Formica constricta KARAVAJEV, 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 : 156-158

Formica constricta KARAVAJEV, 1926

Formica rufa var. constricta KARAVAJEV, 1926 [type investigation]

Investigated were two syntype workers on one pin labelled „ Akmolin. ob. Kokchetav. g. bl. Borovoye. Bej-Bijenko”, “3269. coll Karavaiev”, “Form. (Form.) rufa v. constricta Karavaiev typ” (Karavajev’s handwriting), “ Syntypus Formica rufa constricta Karaw. ” (label of Radchenko) and three syntype workers on another pin labelled “3269. coll Karavaiev”, “ Syntypus Formica rufa constricta Karaw. ” (label of Radchenko); depository SIZ Kiev. The type locality Borovoye is situated in the geographic zone (see below) where hybrids between Formica aquilonia and Formica polyctena do regularly occur. The status of the types was tested using the same 16 characters as in the analysis in the previous section. If run as wild-cards in a three-class LDA and comparing F. aquilonia (class 1), hybrids and backcrosses F. aquilonia × polyctena (class 2) and F. polyctena (class 3), the type series is allocated to these classes with p = 0.0152, p = 0.8019, and p = 0.1829, respectively ( Fig.25 ). These investigations considered 75 nest samples with 345 workers of F. aquilonia , 27 nest samples and 148 workers of F. aquilonia × polyctena hybrids or backcrosses, and 57 nest samples with 217 workers of F. polyctena . Under this setting, the type series of Formica major was allocated in a wild-card run to the three classes with p = 0.0021, p = 0.5244, and p = 0.4735, respectively.

All material examined. The full set of numeric phenotypical data was recorded in 27 nest samples with 148 workers and 18 gynes. These originated from Finland (13), Kazakhstan (one), Mongolia (one), and Russia (12). For details, see SI1, SI2, and SI3.

Geographic range. The geographic range where hybrids Formica aquilonia × polyctena are known to occur corresponds to the transition zone between temperate and boreal climate and ranges from 19.8° E (Aaland Isles / Finland) to 107° E (Baikal Region and Bogdkhan NP / Mongolia). With increasing continentality, this zone moves

south: It extends in Finland between 59.8 and 63.3° N, in West Siberia (about 62° E) between 53.1 and 60.4° N, and in Central Siberia (about 104° E) between 47.8 and 53.2° N. Hybrid occurrence and introgression should also occur in the Alps somewhere in the submontane or montane zone.

Diagnosis of worker ( Tab. 2 , key). The hybrids are intermediate in all characters in which the parental species show notable differences ( Tab.2 ).

Diagnosis of gyne ( Tab. 6 ). Except for one specimen, all examined gynes are from a single supercolony near Tvärminne / Finland in which the genetic structure was thoroughly investigated by KULMUNI & al. (2010) and KULMUNI & PAMILO (2014). The data in Table 6 are thus biased to a local situation and probably not representative for the Palaearctic hybrid population. Yet, the intermediate position of the hybrids becomes obvious in characters showing the most obvious differences of the parental species: SL / CS, SL / Smax, FodG, and GuHL.

Taxonomic comments and clustering results. The earliest indications of this hybridization came from a West Siberian sample (SaNo 156, Yekaterinburg-1998-U23) combining a clear Formica polyctena phenotype with a mtDNA of Formica aquilonia ( GOROPASHNAYA & al. 2004) and observation of viable laboratory crosses ( SORVARI 2006). In the time since then, hybridization of F. aquilonia and F. polyctena has been confirmed and thoroughly investigated by morphometric analyses and investigation of nuDNA ( KULMUNI & al. 2010, BERESFORD & al. 2017). A nuDNA study of the latter authors in 17 sites within an area of 3000 km ² in South Finland revealed extremely frequent hybridization and introgression between F. aquilonia and F. polyctena . This investigation showed that nest populations with a hybrid history but having developed their nuclear DNA close to the situation in the F. aquilonia parent preferentially had the mtDNA of F. polyctena , whereas a majority of those with a nuDNA approaching F. polyctena had the mtDNA of F. aquilonia .

Hybrids in the Irkutsk Region (Central Siberia) seem to form an own self-sustaining population – at least they are no result of a very recent hybridization because Formica polyctena is not confirmed so far to occur there and because its presence is unlikely for climatic reasons (mean January temperature -21°C).

Results of clustering worker samples are commented above ( Figs. 24 , 25 ). Due to introgression, it is not possible to demonstrate three separate clusters. A PCA of the gynes, considering all 24 characters presented in Table 6 , provided a rather good separation of the three entities ( Fig. 26 ). However, there are no backcrosses in the gyne hybrid cluster in which 94% of specimens came from a single, isolated supercolony.

Figures

Fig.25: Position of the type samples of Formica major NY- LANDER, 1849 (MA) and Formica constricta KARAVAJEV,1929 (CO) in a linear discriminant analysis considering 58 nest samples of Formica polyctena (black squares), 27 nest samples of Formica aquilonia × polyctena or backcrosses (white dots), and 75 nest samples of F. aquilonia (black rhombs). The type samples were run aswild-cards.Sixteen phenotypiccharacters were considered.

Fig.24: Position of the type samples of Formica major NY- LANDER, 1849 (MA) and Formica constricta KARAVAJEV, 1929 (CO) in a principal component analysis considering 58 nest samples of Formica polyctena (black squares) and 27 nest samples of Formica aquilonia × polyctena or backcrosses (white dots). The F. polyctena sample deeply placed within the hybrid cluster is aberrant and cannot be a hybrid for zoogeographical reasons. Seven phenotypic characters were considered.

Fig.26:Principal componentanalysisof gynes ofFormicapolyctena (black squares, n = 33), Formicaaquilonia × polyctena or backcrosses (whitedots, n =18),andF.aquilonia (black rhombs, n = 29). Twenty-four phenotypic characters were considered.