Pachycondyla Smith, F.

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 : 152-154

Pachycondyla Smith, F.

Fig. 31

Pachycondyla Smith, F., 1858: 105 (as genus in Poneridae). Type-species: Ponera crassinoda Latreille, 1802b: 198 ; by subsequent designation of Emery, 1901: 42.

Pachycondyla has been the focus of the greatest taxonomic confusion within Ponerinae , and was previously considered the senior synonym of numerous genera which are here considered distinct. Pachycondyla is in reality a small Neotropical genus (11 described species) that is closely related to Dinoponera . Relatively little is known about its habits.

Diagnosis. Pachycondyla workers are fairly generalized and lack any obvious autapomorphies, making their diagnosis more complicated than for most ponerine genera. They can most easily be identified by the following combination of characters: mandibles triangular, anterior clypeal margin without projecting teeth, metanotal groove at most present as a faint suture, propodeal spiracles slit-shaped, metapleural gland orifice with a posterior U-shaped cuticular lip, arolia not prominent, tarsal claws unarmed, petiole a thick block-like node, stridulitrum absent from pretergite of A4, and hypopygium with a row of stout spines on either side of the sting. Pachycondyla is most likely to be confused with Dinoponera , Neoponera , Ectomomyrmex , or Bothroponera , but Pachycondyla differs from Dinoponera in its smaller size, triangular mandibles, unarmed clypeal margin and tarsal claws, and block-like petiole; from Neoponera in its lack of a stridulitrum on the pretergite of A4 and by its hypopygial spines; from Ectomomyrmex in its complex metapleural gland orifice and hypopygial spines; and from Bothroponera in its hypopygial spines.

Synoptic description. Worker. Medium to large (TL 7–20 mm) robust ants with the standard characters of Ponerini . Mandibles triangular, sometimes with a faint basal groove. Anterior margin of clypeus convex and often medially emarginate. Frontal lobes moderately large. Eyes of moderate size and located anterior of head midline. Pronotum often with sharp lateral margins. Mesopleuron variable: fully, partially, or not at all divided by a transverse groove. Metanotal groove absent or at most present as a faint suture. Propodeum broad dorsally. Propodeal spiracles slit-shaped. Metapleural gland orifice with a posterior U-shaped cuticular lip and a lateral depression. Metatibial spur formula (1s, 1p). Petiole with a thick block-like node which widens posteriorly. Gaster with only a weak girdling constriction between pre- and postsclerites of A4. Hypopygium with a row of stout spines on either side of the sting. Head and body densely punctate to striate (rugoreticulate in at least one population of P. harpax ), with abundant pilosity and dense pubescence. Color dark brown to black.

Queen. Winged, with ocelli and the other modifications typical of ponerine queens, and slightly larger than the worker, but otherwise very similar to that caste.

Male. See descriptions for individual species in Smith (1858) and Santschi (1921).

Larva. Described for individual species by Wheeler & Wheeler (1952).

Geographic distribution. The range of Pachycondyla extends from the southern United States (Louisiana and Texas) to northern Argentina, and includes some islands of the Caribbean ( Kempf, 1961). P. harpax covers most of the range of the genus, but most other Pachycondyla species have a much more restricted range.

Ecology and behavior. Relatively little is known about the ecology and behavior of Pachycondyla . Longino (2013) reports that P. harpax and P. impressa forage on the forest floor and are never observed foraging arboreally. They are presumably generalist predators and scavengers, though published accounts of their food preferences are scant. Wheeler (1900b) reported that P. harpax workers in captivity would feed on egg yolk and sugar but ignored termites, Overal (1987) stated that P. harpax eats soft-bodied insects (including termites) and myriapods, and Garcia-Pérez et al. (1997) observed P. harpax preying predominantly on termites. P. striata will readily harvest and consume fruits and the arils of seeds from the forest floor, though it is unknown if this behavior occurs in other members of the genus ( Pizo & Oliveira, 1998, 2001; Passos & Oliveira, 2002, 2003, 2004; Raimundo et al., 2004). Nestmates are apparently recruited to food sources via tandem running (observed in P. harpax and P. impressa ; S. Levings, pers. comm. cited in Hölldobler & Wilson, 1990).

When reported, nests are constructed in the ground ( P. harpax and P. impressa ; Wheeler, 1900b; Overal, 1987; Longino, 2013) or in soil collected in the crowns of palms ( P. harpax ; Overal, 1987). Mating occurs via typical nuptial flights ( P. harpax: Longino, 2013 ; P. impressa: Ortius & Lechner, 1997 ). Wheeler (1900b) reported on egg production by workers of P. harpax , which he interpreted as being ergatoid queens but which are more likely just normal workers laying haploid eggs, as is common in Ponerinae . The mandibular, Dufour’s and venom gland secretions of P. striata were studied by Morgan et al. (1999, 2003; the mandibular gland of this species was also studied by Tomotake et al., 1992, and Mathias et al., 1995), the ovaries and corpora allata of P. striata queens and workers were compared by Thiele & Mathias (1999) and Figueira & Mathias (2002), respectively, the fat body of P. striata queens was studied by Thiele & Mathias (2003), and the structure of the venom gland in P. striata was described by Ortiz & Mathias (2003, 2006). Overal (1987) observed that P. harpax produces a foamy defensive secretion from the tip of the abdomen, similar to the behavior exhibited by Pseudoneoponera (see the description under that genus). P. harpax also injects venom from the sting, and Orivel & Déjean (2001) measured the toxicity of this species’ venom.

Phylogenetic and taxonomic considerations. The taxonomic status of Pachycondyla and its putative synonyms has been one of the central problems in ponerine systematics for many years. In fact, the taxonomic chaos represented by Pachycondyla was the initial motivation for this revision of the Ponerinae . From the very first description of Pachycondyla ( Smith, 1858) , and continuing until the present day, the true boundaries of this genus have been obscured by excessive synonymy and a lack of serious phylogenetic consideration. We will briefly review the taxonomic history of Pachycondyla before discussing the results of Schmidt’s (2013) molecular phylogenetic analyses and our morphological observations as they relate to Pachycondyla .

Smith (1858) erected Pachycondyla based on a suite of morphological traits now shown to be of dubious phylogenetic value, including a subquadrate head, a convex anterior clypeal margin, large denticulate mandibles, clavate antennae (this character is mysterious, as the species that Smith included in Pachycondyla have more or less filiform antennae), medium-sized eyes that are located anteriorly on the sides of the head, four-segmented labial and maxillary palps, pectinate tibial spurs (presumably he meant only the larger spur), a thick and wide petiolar node, and an elongate abdomen. While this long list of characters may seem to be a reasonable basis for defining a genus, most or all of these characters are probably plesiomorphic within the Ponerini . The species originally included in Pachycondyla by Smith are now dispersed into several distinct genera: Pachycondyla , Pseudoneoponera , Ectomomyrmex , Paltothyreus , and even Platythyrea .

Smith did not designate a type species for Pachycondyla , but Emery (1901) later designated P. crassinoda as the type, presumably because it was the first species listed by Smith under Pachycondyla . Latreille (1804) had previously designated P. crassinoda as the type species of Ponera , but Westwood (1840) subsequently designated Ponera coarctata as the type species of Ponera . We continue to recognize the traditional application of the generic names Ponera and Pachycondyla , which has been nearly universal since Emery’s designation of P. crassinoda as the type species of Pachycondyla . See Taylor (1967) for more on this controversy.

After Smith’s original description, Pachycondyla experienced more than a century of relative taxonomic stability, with the most significant change being Emery’s (1901) designation of Bothroponera , Ectomomyrmex , and Pseudoponera as subgenera of Pachycondyla . Emery (1911) later removed Pseudoponera from the genus and rediagnosed Pachycondyla by a presence of “subtriangular” toothed mandibles, convex anterior clypeal margin, the location of the eyes, a lack of preocular carinae, an obsolete metanotal groove, and a thick petiole. Subsequent authors variously treated Bothroponera and Ectomomyrmex as valid genera or as subgenera of Pachycondyla (see Bolton, 2006).

W. L. Brown worked for decades on a broad revision of Pachycondyla , and though he died before publishing his formal revision, his planned taxonomic changes became entrenched in the myrmecology community through various publications (principally Brown, 1973; Snelling, 1981; Hölldobler & Wilson, 1990; Bolton, 1994, 1995, 2003, 2006). These changes amounted to a broad synonymization of no fewer than 18 distinct generic names under Pachycondyla , without phylogenetic justification: Bothroponera , Brachyponera , Ectomomyrmex , Eumecopone , Euponera , Hagensia , Megaponera , Mesoponera , Neoponera , Ophthalmopone , Paltothyreus , Pseudoneoponera , Pseudoponera , Syntermitopone , Termitopone , Trachymesopus , Wadeura , and Xiphopelta. Brown apparently included in Pachycondyla any ponerine species whose workers have triangular mandibles, eyes, two metatibial spurs, and the absence of any apomorphies extreme enough to justify a separate genus. These characters are almost certainly plesiomorphic, rendering them uninformative about the monophyly of the group as thus defined. Given its extensive morphological diversity and the apparent close relationship between some of its species and other recognized genera, Pachycondyla (sensu Brown) was almost certainly bound to be non-monophyletic based on morphological evidence alone.

Schmidt's (2013) molecular phylogeny of the Ponerinae confirms the vast non-monophyly of Pachycondyla . Schmidt (2013) sampled representatives from nearly all junior synonyms of Pachycondyla , and none of them are inferred to even be the sister group of true Pachycondyla , which is represented in the phylogeny by P. crassinoda , P. harpax and P. impressa . From morphology we are also confident that those junior synonyms which Schmidt (2013) did not sample ( Wadeura and Xiphopelta) are also not closely related to Pachycondyla . The actual sister group of Pachycondyla is Dinoponera , which ironically has never been considered its junior synonym. Their close relationship is supported by strong molecular and morphological evidence (see the discussion under Dinoponera for more on their morphological synapomorphies). True Pachycondyla is a small Neotropical genus consisting of the type species P. crassinoda and its close relatives. Pachycondyla workers are united morphologically by their combination of triangular mandibles, unadorned anterior clypeal margin, medium-sized eyes, unarmed tarsal claws, block-like petiole, absence of a stridulitrum from the pretergite of A4, and a row of stout spines on the hypopygium on either side of the sting.

Figures

FIGURE 31. Worker caste of Pachycondyla crassinoda: lateral and dorsal view of body and full-face view of head (CASENT0249138, Ryan Perry and www.antweb.org); world distribution of Pachycondyla.