Formica ussuriensis, Seifert, 2021

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 : 158-159

Formica ussuriensis sp.n.

Etymology. Referring to the region of the river Ussuri in which the species occurs.

Type material. Holotype worker plus four paratype workers labelled “ RUS: Ussuri: 43.24N, 133.39E 770m, ober. Povarotnaja-Tal, lehmiger Hangschutt, Sandboden mit Pioniervegetation, 1999.09.14 -050 (L.Kanter)”; 5 paratype workers labelled “ RUS: Ussuri : 43.01N, 133.21E, 850m; S- Mt. Lysaya Sopka, dunkle Fichten-Tannen-Taiga, 1999.09.03 -037 (L.Kanter)”; 5 paratype workers labelled “ RUS: Ussuri: 43.24N, 133.39E, 555 m; ober. Povaratnaya-Tal; sandige Flussterrasse, 1999.09.14 -051 (L.Kanter)”; depository SMN Görlitz.

All material examined. Numeric phenotypical data were recorded in 10 nest samples with 41 workers and three gynes. All these originated from Russian Far East. For details, see SI1, SI2, and SI3.

Geographic range. Known are eight sites in the Ussuri River / Sichote Alin region situated at altitudes between 270 and 850 m, and latitudes between 43.0 and 48.3° N.

Diagnosis of worker ( Tab. 2 , Figs. 5 and 6 , key). S imilar to Formica aquilonia ; slightly smaller, mean and maximum CS over all social types 1537 and 1808 µm. Scape as short but less thickset than in F. aquilonia, SL / CS 1750 0.903, SL / Smax 1750 9.51. Petiole on average wider than in any other species, PeW / CS 1750 0.519. Setae on eyes rather short, EyeHL 1750 26 µm; setae on dorsal plane of scape much more numerous than in F. aquilonia , nSc 1750 10.8; setae on head margin behind eyes more numerous than in F. aquilonia and slightly longer, nCH 1750 10.9, OccHL 1750 80 µm; gular, pronotal, propodeal, and metanotal setae sparse and short as in F. aquilonia with exception of clearly longer metanotal setae, nGu 1750 5.6, GuHL 1750 117µ m, nPn 1750 7.1, mPnHL 1750 47µ m, nPr 1750 3.5; mMet 1750 3.8, MetHL 1750 141µm; setae on lateral mesopleuron as numerous as in F. aquilonia , nMes 1750 15.4. Pigmentation without specific characters.

Diagnosis of gyne ( Tab. 6 , Fig. 7 ). Clearly larger than Formica aquilonia , mean and maximum CS 2225 and 2357 µm. Hind margin and sides of head more linear, as result head shape more trapezoid. Scape short and thickset, SL / CS 0.806, SL / Smax 8.27. Setae on eyes rather short, EyeHL 33µm; setae on head margin behind eyes much more numerous than in F. aquilonia and slightly longer, nCH 15.0, OccHL 1750 65 µm; gular setae much more numerous and longer than in F. aquilonia , nGu 10.8, GuHL 107 µm; setae on metapleuron and frontal face of first gaster tergite much more numerous and much longer than in F. aquilonia , nMet 12.2, MetHL 167µm, nGfr 26.3, GfrHL 257µm. Distance of pubescence and of foveolae on paramedian surface of first gaster tergite as in F. aquilonia , sqPDG 10.12, FodG 25.3 µm. Pigmentation without diagnostic characters.

Taxonomic comments and clustering results. The species is similar to Formica aquilonia and probably closely related. The geographically closest finding of F. aquilonia in the south of Amur Oblast’ (49.16° N, 130.67° E) is situated about 340 km west of the next known site of Formica ussuriensis at 48.22° N, 135.06° E. Accordingly, occurrence of hybridization and introgression has to be checked in the region of the lower course of river Amur. Yet, the data currently available provide clearly separate clusters in exploratory data analyses. Considering the characters CL / CW 1750, SL / Smax 1750, nSc 1750, nCH 1750, OccHL 1750, nMet 1750, MetHL 1750, and nPr 1750, 10 worker nest samples of F. ussuriensis were separated from 75 Panpalaearctic samples of F. aquilonia by NC-Ward, NC-part.kmeans, NC-NMDS-kmeans, and a PCA with an error rate of 0%, whereas NC-part.hclust misclassified 2.4% of the samples ( Fig. 27 ). Using the same character system, an LDA classified 98.7% of 386 worker individuals in agreement with the classification provided by four ex- ploratory data analyses. Regarding gynes, the first factor of PCA considering the characters CS, EyeHL, nCH, nMet, and MetHL scored 2.663 ± 0.221 (2.413, 2.832) in three gynes of F. ussuriensis but -0.275 ± 0.515 (-0.913, 0.784) in 29 gynes of F. aquilonia . A full separation by the PCA was also given when all 24 characters shown in Table 6 were considered unselectively.

Habitat and biology. It formed monodomous and polydomous colonies and was found in often very dark spruce ( Picea ), fir ( Abies ), and broadleaf forests. These biomes have a boreal to subboreal character due to the influ- enceofcoldwatersofthePacificOcean.Thisleadstoashiftof biomes to more southern latitudes and lower altitudes than observed in comparable biomes in Europe. The 10 known sites are situated at altitudes of 622 ± 213 (270, 850) m.

Figures

Figs.5-13: (5-ussu) Formica ussuriensis sp.n., worker, holotype, head. (6-ussu) Formica ussuriensis sp.n., worker, holotype, lateral.(7-ussu) Formica ussuriensis sp.n., gyne, head; note the more trapezoid headshape.(8-aqui) Formica aquilonia, gyne, head; note the more rounded head shape.(9-prat) Formica pratensis, worker, neotype, head; note the more reticulate microsculpture of central vertex compared with Formica lugubris (Figs.14, 15), producing a matt surface appearance.(10-prat) Formica pratensis, worker, neotype, lateral aspect. (11-prat) Formica pratensis, gyne, P morph, lateral; almost no setae on head, mesosoma, and first gaster tergite. (12-prat) Formica pratensis, gyne, N morph, lateral; many setae on head, mesosoma, and first gaster tergite. (13-kupy) Formica kupyanskayae, gyne, head.

Fig.27: Classification by four variants of NC-clustering of 75 nest samples of workers of Formica aquilonia (grey bars) and 10 nest samples of Formica ussuriensis sp.n. (black bars). The mean error of four exploratory data analyses is 0.6%. Eight phenotypic characters were considered.