Formica unicolor RUZSKY, 1926

Seifert, Bernhard, 2021, A taxonomic revision of the Palaearctic members of the Formica rufa group (Hymenoptera: Formicidae) - the famous mound-building red wood ants, Myrmecological News 31, pp. 133-179 : 165-166

Formica unicolor RUZSKY, 1926

Formica pratensis ssp. unicolor RUZSKY, 1926 [description, diagnosis of DLUSSKY (1967)]

This taxon was described on the basis of a single worker collected at Surgut (West Siberia, 62.25° N, 73.42° E) on 21 June 1913. A synonymy with Formica lugubris appears possible from description. DLUSSKY (1967), who might have seen the type specimen, interpreted this taxon as a light coloured F. lugubris without a dark patch on dorsal mesosoma. Such specimens are more frequent in Siberia than in Europe.

All material examined. Numeric phenotypical data were recorded in 224 nest samples with 1108 workers and 109 gynes. These originated from Austria (seven samples), Bulgaria (seven), Czechia (four), Finland (42), France (28), England (two), Germany (18), Italy (15), Mongolia (two), Norway (10), Russian West Siberia (seven) Russian East Siberia (15), Sweden (24), and Switzerland (44). For details, see SI1, SI2, and SI3.

Geographical range. Eurosiberian, boreo-montane. The huge boreal range extends from the British Isles east to Kamchatka. In Fennoscandia from S Sweden (55.5° N) to North Cape (71° N). The northern distribution in Siberia is limited by 65° N. Occurrence at low latitudes and altitudes in the Ussuri region (43.17° N, 132.79° E, 350m) is explained by influence of cold water of the West Pacific. The montane-subalpine population in Europe extends over the Pyrenees, Massif Central, Alps, Vosges, Schwarzwald, Bayrischer Wald, the whole Carpathians, Stara Planina, Vitosha, Rila, Pirin, and Rhodopes. In the Alps occurring at altitudes between 550 and 2510 m. Under influence of Atlantic climate descending to 250m (Vosges, France) and 50 m ( Ireland).

Diagnosis of worker ( Tab. 3 and 4, Figs. 14 and 15, key). Extremely polymorphic, with regional differences shown in Table 3 . Rather large, mean and maximum CS over all morphological and social types 1805 and 2184 µm. Scape shorter and much less slender than in Formica pratensis, SL / CS 1750 0.894, SL / Smax 1750 9.30. Petiole wider than in F. pratensis , PeW / CS 1750 0.489. Setae on eyes long, EyeHL 1750 33 µm; setae condition on dorsal plane of scape most variable, nSc 1750 usually 0 - 5 but in Fennoscandian Hippie-morph ( SEIFERT 2003) up to 40. Setae on head margin behind eyes always numerous but most variable in length, nCH 1750 25.0; average OccHL 1750 usually 115µm but up to 235 µm in Fennoscandian Hippie-morph. Gular setae always numerous and long, nGu 1750 15.1, GuHL 1750 188 µm. Pronotal setae numerous but most variable in length, average mPnHL 1750 usually 84 - 112µ m but in Fennoscandian Hippie-morph up to 176µm. Number and length of mesopleural, propodeal, and metanotal setae usually large, nMes 1750 28.1, nPr 1750 21.7; mMet 1750 10.3, MetHL 1750 182 µm. Pigmentation without specific characters. The dark patch on mesosoma is usually large with diffuse margins in European popu- lations but may also be reduced.

Diagnosis of gyne ( Tab. 7 , Fig. 3 , key). Extremely polymorphic. Mean number and length of setae is lowest in morph A3 from the Alps ( SEIFERT 2018) and highest in the Fennoscandian Hippie-morph ( SEIFERT 2003). The remaining morphs, such as the most abundant morphs A1 from the Central European mountains or morph N1 from Fennoscandia, are intermediate. The numeric data given in the following summarize data of 109 gynes from the whole geographic range and of any social and morphological type. Rather large, CS 2213 ± 80 (1996, 2382) µm. Head short, CL / CW 0.998 ± 0.020 (0.950, 1.052). Scape short and thickset, SL / CS 0.789 ± 0.026 (0.708, 0.857), SL / Smax 8.13 ± 0.37 (7.12, 9.04). Eyes always with setae, the longest occur in the Fennoscandian Hippie-morph, EyeHL 48 ± 18 (30, 151) µm. Dorsal plane of scape with most variable setae numbers, which are highest in Fennoscandian Hippie-morph, nSc 2.1 ± 3.5 (0, 21). Posterior margin of head always with setae, but these are most variable in length and number, nCH 23.2 ± 8.8 (10.5, 65.0), OccHL 156 ± 91 (40, 320) µm. Underside of head, all surfaces of mesosoma, and petiole scale always with setae of most variable length and number, nGu 18.3 ± 6.7 (8, 36), GuHL 244 ± 111 (49, 425) µm, PnHL 208 ± 93 (34 - 411), MetHL 260 ± 97µm (40, 375), nPe 15.5 ± 6.5 (2,33). Dorsalsurfaceofgasterappearsatlowermagnifica- tion more or less shiny. Transverse microripples on dorsum of first gaster tergite usually very weak or absent but occa- sionally more developed, then approaching the situation in Formica pratensis . Foveolae and pubescence on dorsum of first gaster tergite on average more densely packed than in Formica rufa or Formica polyctena , FodG 25.2 ± 5.7 (17.9, 50.8) µm, sqPDG 4.84 ± 1.14 (3.13, 8.06) µm.

Taxonomic comments and clustering results. The European population is extremely polymorphic, being a mixture of (a) sympatrically occurring most different phenotypes, as for example observed in Fennoscandia ( SEIFERT 2003) or in the Alps ( SEIFERT 2018), and (b) of deviating but rather monomorphous regional populations, such as found in the Pyrenees or the Balkan mountains. Clustering of morphological data by exploratory data analyses and assessment of putative clusters by discriminant analyses did not allow to give one of these entities a taxonomic significance (for the special case of Formica helvetica sp.n., see section “ Formica helvetica sp.n. ”, p. 166). Considering this very complicated structure, it appears astonishing that the separation from Formica pratensis all over the Palaearctic range was such clear in workers and gynes (see section “ Formica pratensis RETZIUS, 1783 ”, p. 159 or SEIFERT & GOROPASHNAYA 2004), and that also Formica paralugubris was sufficiently separable in both castes (see section “ Formica paralugubris SEIFERT, 1996 ”, p. 167, and SEIFERT 2016a). Sections “Hybrids Formica aquilonia × lugubris ” (p.173), “Hybrids Formica pratensis × lugubris ” (p.174) and “Hybrids Formica lugubris × rufa ” (p.174) report on hybridization of F. aquilonia × lugubris , F. pratensis × lugubris , and Formica rufa × lugubris .

Biology. See the species profile given by SEIFERT (2018).

Figures

Fig.3: Formica lugubris, gyne; paramedian surface of the dorsum of first gaster tergite. The transverse microsculpture is as weak as in Formica rufa, but the density of pubescence and microfoveolae is much higher.