Monomorium

Genus Monomorium ^HNS Mayr

Monomorium ^HNS Mayr 1855:452. Type-species: Monomorium monomorium Bolton ^HNS (replacement name for Monomorium minutum Mayr ^HNS , 1855:453, a junior secondary homonym of Atta minuta Jerdon ^HNS 1851:105 [= m. pharaonis ^HNS (l.) 1758: 580]); by monotypy (Bolton 1987:287).

Phacota ^HNS Roger 1862a: 260. Type-species: Phacota sichelii ^HNS , by monotypy. Phacota ^HNS junior synonym of Monomorium ^HNS : Ettershank 1966:82, syn. rev. Bolton 1987:281. [Synonymy by Fernandez (in press) 2.] Nothidris ^HNS Ettershank 1966:105. Type species: Monomorium latastei ^HNS by original designation. [Synonymy by Fernandez (in press) 2.]

Antichthonidris Snelling ^HNS 1975:5. Type-species: Monomorium denticulatum ^HNS , by original designation.

[Synonymy of genus by Heterick 2001:361 without species-level nomenclatural changes, synonymy of a. denticulata Fernandez ^HNS (in press) 2.]

Epelysidris ^HNS Bolton 1987:279. Type-species: Epelysidris brocha ^HNS , by original designation. [Synonymy by Fernandez (in press) 2.]

(For synonymy in the genus Monomorium ^HNS prior to 1988, see Bolton, 1987:287-288.)

Diagnosis of worker of Malagasy species.- Minute to moderate (total length approximately1.5-4.5 mm) monomorphic to polymorphic myrmicine ants. Palp formula 5,3, 3,3 3,2, 2,2 or 1,2. Mandible smooth or longitudinally striolate, with three to six teeth and denticles, apical tooth always much larger than the preceding tooth; basal tooth often reduced to a small or minute denticle or angle but enlarged in one species, basal tooth often separated by a diastema from remainder of the dentition in members of the M. hildebrandti ^HNS group; mandibular shape triangular, linear-triangular, or strap-like with inner and outer edges parallel or nearly so. Median clypeal seta conspicuous in most Malagasy species and positioned at or slightly above a distinct anteromedian clypeal margin except in M. hildebrandti ^HNS group, where it is positioned on underside of a protruding shelf, near to the true anteromedian clypeal margin; paired setae (one often shorter than the other) straddling midpoint of anteromedian clypeal margin present in some large workers of M. aureorugosum ^HNS , M. fisheri ^HNS and M. infuscum ^HNS and some queens of M. fisheri ^HNS . Clypeus raised medially, usually bicarinate, though carinae may be obscure or in form of multiple weak ridges; in full-face view, the anteromedian clypeal margin often narrow and projecting, but this sector broad and abruptly declivous (i.e., when viewed in profile) in several members of M. monomorium ^HNS and M. hildebrandti ^HNS groups. Frontal carinae straight or diverging slightly posteriad, absent behind frontal lobes. Frontal lobes weakly sinuate or more-or-less parallel in full-face view. Antennal scrobes absent. Antennae 11- to 12-segmented; club usually with three distinct segments, sometimes four, or without a distinct club, but club never two-segmented. Eyes often reduced (sometimes to one or two ommatidia) in M. hildebrandti ^HNS group, small to fairly large in other groups; in full-face view, eyes generally set at about midline of head capsule, or slightly above or below, but occasionally set well into anterior sector of head capsule; in profile, eyes usually set at about midline or behind midline of head capsule, rarely in front of midline; eye shape usually elliptical, with more pronounced curvature of the inner margin, but can be elongate or ovoid and narrowed to a point anteriad.

