Tetramorium sibiricum

All seven known nests of Tetramorium sibiricum were collected under stones. The sparse information currently available suggests that this species is distributed in more natural steppe habitats whereas sympatric Tetramorium caespitum seems to occur in habitats with anthropogenous influence.

Identification
Tetramorium sibiricum differs from Tetramorium indocile in having a longer scape, a more developed sculpture on postocular head sides, a narrower petiole and postpetiole, longer pronotal setae and a longer mesosoma and eye. The main differences to Tetramorium caespitum are the narrower petiole and postpetiole, the more developed sculpture and microsculpture on postocular head sides and on dorsum of 1st gaster tergite, the higher postpetiole, the longer scape and eye and a longer distance from spine tip to dorsocaudal corner of metapleural lobe.

Key to Siberian Species
Three species of the T. caespitum complex occur in Siberia west and north of the Reinig Line. This faunal divide separates East Siberian, Inner Mongolian, Chinese and Tibetan species from those of Central Siberia, West Siberia and the Turanian region (DE LATTIN, 1967).

The methodology of species identification applied by Seifert (2021) is extremely complex and data recording is by far the most time-consuming of any ant genus investigated so far by the author – a challenge even for experienced and specialized investigators having access to adequate equipment. An attempt to simplify the separation of the three West and Central Siberian species was done in writing a key that uses absolute primary data (i. e. without RAV-correction) and a strongly reduced character set.

1. Postoculo-temporal area of head with rather many costae and costulae, POTCos 11.4 ± 2.1. Anterior dorsum of 1st gaster tergite with more complex elements of stickman-like or reticulate microsculpture, MC1TG 16.6 ± 3.2. Propodeal spines and eye slightly longer. With all linear measurements given in mm, discriminant function 0.183*POTCos + 0.12*MC1TG – 34.79*FL + 46.67*EL + 17.54*ML + 28.28*MPSP – 99.07*PeW – 3.793 > 0 [error 0 % in 21 specimens] => Tetramorium sibiricum

– Postoculo-temporal area of head with fewer costae and costulae, POTCos 8.4 ± 2.4. Anterior dorsum of 1st gaster tergite with less complex elements of stickman-like or reticulate microsculpture, MC1TG 11.2 ± 3.0. Propodeal spines and eye slightly shorter. Discriminant < 0 [error 0 % in 338 specimens] => 2

2. Longest hair near anterolateral pronotal corner shorter, PnHL 0.168 ± 0.020 mm. Anterior dorsum of 1st gaster tergite with more complex elements of stickman-like microsculpture, MC1TG 13.5 ± 2.8. With all linear measurements given in mm, discriminant 0.127*POTCos – 0.173*MC1TG + 85.54*SWd – 49.08*MPSP + 62.52*MPPL + 21.985*PnHL – 9.026 < 0 [error 9.7% in 72 specimens] => Tetramorium indocile

– Longest hair near anterolateral pronotal corner longer, PnHL 0.212 ± 0.022 mm. Anterior dorsum of 1st gaster tergite with only scattered and less complex elements of stickman-like microsculpture, MC1TG 10.6 ± 2.7. Discriminant > 0 [error 1.9 % in 266 specimens] => Tetramorium caespitum

Distribution
Only known so far from the two type localities. Apparently, a species restricted to Siberia.

The Reinig Line faunal divide separates East Siberian, Inner Mongolian, Chinese and Tibetan species from those of Central Siberia, West Siberia and the Turanian region (DE LATTIN, 1967). In ants, the Reinig Line is crossed only by a cold resistant species including Camponotus herculeanus, Formica exsecta, Formica gagatoides, Formica lugubris, Formica manchu, Formica picea, Formica pisarskii, Formica uralensis, Lasius flavus, Leptothorax acervorum and Tetramorium sibiricum (DLUSSKY, 1967; FRANCOEUR, 1983; SEIFERT, 2000, 2021a, 2021b).

Distribution based on Regional Taxon Lists
Palaearctic Region: Russian Federation.

Nomenclature

 * . Tetramorium sibiricum Seifert, 2021: 21, figs. 4-9, tab. 1 (w.) RUSSIA (Siberia).

Type Material
Depository of all specimens: SMN Görlitz (Germany).
 * Holotype plus four paratype workers labelled “RUS: 51.04806 N, 106.16686 E, Gusinoye Ozero – 10 SW, 615 m, stony steppe, under stone, I. ANTONOV 2013.07.04 – 153_S”.
 * Five paratype workers labelled “RUS: 51.04742 N, 106.16703 E, Gusinoye Ozero – 10 SW, 601 m, stony steppe, under stone, I. ANTONOV 2013.07.04 – 154_S".
 * Four paratype workers labelled “RUS: 51.04786 N, 106.16694 E, Gusinoye Ozero – 10 SW, 609 m, stony steppe, under stone, I. ANTONOV 2013.07.04 – 155_S”.
 * Four paratype workers labelled “RUS: 51.04778 N, 106.16689 E, Gusinoye Ozero – 10 SW, 608 m, stony steppe, under stone, I. ANTONOV 2013.07.06 – 156_S”.
 * Four paratype workers labelled “RUS: 51.04772 N, 106.16689 E, Gusinoye Ozero – 10 SW, 600 m, stony steppe, under stone, I. ANTONOV 2013.07.06 – 157”.
 * Four paratype workers labelled “RUS: 51.04800 N, 106.16697 E, Gusinoye Ozero – 10 SW, 615m, stony steppe, under stone, I.Antonov 2013.07.06 – 176_S”.
 * Four paratype workers labelled “RUS: 50.43683 N, 106.12525 E, Naushki village – 5 km N, 851 m, in soil, dirt road, forest-steppe, I. ANTONOV 2013.07.10 – 145_S”.