Formica polyctena × rufa

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 : 155

Formica polyctena × rufa

– hybrids and backcrosses

All material examined. The full set of numeric phenotypical data was recorded in 55 nest samples with 345 workers and 16 gynes; for details, see SI1, SI2, and SI3. The total number of mounted samples stored in SMN Görlitz and investigated either subjectively or by partial or complete numeric recording of the phenotypical characters used here was 68. These included 453 workers and 18 gynes and originated from Austria (one sample), Bulgaria (three), Czechia (one), Finland (two), Germany (29), Great Britain (20), Poland (two), Russia (two), Sweden (one), and Switzerland (six). Character recording in ethanol-stored material according to the former investigation protocol of SEIFERT (1991) was done until the year 1993 in further 98 nest samples with about 2700 workers largely from Germany and Russia.

Geographic range. Hybrids are expected to occur wherever the parental species are in contact and hybrid frequency is estimated over the whole range as 6 - 8%. However, there are big regional differences in hybrid frequency. In Britain, where the typical Formica polyctena and Formica rufa are absent, 95% of all samples are phenotypically intermediate and the whole population is supposed to consist of hybrids. The British hybrids are on average smaller and have longer gular setae than the continental hybrids ( Tab. 1 ). Yet, describing them as a separate hybridogenous species is not justified as they cannot be separated from continental hybrids by any form of exploratory or hypothesis-driven data analysis. Anyway, it would be interesting to study their nuclear genome for genetic divergence during the time after the formation of the English Channel 7500 b.p.

Diagnosis of worker ( Tab. 1 , key). Both the continental and the British population are in nearly all characters intermediate between the parental species ( Tab. 1 ). Identification is in most cases possible by dis- criminant functions if sufficiently large nest samples are considered.

Diagnosis of gyne ( Tab. 6 ). Number and length of setae on average lower than in Formica rufa but on individual level often inseparable from either parental species.

Taxonomic comments and clustering results. This issue was thoroughly discussed in section “ Formica rufa LINNAEUS, 1761 ” (p. 152).

Biology. A brief report on the relations between the hybrid and the parental genotypes as well as on the biological properties and the probable adaptive advantage of the hybrid is given in SEIFERT (2018).