Hypoponera

Found throughout the world and represented by more than 170 species. Despite a recent revision that covered regions where there are a large number of species (Bolton and Fisher 2011 for the West Palaearctic and Afrotropical regions) the unremarkable morphology of most species often leads to difficulty in determining samples to species. Hypoponera are small ants that are generally found at or just under the ground surface. They nest under or in rotten wood, in the leaf litter, and in the soil. Most species are assumed to be predators of other arthropods, although direct evidence for this is relatively scant (Levieux, 1983). Some species are widespread tramp species. Several are known to have highly unusual reproductive strategies, including the presence of combative ergatoid males.

Identification
Schmidt and Shattuck (2014) - Hypoponera is morphologically the most generalized of the cryptobiotic ponerine genera, as it lacks any obvious autapomorphies. The genus also shows greater variability than most ponerine genera in many characters typically useful for generic diagnosis. Despite these complications, Hypoponera workers are generally diagnosable by the following combination of characters: mandibles triangular, with a variable number of small teeth and without basal pits or grooves; frontal lobes small and closely approximated; metanotal groove usually shallowly depressed; mesotibiae and meso-/metabasitarsi without stout traction setae; metatibial spur formula (1p); petiole squamiform; subpetiolar process a rounded lobe without paired teeth posteriorly, and usually without an anterior fenestra; and head and body without strong sculpturing and usually with a relatively dense pubescence. Hypoponera is morphologically most similar to Ponera, Cryptopone, Pseudoponera, Brachyponera, some Euponera, Belonopelta, and Emeryopone. Hypoponera most consistently differs from Ponera in the structure of the subpetiolar process: in Ponera the subpetiolar process has an anterior fenestra and a pair of teeth posteriorly, whereas in Hypoponera the subpetiolar process is a simple rounded lobe, only rarely with an anterior fenestra. Hypoponera differs from Cryptopone in lacking stout spines on the middle and hind legs, from Euponera, Pseudoponera and Brachyponera in having only a single metatibial spur, and from Belonopelta and Emeryopone in having triangular mandibles without a series of long attenuated teeth.

Distribution
Schmidt and Shattuck (2014) - Hypoponera is the most cosmopolitan of all ponerine genera, occurring on every continent except Antarctica and extending into many temperate regions. Endemic species are apparently absent from many island groups (e.g., Polynesia), but several widespread tramp species have become established even in these locations (Taylor, 1967; Ingram et al., 2006).

Biology
Schmidt and Shattuck (2014) - Hypoponera is probably the most common and diverse ponerine genus worldwide and is consistently one of the most abundant and diverse ant genera collected in quantitative surveys of leaf litter and soil ant communities, especially in the tropics (e.g., Argentina: Theunis et al., 2005; Australia: King et al., 1998; Brazil: Soares & Schoereder, 2001; Costa Rica: Longino et al., 2002; Ghana: Belshaw & Bolton, 1994; Guyana: LaPolla et al., 2007; Madagascar: Fisher, 1999; Melanesia and New Caledonia: Wilson, 1976; generally: Ward, 2000). Though Leptogenys currently boasts many more described species than Hypoponera, the true species diversity of Hypoponera is probably grossly underestimated and may rival or exceed that of  Leptogenys given their cryptobiotic habits, lack of revisionary taxonomic work, and the likely occurrence of cryptic species complexes. Fisher (1999) found that Hypoponera diversity was a good surrogate for total ant diversity in forests in eastern Madagascar, indicating that it may be a useful indicator genus for faunal surveys.



