Formica helvetica, 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 : 166-167

Formica helvetica sp.n.

Formica lugubris -A2 ( BERNASCONI & al. 2011)

Formica lugubris, morph A2 ( SEIFERT 2018)

Etymology. Referring to Helvetia, the Latin name of Switzerland.

Type material. Holotype worker plus four paratype workers labelled “SWI: 46.7218° N, 10.2988° E, Scuol, Pinus forest, 1767m, polydomous, Bernasconi 2005.05.13 - MIN7 ”; another nine nest samples from the same supercolony with 47 paratype workers and 30 paratype gynes collected by C. Bernasconi in the years 2005 - 2008, sample numbers MIN8 , MIN11 , MIN13 , MIN15 , MIN17 , MIN18 , MIN20 , MIN35 , and MIN36 ; depository SMN Görlitz.

All material examined. Numeric phenotypical data were recorded in nine nest samples with 30 workers and 28 gynes. All originated from the supercolony of the type locality. For details, see SI1, SI2, and SI3.

Geographic range. Only known from the type locality in Mingèr Valley in the Eastern Swiss Alps at altitudes between 1700 and 2000 m.

Diagnosis of worker ( Tab. 3 , Figs. 16 and 17 ). Small, as it is expected for a supercolonial social phenot ype, mean and maximum CS 1663 and 1966µm. Scape as short as but on average less thickset than in Alpine Formica lugubris, SL / CS 1750 0.904, SL / Smax 1750 9.47. Petiole width and setae number as in Alpine F. lugu- bris but setae length on average larger, EyeHL 1750 37µm, OccHL 1750 132µm, mPnHL 1750 111µm, MetHL 1750 188 µm.

Diagnosis of gyne ( Tab. 7 ). Size slightly smaller than in Alpine Formica lugubris , mean and maximum CS 2126 and 2278 µm. Head short, CL / CW 0.999. Scape on average longer and less thickset than in morph A3 of Alpine F. lugubris , SL / CS 0.797, SL / Smax 8.41. Eyes always with rather long setae, EyeHL 44µm. Dorsal plane of scape usually without or very few setae, nSc 0.4. Posterior margin of head always with setae, these on average longer than in morph A3 of Alpine F. lugubris , nCH 18.5, OccHL 179µm. Setae number comparable with morph A1 and A3 of Alpine F. lugubris but seta length larger than in morph A3, nGu 17.2, GuHL 303µm, PnHL 236µm, MetHL 287µm, nPe 13.7. Dorsal surface of gaster appears at lower magnification more or less shiny. Dorsum of first gaster tergite usually with weak transverse microripples and with foveolae and pubescence being on average more densely packed than in Formica rufa or Formica polyctena , FodG 26.1 µm, sqPDG 4.84 µm.

Taxonomic comments and clustering results. Formica helvetica sp.n. is the first ant species I describe as new without having a sufficiently clear mor- phological diagnosis. This decision is certainly a risk, considering the patchwork situation in Alpine Formica lugubris populations. However, this taxonomic act is intended as a constructive, positively provocative hypothesis for future ant students to re-investigate the case with more advanced methods. The recognition as species here is largely based on an apparently clear clustering by nuclear DNA and moderate support by gyne morphology. BERNASCONI & al. (2011) investigated nine microsatellite markers in seven Formica rufa group species in and around the Swiss National Park in East Switzerland. They showed a clear difference between F. helvetica sp.n. and F. lugubris (in Mingèr Valley represented by morph A1) and five other F.rufa group species sympatrically occurring in the area. The genetic distance between F. helvetica sp.n. and F. lugubris (Fst = 0.101) was comparable with those between Formica aquilonia and Formica paralugubris (Fst = 0.117), or between F. lugubris and F. aquilonia (Fst = 0.130) but lower than between monodomous and polydomous populations of F. lugubris in another area of the Swiss National Park ( BERNASCONI & al. 2005). The mtDNA of F. helvetica sp.n. clustered with that of F. paralugubris and F. aquilonia , which may suggest a hybridogenous evolutionary history, but also that there was no influx of genes by immigration of F. lugubris gynes.

The morphological clustering of workers failed when the whole Alpine population from the French Jura to Eastern Austria was considered. Running an LDA with the characters CS, CL / CW 1750, SL / CS 1750, nSc 1750, nCH 1750, OccHL 1750, mPnHL 1750, and nMet 1750, all nine worker nest samples of Formica helvetica were allocated to the same cluster, but this cluster was shared with nine Formica lugubris samples of the morph A1 from nine different lo- calities. This meant a classification error of 9.3% in a total of 97 worker samples. The misplaced F. lugubris samples came from all over the Alps and included a population from Grande Rolat in Swiss Jura which had been intensively studied biologically, genetically and morphologically over many years.

The situation in gynes appears better, but the low sample size of only 28 specimens in Formica helvetica sp.n. required a strong character reduction, performed by a stepwise LDA. Using the eight characters SL / CS, SL / Smax, PeW / CS, ML / CS, nSc, nMes, GuHL, and nHT, the nest sample means of the LDA scores provide a rather good separation of F. helvetica sp.n. ( Fig. 31 ), but the figure also shows that the first component of the PCA (calculated from the same eight characters as the LDA) does not expose F. helvetica but separates instead the Formica lugubris morphs A1 and A3.

Habitat and biology. The supercolony stretched along a transect of about 1.6k m length within a Pinus forest on limestone ground. The social structure is comparable with that of Formica aquilonia , with mating intranidally or within the colony borders and high genetic viscosity.

Figures

Figs.14-20: (14-lugu) Formica lugubris, worker, normal morph, head; central vertex suggestedly shiny due to weaker transverse microsculpture. (15-lugu) Formica lugubris, worker, Hippie morph, head; central vertex suggestedly shiny due to weaker transverse microsculpture. (16-helv) Formica helvetica sp.n., worker, holotype, head. (17-helv) Formica helvetica sp.n., worker, holotype, lateral. (18-trun) Formica truncorum, worker, head. (19-trun) Formica truncorum, gyne, head. (20-sine) Formica sinensis, worker, lateral; note the contrast between weak pronotal and strong gular pilosity.

Fig. 31: Nest-sample means of a linear discriminant analysis and principal component analysis of Formicalugubris complex gynes considering eight phenotypic characters; Formica helvetica sp.n. (white dots), F.lugubris morph A1 (black squares), F.lugubris morph A3 (squares with white center). The means were calculated from 28, 38, and 18 individuals foreach entity.