Myrmica gebaueri

Found on montane to subalpine grassland, usually pastures. Nests in soil, under stones or in grass tussocks. Polygynous.

Identification
The separation of Myrmica gebaueri and M. tibetana is most difficult and a safe discrimination on the worker individual level is only possible by the multivariate analyses described by Seifert et al. (2018). Compared to M. tibetana, M. gebaueri shows smaller eyes and longer and more diverging propodeal spines. A parsimonious morphometric method allows a determination on nest sample level if two or three workers per sample are measured. We simplified the species delimitation procedure by using absolute linear measurements and by reducing the number of characters for the condition that the error at nest sample level was zero. We emphasize at this point that the measuring instructions for each character have to be considered. The extracted morphometric method requires five minutes working time in a mounted specimen. With all measurements recorded in mm, a linear discriminant function

D(3) = 62.835 EYE + 44.41 SPBA - 50.213 SP - 15.713

resulted in an error of 0% on the nest sample level. Samples with D(3) < 0 are classified as Myrmica gebaueri, those above this threshold as M. tibetana. The error on the worker individual level was 5.6% in 126 specimens.

The easy separation from Myrmica bactriana, the three species of the M. smythiesii complex (Myrmica fortior, Myrmica smythiesii,  Myrmica wittmeri) and from Myrmica tenuispina has been treated in the section considering possible synonymies in Seifert et al. (2018).

Distribution
NE Tibet between 35.5 and 38.0° N and 99.8 and 102.8° E, in altitudes of 2900 - 3500 m.

Distribution based on type material
Tibet.

Nomenclature

 *  gebaueri. Myrmica gebaueri Seifert et al., 2018: 105, figs. 7-11 (w.) TIBET.

Worker
Most similar to Myrmica tibetana. One of the smallest species of the genus (CS 918 μm). Head with a weakly concave to straight posterior margin and strongly convex sides (Fig. 7) and rather elongated (CL / CW 1.129). Postocular distance rather low (PoOc / CL 0.410). Frontal lobes broad and significantly diverging (FL / CS 0.482, FL / FR 1.190), their lateral outline more angulate than convex, usually forming an angle ± 110°, frontal carinae merging with the rugae that surround antennal sockets. Eyes with few microsetae and rather small (EYE / CS 0.191), distinctly smaller than in Myrmica tibetana (EYE / CS 0.205). Clypeus in dorsal view of head produced, its anterior margin more angulate than curved, forming an angle of 115 - 125°. Scape moderately long (SL / CS 0.794), with a slender, evenly curved basal part which performs a total bend of ± 35° when viewed in the frontal or caudal standard viewing positions (SVP f or c in Seifert & al. 2014; Fig. 11 does not show a fully caudal aspect). Dorsal profile of mesosoma with a strongly convex promesonotal part, a strong metanotal depression and a convex dorsal part of propodeum (Fig. 9). Propodeal spines acute and short but on average longer than in Myrmica tibetana (SP / CS 0.179 but 0.155 in the latter), spine axis in lateral view deviating from longitudinal mesosomal axis by 35 - 45°. Spines slightly diverging (Fig. 8): distance of spine base usually smaller than distance of tips (SPBA / CS 0.271, SPTI / CS 0.284) – in Myrmica tibetana there is usually no divergence of spines (SPBA / CS 0.282, SPTI / CS 0.263). Central height of propodeal lobe only slightly larger than equal-level height of subspinal excavation (MetL / CS 0.226, MetSp 0.200). Petiole rather low (PEH / CS 0.323) and in lateral view with a concave anterior profile, a rounded dorsum of node and a slightly concave to almost straight caudodorsal profile (Fig. 10). Petiole in dorsal view with rather straight sides, slightly diverging caudad, its width about 65% of postpetiolar width. Setae are present on all dorsal parts of body and rather long (PPHL / CS 0.206). Vertex moderately strong longitudinally rugose, posterior vertex reticulate; about 16 - 23 rather linear rugae are found between the most approximated parts of frontal carinae. Mesosoma and waist with a weak sculpture in terms of genus Myrmica, larger surface areas may be smooth. Dorsum of promesonotum as a rule reticulate-rugose, meso- and metapleuron longitudinally carinulate. Dorsal propodeum weakly carinulate-rugulose, substantial parts of its surface often completely smooth. Dorsum of petiole reticulate-rugulose, central dorsum of postpetiole at lower magnification always appearing smooth and shining, a delicate microreticulum becomes visible at larger magnifications. Whole body usually rather uniformly medium brown with a weak yellowish component and sometimes with a lighter mesosoma.

Type Material

 * Holotype labeled “CHI: 37.1852° N, 102.7844° E Tianshu station-1.2 S, 2939 m moist pasture, under stone R.Schultz 2011.08.04-044” and “Holotype Myrmica gebaueri Seifert et al. 2018”,.
 * Two worker paratypes on a different pin, 21 worker and 14 male paratypes stored in ethanol – all from the same nest sample and with equal collecting data label as the holotype; all material stored in . Three worker paratypes with the same labeling in.

Etymology
Named after the German naturalist Axel Gebauer who made several expeditions to the Tibetan Plateau and was the first to collect this species in 1992.