Mesoponera Emery

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 : 107-110

Mesoponera Emery

Fig. 17

Mesoponera Emery, 1900b: 668 (as subgenus of Euponera ). Type-species: Ponera melanaria Emery, 1893b: 260 ; by monotypy. Gen. rev.

Xiphopelta Forel, 1913a: 108 (as subgenus of Ponera ). Type-species: Ponera (Xiphopelta) arnoldi Forel, 1913a: 108 (junior synonym of Ponera elisae var. rotundata Emery, 1895c: 20 ); by monotypy. Syn. nov.

Mesoponera is a moderately sized genus, with 28 described species and subspecies, restricted to the Old World tropics from Sub-Saharan Africa to Australia and the Solomon Islands.

Diagnosis. Mesoponera workers are perhaps the least derived of any ponerine genus, as they lack any obvious apomorphies. Mesoponera bears superficial resemblance to a number of other relatively plesiomorphic genera, especially Fisheropone , Neoponera , Mayaponera , Pseudoponera , and Hypoponera , and to a lesser degree genera such as Hagensia , Megaponera , and Paltothyreus . Mesoponera can be separated from these genera by the following combination of characters (most of which are probably plesiomorphic): mandibles without a basal groove, frontal lobes very small and closely approximated, eyes relatively small and placed anterior of head midline, preocular carinae absent, pronotum without sharp lateral margins, metanotal groove shallow to moderately deep (in M. subiridescens and “ Xiphopelta ” species), propodeum narrowed dorsally, metapleural gland orifice without a U-shaped posterior lip, metatibia with a large pectinate spur and a smaller simple spur, petiole surmounted by a simple scale which lacks sharp lateral margins, gaster with only a moderate constriction between A3 and A4, metatibiae with two spurs, arolia not prominent, and head and body only weakly sculptured with sparse pilosity but dense pubescence.

Synoptic description. Worker. Medium (TL 5–9.5 mm) slender ants with the standard characters of Ponerini . Mandibles triangular, relatively long; mandibles crossed when closed in the M. melanaria group. Eyes small, placed anterior of head midline; absent or reduced to a small pigmented spot in a few species. Frontal lobes very small and closely approximated. Mesopleuron usually not divided by a transverse groove. Metanotal groove shallow to moderately deep (in “ Xiphopelta ” species). Propodeum narrowed dorsally. Propodeal spiracles small and round in most M. melanaria group species, but slit-like in the M. ingesta group. Metatibial spur formula (1s, 1p). Petiole squamiform. Gaster with only a weak girdling constriction between pre- and postsclerites of A4. Stridulitrum sometimes present on pretergite of A4. Head and body finely punctate, with sparse pilosity but a dense fine pubescence. Color variable. (Note: This description excludes M. subiridescens , which we place within Mesoponera only tentatively. M. subiridescens differs from the above description by its shining cuticle, relatively large eyes, mesopleuron divided by a transverse groove, deep metanotal groove, and long narrow toothless mandibles which have distinct basal grooves and basal margins that are not concealed by the clypeus when closed.)

Queen. Similar to worker, but winged and with the other differences typical for alate ponerine queens.

Male. See descriptions in Arnold (1915) and Donisthorpe (1942).

Larva. Described by Wheeler & Wheeler (1971b).

Geographic distribution. Members of this genus are found throughout Sub-Saharan Africa (including Madagascar) extending to Yemen ( M. flavopilosa, Collingwood & van Harten, 2005 ) and the Seychelles ( M. melanaria macra ), with a second set of species occurring from Sri Lanka eastward to northern Australia and the Solomon Islands.

Ecology and behavior. Almost nothing is known about the ecology or behavior of most Mesoponera species , especially members of the M. melanaria and M. subiridescens groups. Donisthorpe (1941) and Wilson (1958c) note that M. papuana nests in rotting wood and forages diurnally in leaf litter, and that M. manni nests in rotting wood or soil, but otherwise reports of their habits are scarce.

Most species in the M. ingesta group are similarly unstudied, but M. caffraria has received a fair bit of attention. This species is a predator of insects and also collects sugary liquids. It is locally abundant ( Lévieux, 1983) and colonies are fairly small (roughly 60 to 120 workers; Agbogba, 1992, 1994). Nesting occurs in the ground (Villet, 1990b) or in active or abandoned termitaries (Agbogba, 1992; Déjean et al., 1996, 1997), and colony founding is semiclaustral (Villet, 1990b). Queens inhibit reproduction by workers, but orphaned workers lay fertile eggs ( Villet & Duncan, 1992). The division of labor of M. caffraria workers has been well studied and is unusual. Rather than displaying a typical age-dependent polyethism, individual workers show a remarkable degree of task specialization, which is determined at an early age (Agbogba, 1992, 1994). Apparently only a low rate of role change occurs after this initial specialization ( Bonavita & Poveda, 1970; Agbogba, 1992). Roughly two-thirds of workers specialize on intra-nest activities (studied by Agbogba, 1991), while the remainder specialize on foraging ( Bonavita & Poveda, 1970). Foragers further specialize on the collection of sugary liquids or on either the stinging or retrieval of insect prey. When hunting termites, the behavior of M. caffraria foragers varies depending on the species and caste of the termites encountered ( Agbogba, 1985). Interestingly, large groups of M. caffraria foragers will attack termite nests, and the entire ant colony will then emigrate into the nest, at least temporarily ( Agbogba, 1990, 1992). Both the recruitment of foragers and the movement of the colony are coordinated through tandem running, using both visual and chemical cues ( Agbogba, 1984 and 1992). Masson (1970a, 1970b, 1972) studied the neuroanatomy and neurodevelopment of M. caffraria, Bonavita & Lemasne (1970) studied food exchange between M. caffraria workers, and Bonavita & Poveda (1972) examined intestinal structure in M. caffraria larvae.

Phylogenetic and taxonomic considerations. Mesoponera was erected by Emery (1900b) as a subgenus of Euponera to house the single species Ponera melanaria Emery. He caused confusion the next year ( Emery, 1901) by redescribing the genus as new and making Ponera caffraria F. Smith the type species. Most subsequent authors treated M. caffraria as the type species, until Bolton (2003) reconfirmed the status of M. melanaria as the type species. Most authors also continued to treat Mesoponera as a subgenus of Euponera (except Bingham, 1903) until Wilson (1958c) raised it to full genus status. Brown (1973) and most subsequent authors have treated Mesoponera as a junior synonym of Pachycondyla . Forel (1917) moved Xiphopelta from being a subgenus of Ponera to being a subgenus of Euponera but this was short lived, with Wheeler (1922) synonymizing Xiphopelta with Mesoponera , a treatment that we support and follow here.

Mesoponera acted as a repository for ponerine species which exhibited a suite of characters that are clearly either plesiomorphic or convergently derived. Emery (1911) gave the following basic worker diagnosis for Mesoponera (at the time a subgenus of Euponera ): mandibles elongate and armed with many teeth, maxillary palp with four segments, first funicular segment shorter or the same length as the second, mesonotum an oval disk surrounded by distinct sutures, and mesotarsi without stiff spines dorsally. Species placed in Mesoponera also have tended to share weak sculpturing, a squamiform petiole, and relatively small eyes. All or most of these characters are likely plesiomorphic within the Ponerini , making it highly likely that Mesoponera would prove to be nonmonophyletic. Schmidt's (2013) molecular phylogeny confirms this expectation. Schmidt (2013) sequenced five species formerly considered to be in Mesoponera , and they turned out to be widely scattered across the phylogeny of Ponerini , in Pseudoponera , Neoponera , the new genus Mayaponera , and Mesoponera itself (which is probably still not monophyletic; see below).

We are reviving Mesoponera to full genus status based on both morphological and molecular evidence. Morphologically, Mesoponera as we have defined it lacks any clear autapomorphies and this makes diagnosis difficult. It certainly lacks those combinations of characters diagnostic of other ponerine genera. Additional justification for full genus status for Mesoponera comes from Schmidt's (2013) molecular phylogeny, which places both the M. melanaria and M. ingesta groups within the Odontomachus group ( M. subiridescens was not sampled), but without a clear sister group for either one. They are certainly not closely related to Pachycondyla . The monophyly of Mesoponera as we have defined it is not strongly supported by Schmidt's phylogeny. Additionally, recent preliminary data from P.S. Ward (pers. comm.) found that an Asian species ( M. melanaria ) did not group with an African species ( M. ambigua ), both of which we place within Mesoponera . These results suggest that Mesoponera as conceived here is not monophyletic.

Based on the available molecular evidence as well as the morphological diversity within Mesoponera we explored the possibility of erecting several closely related genera for the species placed here. For example, species related to M. melanaria have a round propodeal spiracle (spiracle elongate in other species), those related to M. ingesta have relatively short mandibles (elongate in others) while M. subiridescens has the mesopleuron strongly divided and the metanotal groove well developed. However, when examining species from across the genus the propodeal spiracle shape shows considerable variation, with all shapes from round to elongate being present, and a divided mesopleuron can be found in species with both round and elongate propodeal spiracles. Thus it became impossible to develop clear diagnoses for groups of species based around these apparently informative characters. Additionally, Schmidt's (2013) molecular data for the M. melanaria group species ( M. rubra ) and Ward’s data are incomplete, making robust conclusions hard to draw. Given these uncertainties, we are choosing to be conservative in keeping these groups together within Mesoponera until additional data can be collected, with anticipation that the genus as conceived here will need to be modified in the future.

Figures

FIGURE 17. Worker caste of Mesoponera melanaria: lateral and dorsal view of body and full-face view of head (CASENT0249169, Ryan Perry and www.antweb.org); world distribution of Mesoponera.