Except for their unusual reproductive and larval behaviors (see below), surprisingly little work has been done on the ecology and behavior of Hypoponera. They are cryptobiotic, nesting in soil, under rocks, or in rotting wood, and foraging there or in leaf litter and other sheltered microhabitats (Wilson, 1958c; Onoyama, 1989; Yamauchi et al., 1996; Terayama, 1999; Foitzik et al., 2002; pers. obs.). Reports on the sizes of Hypoponera colonies are scarce, but colonies usually have fewer than 100 workers and only occasionally more (e.g., Wilson, 1958c; Villet et al., 1991; Peeters & Hölldobler, 1992; Peeters, 1993; Hashimoto et al., 1995; Yamauchi et al., 1996; Foitzik et al., 2002). They are typically reported to be generalist predators of small arthropods or scavengers (e.g., Wilson, 1958c; Agbogba, 1984; Escoubas et al., 1987; Brown, 2000; Seifert, 2004), though some species probably have stricter diets (e.g., one African species is reported to feed principally on collembolans; Lévieux, 1983). Foraging is probably generally performed by solitary workers, though at least one species is known to recruit nestmates to help dismember large prey (Agbogba, 1984). Hölldobler (1985) observed tandem running in an unidentified Hypoponera species but did not clarify its purpose.

While in most respects Hypoponera are fairly typical ponerines, members of the genus exhibit many unusual social or reproductive traits, including one of only two known instances of adult trophallaxis in the Ponerinae (Hashimoto et al., 1995), as well as obligate worker sterility (Villet et al., 1991; Ito & Ohkawara, 1994; Yamauchi et al., 2001), male polymorphism, and larval cannibalism. As a genus Hypoponera displays an interesting diversity of reproductive strategies, with species variously having almost every conceivable combination of alate and ergatoid queens as well as alate and ergatoid males. At least three Hypoponera species are known to have both winged and ergatoid males (Hypoponera eduardi, Hypoponera nubatama and Hypoponera opacior), at least three species apparently have only ergatoid males (Hypoponera ergatandria, Hypoponera gleadowi (=Hypoponera ragusai) and Hypoponera punctatissima), and still other species are thought to have only winged males (Yamauchi et al., 2001; Bolton & Fisher, 2011). A similar variation occurs in the queen caste, with some species having both alate and ergatoid queens and others probably having only one or the other (e.g., Hashimoto et al., 1995; Yamauchi et al., 1996, 2001). In what are probably the most complex mating systems known for any ponerine, H. nubatama and  H. opacior have alate queens, ergatoid queens, alate males, and ergatoid males, often all in the same colony (Yamauchi et al., 2001; Foitzik et al., 2002; Rüger et al., 2008). Some colonies of H. opacior are polygynous and polydomous, with 2 to 15 ergatoid queens and multiple nest sites connected by subterranean tunnels. Ergatoid males remain in their natal nest and mate with virgin queens (either alate or ergatoid) which are still in their cocoon (Foitzik et al., 2002).

The behavior of ergatoid Hypoponera males is both unusual and varied within the genus. At one extreme is Hypoponera ergatandria, whose males are dimorphic, the minor males mimicking females and utilizing a sneaky mating strategy, and the major males fighting and killing one another to secure mating opportunities (Yamauchi et al., 1996). Similar fighting was also observed among ergatoid males of Hypoponera punctatissima, though it is unclear whether they are dimorphic (Hamilton, 1979). Ergatoid males of H. nubatama do not fight directly but instead kill other males before they eclose from their cocoon (Yamauchi et al., 2001). Finally, ergatoid males of H. opacior do not fight but monopolize their mates by copulating with them for up to 40 hours, the longest copulations ever observed in ants (Foitzik et al., 2002). Given the presence of ergatoid males in virtually all tramp species of Hypoponera, Taylor (1967) hypothesized that the consequent simplification of the mating process in these species may facilitate their spread.

Hypoponera larvae have two pairs of sticky tubercles, with which they attach to the walls and ceilings of their nest cavities (Taylor, 1967; Escoubas et al., 1987; Peeters & Hölldobler, 1992). This may assist the larvae in feeding or may function to protect the larvae from excess humidity (Peeters & Hölldobler, 1992), but may also function to separate larvae sufficiently to prevent larval cannibalism, which has been observed in at least three species (Rüger et al., 2008).

Castes
Monomorphic workers. Queens are winged and distinctive in many Hypoponera. Intermediate ergatoid (worker-like) forms are also known for some species. Males are the least well known of all the castes but most species apparently only produce winged males. Ergatoid males have been found in a limited number of species.

