Megaponera Mayr

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 : 104-107

Megaponera Mayr

Fig. 16

Megaponera Mayr, 1862: 714 (as genus in Ponerinae [Poneridae]). Type-species: Formica foetens Fabricius, 1793: 354 (junior

primary homonym in Formica , replaced by Formica analis Latreille, 1802a: 282 ); by monotypy. Gen. rev. Megaloponera Roger, 1863b: 17 (incorrect subsequent spelling of Megaponera ).

Megaponera is a monotypic genus (with an additional five subspecies) widespread in Sub-Saharan Africa. It is notable for its ergatoid queens, polymorphic workers, obligate group foraging, and specialized termite predation.

Diagnosis. Diagnostic morphological apomorphies of Megaponera workers include the presence of preocular carinae and size polymorphism, which do not occur in combination in any other ponerine. Preocular carinae occur in Odontoponera and many Neoponera species , but Megaponera lacks Odontoponera’s striate sculpturing and denticulate clypeus, and Neoponera’s prominent white projecting arolia, simple tarsal claws and U-shaped cuticular lip posterior to the metapleural gland orifice.

Synoptic description. Worker. Large to very large (TL 9–18 mm) ants with the standard characters of Ponerini . Workers polymorphic, varying principally in size and pubescence. Mandibles triangular. Eyes large, located near head midline, with distinct preocular carinae. Frontal lobes widely separated anteriorly and appearing flattened in frontal view. Scapes flattened, with distinct anterior margins. Metanotal groove shallow. Propodeum moderately narrowed dorsally. Propodeal spiracles slit-shaped. Tarsal claws with a preapical tooth. Metatibial spur formula (1s, 1p). Petiole nodiform. Constriction between pre- and postsclerites of A4 indistinct. Stridulitrum present on pretergite of A4. Head and body finely punctate, with scattered pilosity and dense pubescence (sparse in minor workers). Color black.

Queen. Wingless, similar to a major worker but larger (TL 18.5 mm), with more extensive sculpturing, denser pilosity, a deeper metanotal groove, an anteriorly slanting squamiform petiole, and a more expansive gaster. (Adapted from Arnold, 1915.)

Male. See descriptions in Emery (1897b), Arnold (1915), and Wheeler (1922b).

Larva. Described by Wheeler & Wheeler (1952).

Geographic distribution. Megaponera is widespread in tropical Sub-Saharan Africa. Wheeler (1922b) shows the range as encompassing the African continent from roughly 10° N latitude to 30° S latitude. We have seen two specimens of Megaponera in the USNM labelled as coming from India (with no additional collection information), but this is almost certainly in error as we know of no other collections of this genus from outside Africa .

Ecology and behavior. Megaponera analis has an unusual suite of ecological, behavioral, and social adaptations relative to most ponerines. The typical ponerine species has small colonies (usually fewer than 100 individuals), alate queens, and monomorphic workers which forage singly. Megaponera has diverged significantly from this basic pattern, having relatively large colonies, flightless queens, and polymorphic workers which are specialized mass raiders of termites.

Megaponera nests in the ground, in deserted termite mounds, or even partially in rotting logs ( Lèvieux, 1976 B; Longhurst & Howse, 1979a), and has relatively large colonies by ponerine standards, with from 500 to 2,000 workers ( Peeters, 1991b; Hölldobler et al., 1994). The nests are host to a diverse assemblage of myrmecophiles (Arnold, reprinted in Wheeler, 1922b). Colonies have a single highly fecund ergatoid queen, which in most respects resembles a large major worker but is endowed with a rich array of glands for chemical communication with the workers ( Peeters, 1991b; Hölldobler et al., 1994). Males locate virgin queens by following the recruitment trails of workers back to their nests ( Longhurst & Howse, 1979b). Workers retain spermathecae and ovarioles, but do not appear to mate and do not produce viable haploid eggs (Villet, 1990a; Villet & Duncan, 1992). Workers are continuously polymorphic for size ( Longhurst & Howse, 1979a; Crewe et al., 1984), though they are often referred to as “majors”, “medias” and “minors”. They are known to emit a strong odor, to stridulate loudly when disturbed, and to have a very painful sting ( Arnold, 1915).

