Oxypoda (Baeoglena), THOMSON, 1867

Assing, Volker, 2019, Revision of theBaeoglena species of the West Palaearctic Region (Coleoptera: Staphylinidae: Aleocharinae), Beiträge Zur Entomologie = Contributions to Entomology 69 (1), pp. 1-32 : 3-5

The subgenus Baeoglena in the West Palaearctic region

Diagnosis of subgenus: Species of relatively small size (2.0–3.5 mm). Whole body with fine and dense punctation. Pronotum large in relation to head (Fig. 40), rather strongly convex in cross-section, broadest at or near posterior angles. Head somewhat resembling that of Myllaena ERICHSON, 1837 , i.e., wedge-shaped, somewhat elongated anteriorly, and with conspicuously elongated maxillary palpi ( Fig. 60 ). Antennae (Figs 40, 60) relatively short, gradually incrassate apically, and with distinctly transverse antennomeres V–X. Abdomen (Figs 40, 60) wedge-shaped, i.e., gradually narrowed from base to apex. Sternite VIII with weakly pronounced sexual dimorphism.

: posterior margin of sternite VIII convex (not angularly or acutely produced in the middle); median lobe of aedeagus rather slender, often with small crista apicalis (e.g., Figs 1–4 ); ventral process slender in ventral view, in continental species apically blunt or truncate, rarely acute in lateral view; internal sac with a moderately long apical flagellum, with additional apical spines, and often with an apico-ventral filiform structure (“fs” in Figs 39 , 48); paramere much longer than median lobe, with very long, nearly straight, basally more or less strongly dilated, and apically very slender and straight apical lobe, basal portion often with species-specific modifications.

: posterior margin of sternite VIII weakly convex; spermatheca (e.g., Fig. 9 ) of simple (and uniform) shape, without evident modifications.

Comparative notes: Baeoglena species are best distinguished from representatives of other subgenera with elongated maxillary palpi (e.g., O. lurida , O. recondita ) by the characteristic morphology of the median lobe and the paramere of the aedeagus. Among West Palaearctic Oxypoda , the paramere most resembles that of species of the subgenus Deropoda BERNHAUER, 1902 , from which Baeoglena is distinguished by much finer punctation of the forebody, the shape of the head, a broader and shorter body with a more wedge-shaped abdomen, longer maxillary palpi, a weakly pronounced sexual dimorphism of sternite VIII, and by the internal structures of the aedeagus.

In the material examined, specimens erroneously identified as Baeoglena species, mostly belonged to Oxypoda annularis (MANNERHEIM, 1830) , some also to O. lurida , O. recondita , and other Oxypoda species. Misidentified O. annularis were even found among the Baeoglena material in the Bernhauer collection.

Wing polymorphism: Wing development was not examined systematically, but based on samples of all the species studied, O. praecox and O. kuehnelti are apparently wingdimorphic with the hind wings in the brachypterous morph of O. praecox of distinctly reduced length and in the submacropterous morph of O. kuehnelti of slightly reduced length. Oxypoda derecta is micropterous. No brachypterous or micropterous specimens were observed in the four remaining species.

Intraspecific variation: The present study revealed that the species of the West Palaearctic region exclusive of the Canary Islands are subject to remarkable intraspecific variation of all the external characters previously used for identification (body size, coloration, punctation, etc.). Intraspecific variation of colour and size is partly clinal. For instance, Iberian populations of O. fusina are usually of more or less uniformly reddish coloration, whereas specimens from Corsica are often rather dark, sometimes dark-brown with blackish head. Similarly, material of O. rectacia is more or less distinctly bicoloured in much of its range, but may also be mostly reddish in some regions or dark-brown with blackish head (especially in Cyprus).