Mesosoma with standing setae in most groups, these setae lacking in some members of M. salomonis ^HNS group; standing setae short and bristle-like in members of M. shuckardi ^HNS group. Metanotal groove most commonly deeply impressed, but weakly impressed, vestigial or absent in some taxa. Propodeal dorsum rounded onto declivitous surface, weakly or strongly angulate or armed with short denticles, spines lacking in Malagasy species; standing propodeal setae absent in some cases. Propodeal spiracle distinctly circular or nearly so, usually situated at about midlength, but placed anteriad or posteriad of midlength in some taxa, and close to propodeal dorsum in members of M. shuckardi ^HNS group. Metapleural glands of moderate to small size, never hypertrophied. Propodeal lobes often small to vestigial, rarely acute-angled and prominent. Fore coxae larger than middle or hind coxae. Petiolar peduncle often with small anteroventral flange or protuberance, but this feature vestigial in many species. Petiolar spiracle well in front of node in several endemic species, slightly in front of or in anterior sector of node in remaining taxa, often rather dorsally situated. Petiolar node shape ranging from low and broadly conical or tumular to cuneate and strongly tapered, thick and asymmetrical in profile in some members of M. hildebrandti ^HNS group, but never regularly cuboidal in Malagasy species; underside of node and peduncle commonly with fine, transverse rugulae in larger species of M. hildebrandti ^HNS group. Anteroventral margin of postpetiolar sternite often conspicuous, this feature reduced or absent in members of M. destructor ^HNS , M. pharaonis ^HNS and M. monomorium ^HNS groups. Gaster dorsoventrally compressed, with blunt lateral carinae on gastral tergites. Sting not prominent in Malagasy species.

Diagnosis of queen of Malagasy species.- Larger than conspecific worker, but not greatly so in some taxa. Palp formula, number of mandibular teeth and denticles and number of antennal segments as for conspecific worker. Ocellar triangle of three ocelli typical, but posterior ocelli may occasionally be reduced in size. Eyes large, generally elliptical, sometimes with a concavity in upper outer margin, but circular, semi-circular and ovoid eye shapes also occur.

Seen in profile, mesoscutum ranges from broadly convex to convex anteriad and flattened or even faintly sinuate posteriad. Mesoscutal pilosity always present. Pronotum, mesoscutum and mesopleuron often smooth and shining, but may be striolate or punctate to a greater or smaller degree; mesopleuron always divided by transverse furrow into upper anepisternum and lower katepisternum. Length-width ratio of mesoscutum and scutellum from near 7:3 to about 3:2. Axillae mostly well separated but may be contiguous or even reduced to a strip of thin cuticle, each individual axilla being indistinct. Metapleural sculpture most commonly in form of longitudinal striolae or striae, propodeum often unsculptured except for costulae on declivitous face, but where present frequently more marked than in conspecific worker. Dorsal propodeal face characteristically sloped, often almost vertical. Propodeal processes, where present, in form of small denticles or flanges, at most. Wing veins tubular and sclerotised in M. notorthotenes ^HNS , M. hanneli ^HNS , and in M. hildebrandti ^HNS group, predominantly weak and depigmented in most M. monomorium ^HNS group species, though wing veins are darkly pigmented without accompanying sclerotization in some species. Cross-vein m-cu present in all queens of M. hildebrandti ^HNS group, in all M. notorthotenes ^HNS queens and some M. hanneli ^HNS queens, absent in other M. hanneli ^HNS queens, rarely present in reproductives of M. destructor ^HNS group (per Bolton 1987), and always absent in reproductives of M. monomorium ^HNS and M. salomonis ^HNS groups (information on the latter coming from Bolton 1987). Cross-vein cu -a always present in M. notorthotenes ^HNS , M. hanneli ^HNS and all members of M. hildebrandti ^HNS group, always absent as a distinct vein in members of M. monomorium ^HNS group (very rarely present as a vague shadow). (Alate queens seen only for M. hanneli ^HNS , and M. hildebrandti ^HNS , M. monomorium ^HNS and M. shuckardi ^HNS groups.) Petiole as for that of conspecific worker. No brachypterous queens seen among Malagasy Monomorium ^HNS . Ergatoid females seen for both M. hildebrandti ^HNS and M. monomorium ^HNS groups.

