Ponera species groups

The following species groups were constructed by Taylor (1967. A monographic revision of the ant genus Ponera Latreille (Hymenoptera: Formicidae). Pacific Insects Monograph, 13: 1–112.)

coarctata species group
This group contains a closely related amphiatlantic species pair: Ponera coarctata (Latreille) of Europe, the Middle East and North Africa; and Ponera pennsylvanica Buckley, of E North America. It is distinguished mainly by the fact that the larvae have 4 pairs of glutinous tubercles on the abdominal dorsum, whereas all known Indo-Australian species have 3 pairs. The workers are medium to dark brown in color and of about medium size for the genus (head width 0.50-0.63 mm). The median clypeal denticle is vestigial but there is a longitudinal carina. The eyes are small, no antennal club is differentiated, and the mesometanotal suture is distinctly incised on the mesosomal dorsum. Members of the IndoAustralian species groups of sinensis, taipingensis and elegantula are similar in size to coarctata and pennsylvanica. However, the heads of the sinensis group species are broader (worker cephalic index 89-95 as opposed to 77-85 in the coarctata group); workers of the taipingensis group lack an incised mesometanotal suture; and those of the elegantula group have much larger, more highly faceted eyes.

The females are normal for the genus, and have "coarctata type" wing venation. Males have a 5:3 palpal formula. Most known Indo-Australian Ponera males have a 2:2 palpal formula as in the female castes, but 4:2 and 3:2 formulae are known respectively in incerta and oreas.

elegantula species group
The following 3 species, Ponera augusta (New Guinea), Ponera borneensis (Borneo), and Ponera elegantula (New Guinea), have been grouped together mainly because they all have distinctly larger, more highly faceted eyes than those of any other Ponera species. The compound eyes of the available worker specimens have 9 to 16 facets, whereas all other known species of the genus have less than 6 (except Ponera woodwardi of Samoa which has secondarily enlarged eyes with 7 to 11 facets). Additional points of resemblance are less easily described and involve general habitus. The 3 species are similar, and resemble the members of the sinensis and taipingensis groups. Detailed examination of more specific characters such as the cephalic index, the relative length of the scapes, the nature of the worker mesometanotal suture and details of sculpturation and pubescence, show them to vary considerably, as discussed under elegantula. Indeed variation in these features almost covers the whole range of complexity seen in the sinensis and taipingensis groups.

I may be in error in classifying these species together, as a supposed natural group. In so doing it has been assumed that they represent a line derived from rather primitive stock, of about the selenophora grade, in which the eyes have been secondarily enlarged, and other characters have evolved in parallel to the genus-at-large. These species could represent 3 separately derived large-eyed forms, rather than a single lineage. At present only a subjective decision can be made, and I have weighed the large-eyed character heavily in grouping them together.

If this interpretation is correct the group shows a fine morphoclinal succession, with augusta at the primitive extreme, and elegantula at the derived end (see discussion below under P. elegantula).

japonica species group
A group of 3 species: Ponera japonica Wheeler (Japan, Malaya and Java), Ponera incerta (Wheeler) (Java, E. Melanesia, Samoa) and Ponera swezeyi (Wheeler) (Samoa and Hawaii). The diagnostic characters are: (1) antennal funiculus with an indistinctly to distinctly differentiated 5- segmented club; (2) mesometanotal suture of worker incised on mesosomal dorsum. These species are brown to yellowish brown in color and of small to medium size (head width 0.29-0.50 mm). They form a probably morphoclinal sequence: japonica→incerta→swezeyi. Characters involved in this morphocline include reduction in size, in number of eye facets, in distinctness of the median clypeal denticle, in length of the scapes, in relative breadth of the petiolar node, and in the intensity of coloration.

The larvae are known for incerta and japonica (Teranishi 1940) and are typical for Indo-Australian Ponera. Pupal cocoons occur in incerta and swezeyi, but no pupae of japonica are available. The males of incerta have the primitive palpal formula: Maxillary 4: Labial 2.

These species are all widespread, and evidently have considerable capacities for active dispersal, and for distribution by man, especially in Eastern Melanesia and Polynesia. They are probably derived, through japonica-like stock, from ancestors at about the sinensis/taipingensis grade of organization.

leae species group
The group includes two rather small light brown species (head width 0.36-0.44 mm), Ponera leae Forel of E. Australia, New Caledonia, Norfolk I., and northern New Zealand, and Ponera exotica M. R. Smith, originally described from the SE United States, but almost certainly of Indo-Australian origin. These species superficially resemble the smaller members of the japonica and tenuis groups. They have distinctly 4-segmented antennal clubs, like the tenuis group species, but differ from them in possessing a distinctly incised mesometanotal suture in the worker caste. Females are known for both species, they are typical for the genus. All specimens are dealated; so the wing venation is unknown. Males and larvae are not available. The single pupa studied, that of a leae worker, was enclosed in a cocoon.

