S. Mahunka szerk.: Folia Entomologica Hungarica 49. (Budapest, 1988)
ZOOGEOGRAPHICAL ANALYSIS The Siberian fauna of Diplocephalus is not rich, but quite conspicuous. Out of a total of 9 species/subspecies of this genus in the region, 6 seem to be restricted to eastern Siberia ( D. cristatus angusticeps , D. marusiki, D. mirabilis , D. montanus, D. sphagnicolus , D. uliginosus). Of the remaining 3 species, D. connatus displays connections with Europe, while D. subrostratus with North America (distinctly vicariating with the European D. pici nus ); D. barbatus has a circumpolar high-Arctic pattern. As regards the outlined group of endemic Diplocephalus , it seems noteworthy that D. mirabilis and D. uliginosus are taxonomically well isolated, displaying no clear affinities with the other congeners. On the other hand, D. cristatus angusticeps and D. sphagni colus belong to a rather homogenous species group, namely the cristatus -group, richly represented in Europe, particularly in its mountainous regions (GEORGESCO 1969; THALER 1972; TANASEVITCH 1987). Interestingly, D. cristatus cristatus common both to Europe and North America seems to be absent from Siberia. The last couple of the Siberian endemics, D. marusik i and D. montanus, joins the subgenus Hemistajus Schenkel, 1934 * which also comprises the high-Arctic D. barbatus and the montane Alpine D. rostratus, reported from heights of 2700-3500 m a. s. 1. (THALER 1970). Taxonomically, this group can be split into two pairs of extremely closely related forms, i.e. D. barbatus-D. marusiki and D. rostratusD. montanus. One of the members of each pair is a Siberian endemic; the origin of the circumpolar D. barbatus is also apparently connected with the Siberian sector of the Arctic. It seems to be very likely that the evolvement of the barbatusgroup in general, with its distribution pattern being typically arcto-montane, can be postulated to have been restricted to Siberia. In other words, besides the European D. connatus reaching in the east as far as the Middle-Siberian Tableland, there are further 3 endemic Di plocephalus , D. cristatus angus ticeps, D. sphagnicolus and D. subrostratus, displaying somewhat less clear-cut affinities with Europe. On the contrary, Siberian roots seem to be traceable in one European species, D. subrostratus. Therefore, the conclusion can be drawn that the Siberian and European faunas of Diplocephalus have been developed quite autochthonously. Interexchange has been rather feeble and anisotropic; Europe seems to have served as the main source. It is noteworthy that if eastern Siberia harbours a highly peculiar (though not too rich) fauna of Diplocephalus, the Manchurian Biogeographical Region seems to be almost deficient in its representatives. Only two forms are known in this Region, the Japanese D. bicurvatus Bösenberg et Strand, 1906 (the generic allocation of which is dubious), and the Hokkaidan Diplocephalus sp. (H. SAITO, personal letter of 15. IX. 1986). Quite an opposite pattern is displayed by the genus Savignya. Out of the 12 known representatives, 6 ( S. basarukini , S. kawachiensis, S. saitoi , S. ussurica, S. yasudai and Savignya sp. ) seem to be endemic in the Manchurian Region. Siberia harbours 6 species: S. birostrum , S. borea , S. nenilini , S. zero , S. frontata and S. producta; the first of them reaches Alaska, whereas the ranges of the two latter may be called "western Siberio-European". Therefore, the richness of the regional faunas of Diplocephalus and Savignya displays distinct gradients along the row Europe-Siberia-Manchuria, which are directed, in the first case, from west to east and, in the second case, from east to west. In this connection the hypothesis can be set up that both genera have genetically been associated with the zone of nemoral broad-leaved forests, the first genus within Europe, and the second one within Manchuria. Later both have faced, during their trans-Palearctic expansion (eastwards and westwards, respectively), a very considerable barrier in the form of the harsh, boreal environment of Siberia. Penetration of this region has required from the representatives of both genera concerned particular adaptations, which promoted the evolvement of a number of endemic taxa. These adaptations seem to have been profound enough so as to almost prevent subsequent repopulations of nemoral environments, i.e. invasions of Diplocephalus into Manchuria or of Savignya into Europe. In our opinion, the subgeneric rank of Hemistajus seems to be far too overrated; we regard this complex merely as a separate species group, i.e. the barbatus-group.