Diagnosis of male of Malagasy species.- I have seen males only for M. notorthotenes ^HNS , M. hanneli ^HNS and the M. hildebrandti ^HNS and M. monomorium ^HNS groups, and can associate males with just 12 of the 36 Malagasy Monomorium ^HNS species identified in this work. This is too incomplete a record for a proper diagnosis to be made, but of those males seen, all, except members of the M. salomonis ^HNS group, possess conspicuous, often turreted ocelli. The compound eyes are almost invariably protuberant, tending to elongate in some species. The wing of the male, on the other hand, generally has the same venation as the conspecific female, but vein cu -a is lacking in all males of M. notorthotenes ^HNS and M. hanneli ^HNS . The males of the endemic M. notorthotenes ^HNS are very small in relation to the conspecific queen, even smaller than many workers of this species, and have a distinctly fly-like habitus. Identified males of the M. hildebrandti ^HNS group are also relatively small in relation to the queen and approximately the same size or smaller than the worker. However, the size disparity between queen and male is much less among M. monomorium ^HNS group reproductives, in contrast to the often minute workers, e.g. the HML of the Monomorium madecassum ^HNS queen is 3.01-3.12 mm, compared with 2.80-2.84 mm for the male. (By way of contrast, the HML for the M. madecassum ^HNS worker is only 1.14-1.27 mm).

Malagasy species groups recognized as a result of this project

Despite the fact that Madagascar was separated from Africa in the late Jurassic about 165 MYBP, and from India only 88 MYBP (Krause 2003), the Malagasy Monomorium ^HNS fauna has strong African affinities, and shares a number of species with eastern and southern Africa. However, several shared taxa have their distribution primarily in the middle and western parts of Africa. By way of contrast, the Malagasy representatives of another myrmicine genus, Pyramica, have much more decidedly Asian affinities (Fisher 2003).

Of most interest are four species of a group restricted to Madagascar that has not been previously categorized. I have called this the Monomorium shuckardi ^HNS species group after the only member described prior to this work. Members of this group possess some of the most plesiomorphic characters known for the genus Monomorium ^HNS , most notably a PF of 5,3. The placement of the petiolar spiracle well anteriad of the node and near to the midlength of the petiole is also a primitive feature shared only with a few Australian species in the M. bicorne ^HNS , M. insolescens ^HNS and M. kilianii ^HNS species groups (Heterick 2001), and with members of the M. scabriceps ^HNS group (Bolton 1987). However, other morphological features suggest a relationship at a basal level with the Monomorium destructor ^HNS and Monomorium salomonis ^HNS groups. These include the specialized small males (albeit, only known for Monomorium notorthotenes Heterick ^HNS , sp. nov. ) also found in the M. destructor ^HNS group (Bolton 1987), and the finely microreticulate or striolate body sculpture and lack of standing setae on the propodeum, both characteristic of various members of the M. salomonis ^HNS group. All members of the M. shuckardi ^HNS species group also share a sculptured mandible with the other two groups, the sculpture in this case being predominantly longitudinal striolae or striae. Virtually all collections have been in the south of the island, in Toliara Province.

Two other groups found naturally on Madagascar are the M. hanneli and M. hildebrandti groups. The M. hanneli group (one Malagasy species) is otherwise restricted to West Africa and Kenya, but members of the M. hildebrandti ^HNS group (ten Malagasy species) in which the eye is reduced to one or two ommatidia are also widespread in Africa, Indo-Australia, Australasia, and the Pacific (Wilson and Taylor 1967; Heterick 2001). Monomorium subcoecum ^HNS (not found in Madagascar) was described by Emery from the Antilles, in the Caribbean (Emery 1894b). However, whereas these two entities appear to constitute only a minor fraction of the African Monomorium ^HNS fauna (with the exception of the widespread Monomorium cryptobium ^HNS ), several of the species recognized in this work are abundant and widespread throughout Madagascar. As understood in this work, the M. hildebrandti ^HNS species group includes those species placed by Bolton in the M. fossulatum ^HNS species group. The name hildebrandti ^HNS is here preferred as the designation of this group because this was the earliest named species, and the name " fossulatum ^HNS " has been synonymized under sechellense ^HNS (Bolton 1995).

