Tetramorium alpestre

An inhabitant of alpine mats in the Jara and Alps.

Identification
A member of the Tetramorium caespitum complex. The species can be determined with a discriminant analysis of a set of morphological measurements. See Wagner et al. (2017), Steiner et al. (2010), https://webapp.uibk.ac.at/ecology/tetramorium/ and http://web-resources.boku.ac.at/Discmean/.

Distribution
Wagner et al. (2017) - Iberian mountains, Pyrenees, Massif Central, Mont Ventoux, Corsica, Alps, Apennines, Calabrian Apennines, Monti Nebrodi, Dinaric Alps.

Distribution based on Regional Taxon Lists
Palaearctic Region: Austria, France, Italy, Switzerland.

Biology
Steiner et al. (2010) - Alates recorded inside nests 2 July to 10 September. Only known Western Palearctic species of the T. caespitum/impurum complex with functional polygyny (more than one queen per nest egg-laying) and supercolonies (absence of aggression between workers from different nests) (Steiner et al., 2003).

Two ambiguous nests (#260, #261) from Swiss Jura, not included in description, are inferred to represent hybridisation of T. alpestre and T. impurum; hybridization between these two species could be facilitated by overlapping altitudinal distribution, potentially overlapping nuptial flight phenology, and overall similarity of male genital structure; no indication of hybridization from Alps.

Wagner et al. 2017:

Less thermophilic than all other species of complex. In Alps and Pyrenees often above timberline; never below 900 m a.s.l. Southern Italian population more thermophilous, TAS of three sites 14.8 ± 2.9 °C (t-test, p = 0.000). In Alps, typical habitats are south-facing, non-forested alpine meadows, subalpine dwarf-shrub heathland, dry pastures, stony embankments, or block fields. In Pyrenees, known from stony pine forests. Nests often under stones, but also in moss, rootage, and dead wood.

Facultatively polygynous (Steiner et al. 2003, Krapf et al. 2017).

Adult sexuals in nests on 30 July ± 17d [18 June, 10 September] (n = 34).

Strongylognathus testaceus, Strongylognathus alpinus, and Teleutomyrmex schneideri were found associated with T. alpestre.

Krapf et al. (2018) studied worker interactions, aggression, and relatedness to explore how T. alpestre, and ants in general, can exhibit phenotypic plasticity in certain aspects of their life history. This work was prompted by finding supercoloniality in this species (known from Carinthia, Austria). Supercoloniality is achieved/defined as a species having many nests, many queens, workers that are able to freely move between nests that can be many kilometers from their own, and this occurs across a large area with the ants achieving very high local abundance. Supercoloniality has been observed in numerous ant species that are invasive pests.

Nomenclature

 *  alpestre. Tetramorium alpestre Steiner, Schlick-Steiner & Seifert, in Steiner, et al. 2010: 249, figs. 2-9 (w.q.m.) AUSTRIA.

Worker
General body proportions: small sized (arithmetic mean CS 0.753 mm). Eye short and narrow (EL/CS 0.196, EW/CS 0.150). Compared to Tetramorium impurum, scape thicker (SWd/SLd 12.75% vs. 12.25%), mesosoma longer (ML/CS 1.201 vs. 1.167) and wider (MW/CS 0.648 vs. 0.634), setae on pronotal corners shorter (PnHL/CS 0.237 vs. 0.252), spine tips more distant (SPWI/CS 0.305 vs. 0.295), petiolar and postpetiolar nodes wider (PEW/CS 0.335 vs. 0.321, PPW/CS 0.421 vs. 0.410) and postpetiolar node higher (PPH/CS 0.368 vs. 0.355). Body sculpture similar to Tetramorium caespitum et sp. B. Typical but not always reliable differences to T. impurum are: central dorsum of postpetiolar node often fully smooth and brilliantly shining. Paramedian and lateral postpetiole in dorsal view with regular, convexly curved carinulae or carinae; these are usually not wrinkled as often seen in T. impurum. Interspaces between longitudinal rugae on dorsal pronotum often almost smooth with absent or less developed fine anastomoses or delicate microreticular structures. Colouration on average darker and more homogeneous than in T. impurum, with whole body usually medium to dark brown. Mesosoma frequently not distinctly lighter than head and gaster, dirty yellowish brown colour component (as frequently seen in T. impurum) missing. Only reliable distinction from T. caespitum et sp. B and T. impurum: DA using nest mean values (at least two but ideally three workers) and characters CL/CW, CS, dCV, FL/CS, ML/CS, MPSP/CS, MW/CS, PENL/CS, PEW/CS, PnHL/CS, Pos-SPu/CS, PreOc/CS, SLd/CS, TAS. DA can be performed using a freely accessible identification tool embedded in the internet, at: http://web-resources.boku.ac.at/Discmean/.