Ergatoid queens have been confirmed in the following species that occur in the Afrotropical region. H. abeillei group: Hypoponera austra, Hypoponera importuna, Hypoponera lepida, Hypoponera producta. H. punctatissima group: Hypoponera eduardi, Hypoponera ragusai, Hypoponera punctatissima. Ergatoid queens are also suspected in Hypoponera ignavia and Hypoponera occidentalis (see discussions of those species). It seems reasonable to assume that ergatoid queens occur in many more species but are not currently represented in collections. It is equally obvious that some species, such as the extremely common Hypoponera dulcis, do not produce them. In some previous publications, ergatoid queens have been termed major workers or intercastes (e.g. Forel (1894), Le Masne (1956), Brown (1958)).

Nomenclature

 *  HYPOPONERA [Ponerinae: Ponerini]
 * Hypoponera Santschi, 1938b: 79 [as subgenus of Ponera]. Type-species: Ponera abeillei, by original designation.
 * Hypoponera raised to genus: Taylor, 1967a: 9.

Schmidt and Shattuck (2014) - Santschi (1938) erected Hypoponera as a subgenus of Ponera to house those Ponera species with shallow metanotal grooves. Taylor (1967) raised Hypoponera to full genus status, recognized that Santschi’s definition of the subgenus was phylogenetically meaningless, and instead differentiated the genus from Ponera by its palp formula (1,1 in Hypoponera), absence of an anterior fenestra or posterior teeth in the subpetiolar process, several male characters, and the number of sticky tubercles on the larvae. Hypoponera workers are superficially quite similar to those of Ponera, but they are distantly separated in Schmidt’s (2013) molecular phylogeny of the Ponerinae, suggesting that their morphological similarities are the result of convergence due to their similar cryptobiotic lifestyles. Hypoponera is phylogenetically distinct from other major lineages of Ponerini, diverging from its closest relative (probably the Plectroctena group) quite early in the radiation of the tribe.

Given the absence of strong autapomorphies for the genus and its relatively high morphological diversity, it is possible that Hypoponera as presently defined is non-monophyletic. Schmidt (2013) included in his molecular phylogeny several Hypoponera species presenting maximum morphological diversity from across the range of the genus, to begin to test the monophyly of the genus. To his surprise these species formed a tight clade with strong phylogenetic support. Even more surprising was that three sympatric Hypoponera species from Malaysia, which he included in the phylogeny because they are morphologically quite divergent from one another (to the point that he expected them all to represent distinct genera) turned out to be very closely related to one another, indicating an impressive recent adaptive radiation.

Worker
Schmidt and Shattuck (2014) - Very small to small (TL 1.4–5.5 mm) slender to robust ants with the standard characters of Ponerini. Mandibles triangular, with a variable number of teeth and without a distinct basal groove (though a shallow pit or vestigial groove may be present). Frontal lobes small and closely approximated. Apical segments of antennae sometimes enlarged into a distinct club. Eyes sometimes absent, but usually present, very small and located far anterior on the sides of the head. Mesopleuron usually not divided by a transverse groove, though occasionally faintly present. Metanotal groove usually present and shallowly depressed, though sometimes reduced to a suture, and rarely absent altogether. Propodeum usually moderately to strongly narrowed dorsally, but occasionally broad. Propodeal spiracles round. Metatibial spur formula (1p). Petiole squamiform. Subpetiolar process a rounded lobe, without paired teeth posteriorly and only rarely with an anterior fenestra. Gaster with a weak to strong girdling constriction between pre- and postsclerites of A4. Stridulitrum sometimes present on pretergite of A4. Head and body occasionally glossy, usually finely punctate, sometimes lightly striate on the sides of the mesosoma. Head and body with sparse to scattered pilosity and usually a dense pubescence. Color variable, testaceous to black.

Bolton and Fisher (2011) - Members of subfamily Ponerinae, tribe Ponerini (sensu Bolton, 2003) that principally inhabit rotten wood, leaf litter and topsoil.

1 Mandible triangular and stout, short to moderate in length (MI 27–35), without a basal groove and without a basal pit; with a basal angle between masticatory and basal margins. When mandibles are fully closed there is no space between the masticatory margins, nor between basal margins of mandibles and the clypeus.

