Tetramorium alpestre, Steinera & Seifertb & Moderc & Schlick-Steinera, 2010

Steinera, Florian M., Seifertb, Bernhard, Moderc, Karl & Schlick-Steinera, Birgit C., 2010, A multisource solution for a complex problem in biodiversity research: Description of the cryptic ant species Tetramorium alpestre sp. n. (Hymenoptera: Formicidae), Zoologischer Anzeiger 249 (2010), pp. 223-254 : 249-250

Tetramorium alpestre sp.n. Steiner, Schlick-Steiner and Seifert ( Figs. 2–9 ; Tables 1 and 2 )

Type locality. 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. 3 m 2); 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 ( Fig. 9 ). Worker labelled “AUS: 46.8548 ◦ N, 10.9097 ◦ E, Vent, 2000 m, Weg zur MartinBusch-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) .

Other material examined: see Table 1 .

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

Worker ( Table 2 ): Description: 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 T. 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 T. 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, PosSPu/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 ( Fig. 3 ): Description: 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 jaw of 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 in mm) 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).

Thermal niche: TAS (in ◦ C): arithmetic mean 8.1 ± standard deviation 1.6 [minimum 5.5, maximum 12.2] (n = 22 sites).

mtDNA ( Figs. 5–7 ): 16 haplotypes of cox1 (1113 bp) known; GenBank accession numbers: see Table 1 .

Habitat: Alpine mats.

Geographic and altitudinal distribution ( Figs. 4 and 8 ): The Alps in Austria, France, Italy and Switzerland, the Jura in Switzerland (indicated by two nests inferred to be hybrids between T. alpestre and T. impurum , see “Remarks” below); 44.42–47.22 ◦ N, 6.65–13.71 ◦ E; 1300–2335 m a.s.l.

Phenology ( Table 1 ): Alates recorded inside nests 2 July to 10 September.

Social organisation: 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).

Remarks: Two ambiguous nests (#260, #261) from Swiss Jura, not included in description, are inferred to represent hybridisation of T. alpestre and T. impurum ; hybridisation between these two species could be facilitated by overlapping altitudinal distribution, potentially overlapping nuptial flight phenology, and overall similarity of male genital structure (see Section 5.4. for details); no indication of hybridisation from Alps.

Figures

Fig. 2. Integration of morphology, ecology and molecular genetics at nest level for T. alpestre sp.n (=T. sp. A), T. caespitum et sp. B and T. impurum; each nest is represented by a thin vertical bar; bars of different methods with identical horizontal position refer to the same nest; all nests of which workers were analysed morphometrically are shown; nests exclusively analysed by molecular genetics are not shown; the four nests to the right are the ambiguous nests from which specimens were available for morphological analysis (#260, #261, #i548, #i613). First row: results of classification by DA using the optimal character combination of 14 characters (CL/CW, CS, dCV, FL/CS, ML/CS, MPSP/CS, MW/CS, PENL/CS, PEW/CS, PnHL/CS, PosSPu/CS, PreOc/CS, SLd/CS, TAS) selected from 33 morphometric worker characters and TAS (thermal niche); the bar of each nest is partitioned into shaded segments that represent the probabilities of its species membership as calculated by DA; nests of holotypes of T. alpestre and T. caespitum var. penninum and of neotypes of T. caespitum and T. impurum are indicated. Second row: species identity resulting from analysis of male genital morphology. Third row: species identity resulting from phylogenetic reconstruction using mtDNA gene cox1 (Fig. 5).

Fig. 3. (A–F) Lateral (A, C, E; right side depicted) and dorsocaudal (B, D, F) view of male genitalia in (A and B) Tetramorium alpestre sp.n. (=T. sp. A.), (C and D) T. impurum and (E and F) T. caespitum et sp. B. The dorsocaudal viewing position is indicated by the arrow in (A). The scale bar equals 1 mm. Pilosity and pubescence omitted.

Fig. 4. Altitudinal and latitudinal distribution of Tetramorium alpestre sp.n. (=T. sp. A), T. caespitum et sp. B and T. impurum; see Section 5.4. for details concerning ambiguous nests #260 and #261.

Fig. 5. Phylogenetic reconstruction based on mtDNA. The tree is a consensus tree resulting from a Bayesian analysis of 1113 bp of cox1, broken down to haplotypes. The node-support values are posterior probabilities, values of 1.0 being depicted as filled circles; values for nodes following the basal divergence within species are omitted. The scale bar denotes 0.1 substitutions/site.Haplotypes are numbered as in Table 1. For country codes see Table 1. “?” denotes ambiguous nests; see Section 5.4 for details.

Fig. 6. Graphical method following Evanno et al. (2005) to detect the number K* of clusters that best fit the data, using 133 SNPs from the 67 haplotypes of 1113 bp of cox1 of Tetramorium caespitum, ambiguous nests (denoted by “?” in Fig. 5; see Section 5.4 for details), T. alpestre sp.n. (=T. sp. A), T. sp. B and T. impurum. (A) Mean L(K) over 20 runs for each K value; vertical bars indicate 1 standard deviation. (B) Delta K; the value of K with the highest value of the delta K distribution, i.e., 5, is K*. Note that delta K is not plotted for K = 1, because the calculation of delta K requires values of L(K − 1).

Fig. 7. Estimated structure in the mitochondrial DNA data of Tetramorium caespitum, ambiguous nests (denoted by “?” in Fig. 5; see Section 5.4. for details), T. alpestre sp.n. (=T. sp. A), T. sp. B and T. impurum, using 133 SNPs from the 67 haplotypes of 1113 bp of cox1, and K = 5, identified as the number of clusters that best fit the data (Fig. 6). Each haplotype is represented by a vertical bar which is partitioned into up to K shaded segments that represent the haplotype’s estimated membership fractions in K clusters. Haplotypes are numbered as in Table 1.

Fig. 8. Geographic distribution of Tetramorium alpestre sp.n. (=T. sp. A), T. caespitum et sp. B (not shown: nests #i652, #i653, #i654, and #i769 from Russia and Armenia) and T.impurum; see Section 5.4. for details concerning ambiguous nests #260 and #261.Map from ArcEditor 9.3.1 (ESRI) software, elevation data added from WorldClim database (Hijmans et al., 2005).

Fig. 9. Tetramorium alpestre sp.n. (holotype worker). (A) Lateral view from left. (B) Dorsal view. (C) Head, frontal view.The scale bars equal 0.5 mm. ©NHMW Image Database and www.antbase.net (A and B), and Senckenberg Museum of Natural History Görlitz (C), published with permission.