Brachyponera Emery

Fig. 9

Brachyponera Emery, 1900a: 315 (as subgenus of Euponera). Type-species: Euponera (Brachyponera) croceicornis Emery, 1900a: 315; by monotypy. Gen. rev.

Brachyponera is a fairly large genus, with 24 described species and subspecies, and ranges from southern Africa to Australia. Brachyponera is unusual among ponerines in having a distinct size dimorphism between workers and queens, and in the invasiveness of some of its species.

Diagnosis. Workers of Brachyponera can be differentiated from those of other ponerine genera by the following combination of characters: Mandibles usually with a basal pit (obsolete or vestigial in some species), eyes small and placed near the mandibular insertions, metanotal groove deep, propodeum at a lower elevation than the thorax and usually strongly narrowed dorsally, propodeal spiracle small and round, petiole squamiform, prora reduced and not externally visible, gaster with only a slight girdling constriction, and metatibiae with two spurs. None of these characters is autapomorphic within the Odontomachus group, but this combination of characters is unique. Brachyponera is most likely to be confused with species of Pseudoponera, but Pseudoponera lacks the mandibular pits, deep metanotal groove, and lowered propodeal elevation of Brachyponera.

Synoptic description. Worker. Small to medium (TL 3–7 mm) ants with the standard characters of Ponerini. Mandibles triangular and usually with a small basal groove/pit. Frontal lobes small. Eyes small and placed far anterior near the mandibular insertions. Mesopleuron sometimes fully or partially divided by a shallow transverse groove. Metanotal groove deeply impressed. Propodeum at a lower elevation than the thorax, and usually strongly narrowed dorsally. Propodeal spiracle small and round. Metatibial spur formula (1s, 1p). Petiole squamiform. Girdling constriction between pre- and postsclerites of A4 apparent. Stridulitrum sometimes present on pretergite of A4. Head and body shiny to lightly punctate, sometimes with lateral striations on the mesosoma. Head and body with sparse pilosity and patchy pubescence. Color orange to black.

Queen. Similar to worker but larger (sometimes much larger, as in B. lutea; Wheeler, 1933b), winged, with a wider and broader petiole, and with the other caste differences typical in ponerines. See description by Ogata (1987) for further details.

Male. See description by Ogata (1987).

Larva. Described by Wheeler & Wheeler (1971a, 1976, 1986b).

Geographic distribution. Brachyponera is widespread from Africa through southern Asia to Australia. It is most species-rich in Southeast Asia. B. chinensis was accidentally introduced to the southeastern United States and is now locally abundant (Nelder et al., 2006); it has also been introduced to New Zealand.

Ecology and behavior. Brachyponera workers are among the smallest of the Odontomachus group, but like most members of the group are solitary epigeic generalist predators and scavengers. Nests are generally constructed in soil or rotten wood (B. chinensis: Ogata, 1987; Matsuura, 2002; Matsuura et al., 2002; Gotoh & Ito, 2008; B. croceicornis: Wilson, 1958c; B. lutea: Wheeler, 1933b; Haskins & Haskins, 1950; B. luteipes: Kikuchi et al., 2007; B. mesoponeroides: Radchenko, 1993; B. pilidorsalis: Yamane, 2007). Brachyponera is unusual among ponerines in that it displays a marked reproductive dimorphism between workers and queens, with the workers having completely lost their reproductive organs and queens having a large number of ovarioles (Ito & Ohkawara, 1994; Gotoh & Ito, 2008). Brachyponera also has the distinction of containing some of the only ponerine species considered to be pests: B. chinensis and B. sennaarensis, which are invasive and have potentially dangerous stings (see below).

Due to its pest ant status, B. chinensis has received more attention than most Brachyponera species. It seems to be fairly representative of the genus. B. chinensis is a generalist predator and scavenger, (Teranishi, 1929; Matsuura, 2002; Matsuura et al., 2002; Matsuura & Nishida, 2002), its nests are apparently polydomous (Gotoh & Ito, 2008), and its colonies average between 30 and 100 workers (Gotoh & Ito, 1998; Matsuura, 2002). Colony founding in B. chinensis is apparently semi-claustral (Koriba, 1963), and both monogynous and polygynous colonies have been observed (Gotoh & Ito, 1998). It is an invasive pest ant in the southeastern United States, having been accidentally introduced sometime before 1932 (Smith, 1934). The species is a public health concern due to the relative frequency of life-threatening anaphylaxis and other reactions to its venom (in Japan: Fukuzawa et al., 2002; in Korea: Cho et al., 2002; in the United States: Leath et al., 2006; Nelder et al., 2006).

