Tetramorium schaufussii species group

Every Ant Tells a Story - And Scientists Explain Their Stories Here
Jump to navigation Jump to search

Tetramorium cognatum species complex

Tetramorium schaufussii species complex

Based on Bolton 1979 and Hita Garcia and Fisher 2011, 2014.

You may also be interested in:

Overview

Characters separating the two species complexes:

  • First gastral tergite with appressed pubescence of varying length and without any standing hairs (Fig. 20A, B) [Madagascar and Comoros] . . . . . Tetramorium cognatum species complex
Hita Garcia and Fisher, 2014. Figure 20.

With 20 recognised species the T. schaufussii species group is second in terms of species-richness in the Malagasy region, following the T. tortuosum group with 22 (Hita Garcia and Fisher 2012b). This group is of special importance for Madagascar since many of its members are very widespread, common, and/or abundant. Almost all species prefer rainforests or montane rainforests, and with few exceptions, live in the forest leaf litter stratum.

The T. schaufussii species group is a very distinctive group among the thirteen groups with eleven-segmented antennae, and most of its members are unlikely to be mistaken for any other group. In general, most T. schaufussii group species are small to medium-sized ants, have a comparatively low and elongated mesosoma, and short to very short propodeal spines. Even though these characters are not unique to this group its members are usually easily recognisable. One interesting feature of the T. schaufussii group is that the mandibles of all species are completely unsculptured, smooth, and shining. This character alone already separates the T. schaufussii group from the T. bessonii, T. bonibony, T. kelleri, T. tortuosum, and T. weitzeckeri groups, in which all species have noticeably sculptured mandibles. In most other groups this character, however, is variable. Some species of the T. dysalum group have unsculptured mandibles, but these have either much longer propodeal spines or a much higher mesosoma. Another important group character is the lack of sculpture on the waist segments. The T. schaufussii group shares this character with a number of other groups, but it does distinguish the group from the T. kelleri, T. ranarum, and T. tortuosum groups, as well as from parts of the T. bonibony and T. dysalum groups. All these groups have at least one waist segment with distinct sculpture, but most of their species have conspicuous sculpture on both. Furthermore, in the T. schaufussii group the antennal scrobe is either weakly developed or absent distinguishing it immediately from the T. plesiarum group and a few species of the T. ibycterum complex of the T. ranarum group with moderately to very deep scrobes with clearly defined margins all around.

Moreover, all species of the T. schaufussii species group have relatively well developed cephalic and mesosomal sculpture. The sculpture on the cephalic dorsum between the frontal carinae is always well developed, whereas sculpture on the mesosomal dorsum can be weak in some species (but remains distinctly present). This separates the group from the T. bessonii, T. marginatum, T. tsingy groups, which usually have strongly reduced sculpture on the head and mesosoma. The members of the T. marginatum group that possess more sculpture have strongly cuneiform and/or triangular petiolar nodes, and are thus not confusable with the T. schaufussii group. The groups being morphologically most similar to the T. schaufussii group are the T. naganum and T. severini groups, as they share the usually high nodiform petiolar node and completely unsculptured waist segments. The only previously known species of both groups, T. naganum and T. severini, were initially recognised as members of the T. schaufussii group by Bolton (1979), but recently split by Hita Garcia and Fisher (2011, 2012a, 2012b). The separation from the T. severini group is relatively straightforward. The latter species is very large, very darkly coloured, and has very long to extremely long and curved propodeal spines that easily distinguish its members from the T. schaufussii group. The distinction between the T. schaufussii and the T. naganum group is less clear. The members of the T. naganum group usually have much more strongly developed frontal carinae, a generally broader head (CI 92–99), a higher mesosoma (LMI 40–46), and usually longer propodeal spines (PSLI 25–37). Some of these values overlap with a few species of T. schaufussii group, but they separate the bulk of species comparatively well.

Bolton (1979) divided the group into two complexes on the basis of the absence (T. cognatum complex) or presence (T. schaufussii complex) of long, standing pilosity on the first gastral tergite. We follow this division and have placed all the new species into these two complexes even though at present we have no more evidence that these complexes represent monophyletic, mutually exclusive clades or lineages within the species group. Indeed, the only separating character is gastral pilosity, and future studies on the group that ideally include molecular data will likely yield different groupings. However, with 20 species the group is relatively species-rich and the clear-cut division into these two complexes facilitates the taxonomic organisation of the species group.