Male
Relatively small-sized (values in mm): CW: arithmetic mean 0.900±standard deviation 0.042 [minimum 0.831, maximum 0.969]; ML 2.284 ± 0.081 [2.152, 2.366] (n = 10 individuals). Head, mesosoma and waist segments homogeneously blackish (in T. impurum usually with brownish colour component). Surface sculpture variable: mesonotum varying from almost smooth and shining with reduced longitudinal carinulae to almost completely covered by diagonal, curved or semicircular carinulae. Morphological asymmetries and malformations frequent in non-genital body parts. Distinction from T. caespitum et sp. B and T. impurum is best possible by genitalia. Overall spatial structure of genitalia in T. alpestre more similar to T. impurum. In lateral view, stipes of T. alpestre and T. impurum differ from T. caespitum et sp. B by rounded apex and apodeme positioned more anterior than apical level. In T. caespitum et sp. B, apex and apodeme positioned at almost same transversal level, both with roughly rectangular profile of apical stipes and much more pronounced apodeme. Best separation of T. alpestre and T. impurum in dorsocaudal aspect: in T. alpestre, gripping jawof stipes with three dents or protrusions, the dent intermediate between anteriormost (formed by apodeme) and caudalmost, apical protrusion being acute; in T. impurum, intermediate dent absent or only shallow and blunt. Absolute genital sizes of T. alpestre and T. impurum typically different, but with slight overlap: maximum distance from dorsal posterior margin of cardo to stipal apex in T. alpestre (values inmm) arithmetic mean 0.812 ± standard deviation 0.044 [minimum 0.748, maximum 0.871] (n = 10 individuals), in T. impurum 0.977 ± 0.061 [0.859, 1.098] (n = 21).

Type Material
Austria (Tyrol): Vent, 46.8548°N, 10.9097°E, 2000 m a.s.l.; immediately above timber line; vegetation mainly grass with interspersed dwarf shrubs (Erica sp. and others; ca. 10–20 cm high) and patches free of vegetation (small rocks, stones, bare soil); holotype nest large (ca. 3m2); other ant species found close to holotype nest: Formica lemani Bondroit, 1917, Leptothorax acervorum (Fabricius, 1793), Myrmica sulcinodis Nylander, 1846; all information provided by H. Müller.

Holotype. Worker labelled “AUS: 46.8548°N, 10.9097°E, Vent, 2000 m, Weg zur Martin-Busch-Hütte, leg. H. Müller 2007.08.15-1, #251”. Collection date: 15 August 2007. Deposition: Senckenberg Museum of Natural History Görlitz.

Paratypes: 4 workers, 2 males, 3 gynes from holotype nest series (Senckenberg Museum of Natural History Görlitz); 7 workers, 1 male, 1 gyne from holotype nest series Museum of Natural History Vienna); 7 workers, 1 male, 1 gyne from holotype nest series (Tiroler Landesmuseum Ferdinandeum in Innsbruck); 6 workers, 1 male, 1 gyne from holotype nest series (collection of B. C. Schlick-Steiner and F. M. Steiner, housed by the Institute of Ecology of the University of Innsbruck); 5 workers, 3 gynes with same data as holotype nest series but #252 (Senckenberg Museum of Natural History Görlitz); 16 workers, 2 gynes with same data as holotype nest series but #252 (collection of B. C. Schlick-Steiner and F. M. Steiner, housed by the Institute of Ecology of the University of Innsbruck).

Etymology
The species epithet is an adjective derived from alpes (lat.).