Identification of species: In view of general uniformity combined with pronounced intraspecific variation, a reliable identification based on external characters is usually not possible. The only exception is the micropterous O. derecta from the Caucasus region. Moreover, the spermatheca may be suitable for distinguishing species groups, but is otherwise too uniform and at the same time too variable to be of any significance for an identification at the species level. The only characters allowing a reliable identification are the shape of the median lobe (shape of the ventral process and of the crista apicalis), the shapes of the apical spines and the apico-ventral filiform structure in the internal sac (“fs” in Figs 39 , 48), and in some species also certain modifications ( Figs 27, 35 ) of the basal portion of the paramere. Hence, a reliable identification requires a dissection of the aedeagus and often also an examination of its internal structures.

Diversity and zoogeography: Baeoglena is currently represented in the Palaearctic region by 20 species. Six of them have been reported from the Himalaya and Japan ( SCHÜLKE & SMETANA 2015). Their systematic status and identities are unclear, as they have not yet been revised. However, I have seen true Baeoglena species from Pakistan and Nepal, so that the subgenus is undoubtedly present also in the East Palaearctic. The vast majority of East Palaeartic Oxypoda species has been described by Roberto Pace, who may not have fully embraced Baeoglena , as can be inferred from the fact that he attributed O. giachinoi , the only West Palaearctic representative of the subgenus he described, to the subgenus Mycetodrepa . It can be concluded that an uncertain number of described East Palaearctic Baeoglena species may currently be assigned to other subgenera.

Fourteen species are at present known from the West Palaearctic region, seven of them endemic to the Canary islands Tenerife and La Gomera, and the remainder distributed in Europe, Asia minor, the Middle East, and the Caucasus region. Except for the micropterous O. derecta , all of the latter seven species are rather widespread. Baeoglena species are unknown from North Africa, except for one female-based record of uncertain identity from Morocco.

Remarkably, the distributions of the seven continental species are mostly allo- or parapatric with generally very little overlap ( Map 1 ). Such zones of narrow overlap are the south of mainland Greece ( O. nova and O. rectacia ) and Bulgaria ( O. nova and O. praecox ). The only exception from this rule is North Turkey where both O. caucasica and O. nova occur. It seems noteworthy, however, that (1) O. caucasica is much rarer in Northwest Anatolia and more common in Northeast Anatolia than O. nova , that (2) O. caucasica and O. nova were, on rare occasions, even found in the same locality, and that (3) O. caucasica and O. nova belong to different lineages.

From a zoogeographic perspective, the most interesting region is the southern Balkans ( Maps 1 , 5 ). The distributions of the three species present in this region ( O. nova , O. kuehnelti , O. rectacia ) are both remarkably parapatric and, especially in the case of O. nova , conspicuously discontinuous. The only plausible explanation for such a distribution pattern is interspecific competition among these species. Another such region with distributions parapatrically bordering on each other is South Italy, where the known distribution of O. nova is confined to Calabria and in the north limited by that of O. fusina . Here the range of O. nova is also remarkably discontinuous, with the geographically nearest populations in Croatia and the southern Balkans. Except for rare cases in North Turkey ( O. nova and O. caucasica ; see above), a syntopic occurrence of two or more Baeoglena species was never observed. This even applies to Oros Kallidromo (South Greece: Fthiotis), from where both O. nova and O. rectacia were recorded, but never in the same sample. To my knowledge, a similar example of interspecific competition clearly determining distributions in Staphylinidae as been observed only in the genus Othius STEPHENS,1829 , with closely related speciesoutcompeting each other in parts of their ranges ( O. lapidicola MÄRKEL & KIESENWETTER, 1848 – O. subuliformis STEPHENS, 1833 – O. crassus MOTSCHULSKY, 1858 ; O. subuliformis – O. wunderlei ASSING, 1997 – O. brevipennis KRAATZ, 1857 ) ( ASSING 2003). What Othius and Baeoglean species have in common, too, is that they inhabit the leaf litter layer and often occur at high densities.

The examined collections contained only little material of Baeoglena from France and none from North Italy. Material from these regions would be required to determine the western and southwestern limit of O. praecox , the northern distribution limit of O. fusina , and to clarify whether or not the mainland distribution of O. fusina is discontinuous, i.e., if the South Italian and Iberian populations are really separated by such a remarkable distance.