Megaponera are specialized mass raiders of termites ( Wheeler, 1922b, 1936; Weber, 1964; Lévieux, 1966). Longhurst & Howse (1979a) studied their foraging behavior in detail and described the sequence of events in a typical raid (see also the account by Weber, 1964). Raids begin when a solitary major worker locates foraging termites. This scout returns directly to its nest, laying a trail of poison gland-derived pheromones exuded through its sting (Longhurst et al., 1979A), and recruits up to several hundred of its nestmates ( Corbara & Déjean, 2000). They proceed as a column to the termites’ protected foraging tunnels, which the major workers tear open. Minor workers then haul out termites. When this process is complete, the major workers stack the termites in their mandibles and the ants return as a column to their nest. Corbara & Déjean (2000) compared the behavior of minor and major workers during prey capture and found that though they are generally similar, major workers are more likely to attack termite soldiers than are minor workers. Longhurst & Howse (1979a) reviewed the literature on Megaponera foraging behavior and found significant regional variation in how raids are conducted. Taylor (2008) hints that this variation supports his hypothesis of multiple species within Megaponera .

Hölldobler & Wilson (1990; see also Wilson, 1958a) hypothesized that the Megaponera style of foraging, in which scouts lead columns of workers on raids of other social insects, could be the first step in the evolution of true legionary behavior, such as that of the dorylines (see also Oster & Wilson, 1978). Of the hallmarks of legionary behavior identified by Brady (2003), Megaponera exhibits obligate collective foraging and a weak form of nomadism, by which colonies frequently emigrate to new nest sites. This latter behavior was described in detail by Arnold (reprinted in Wheeler, 1922b) and Longhurst & Howse (1979a). Wheeler (1922b) also discussed the adaptations of Megaponera brood to emigration. The reasons for these frequent emigrations are unknown, but Longhurst & Howse (1979a) argue that they are not likely caused by prey shortages and may be a response to predation by Dorylus driver ants. In an interesting observation, Beck & Kunz (2007) found cooperative altruistic defensive actions among Megaponera workers under attack by Dorylus .

Phylogenetic and taxonomic considerations. The genus Megaponera was erected by Mayr (1862) to hold the single species Formica analis Latreille. The original specific epithet “ foetens ” was a junior primary homonym but has been used incorrectly in much of the extensive literature on this species. Megaponera experienced relative taxonomic stability until W. L. Brown (in Bolton, 1994) synonymized it under Pachycondyla without phylogenetic justification.

We are reviving Megaponera to full genus status based on both morphological and molecular evidence. Schmidt's (2013) molecular phylogeny of the Ponerinae places Megaponera with strong support within the Odontomachus group as sister to Ophthalmopone , and not at all close to Pachycondyla . A sister group relationship with Ophthalmopone is also strongly supported by morphology. Workers of the two genera are remarkably similar, differing significantly only in Megaponera’s preocular carinae and size polymorphism and Ophthalmopone’s slender build, huge posteriorly set eyes, and armed hypopygium.

These genera also share derived ecological and behavioral attributes. Both are specialist termite predators, with Megaponera and some Ophthalmopone species raiding termites in large groups. It is possible that the common ancestor of these genera was a mass raider of termites, with a reversal to solitary foraging being favored in some Ophthalmopone species. Alternatively, mass raiding may have evolved independently in Megaponera and Ophthalmopone . Both genera also lack a winged queen caste, though reproduction in Megaponera is performed by ergatoid queens and in Ophthalmopone it is performed by gamergate workers. The reproductive caste in the ancestor of these genera could conceivably have been either ergatoid or gamergate (or neither). The close relationship of these taxa make them excellent models for studying the selective forces driving the evolution of alternative reproductive strategies in ants, as well as the evolution of mass foraging.

While Megaponera and Ophthalmopone could arguably be synonymized, the age of their divergence is consistent with that of other ponerine genera ( Schmidt, 2013) and we feel that their morphological and behavioral distinctiveness warrant separate generic status. The sister group of Megaponera + Ophthalmopone is still unknown, but a close relationship with Hagensia is plausible (see discussion under that genus).

Figures

FIGURE 16. Worker caste of Megaponera analis: lateral and dorsal view of body and full-face view of head (CASENT0249196, Estella Ortega and www.antweb.org); world distribution of Megaponera.