Formica truncorum FABRICIUS, 1804 [type investigation]
The taxon was described from Moravia / Czechia from a nestinadeadtreetrunk.Investigatedweretwotypespecimens from ZM Copenhagen: one worker labelled “ Formica truncorum 403.31 Kiel ” (a permanent loan from ZM Kiel) and with a handwritten fragmentary label “ trunca fusca ”, and a strongly damaged alate gyne labelled “ Formica truncorum 403.31 Kiel ” but without a second label. Both specimens are fully consistent with the established conception of F. truncorum. A synonymy with Formica frontalis is excluded by zoogeography and the higher setae numbers on scape and metapleuron. Data of the worker are: CS 1957 µm, CL / CW 1.046, SL / CS 0.978, PeW / CS 0.483; nGu 29, OccHL 124 µm, GuHL 220 µm, mPnHL 81.6 µm, nPr 44.5, nMet 24.5, MetHL 170 µm (setae data of damaged body parts were estimated and are not given here). The gyne fragment, consisting of the dorsal mesosoma with wings, petiole, both hindlegs, and one foreleg, is a typical reddish F. truncorum with all surfaces covered by a profuse, thin, and very long pilosity. The wings are notably infuscated, matching the original description.
Formica truncicola NYLANDER, 1846
Formica truncicola NYLANDER, 1846 [type investigation]
Investigated were four type specimens from ZM Helsinki: one worker syntype pinned together with an alate gyne, both with detached heads glued on a separate cardboard, labelled “Kuusamo \ W. Nyland. \ Coll. Nyland \ Mus. Zool. H:fors Spec. typ. No 5026 Formica truncicola Nyl. ”; one alate gyne on another pin with same labels but “...Spec. typ. No 5024”; one male on a third pin with same labels but “...Spec. typ. No 5025”. All specimens fully match the established conception Formica truncorum.
Formica truncicolopratensis FOREL, 1874 Formica rufa var. truncicolopratensis FOREL, 1874 [photo of type]
Forel described the worker and gyne but did not mention a type locality. The taxon was synonymized by all previous authors with Formica truncorum. If a worker specimen in MHN Genève, labelled “ Typus ”, “F. truncicolo-pratensis Mt Ce..ere” and “ANTWEB CASENT 0911086” can be recognized as true type, the synonymy with F. truncorum appears likely after inspecting the z-stack photos shown in AntWeb (ANTWEB 2021) under the specimen identifier CASENT0911086.The photos suggest shiny circular lateral clypeal depressions and the length of the second funiculus segment to be more than twice its width as it is typical for F. truncorum. The more developed dark pigmentation is not contradictory as such specimens do occasionally occur over the whole range of the species.
Formica yessensis WHEELER, 1913
Formica truncorum var. yessensis WHEELER, 1913 [type investigation]
The taxon was described by FOREL (1901) under the infrasubspecific name Formica rufa r. truncorum var. yessensis FOREL, 1901 from Sorachi, some 100 km ENE of Sapporo, Hokaido. Investigated was one type worker from MHN Genève labelled by A. Forel “ Formica truncicola v. yessensis For Type ” and carrying a printed label “Sorachi Prov. Ishikari Yesso V. 1899. Mus.em. 24.XI.1899 ”. The specimen shows below average setae length on eyes and no setae on dorsum of scape, and extensor profile of hind tibia but is in any character within the range of variation known from the Palaearctic population of F. truncorum. For a more detailed argumentation in favor of this synonymization, see below under taxonomic comments.
Formica approximans WHEELER, 1933 Formica truncorum var. approximans WHEELER, 1933 [type investigation]
The taxon was described from Eastern Tomb / China. Investigated were six worker syntypes from MCZ Harvard, labelled “Eastern Tomb July 16, 30 Chi Ho”, “Gift of W.M.Wheeler ”, “ M.C.Z. CoType 1.-6 21720”, and “ Syntypes Formica truncorum var. approximans Wheeler ” (upper side) “S P Cover IX-2006 ” (underside). The specimens fully correspond to the East Palaearctic population of F. truncorum. For a more detailed argumentation in favor of this synonymization, see below under taxonomic comments.