Intrasubgeneric affiliations: Based on the morphology of the aedeagus and of the spermatheca, the seven Baeoglena species of the West Palaearctic region exclusive of the Canary Islands belong to two lineages. The O. caucasica lineage includes two species ( O. caucasica , O. derecta ) and is characterized by a long crista apicalis of the aedeagus ( Figs 55, 61–62 ), an internal sac of the aedeagus ( Figs 55, 61–62, 64 ) with a basally weakly curved and weakly sclerotized flagellum, and a pair of fork-shaped apical structures, a relatively narrow basal portion of the median lobe of the aedeagus in ventral view ( Figs 56, 63 ), a basally rather weakly dilated apical lobe of the paramere, and a minute apical invagination of the spermatheca ( Figs 58, 66–67 ). In the second lineage, which includes the remaining five species, the crista apicalis is very small (e.g., Figs 1–4 ), the flagellum is basally strongly curved (e.g., Figs 1–4 ) and often rather strongly sclerotized, the apical internal structures are spine-shaped, the basal portion of the median lobe is larger in ventral view (e.g., Figs 5 , 15–16 ), the apical lobe of the paramere is basally often more strongly dilated, and the apical invagination of the spermatheca is larger and distinctly bell-shaped (e.g., Fig. 9 ). Among the species of the latter lineage, O. kuehnelti and O. rectacia are evidently sister species, as can be inferred from the similar shape of the ventral process of the aedeagus and from the shared presence of a distinct filiform apico-ventral structure in the internal sac of the aedeagus ( Figs 39 , 48). Oxypoda nova may be the adelphotaxon of the other four species, a conclusion supported by the strongly curved median lobe of the aedeagus, the differently shaped apex of the ventral process both in ventral and in lateral view, the extremely narrow crista basalis, and by the conspicuous modifications of the paramere.

Natural history: All species except O. praecox appear to be ecologically very similar. They inhabit the leaf litter layer of various forest, bush, and shrub habitats at a wide range of altitudes, often at high densities. The habitat requirements of O. praecox are less clear: it has

Checklist of the Baeoglena species of the West Palaearctic region

Figures

Map 1: Distributions of theBaeoglena species of the West Palaearctic region exclusive of the Canary Islands, based on revised records:Oxypoda praecox (white stars);O. fusina (black squares);O. nova (white circles);O. kuehnelti (black diamonds);O. rectacia(black triangles);O. caucasica (black circles);O. derecta (white triangles).

Figs 55–67:Oxypoda caucasica (55–58) andO. derecta(59–67): median lobe of aedeagus in lateral and in ventral view (55–56,

Figs 1–9:Oxypoda praecox from Germany (1–2, 5–9), Bulgaria (3), and Slovakia (4): median lobe of aedeagus in lateral and in ventral view (1–5); apex of median lobe of aedeagus in lateral view (6–7); paramere (8); spermatheca (9). Scale bars: 1–5, 8–9: 0.2 mm; 6–7: 0.1 mm.

Figs 37–39:Oxypoda kuehnelti: apex of median lobe of aedeagus in lateral view; “fs” = apico-ventral filiform structure. Scale bar:

Figs 23–36:Oxypoda nova from South Italy (23, 25–27) and Croatia (24, 28), andO. kuehnelti(29–36): median lobe of aedeagus in lateral and in ventral view (23–25, 29–33); apex of median lobe of aedeagus in ventral view (26, 34); paramere (27, 35; “ds” = dark structure); spermatheca (28, 36). Scale bars: 23–25, 27–33, 35–36: 0.2 mm; 26, 34: 0.1 mm.

Map5: Distributions ofOxypoda nova (black circles) andO. kuehnelti (white diamonds) in the East Mediterranean, based on revised

Figs 10–22:Oxypoda fusina from Spain (10, 17), Sardinia (11–12, 15, 19, 22), and Corsica (13–14, 16, 18, 20–21): median lobe of