Folsomia inoculata Stach, 1947

Potapov, Mikhail, Hasegawa, Motohiro, Kuznetsova, Natalia, Babenko, Anatoly & Kuprin, Alexander, 2018, Isotomidae of Japan and the Asiatic part of Russia. I. Folsomia ' inoculata' group, ZooKeys 750, pp. 1-40 : 27-30

Folsomia inoculata Stach, 1947 Figs 7, 81-89, 90

Syn.: Folsomia ezoensis Yosii, 1965

Type material of J. Stach.

Two adult females from the collection of J. Stach labelled as "Polonia, Czarhohora, 28.VI.1922, leg. Smraczynski. F. inoculata ". Kept in the Institute of Systematics and Evolution of Animals, Polish Academy of Sciences in Krakow, Poland.

Additional material.

East Asia. Japan, Honshu Island. Nagano Prefecture, E Chino city, Kitayama, surroundings of Mugikusa Hutte, 2255 m alt., 36.0404°N, 138.3679°E, coniferous green moss forest with Tsuga , north slope, litter, 10.viii.2016; ibidem, 36.0653°N, 138.3410° E, stony meadow, grass turf, 11.viii.2016, coll. M. Potapov and N. Kuznetsova; Hokkaido Island. Japan, Hokkaido Island, Shiretoko Peninsula, trail to Mont. Rausu, different forests, litter and rotten wood, 19.viii.2016, from 350 to 1100 m alt.; Shiretoko Peninsula, nearby Shiretoko Pass, 593 m alt., 44.0617°N, 145.0913°E, stony mixed forest with Betula ermanii , 17.viii.2016; Shiretoko Peninsula, surroundings of Utoro, 500-year mixed forest, rotten wood, 20.viii.2016, 97 m alt., 44.1006°N, 145.0584°E, coll. M. Potapov and N. Kuznetsova.

China: Jilin Province, 5.viii.2009, Nearby Tian Lake, Changbai Mts., 1718 m alt., coniferous forest, soil under tree, coll. D. Wu.

Far East of Russia, Primorsky Krai, Shkotovsky District, Pidan Mount, ~800 m alt., rotten wood, 20.ix.2004, coll. M.Potapov, L.Deharveng, R.Pomorski, and A. Bedos; Shkotovsky District, trail to Mont. Khualaza, deciduous forest, rotten wood. 21.vii.2016, coll. M. Potapov and N. Kuznetsova; Sakhalin, Kholmsky District, South Kamysh Ridge of the Western Sakhalin Mountains, Spamberg Mt., mixed forest on slope, litter, 15.vi.2017, coll. A. Kuprin; Yuzhno-Sakhalinsk, Susunaysky Range, