Asphinctopone Santschi

Schmidt, C. A. & Shattuck, S. O., 2014, The Higher Classification of the Ant Subfamily Ponerinae (Hymenoptera: Formicidae), with a Review of Ponerine Ecology and Behavior, Zootaxa 3817 (1), pp. 1-242 : 70-72

Asphinctopone Santschi

Fig. 7

Asphinctopone Santschi, 1914: 318 (as genus). Type-species: Asphinctopone silvestrii Santschi, 1914: 318 ; by monotypy.

Lepidopone Bernard, 1953: 207 (in Ponerinae , Ponerini ). Type-species: Lepidopone lamottei Bernard, 1953: 208 (junior synonym of Asphinctopone silvestrii Santschi, 1914 ); by monotypy. Brown, 1953b: 2 ( Lepidopone as junior synonym of Asphinctopone ).

Asphinctopone is a small genus (three described species) restricted to tropical Africa. Nothing is known about its habits.

Diagnosis. Asphinctopone is morphologically distinctive and unlikely to be confused with any other genus. Important diagnostic apomorphies of the genus include the complex clypeus (see description below), the long apical antennomere, the strongly impressed metanotal groove, the divided mesopleuron, and the lack of differentiated presclerites in A4. Additional apomorphies of Asphinctopone include characters of the subpetiolar process and the helcium (described in detail by Bolton & Fisher, 2008a). The presence of a small process on the basal mandibular margin and strongly impressed promesonotal suture, previously thought to be apomorphies, do not occur in all known species and are therefore not of use in diagnosing this genus ( Hawkes, 2010). Superficially, workers of Asphinctopone perhaps most resemble small Brachyponera , due to their similarly impressed metanotal grooves, strongly narrowed propodeal dorsa, round or ovoid propodeal spiracles, squamiform petioles, and absent or weak gastral constriction. These genera strongly differ in many characters, however, including those of the mandibles (triangular and with a basal pit in Brachyponera , subtriangular and with a unique process on the basal margin in Asphinctopone ) and clypeus (broadly convex in Brachyponera , complex in Asphinctopone ), their metatibial spur count (two in Brachyponera , one in Asphinctopone ), and many other characters.

Synoptic description. Worker. Small (TL 3.3–3.7 mm) ants with the standard characters of Ponerini . Mandibles subtriangular, with five teeth, a small process on the basal margin near the mandibular articulation present in some species, and a faint basal groove. Clypeus projecting anteriorly, with a small rounded lobe medially, on either side of which is a shallow concavity and then an angular projection. Frontal lobes closely approximated and of moderate size. Antennae with the three or four apical antennomeres forming a weak club, the apical antennomere longer than the preceding five (or four) segments combined. Eyes small, located anterior of head midline. Promesonotal suture sometimes relatively deeply impressed, the metanotal groove always deeply impressed. Mesopleuron divided by a transverse groove. Propodeal dorsum strongly narrowed and relatively short, the posterior face relatively long. Propodeal spiracles ovoid. Metatibial spur formula (1p). Petiole squamiform, the scale thin in side view but broad in dorsal view. A4 without differentiated presclerites, and hence the gaster without a girdling constriction. Head and body shiny to very sparsely punctate, with sparse pilosity and pubescence. Color orange to reddish brown. See description by Bolton & Fisher (2008a) and Hawkes (2010) for further details and for discussion of additional important characters, such as those of the helcium and subpetiolar process.

Queen. Similar to worker but slightly larger, winged, with ocelli and larger eyes, and with the other characters typical of winged ponerine queens ( Bolton & Fisher, 2008a).

Male. Unknown.

Larva. Not described.

Geographic distribution. Asphinctopone is rarely collected and seems to be at low density where it occurs, but is widespread in central and western Africa with a single species known from eastern Africa, having been collected in the Ivory Coast, Nigeria, Cameroon, the Central African Republic, Ghana, Guinea, Gabon and Tanzania ( Bolton & Fisher, 2008a; Hawkes, 2010).

Ecology and behavior. Nothing definite is known about the habits of Asphinctopone . Specimens have been collected in leaf litter, soil, rotting wood, and an abandoned termitary (Déjean et al., 2006; Bolton & Fisher, 2008a) while one worker was collected during the evening ( Hawkes, 2010). The presence of Asphinctopone workers in these microhabitats, along with their reduced eyes, implies a cryptobiotic existence. Bolton & Fisher (2008a) suggest that the derived mandibular structure of the genus is indicative of prey specialization, though its feeding habits remain unknown.

Phylogenetic and taxonomic considerations. Santschi (1914) described Asphinctopone as a monotypic genus to hold his new species A. silvestrii . Bernard (1953) later erected the genus Lepidopone for his new species L. lamottei . Bernard differentiated his new genus from the obviously closely related Asphinctopone by supposed differences of the coxae, petiole and gaster. Brown (1953c) concluded that the justification for separating Lepidopone from Asphinctopone was weak, and synonymized them. Bolton & Fisher (2008a) revised the specieslevel taxonomy of Asphinctopone .

Schmidt (2013) was unable to include Asphinctopone in his phylogeny of Ponerinae , and the morphological traits of the genus give only a few clues to its phylogenetic position. Ouellette et al. (2006) included an unidentified Asphinctopone species in their 28S phylogeny of the poneroid subfamilies, and found weak support for a close relationship between Asphinctopone and Odontomachus or Anochetus , suggesting membership of Asphinctopone in the Odontomachus Genus Group. Morphological evidence does not give a strong indication of the phylogenetic relationships of Asphinctopone , though after considering the various possibilities we conclude that Asphinctopone most likely is a member of the Odontomachus Group, as suggested by Ouellette et al. ’s (2006) molecular results. Bolton & Fisher (2008a) found similarities in the structure of the petiolar sternite and helcium in Asphinctopone , Phrynoponera , and Brachyponera , though they argued against these similarities representing synapomorphies of all three genera or any given pair of them. Still, the possibility cannot be rejected, especially given other superficial similarities between Asphinctopone and both Phrynoponera and Brachyponera .

The presence of only a single metatibial spur in Asphinctopone would be unusual among Odontomachus group genera, but some species of Anochetus have a similar reduction in spur count. Spur count is roughly correlated with body size, so the loss of the second spur in Asphinctopone could be the result of a reduction in body size, and would not exclude its placement in the Odontomachus group. Other morphological arguments for a placement in the Odontomachus group include the unconstricted gaster (present to a less extreme degree in most members of the group), the impressed metanotal groove (more commonly impressed in the Odontomachus group than in other genus groups), and the relatively large frontal lobes, which would argue against a placement in the Ponera group, nearly all of which have very small frontal lobes. A placement of Asphinctopone within the Plectroctena group is unlikely, given its posteriorly-opening metapleural gland orifice, impressed metanotal groove, and narrowed propodeal dorsum. The possibility of a close relationship between Asphinctopone and Hypoponera cannot be rejected, but is not supported by any particular putative synapomorphy. Finally, the biogeography of Asphinctopone (restricted to central and western Africa) lends credibility to a placement in either the Plectroctena or Odontomachus groups, which are apparently Afrotropical in origin. Weighing all the evidence, we find it most likely that Asphinctopone is simply an unusually small member of the Odontomachus group, and we therefore tentatively include it there.

Figures

FIGURE 7. Worker caste of Asphinctopone silvestrii: lateral and dorsal view of body and full-face view of head (CASENT0006811, April Nobile and www.antweb.org); world distribution of Asphinctopone.