Geostiba (Sibiota), CASEY, 1906

Assing, Volker, 2017, On the Geostiba fauna of Armenia (Coleoptera: Staphylinidae: Aleocharinae), Linzer biologische Beiträge 49 (2), pp. 1075-1092 : 1078

Subgenus Sibiota CASEY, 1906 ( Map 2 )

In Armenia, Sibiota is the most speciose staphylinid taxon including exclusively micropterous, microphthalmous, and more or less locally endemic species. Including the species treated below, seven described species and one or two undescribed species are known from Armenian territory at present.

Based on available evidence, the Armenian Sibiota species are closely related ( ASSING 2016b), and they are inhabitants of the litter layer of montane forest and bush habitats. The altitudes range from 1350 to 2500 m, with the majority of specimens collected between 1700 and approximately 2100 m. Sibiota is apparently not evenly distributed in Armenia. Most of the records are from the north and from the southeast, and there are some evident gaps in the region to the west of Sevan lake and in the southwest of Armenia ( Map 2 ). The currently known distribution basically coincides with the regions that have - or had - native forests (GHREJYAN pers. comm.). The distributions of the species from North Armenia largely overlap. However, only on one occasion were two species collected in the same sample plot.

When studying the material available from the field trip in 2016 ( ASSING 2016b), a separation and identification of the Armenian Sibiota species seemed fairly straightforward. The male secondary sexual characters and the spermatheca appeared to be reliable diagnostic characters. A study of significantly more material collected in numerous additional localities in 2017, however, revealed an enormous extent of intraspecific variation particularly of the male secondary sexual characters, rendering a reliable separation and identification of the species difficult, especially when only few specimens are available. The modifications of the male tergite VII are particularly variable. Not only do they vary from completely absent (smaller males) to fully pronounced (larger males). In two species ( G. pambakica , G. tigrani ), which usually have a pair of carinae on the male tergite VII, these carinae may exceptionally even be completely fused and form a single tubercle similar to the typical condition in other species. Due to enormous intraspecific variability and at the same time considerable interspecific overlap, the modifications of the male elytra are unsuitable for diagnostic purposes. A reliable identification is further impeded by the uniformity and consequently low interspecific variation of the shape of the median lobe of the aedeagus. The only character that seems to be subject to distinct inter- and at the same time little intraspecific variation is the shape of the spermatheca.

Figures

Map 2: Distribution of Sibiota species in Armenia (black circles). Sampled localities with suitable habitats where no Sibiota was found are shown as white circles.