Formica nigropratensis BETREM, 1962

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 : 161-163

Formica nigropratensis BETREM, 1962

Formica nigropratensis BETREM, 1962 [unnecessary replacement name]

This new name is an objective junior synonym as it was referred by BETREM (1962) simultaneously to the available names Formica thyssei STÄRCKE, 1947 , Formica pratensoides GÖSSWALD, 1951 , and Formica staerckei BETREM, 1960 .

All material examined. Numeric phenotypical data were recorded in 96 nest samples with 331 workers and 21 gynes. These originated from Bulgaria (seven samples), Czechia (one), Georgia (one), Finland (two), France (six), Germany (37), Hungary (two), Italy (one), Kazakhstan (four), Kyrgyzstan (three), Poland (one), Romania (two), Russia (21), Sweden (seven), and Switzerland (one). For details, see SI1, SI2, and SI3. Character recording in ethanol-stored material according to the former investigation protocol of SEIFERT (1992) had been done until the year 1991 in 224 nest samples with 1756 workers and 295 gynes originating from Europe.

Geographic range. Continuously distributed through the temperate and submeridional zones of the Palaearctic , from Spain (9° W) to Irkutsk (104° E) at least. In Europe from 37° N (S Spain) to 63.9° N ( Fennoscandia ). In the Alps ascending to 1500 m (46.0° N), in the Pyrenees and Bulgaria to 1800 m (42° N), and in the Tian Shan to 2100m (42.2° N). Reports from higher elevations in Europe should be checked for confusion with Formica lugubris .

Diagnosis of worker ( Tabs. 3 and 4, Figs. 9 and 10 , key). Dimorphic, with P and N morphs frequently occurring within the same nest. According to the data of SEIFERT (1992), then measured in ethanol-stored specimens, the less hairy P-morph had nCH 17.9 ± 5.7, OccHL 103 ± 25 µm, nHT 17.8 ± 5.7, and CS 1820 ± 220 (1050, 2250) µm in 962 workers, and the hairier N-morph nCH 28.2 ± 6.4, OccHL 132 ± 20 µm, nHT 25.1 ± 5.1 and CS 1770 ± 220 (1040 - 2180) µm in 794 workers. Large species; mean and maximum CS over all social types and both morphs in dry mounted specimens (with slight bias to selecting larger specimens) 1819 and 2239 µm. Head elongated, CL / CW 1750 1.111. Scape much longer and slender than in Formica lugubris, SL / CS 1750 0.927, SL / Smax 1750 10.66. Petiole scale clearly narrower than in F. lugubris , PeW / CS 1750 0.453. Setae number and length extremely variable but even in the least hairy phenotypes larger than in Formica rufa ; separation from F. lugubris by seta characters impossible due to extreme setae polymorphism also in this species; for variance of setae data, see Tables 3 and 4. All body surfaces except the frontal triangle matt due to developed microsculpture. The blackish patch on promesonotum is often larger than on average seen in other species and is often sharply demarcated from the reddish surface.

Diagnosis of gyne ( Tab. 6 ; Figs. 4 , 11 , 12 ). Dimorphic, P- and N-morphs frequently occurring within the same nest, and more clearly separable than workers. According to the data of SEIFERT (1992), then measured in ethanol-stored specimens, the less hairy P-morph had nCH 0.2 ± 0.8, OccHL 30 ± 20µm, nHT 0.6 ± 1.0, and CS 2290 ± 80 (2090, 2511) µm in 172 gynes, and the hairier N-morph nCH 16.2 ± 14.1, OccHL 218 ± 82 µm, nHT 8.4 ± 4.3, and CS 2250 ± 70 (2040 - 2400) µm in 123 gynes. Large; mean and maximum CS over all social types and both morphs in 21 mounted specimens 2296 and 2432 µm. Head moderately elongated, CL / CW 1.024. Scape much longer and more slender than in species related to Formica rufa , Formica aquilonia , or Formica lugubris, SL / CS 0.853, SL / Smax 9.75. Petiole scale relatively narrow, PeW / CS 0.628. Strong pilosity dimorphism: setae number, distribution, and length extremely variable ( SEIFERT 1992). Setae on eyes always present and rather long to very long, EyeHL 46 - 86µm. The least hairy gynes of the P-morph have no setae on posterior margin of head, scape, scutellum, propodeum, petiole scale above spiracle, frontal face of first gaster tergite, and extensor profile of hind tibiae. The hairiest gynes of the N-morph have an extremely rich pilosity on nearly all body surfaces with seta length reaching 453µm on scutellum and 432µm on frontal face of first gaster tergite.All body surfaces, with exception of the frontal triangle, matt due to developed microsculpture. At magnifications> 100x, the dorsum of gaster tergites shows strong transverse microripples and a dense pubescence; sqPDG 4.0 ± 0.5.

