Tetramorium setigerum species group

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Based on Bolton 1980 (Afrotropical) and Hita Garcia and Fisher 2015 (Malagasy).

Species

Afrotropical

The setigerum group is divided into four complexes

Malagasy

There is one species:

Identification

Afrotropical

Madagasar

  • use the Malagasy Tetramorium species groups key; if your determination ends at the terminal couplet for the setegerum group you likely have the species (T. cavernicola) of this group that occurs in the Malagasy region

Diagnosis

Afrotropical

Bolton (1980) - Antennae with twelve segments. Sting appendage usually dentate or pennant-shaped but sometimes elongate and roughly spatulate (Tetramorium youngi). Mandibles longitudinally striate except in agile. Anterior clypeal margin entire, without trace of a median notch or impression. Antennal scapes relatively long, SI always > 100. Frontal carinae variably developed; strong and almost reaching occipital margin in setigerum- complex, weak but of similar extent in youngi-complex, weak and ending at or just behind level of eyes in doriae- and perlongum-complexes. In all the frontal carinae tend to be rather close together, their maximum separation (usually at eye-level) rarely exceeding 0.50 x HW. Propodeal spines moderate to long, usually longer than the metapleural lobes (shorter in some samples of Tetramorium avium). Petiole nodiform, with a long anterior peduncle. All dorsal surfaces of head and body with numerous standing hairs which are commonly quite stout and blunted apically. Tibiae of middle and hind legs only with short, fine pubescence which is subdecumbent to appressed; never with hairs nor with erect pubescence.

Afrotropical Species complexes

Bolton (1980) - The group divides into four complexes of closely related species. The first of these, the perlongum-complex, contains only Tetramorium perlongum and Tetramorium dolichosum. The complex is characterized by the enormously elongated scapes which the species possess (Fig. 55), SI being greater than 150. (Throughout the remainder of the group the range of SI is 103-119.) Besides the very long scapes the two species of this complex have short frontal carinae which end at or just posterior to the level of the posterior margins of the eyes, and the carinae are very close together, their maximum separation < 0.40 x HW. The propodeal spines are very long, much longer than the maximum diameter of the eye, and the metapleural lobes are low and rounded, not triangular. These two species represent the group in Angola and Zaire and are the most bizarre members of the setigerum-group.

Closely related to the above are the two small species of the youngi-complex, Tetramorium youngi and Tetramorium metactum. In these the SI range is 105—113. The frontal carinae are long, reaching back almost to the occipital margin, but they are only weakly developed. The propodeum is equipped with very long spines which are slightly downcurved along their length and which are much longer than the eye diameter. Metapleural lobes are short and triangular. The petiole node in dorsal view is longer than broad, and in profile the length of the dorsum is about equal to or slightly shorter than the tergal height. The two species in this complex are known from Kenya and Angola.

The doriae-complex (Tetramorium doriae, Tetramorium gracile, Tetramorium praetextum) inhabits dry or semi-desert areas and is known from South West Africa and Ethiopia; one of the species extends its range from Ethiopia into Yemen and Saudi Arabia. In these three the frontal carinae are feeble, only developed to the level of the posterior margins of the eyes and thereafter fading out or becoming confused with the sculpture (Fig. 53). SI range is 103-111. The propodeum is armed only with tiny denticles or is merely angular, without developed armament at all. The petiole node in dorsal view is longer than broad and in profile is roughly rectangular, the dorsal length usually greater than the height of the tergal portion.

The fourth and final complex is the largest. The setigerum-complex includes Tetramorium agile, Tetramorium avium, Tetramorium frenchi, Tetramorium laevithorax, Tetramorium parasiticum and Tetramorium setigerum. These are predominantly species of the southern half of Africa although both T. laevithorax and T. setigerum are known to occur as far north as Sudan. Excluding T. parasiticum, known only from an inquiline female in a nest of T. avium, the remainder of the complex have strongly developed frontal carinae which almost reach the occipital margin (Fig. 56). The carinae are usually surmounted by a raised rim or flange for most or all of their length. Scapes have an SI range of 103-119. The propodeal spines are quite short, always shorter than the maximum diameter of the eye but longer than the triangular metapleural lobes except in some samples of T. avium. The petiole node is broader than long in dorsal view and quite narrow in profile, the dorsal length being less than the height of the tergal portion of the node.