2 Masticatory margin of mandible with 7 to about 18 teeth and denticles in total.

3 Palp formula 1,1 or 1,2, the maxillary palp usually minute.

4 Clypeus simple, without extended lobes or teeth on either the median or the lateral portions and usually unarmed anteromedially. Median portion of clypeus inserted as a small narrow triangle between the extreme anterior ends of the frontal lobes.

5 Frontal lobes small, almost confluent medially, separated only by a median longitudinal impression; the frontal lobes not raised or specialised in any way and their anterior margins well behind the anterior clypeal margin. Frontal carinae and antennal scrobes absent.

6 Eyes absent or present; when present always small (generally of 1 to about 20 ommatidia), lateral and located well in front of the midlength of the head.

7 Antenna with 12 segments, the apical 4–6 antennomeres gradually incrassate; only extremely rarely with a sharply differentiated club.

8 Dorsum of mesosoma with or without a metanotal groove.

9 Mesopleuron without a distinct transverse sulcus that conspicuously divides it into anepisternum and katepisternum.

10 Epimeral sclerite usually absent.

11 Metapleural gland orifice small and simple, opening posteriorly.

12 Metasternal process small and simple.

13 Propodeal spiracle small, circular to slightly elliptical, located far down on the side, usually close to the bulla of the metapleural gland.

14 Propodeum unarmed; propodeal lobes vestigial to absent.

15 Mesotibiae, metatibiae, mesobasitarsi and metabasitarsi all without spines and without enlarged prominent setae to enhance traction on their dorsal (outer) surfaces.

16 Mesotibia and metatibia each with only a single spur; metatibial spur always pectinate.

17 Pretarsal claws small and simple, without preapical teeth.

18 Petiole tergite nodiform to squamiform, always unarmed.

19 Subpetiolar process usually simple, a rounded to angulate ventral lobe; never with paired prominent teeth at the posteroventral corner of the lobe; subpetiolar process usually without an anterior fenestra or thin-spot but a fenestra present in some abeillei group members.

20 Articulation of petiole to helcium simple.

21 Helcium arises low down on anterior face of first gastral tergite (Abd. III) and is always simple; anterior surface of first gastral tergite forms a tall vertical surface above the helcium.

22 Prora usually present (absent in only one Afrotropical species): an arched tranverse crest that extends across the first gastral sternite below the helcium; usually the prora extends up the anterior face of the first sternite on each side, so that the entire prora is broadly U-shaped in anterior view.

23 Cinctus of second gastral tergite (Abd. IV) present, usually conspicuous.

24 Stridulitrum absent or present on pretergite of abdominal segment IV. In addition, fine sculpture is predominantly present, uncommonly entirely absent. The sculpture is expressed as various forms of punctation, that varies in density and intensity on different parts of the body and sometimes differs between species. Coarse, dense sculpture, such as rugae, costulae, or strong striation, appears never to be developed.

Queen
Schmidt and Shattuck (2014) - Similar to worker; usually alate, with ocelli and larger compound eyes. Queens are sometimes ergatoid or intermorphic (Yamauchi et al., 1996). See further description in Taylor (1967) and Bolton & Fisher (2011).

Bolton and Fisher (2011) - Characters as listed for workers except for worker characters 6, 8, 9; with the following differences. 1 Eyes always present and large, usually obviously with > 50 ommatidia. Eyes are located in front of midlength of head and all species examined have small setae that project between the ommatidia.

2 Ocelli present.

3 Mesopleuron with a well developed transverse suture that divides it into anepisternum and katepisternum.

4 Mesosoma with a full complement of flight sclerites (alate when virgin).

5 Jugal lobe absent from hindwing.

6 Venation almost complete (only cross-vein 1r-rs absent); with 8 or 9 closed cells including the pterostigma (8 cells in those species with Cu2 incomplete or absent); Rs.f5 meets R1.f3 on the anterior margin (i.e. marginal cell always closed); cross-veins 2r-rs, 2rs-m, 1m-cu and cu-a all present; cu-a arises from M+Cu (i.e. proximal of point where M+Cu divides into M and Cu; 2rs-m distal of 2r-rs; a free abscissa of M (M.f2) present between Rs+M and 1m-cu; an angle or bend sometimes present in Rs.f2&3; a fenestra present in cu-a and fenestrae sometimes visible in Rs.f2&3 and 2rs-m, but not in minute species.