scabra species group
The following two species, Ponera chapmani and Ponera scabra, are apparently related. Structurally they are at about the same grade as Ponera xenagos, and could perhaps be affiliated with it at the species group level. They are fairly large (head width 0.61-0.67 mm), with a tendency towards reduction of the median clypeal tooth in smaller specimens. The scapes are long, the funiculus lacks a differentiated club; and the eyes are small. The propodeal angles are not as strongly marked as in alpha or selenophora, and the contours of the node are more rounded, much as in xenagos. The angle between the dorsal and posterior faces of the node of scabra is fairly marked so that the two faces are more discreet than in most primitive Ponera, where a continuous arched postero-dorsal face is seen. The head is narrower than that of xenagos (cephalic index 78-85) and the sculpturation more distinctly developed. Females of chapmani have peculiar wing venation, unlike that of all other known Ponera, except the distantly related Ponera swezeyi. The wing venation of scabra is unknown. Males, larvae and pupae are not known for either of these species.

sinensis species group
The following two species, Ponera oreas (Philippines) and Ponera sinensis (Hong Kong), are closely related and probably cognate. They are considerably smaller than any of the preceding species (head width 0.47-0.54 mm) and the head is much broader than in other Ponera of similar size (cephalic index 89-95). A median clypeal denticle is lacking and the eyes are small with 3-6 facets. The scapes reach or slightly exceed the median occipital border and the club is at most feebly marked, although there is a distinct tendency for it to be segmentally differentiated — in most specimens it is fairly distinctly 4 or 5 segmented. The mesometanotal suture is sharply incised, and the form of the propodeum and petiole generally as in Ponera xenagos. These species are probably descended from a stock much like P. xenagos, from which they differ mainly in their smaller size, high cephalic indices, and in the tendency for differentiation of the antennal club. The latter character is of frequent occurrence among the smaller species of Ponera, and has apparently been separately evolved in several groups.

taipingensis species group
The following 5 species form a well circumscribed group, distributed as shown in fig. 55. The first 4 — Ponera taipingensis (Malaya), Ponera syscena (New Guinea), Ponera colaensis (Fiji) and Ponera loi (Samoa) are apparently a closely related series, referred to here as the "taipingensis complex", the 5th species, Ponera woodwardi (Samoa) is evidently a specialized peripheral offshoot of this group.

Workers of the "taipingensis complex" are of about the same size as those of the sinensis group (head width 0.48-0.56 mm), but differ from them in having proportionately narrow crania (cephalic index 79-86) and in reduction of the mesometanotal suture on the mesosomal dorsum; it may be totally lacking, or represented by a shallow transverse depression, or it may be marked by a finely incised, but very weak line. A distinct clypeal denticle may be developed or it may be represented by a low tumosity. The eyes are small, with 1 to 6 facets, and the apices of the scapes are approximately contiguous with the median occipital border or fall slightly short of it.

P. woodwardi workers resemble the other species in postcephalic structure. However, the head is narrower (cephalic index 77-81) and the scapes longer (scape index 98-102), clearly exceeding the occipital border. The eyes are apparently secondarily enlarged and have 5 to 8 facets.

The known sexuals are normal for the genus, with wing venation of the coarctata type. The larvae have 3 pairs of glutinous tubercles on the abdominal dorsum, and the pupae, where known, have cocoons.

The taipingensis group is probably cognate with the sinensis group. Among its species syscena and 1oi are closely related, in fact loi seems to represent a not-too-divergent derivative from syscena-like stock. taipingensis and colaensis are similar, and will probably prove to have close relatives in New Guinea and Indonesia. P. woodwardi may have been derived from stock much like colaensis.

Sarnat and Economo (2012) place Ponera manni in this species group.

tenuis species group
Characterized by possession of a 4-segmented antennal club in the female castes, and lack of an incised dorsal mesmetanotal suture in the workers. They superficially resemble the leae group, and the smaller members of the japonica group (Ponera incerta and Ponera swezeyi), being small light-brown species with worker head width ranging 0.30-0.45 mm.

The group is New Guinea based, with one species, Ponera tenuis, ranging eastward to Samoa. tenuis is distinguished by relatively large size from the remaining species (Ponera petila, Ponera szaboi, and Ponera szentivanyi), which form a closely related series (referred to here as the szentivanyi complex).

Sexuals are known only for tenuis. They are normal for the genus, with wing venation of the “coarctata type.” Larvae of tenuis have 3 pairs of dorsal abdominal “doorknob” tubercles, as usual in Indo-Australian species. Its pupae are unusual, in that they lack cocoons, a character differentiating them from all other species of the genus for which this stage is known. Pupae of the szentivanyi complex are not known. If they lack cocoons my worker-based species-group classification of the smaller Ponera species would gain support.

The species of the szentivanyi complex were all described by Wilson (1957). They are known only from the types; so my discussion of them essentially paraphrases that of Wilson, with a few supplementary descriptive notes. I am dubious about the status of these species. szaboi could be an ecological variant of tenuis, especially considering the variability seen in P. leae around Sydney (see above). szentivanyi is probably based on small nanitics of tenuis. The dimensions of the two known specimens appear to set them apart, but their apparent distinctiveness could be due to abberation caused by shrinkage, since both are callow. Increase of only 0.02 mm in the head width measurements of these specimens would bring their divergent cephalic and scape indices within the ranges of the tenuis material. petila, on the other hand, seems to represent a good species.