Malagasy

Hita Garcia and Fisher (2015) - Twelve-segmented antennae; antennal scapes very long (SI 120–123); anterior clypeal margin entire and clearly convex; frontal carinae well-developed, ending at or approaching posterior head margin; eyes moderate (OI 23–26); anterior face of mesosoma weakly developed, no distinct margination between lateral and dorsal mesosoma; propodeum armed with short triangular to elongate-triangular teeth (PSLI 7–11), propodeal lobes moderately developed, triangular to elongate-triangular, slightly longer and broader than propodeal teeth; petiolar node relatively small, nodiform, with weakly angled anterodorsal and posterodorsal margins, and comparatively long peduncle, petiolar dorsum flat to very weakly convex, node in profile between 1.2 to 1.4 times higher than long (LPeI 73–79), node in dorsal view between 1.2 to 1.3 times longer than wide (DPeI 121–127); postpetiole in profile approximately globular, around 1.0 to 1.1 times higher than long (LPpI 90–98); mandibles striate; clypeus longitudinally rugose/rugulose with well-developed median ruga and usually one or two weaker, sometimes irregular, lateral rugae/rugulae on each side; sculpture on cephalic dorsum irregularly longitudinally rugose to reticulate-rugose; mesosoma laterally irregularly rugulose, dorsally reticulate-rugulose to irregularly rugulose; petiole and postpetiole conspicuously rugulose; ground sculpture on mesosoma and waist segments distinctly reticulate-punctate, much weaker on head; gaster unsculptured, smooth, and shiny; all dorsal surfaces of body with short to moderately long, thick, and apically blunt pilosity; sting appendage triangular to dentiform.

Notes

Afrotropical

Bolton (1980) - The 13 members of this group are predominantly species of southern and eastern Africa, ranging up the eastern side of the continent to Ethiopia and also occurring in Arabia. A couple of species are known from Angola and Zaire but the group as a whole seems to be absent from the west African rain forest zone.

Malagasy

Hita Garcia and Fisher (2015) - Prior to this study, the T. setigerum species group appeared endemic to the Afrotropical region where it is widely distributed. Of the 13 species recognised by Bolton (1980), most are found in more arid areas of eastern and southern Africa, a few are distributed in the rainforests of Central Africa, while two species are also found in Ethiopia and the southwestern Arabian Peninsula. The recent finding of T. cavernicola in Madagascar was unexpected since there was no previous indication of the presence of the group on Madagascar or any of the surrounding islands of the South West Indian Ocean. However, considering the strong biogeographical affinities of the Tetramorium ant fauna of Madagascar with the Afrotropical region, this is less of a surprise. Indeed, the T. setigerum group has its highest abundance and diversity in South and Southeast Africa, which is geographically comparatively close to Madagascar. As outlined above, other species or species groups that made it from Africa to Madagascar are often of predominantly eastern and southern African origin; examples include Tetramorium humbloti from the Tetramorium weitzeckeri group and Tetramorium delagoense from the Tetramorium simillimum group.

Hita Garcia and Fisher 2015. Figure 29

The T. setigerum group cannot be mistaken for any other Malagasy species group. Its possession of twelve-segmented antennae, an entire and convex clypeal margin, and simple pilosity distinguish it from most other groups, except the Tetramorium sericeiventre, Tetramorium simillimum, and Tetramorium tosii groups. In the T. sericeiventre group the clypeus is distinctly modified, with the lateral portion being very prominent and raised into a tooth/denticle in full-face view while the clypeus of the T. setigerum group lacks such a tooth/denticle. Also, the species of the T. simillimum group possess much shorter antennal scapes (SI always much shorter than 100) than the T. setigerum group (SI over 120). The differentiation of the latter from the T. tosii group is more problematic. Despite the fact that the only representative of the T. setigerum group in Madagascar and the two species of the T. tosii group are easily separable (see key couplets 4 to 6), only a few morphological characters separate both groups if one also considers all members of the T. setigerum group from the Afrotropical region. Nevertheless, we prefer to keep both groups separate for the following reasons. First, the shape of the petiolar node is low, elongate, clublike, and always longer than high in the T. tosii group (Fig. 29A), whereas it is variably nodiform in the T. setigerum group, but usually higher than long and never low and elongate (Fig. 29B, C, D, E, F). Second, the standing pilosity in the T. tosii group consists of long, fine, acute hairs (Fig. 29A), whereas the pilosity in most members of the T. setigerum group is thick, short to moderately long, and usually blunt apically (Fig. 29B, E, F). Nevertheless, this is not the case in Tetramorium metactum and Tetramorium youngi since they have long and fine pilosity (Fig. 29C, D). This may seem contradictory, but leads to our next argument. Third, we strongly suspect that the T. setigerum group is not a monophyletic group, but might be composed of different lineages that share a number of morphological characters that have evolved convergently. For example, the morphology of T. cavernicola from Madagascar is certainly closer to the species complex around T. setigerum Mayr and allies (Bolton, 1980) than to T. metactum or T. youngi. In sum, the relationships between the T. tosii and the T. setigerum groups, as well as within the latter group, remain unclear, and we prefer to keep the groups as they are until additional data can provide better resolution of the groupings.

Additional Resources

References