7 Petiole node in profile is usually more slender, and often more tapered dorsally, than in the conspecific worker.

Generally slightly larger than conspecific worker; gaster sometimes distinctly larger.

ergatoid queen

Characters as conspecific worker but always with much larger eyes (7–30 ommatidia in Afrotropical species in which workers have 0–7 ommatidia), but without ocelli; often with a shorter petiole node in profile and a somewhat enlarged gaster; sometimes with a gyne-like transverse sulcus on mesopleuron. One ergatoid queen of Hypoponera punctatissima was dissected: a spermatheca was present and the ovaries were enlarged, though much smaller than in the gyne (see also Yamauchi, et al. (1996)).

Male
Schmidt and Shattuck (2014) - Usually winged, but sometimes ergatoid. See general description in Taylor (1967) and Bolton & Fisher (2011) and descriptions of ergatoid males in Yamauchi et al. (1996).

Bolton and Fisher (2011):

1 Mandible lobiform to unidentate (apical tooth only present), not meeting at full closure. Basal cavity of mandible extends to its front face and is visible in full-face view.

2 Eyes large and conspicuous, with minute setae projecting from between the ommatidia. Three distinct ocelli present.

3 Antenna with 13 segments, filiform.

4 Scape short, shorter than second funicular segment.

5 Second funicular segment longer than the first and also longer than the third.

6 Palp formula 1,1; 1,2; 1,3; 1,4; very rarely maxillary palp of 2 segments.

7 Mesonotum in profile not overhanging pronotum.

8 Mesoscutellum convex in profile.

9 Notauli absent; parapsidal grooves present but sometimes very faint.

10 Epimeral sclerite absent.

11 Mesotibia and metatibia each with a single spur; metatibial spur always pectinate.

12 Pretarsal claws simple.

13 Venation as alate gyne.

14 Jugal lobe absent from hindwing.

15 Petiole unspecialised ventrally; helcium very low on anterior face of first gastral segment.

16 Prora present, small.

17 Cinctus of second gastral tergite (Abd. IV) present.

18 Tergite of abdominal segment VIII (pygidium) without a median downcurved spine.

19 Pygostyles (= cerci) present.

ergatoid male

1 Body form extremely worker-like but male genitalia present.

2 Mandibles reduced (similar to alate males) or worker-like.

3 Antenna with 12 or 13 segments, worker-like or specialised but without the basal segment arrangement of alate males (male characters 4 and 5, above). Scape distinctly shorter than in conspecific worker.

4 Eyes present or absent.

The characters above are based on Hypoponera eduardi, Hypoponera punctatissima and Hypoponera ragusai, but ergatoid males are also produced by Hypoponera opacior, Hypoponera opaciceps and Hypoponera nubatama.

At first glance ergatoid males can easily be mistaken for workers, especially as the characteristic male genitalia are retractile and may be almost entirely concealed within the body. The ergatoid male of H. eduardi is monomorphic, with reduced mandibles, 13-segmented antennae and small eyes present. The ergatoid male of punctatissima is dimorphic. Both morphs have worker-like mandibles and head shape and 12-segmented antennae, but the larger morph is brown and has small eyes, while the smaller morph is yellow and lacks eyes. Ergatoid males of ragusai have not yet been found in the Afrotropical region, but specimens from the U.S.A. have a worker-like head and mandibles, as punctatissima, but possess 13-segmented antennae.

Larva
Schmidt and Shattuck (2014) - Hypoponera larvae were described generically by Taylor (1967) and for various species by Wheeler & Wheeler (1964, 1971a, 1990). Detailed histological or morphological studies of Hypoponera larvae were performed by [[Media:Peeters Psyche 92 Hypoponera larvae.pdf|Peeters & Hölldobler (1992)]] and Escoubas et al. (1987). Unusually among ponerines, sufficient research has been conducted on Hypoponera larval structure to yield a meaningful diagnostic character: Hypoponera larvae have two pairs of sticky tubercles on A4 and A5, whereas Ponera larvae have three or four pairs (Taylor, 1967).