B. sennaarensis is another invasive Brachyponera species. It is widespread in Sub-Saharan Africa and has recently been spreading northeastward through the Middle East (reaching as far as Iran), where it takes advantage of the relatively cooler and wetter climatic conditions provided by urban areas (Collingwood et al., 1999; Tirgari & Paknia, 2005; Paknia, 2006; Wetterer, 2012b). The species is very adaptable, occurring in both dry and humid habitats in its native range and having a very flexible diet (Déjean & Lachaud, 1994; L, 1994; Déjean et al., 1999). B. sennaarensis is a generalist omnivore but like many other Brachyponera species (and unusually for ponerines) will utilize seeds for food (Arnold, 1925; Lévieux & Diomande, 1978; Lévieux, 1979; Déjean & Lachaud, 1994; Lachaud & Déjean, 1994). Workers forage individually and will only recruit nestmates in times of general starvation (Lachaud & Déjean, 1994). B. sennaarensis is notable for the large size of its colonies (about 1,000 workers on average) and the striking size dimorphism between workers and queens (Déjean & Lachaud, 1994). Even more unusual is the presence of size polymorphism within the worker caste, which is rare among ponerines (Déjean & Lachaud, 1994). B. sennaarensis nests are constructed in soil and are multichambered, the chambers being connected by tunnels (Déjean & Lachaud, 1994). Tandem-running is used during emigrations to new nest sites (Lachaud & Déjean, 1994). Like B. chinensis, the sting of B. sennaarensis can cause life-threatening anaphylaxis (Dib et al., 1992). Longhurst et al. (1978) examined the mandibular gland secretions of B. sennaarensis.

The abundant and adaptable Australian species B. lutea displays even more extreme size differences between the workers and queens than does B. sennaarensis (Wheeler, 1933b). The workers are tiny and hypogeic (unlike most Brachyponera). The large size of the queens enables claustral colony founding, though semiclaustral founding also occurs, as is the case with B. sennaarensis (Haskins & Haskins, 1950; Lachaud & Déjean, 1991b; Déjean & Lachaud, 1994). B. lutea has large colonies of over 2,000 workers, and is apparently largely predacious (Wheeler, 1933b; Haskins & Haskins, 1950).

Very little has been reported about other species of Brachyponera. B. luteipes is polygynous and may be polydomous or unicolonial, though the data on this are not conclusive (Takahashi et al., 2005; Kikucho et al., 2007). Interestingly, B. luteipes workers are aggressive toward queens of foreign colonies but not toward foreign workers (Kikucho et al., 2007). Like B. sennaarensis, B. luteipes is known to feed on seeds (Zhou et al., 2007). Wilson (1958c) reports that B. croceicornis is one of the most abundant and widespread ants in New Guinea, inhabiting a wide array of habitats; its colonies have about 100 workers.

Phylogenetic and taxonomic considerations. Brachyponera first appeared in the literature as a subgenus of Euponera (Emery, 1900a), with B. croceicornis Emery as the type species. The next year, Emery (1901) again described Brachyponera as new and designated B. sennaarensis Mayr as the type species, though this was unjustified given the earlier designation of B. croceicornis. Most authors continued to treat Brachyponera as a subgenus of Euponera (except Bingham, 1903) until Wilson (1958c) raised it to full genus status, where it generally remained until Brown (in Bolton, 1994) synonymized it with Pachycondyla (see also Snelling, 1981).

We are reviving Brachyponera to full genus status based on both molecular and morphological evidence. Schmidt's (2013) molecular phylogeny of the Ponerinae places Brachyponera with strong support within the Odontomachus group. Its sister group is unresolved, but Brachyponera is not closely related to Pachycondyla, and a sister relationship with Euponera cannot be rejected.

Morphologically, Brachyponera does not share any obvious apomorphies with any other genera, with the possible exception of basal mandibular pits, which also occur in Euponera, and the lack of a prora, which is also absent in Iroponera and Phrynoponera. Brachyponera and Euponera also share deep metanotal grooves and divided mesopleura (only in some Brachyponera), though these easily could be convergent. The lack of the prora is most likely convergent as there is little additional evidence suggesting a close relationship among these three genera. Brachyponera’s round propodeal spiracle suggests a possible placement near Myopias and Leptogenys, though the absence of a strong gastral constriction argues against this placement. In sum, both the molecular and morphological evidence is inconclusive about the exact phylogenetic position of Brachyponera, though it is certainly distinctive enough to warrant full genus status.