Formica finzii STITZ, 1939
Formica truncorum var. finzii STITZ, 1939 [description and zoogeography]
This taxon was described in a gyne from near Eberswalde (Germany) under the unavailable name Formica rufa ssp. truncicola var. finzii KRAUSSE, 1926. Types are unknown. Within the four species known to occur in the vicinity of Eberswalde, the description matches the situation in F. truncorum.
Formica menozzii STITZ, 1939
Formica truncorum var. menozzii STITZ, 1939 [description and zoogeography]
This taxon was described from near Eberswalde (Germany) under the unavailable name Formica rufa ssp. truncicola var. menozzii KRAUSSE, 1926. Types are unknown. Within the four species known to occur in the vicinity of Eberswalde, the description matches the situation in F. truncorum.
Formica staegeri STITZ, 1939
Formica truncorum var. staegeri STITZ, 1939 [description and zoogeography]
This taxon was described from near Eberswalde (Germany) under the unavailable name Formica rufa ssp. truncicola var. staegeri KRAUSSE, 1926. Types are unknown. Within the four species known to occur in the vicinity of Eberswalde, the description matches the situation in F. truncorum.
Formica stitzi STITZ, 1939
Formica truncorum var. stitzi STITZ, 1939 [description and zoogeography]
This taxon was described from near Eberswalde (Germany) under the unavailable name Formica rufa ssp. truncicola var. stitzi KRAUSSE, 1926. Types are unknown. Within the four species known to occur in the vicinity of Eberswalde, the description matches the situation in F. truncorum.
A l l m a t e r i a l e x a m i n e d. Numeric phenotypical data were recorded in 50 samples with 92 workers and in 22 gynes. These originated from Belarus (one sample), China (seven), Czechia (one), Denmark (one), Finland (two), France (three), Germany (12), Japan (two), Kazakhstan (seven), Kyrgyzstan (11), Norway (one), Russia (two), and Ukraine (one). For details, see SI1, SI2, and SI3. The total of samples investigated either numerically or subjectively was 136.
G e o g r a p h i c a l r a n g e. Eurosiberian, temperate to boreal; from Netherlands and E France (5° E) to Yakutsk at least (62° N, 130° E). In NE China, the Ussuri region, Sakhalin, Hokkaido, the northern half of Honshu, and the Western Kurils (148° E), it is replaced by the weakly deviating East Asian population. The southern and northern distributional limits in Europe are 42° N (Bulgaria) and 71° N (North Cape). These are in Central Siberia, along the 100 th degree of longitude, 46° N and 67° N. In Europe occurring from the planar to montane zone, in the Alps ascending to 1800m. Rare in the Crimea and Caucasus (DLUSSKY 1967). A population isolated from the Eurosiberian one is found in the Central Asian mountains – in Dzungarian Alatau, Tian Shan (here at 43° N up to 2700 m), and Pamir south to Karakoram (35° N).
D i a g n o s i s o f w o r k e r (T a b. 5, F i g. 1 8, k e y). Polymorphic, with regional differences shown in Table 5. Medium-sized, mean and maximum CS over all morphological and social phenotypes 1754 and 2177µm. Head moderately elongated, CL / CW 1750 1.099. Middle part of lateral clypeus more deeply depressed than in the Formica rufa species complex, anterolateral clypeus as a result forming a bead; median clypeal carina blunt or absent. Scape long and very slender, SL / CS 1750 0.985, SL / Smax 1750 10.87. Second and third segment of antennal funiculus more slender than in the species treated above, IF2 2.15 ± 0.09 (n = 70). Petiole scale narrow, PeW / CS 1750 0.442. Eyes always with microsetae, EyeHL 1750 40 µm. Dorsal plane of scape usually with more setae than in other species, nSc 1750 10.3. Except for the Hippie-morph of Formica lugubris, setae number on each place of the body larger than in any species of the F. rufa group, nCH 1750 42.5, nGu 1750 40.5, nPn 1750 81.6, nMes 1750 35.8, nPr 1750 46.5, nMet 1750 17.6. Hind margin of head usually with very long setae, but setae length on other body parts lower than in the most hairy morphs of Formica pratensis and F. lugubris, OccHL 1750 136µm, GuHL 1750 187µm, mPnHL 1750 91 µm, MetHL 1750 142 µm. Dorsum of head, in addition to the other elements of microsculpture, with deeper and broader microfoveolae which are usually the base of setae. Typical pigmentation in medium-sized to large workers: whole head, mesosoma, petiole, and frontal part of first gaster segment light orange brown; dark brown or blackish brown patches on vertex and dorsal mesosoma may occur in some samples.
