listed above (e. g. reduction and position of ine compound eyes: simple tarsal claws) appear repeatedly in other ant groups and hence have limited phylogenetic value. Other features, such as the absence of a stridulatory file and the broad attachment of the petiole to the succeeding segment, are possibly pleomorphic. This is almost certainly true of inc presence of a laterotergite on abdominal tergum 2 (also seen, for example, in Myrmecina and some cerapachyines and other ponerines) but the particular ' pinch point' arrangement of

the laterotergite, the ventral petiolar tooth, and the peduncular * flange is more or less confined to Amblyoponini . A ventral petiolar tooth and a peduncular flange are also seen in many other ponerines, but their shape and position in Amblyoponini are distinctive. The petiolar tooth, in particular usually protrudes anteroventrally with the result that, in lateral profile, a notch-like incision is observed at its anterior junction with the sternum proper. Also compelling as synapomorphies are the specialized dentiform clypeal setae which appear to be unique to the tribe: the particular configuration of the metapleural gland which is not duplicated elsewhere: the shape of the petiole, which is rarely seen in other ants ( Typhlomyrmex rogenhoferi Mayr and a few cerapachyines approach this condition); and the broad but primitively unfused connection between the sclerites encircling the metacoxal cavities. As far as known, all amblyoponines are cryptic in their foraging habits and specialized as predators on arthropods, especially centipedes, living in soil or rolling wood (Brown, 1960; Gotwald & Levieux, 1972; Hoelldobler & Wilson, 1986; Masuko, 1986; Ito, 1993) The shape of the mandibles, the powerful sting, and the dentiform clypeal (sometimes also labral) setae no doubt assist physically in prey capture (Brown, 1960), although the clypeal setae probably also have a sensory function.

Excluded from Amblyoponini

1. Apomyrma , known from the single species Apomyrma stygia Brown , Gotwald & Levieux (1971), was originally placed in the Amblyoponini but later transferred to the Leptanillinae by Bolton (1990 a) and then given subfamily status, as Apomyrminae in Baroni Urbani et al. (1992). The clypeal margin of the Apomyrma worker is not adorned with specialised setae but there is a double row of similar, presumably analogous (see also Gotwald & Levieux, 1972) peg-like setae on the labrum. Note that these are different in shape than those of die Amblyoponini (compare Figs. 8 - 11, 14 - 17). Nevertheless dentiform setae are round on both the labrum and the clypeal margin in Onychomyrmex (Fig. 9) and some Amblyopone , suggesting a possible link between the characters. Protanilla , a leptanilline genus, also possesses a pair of stout setae on the labrum (Bolton, 1990 a) but none on the clypeus. Apomyrma workers have no eyes and those of (he queen are placed in a posterior position on the head in agreement with Amblyoponini . With respect to the remaining putative synapomorphies of Amblyoponini , however, Apomyrma exhibits differences; it has a fully closed metacoxal cavity surrounded by a dis-tinct annulus; metapleural gland orifice opening posterolaterally, under a dorsal cuticular flap; non-amblyoponine petiole shape: sharp constriction between the petiole and abdominal segment 3: and an isolated posterior petiolar sternite that is much reduced in size, although flanked by apparent laterotergites (Fig. 39). It must be admitted, however, that most of these conditions could be derived from those seen in Amblyoponini ( Amblyopone mutica provides an uncanny example of a petiole tending towards the Apomyrma condition.) The same could be said for the horizontal toruli, forward-placed spiracle on abdominal tergum 3, palp formula of 2,2, and transverse sulcus behind the helcial sternite (see Bolton, 1990 a: 280). Hence a close relationship between these two cannot be ruled out. The Amblyoponini might even be paraphyletic relative to Apomyrma (and Leptanillinae ), although the morphology of the metapleural gland and gaster suggests otherwise.

2. The ponerine genus Typhlomyrmex , placed in its own tribe but sometimes considered a possible relative of Amblyoponini (Brown, 1974 b), has no specialized clypeal setae, a metapleural gland whose orifice opens dorsolateraly and is not visible in a strict posterior view (Figs 27, 33), open metacoxal cavities whose encircling cuticle does not overlap broadly (Fig. 21), and a differently shaped petiolar sternite (Fig. 40). Typhlomyrmex also lacks a petiolar laterotergite and the broad attachment of the petiole to the postpetiole. Brown (1965) cites additional differences between Typhlomyrmex and Amblyoponini in wing venation and larval mandibles.