Monomorium hanneli ^HNS bears a strong superficial resemblance to members of the M. hildebrandti ^HNS group in which the clypeal carinae are well-developed and the clypeus is projected forward. The appearance of the mesosoma is also similar, if not identical, and the compound eye in workers of M. hanneli ^HNS and workers of most M. hildebrandti ^HNS group species is reduced. However, as Bolton (1987) correctly adjudges, the appearance of both groups is due to convergence. The most highly visible way workers of the two groups are separable is the appearance of the smooth, vertically attenuate node and the smooth, elevated postpetiole found in the M. hanneli ^HNS group. A slightly more subtle but equally important difference is in the placement of the median seta, which, with the ant in full-face view, is set at or slightly above the midpoint of the true anteromedian clypeal margin in M. hanneli ^HNS and its African relatives (i.e., M. guineense ^HNS , M. invidium ^HNS and M. jacksoni ^HNS ), and well underneath a protrusive ledge in those members of the M. hildebrandti ^HNS group with a projecting clypeus. The wing is more strongly sclerotized in those members of the M. hildebrandti ^HNS group that I have seen than it is in M. hanneli ^HNS , and all of the former possess vein m -cu, whereas that vein is missing in M. hanneli ^HNS males and at least some queens.

While the workers of most members of the M. hildebrandti ^HNS group have eyes that are comparatively very small, usually being less than the greatest width of the antennal scape, this is not a universal trait. The general reduction in the size of the worker eye is perhaps a function of a cryptic or mainly subterranean lifestyle, since the colonies of most species in this group appear to favour rotting wood and leaf mould. Transverse ventral rugulae found under the petiole of the medium-size and larger species are absent from the small workers of M. cryptobium ^HNS , M. ferodens ^HNS , M. modestum ^HNS and M. sechellense ^HNS . Very smooth workers of some populations of M. hildebrandti ^HNS also lack these rugulae. Apart from the almost total loss of vision, the species formerly recognized as belonging to the fossulatum ^HNS group (including all those formerly placed in the genus Syllophopsis) share a gestalt common to M. hildebrandti ^HNS and its allies. The very large Monomorium aureorugosum ^HNS and Monomorium infuscum ^HNS workers have distinctively triangular mandibles, well-separated antennal lobes and are heavily sculptured, but share the same petiolar structure (including the fine, transverse, ventral petiolar rugulae and asymmetrical nodal dorsum) of other large members of the species group. Monomorium ferodens ^HNS has an aberrant PF of 3,2, but otherwise clearly belongs here. In summary, this group has the following shared worker apomorphies: (1) smooth, linear-triangular mandibles with a strongly oblique masticatory margin (except for M. aureorugosum ^HNS and M. infuscum ^HNS ), (2) an anteromedian clypeal seta (more rarely, paired setae) positioned well under a protrusive ledge, and (3) a primitively asymmetrical dorsum to the petiolar node. Reduced eyes and transverse, ventral petiolar rugulae are also found in many M. hildebrandti ^HNS group species. Workers of most species in this group share with the M. hanneli ^HNS group and several members of the M. monomorium ^HNS group narrowly separated frontal lobes.

The M. destructor ^HNS and M. salomonis ^HNS species groups are represented by few species, and these are mainly tramp ants. Within the M. destructor ^HNS group, Monomorium destructor ^HNS is adventive to the island, having been brought across by human commerce at some time in the past, but the widespread distribution of Monomorium robustior ^HNS suggests endemicity (thus also Bolton 1987). Within the M. salomonis ^HNS group, Monomorium pharaonis ^HNS and Monomorium subopacum ^HNS , members of different complexes but with similar tramp tendencies, have clearly been introduced. The presence of Monomorium willowmorense ^HNS , known from one worker collected from the north-east coast, is more puzzling. The monotypic Monomorium latinode ^HNS species group is represented by M. latinode ^HNS , which also has tramp tendencies, and is well-dispersed across the Indo-Australian region (Bolton 1987).

