Malagasy Tetramorium tosii species group


 * Tetramorium tantillum
 * Tetramorium tosii

Based on Hita Garcia and Fisher 2011

Tetramorium species groups

The T. tosii species group is the only Malagasy region Tetramorium species group with 12-segmented antennae that is endemic to the region. However, there are striking similarities between the T. tosii group and some members of the T. setigerum group from the Afrotropical region, especially between T. tosii, Tetramorium metactum and Tetramorium youngi. All three possess relatively long antennal scapes, reduced antennal scrobes, a long anterior peduncle, a more clublike petiolar node, and their overall appearance is relatively comparable. Based on these similarities, one could argue for the synonymisation of both groups. Nevertheless, there is also a possibility that the mentioned species have developed independently and their shared morphology is a result of convergent evolution as an adaptation to a more arboreal lifestyle in the vegetation or the canopy strata. In addition, T. tantillum is morphologically less close to these species and possesses relatively short antennal scapes in comparison to T. tosii, T. metactum, and T. youngi. Indeed, the scape index of T. tantillum, with SI 79 – 87, is distinctly lower than that of all T. setigerum group members. Consequently, we continue to consider both species groups as independent with some morphological similarities that are probably a result of convergent evolution.

This group cannot be confused with another Malagasy species group with 12-segmented antennae due to the character combination of entire anterior clypeal margin, long to very long propodeal spines, short propodeal lobes, and large body size. The two species of the T. tosii group can be distinguished easily from each other on the basis of the length of the antennal scapes and propodeal spines, but also by comparing the shape of the eyes and the petiolar node.

Diagnosis
12-segmented antennae; anterior clypeal margin entire and without any media impression; frontal carinae well-developed, ending shortly before posterior head margin; anterior face of mesosoma weakly developed, no distinct margination between lateral and dorsal mesosoma; propodeal spines long to extremely long and spinose; propodeal lobes triangular and short; petiolar node nodiform to clublike, longer than high and longer than wide; postpetiole roughly rounded; mandibles sculptured; cephalic sculpturation well-developed, mostly reticulate-rugose, between frontal carinae generally longitudinally rugose, ground sculpturation of head generally faint or absent; mesosoma irregularly rugose to reticulate-rugose, waist segments weakly sculptured; gaster unsculptured, smooth, and shiny; all dorsal surfaces with long, erect hairs; sting appendage triangular.