D i a g n o s i s o f g y n e (T a b. 8, F i g. 1 9, k e y). On average rather small but extremely size-polymorphic; minimum, mean, and maximum CS over all social phenotypes 1737, 2002, and 2256 µm. Head capsule in dorsal view appears trapezoidal, with more or less linear, frontad converging sides. Middle part of lateral clypeus more deeply depressed than in the Formica rufa species complex, anterolateral clypeus as a result forming a bead; median clypeal carina absent. Scape long and slender, SL / CS 0.903, SL / Smax 9.63. Petiole scale relatively narrow, PeW / CS 0.597. Setae on whole body very numerous, very thin, and usually very long. EyeHL 95 µm, nSc 28.0, nCH 62.6, OccHL 215µm, nGu 65.1, GuHL 267µm, PnHL 242 µm, nMet 38.0, MetHL 249 µm, nPe 15.0. Dorsum of first gaster tergite moderately shiny, with dense transverse microripples, rather dilute pubescence (sqPDG 9.76 µm), and rather large, deep, and widely spaced microfoveolae. The latter may be occasionally absent. Light reddish pigmentation component on all body surfaces more developed than in the F. rufa species complex.
Ta xo n omi c c o mmen t s a nd c lus te r i n g r e s u l t s. Formica truncorum, as any species of the F. truncorum species complex, is rarely confused with other species of the Formica rufa group. Occasional confusion with Formica pratensis is possible due to high similarity in pilosity data and most of the body shape data and due to variation in pigmentation in both species. However, the separation by exploratory and hypothesis-driven data analyses shows an error <1% on the nest sample level in material from the whole Palaearctic range. Furthermore, the shape of clypeus and funiculus segments is usually diagnostic. In gynes, the separation from any species of the F. rufa species complex is also clear in both exploratory and hypothesis-driven data analyses. Less hirsute specimens from Kyrgyzstan, formerly identified as „ Formica cf. frontalis “ (SCHULTZ & al. 2006), were re-classified in this study as F. truncorum. The current data give no indication that F. frontalis does occur outside of Iberia.
The Panpalaearctic population of Formica truncorum cannot reasonably be subdivided into clusters of separate taxonomic identity based on the morphological data available at present. On worker individual level, the West and Central Palaearctic population differs from the East Palearctic one by smaller SL / CS 1750, nPn 1750, and nMet 1750 (Tab.5; ANOVA F 1,90 > 15, p <0.001). Yet, it was not possible by any tested exploratory data analysis to cluster the East Palaearctic population separately – neither on individual nor on nest sample level. As a consequence, Formica yessensis WHEELER, 1913 and Formica approximans WHEELER, 1933 are synonymized here with F. truncorum. A subdivision within the East Palearctic population is also not possible. Using nuDNA (microsatellites), IMAI & al. (2016) investigated the Japanese-Korean population. They could not show genetic differences between populations they had pre-determined as “ F. yessensis ” and “ F. truncorum ” based on subjective assessment of setae numbers on hind tibia. IMAI & al. (2016) reported a “robust” genetic indication for the presence of only a single Japanese-Korean population and a “fragile” morphological classification. For separation from Formica frontalis and Formica sinensis, see section “ Formica frontalis SANTSCHI, 1919 ” (p. 171) and “ Formica sinensis WHEELER, 1913 ” (p. 172).
B i o l o g y. See the species profile given by SEIFERT (2018). Gyne size polymorphism with large disperser gynes having more fat and glycogen and larger flight muscles than smaller inbreeding gynes is more strongly expressed in Formica truncorum than in any other species of the Formica rufa group.