Taxonomic comments and clustering results. Combining big size, a long and slender scape, hairy eyes, and dense transverse microripples on gaster tergites, gynes are easily separable from any species except for the East Palaearctic sister species Formica kupyanskayae (for identification, see section “ Formica kupyanskayae BOLTON, 1995 ”, p. 163). Separation of Formica pratensis workers from those of Formica lugubris is safely possible throughout the Palaearctic range using the characters CS, CL / CW 1750, SL / CS 1750, SL / Smax 1750, PeW / CS 1750, nSc 1750, nCH 1750, OccHL 1750, mPnHL 1750, nMet 1750, and MetHL 1750. Exploratory data analyses considering these characters could clearly distinguish 225 nest samples with 1059 workers of F. lugubris from 77 nest samples with 266 workers of F. pratensis . Classification errors were 0.6% in NC-part.hclust, 0% in both NC-part.kmeans and NC-Ward ( Fig. 28 ), and 2% in a PCA. Separation on individual level by an LDA was also very strong with only 1.6% misclassification in 1325 worker individuals.Yet, the separation of the two clusters in two-dimensional plots of LDA and PCA was not strong enough to allow conclusions on recent hybrid samples. For repeated hybridization of the two species in the past, see section “Hybrids Formica pratensis × lugubris ” (p. 174).

The strong dimorphism in Formica pratensis is most apparent in gynes. A re-analysis of the data of SEIFERT (1992) consisting of the 11 characters head width and number and maximum length of setae on posterior

margin of head, scutellum, extensor part of hind tibia, propodeum, and frontal face of first gaster tergite was performed here. As result, the setae-reduced P-morph and the hairy N-morph can be clearly clustered in a PCA after logarithmic transformation of the raw data ( Fig. 29 ). The low percentage of doubtful (or intermediate) specimens is also indicated by the LDA that classified only 2.4% of 295 gynes with posterior probabilities <0.95. Clear arguments against considering the P-and N-morph as separate species are provided by the presence of both morphs in 21.6% of 37 nest samples and simultaneous observation of sexuals of both morphs at the same mating places ( SEIFERT 1992). The same author also showed that phenotype dimorphism is correlated with ecological adaptations. He explained the demonstrated statistical differences in geographical distribution along a thermal gradient by selection of genotypes with differing climatic adaptations. According to SEIFERT (1992), the P-morph differs from the N-morph by the following traits: It constructs clearly flatter mounds for equal insolation conditions and goes to higher altitudes and latitudes. In Germany, the P-morph is rarer than the N-morph in dry habitats with typical Mediterranean elements but is more frequent than the N-morph on loamy soils.

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

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.4: Formica pratensis, gyne; paramedian surface of the dorsum of first gaster tergite. The strength of transverse mi- croripples is at maximum within the Formica rufa group and pubescence density comparable with Formica lugubris.

Fig.28: Classification by three variants of NC-clustering of 225 nest samples of workers of Formica lugubris (black bars) and 76 nest samples of Formica pratensis (grey bars). The mean error of three analyses is 0.2%. Ten phenotypic characters were considered. The small, well separated sub-branch in the F. lugubris cluster represents Fennoscandian nest samples containing exclusively Hippie morph workers.

Fig.29: Principal component analysis of polymorphism in 295 gynes of Formica pratensis. The P-morph with reduced setae (white dots) is clearly separated from the strongly haired N-morph (black rhombs). Eleven phenotypic characters were considered.