Monomorium monomorium ^HNS species group members found in Madagascar are often abundant, but are not particularly diverse compared with the Afrotropical fauna, only 15 species being recognized here. It should be said, however, that the variability of several nominal species like M. termitobium ^HNS is so great that molecular-based systematics is probably needed to give the taxonomy strong definition. Some of the taxa appear to belong to complexes identified by Bolton (1987), while others seem not to be closely related to members of the group found on the African mainland. Of the described species, M. madecassum ^HNS is clearly referable to Bolton"s leopoldinum ^HNS complex, albeit M. leopoldinum ^HNS itself becomes a junior synonym of M. madecassum ^HNS in this work. Monomorium exiguum ^HNS and M. floricola ^HNS were placed in the boerorum ^HNS complex by Bolton, but this was confessedly for convenience, and even aside from the difference in antennal count (i.e., 11 antennomeres in M. exiguum ^HNS and 12 in M. floricola ^HNS ), the queens of the two species do not appear very similar. Monomorium exiguum ^HNS is actually closely related to the Afrotropical Monomorium rosae ^HNS (see my comments under the former). The other Monomorium ^HNS with an 11-segmented antenna, M. nigricans ^HNS , is of uncertain affinities, but may also belong to the M. exiguum ^HNS complex.

Monomorium termitobium ^HNS is here regarded as the senior synonym of M. binatu ^HNS , M. exchao ^HNS and M. imerinense ^HNS . Through M. binatu ^HNS and M. exchao ^HNS , M. termitobium ^HNS (along with the apparently closely related M. xuthosoma ^HNS and M. sakalavum ^HNS ) is associated with Bolton"s rhopalocerum ^HNS complex, but as here conceived, the morphological parameters of that complex far exceed those designated by Bolton. Workers of Monomorium micrommaton ^HNS and M. chnodes ^HNS bear a close resemblance to hirsute, yellow workers of M. termitobium ^HNS . The queen of M. micrommaton ^HNS is relatively large, with a proportionately massive mesosoma and a broad, cordate head, quite different characters from those of the queen of M. termitobium ^HNS . Monomorium chnodes ^HNS possesses a square propodeum (unlike that seen in any workers of M. termitobium ^HNS ) with a large propodeal spiracle, and some queens and workers have a five-toothed mandible - a feature otherwise unknown in the M. monomorium ^HNS species group. However, preliminary molecular data place Monomorium chnodes ^HNS close to M. platynodis ^HNS , and both species possess a very short clypeus that, when seen in profile, descends towards the arc of the mandibles at almost 90 degrees. Monomorium platynodis ^HNS , in fact, may represent a radiation derived from M. chnodes ^HNS , with a reduction in the size and dentition of the mandible.

In Monomorium chnodes ^HNS , M. flavimembra ^HNS , M. lepidum ^HNS , M. platynodis ^HNS , and M. versicolor ^HNS , the clypeal carinae are obsolete or only weakly defined and the anteromedian clypeal margin is depressed and moderately to strongly declivous when seen in profile - in the case of M. chnodes ^HNS and M. platynodis ^HNS being almost vertical, as mentioned above. In four of these species, the fourth (i.e., basal) tooth is greatly reduced or absent. Only M. chnodes ^HNS has a strongly defined basal tooth. In M. chnodes ^HNS , M. flavimembra ^HNS , and M. lepidum ^HNS , the petiolar node is more-or-less conical and the postpetiole is rounded, but in M. platynodis ^HNS and M. versicolor ^HNS the nodes are high and the petiolar node is strongly cuneate. The group is here called the flavimembra ^HNS complex. Monomorium bifidoclypeatum ^HNS is very similar to these species and almost certainly also belongs to this complex. Monomorium denticulus ^HNS is a small member of the M. schultzei ^HNS complex but does not appear to be conspecific with any of the described African forms.