Diagnosis

Eleven-segmented antennae; anterior clypeal margin medially impressed; frontal carinae variably developed, always present and surpassing eye level, usually weak to moderate and posteriorly merging into the surrounding sculpture, in a few species very well developed, noticeably raised and approaching posterior head margin; antennal scrobes usually weak, shallow, and without clearly defined posterior and ventral margins; anterior face of mesosoma weakly developed; mesosomal outline in profile relatively flat, usually comparatively low and elongated (LMI 35–42), usually moderately marginate from lateral to dorsal mesosoma; propodeal spines usually short to moderately long, triangular to elongate-triangular, long and spinose in a few species (PSLI 7–28); propodeal lobes usually triangular and short; petiolar node in profile rounded nodiform to high rounded nodiform with well-rounded margins, rarely high cuneiform or squamiform, node in profile between 1.2 to 3.0 times higher than long (LPeI 33–81), in dorsal view usually wider than long (DPeI 111–238), rarely longer than wide (DPeI 87–98), anterior and posterior faces parallel in most species; postpetiole in profile globular to subglobular, 1.2 to 1.7 times higher than long (LPeI 60–83), in dorsal view between 1.2 to 1.7 times wider than long (DPpI 120–168); mandibles always unsculptured, smooth, and shining; cephalic sculpture distinct, between frontal carinae predominantly longitudinally rugose; mesosoma usually with well-developed longitudinally rugose/rugulose sculpture, in some species sculpture mainly irregularly rugose/rugulose, rarely irregularly rugose/rugulose to reticulate-rugose; waist segments and gaster unsculptured, smooth, and shiny; standing pilosity always present on head, but variable on remainder of body, first gastral tergite often without standing pilosity at all, appressed pubescence on first gastral tergite variably developed, varying from very short and scarce to long and dense; sting appendage spatulate.

species complexes

Tetramorium cognatum species complex

Key to Tetramorium cognatum species complex workers

This species complex contains a compact assemblage of ten species that are separated from the T. schaufussii species complex by their lack of any long, standing pilosity on the first gastral tergite, a character present in all members of the T. schaufussii complex. The ten species of the T. cognatum complex might be further divided into three smaller groupings: the first of these contains the five small to moderately large species with weak to very weak frontal carinae (T. aspis, T. camelliae, T. cognatum, T. karthala, and T. rumo); the second includes the four larger species with very well developed frontal carinae (T. gladius, T. myrmidon, T. proximum, and T. tenuinode); the third sub-grouping contains only T. freya, which is the only species of the complex lacking standing pilosity on the mesosoma, but it also possesses reduced frontal carinae and a larger body size.

Four species of the complex have very restricted distribution ranges and are endemics to smaller areas or localities in Madagascar or the Comoros (Figs 63, 64): T. aspis (Andringitra and Ivohibe), T. camelliae (Ranomafana), T. karthala (Grand Comore), and T. myrmidon (Ambohijanahary), while T. freya was found only in a few littoral localities ranging from Nosy Be to the northernmost tip of Madagascar. The remaining species (T. cognatum, T. gladius, T. proximum, T. rumo, and T. tenuinode) have much wider distribution ranges, especially T. cognatum and T. proximum, which are found in almost all rainforests and montane rainforests from which material is available. Interestingly, almost all species appear be restricted to or prefer rainforests or montane rainforests, even the widely distributed T. cognatum, T. proximum, and T. tenuinode. However, T. cognatum was occasionally collected in drier habitats and T. freya occurs also in littoral and dry forests.

Tetramorium schaufussii species complex

Key to Tetramorium schaufussii species complex workers

This complex contains ten species, which are characterised and distinguishable from the T. cognatum species complex by their presence of standing pilosity on the first gastral tergite. All species are endemic to Madagascar, except T. schaufussii, which is also known from Reunion. Also, they inhabit rainforests or montane rainforests and are only occasionally found in other habitats. The taxonomy of this species complex is challenging. Some species like T. nassonowii, T. pseudogladius, T. rala or T. scutum are relatively easily recognisable due to species-specific character states, but this is not true for the rest of the complex. Tetramorium schaufussii and T. xanthogaster are especially widespread species with high degrees of intraspecific variation, which causes a number of problems for the delimitation of species boundaries for most member of the complex. Intriguingly, only two species of this complex have very limited distribution ranges: T. scutum is only known from Ivohibe and T. pseudogladius from Zahamena. The remainder are all much more widespread.

References

  • Bolton, B. 1979. The ant tribe Tetramoriini (Hymenoptera: Formicidae). The genus Tetramorium Mayr in the Malagasy region and in the New World. Bull. Br. Mus. (Nat. Hist.) Entomol. 38: 129-181 PDF
  • Hita Garcia and Fisher. 2012. The ant genus Tetramorium Mayr (Hymenoptera: Formicidae) in the Malagasy region—taxonomy of the T. bessonii, T. bonibony, T. dysalum, T. marginatum, T. tsingy, and T. weitzeckeri species groups. Zootaxa 3365: 1-123. PDF