Tetramorium setigerum species group


 * Tetramorium cavernicola

Based on Hita Garcia and Fisher 2015.

Tetramorium species groups

Overview
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. 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.

Diagnosis
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.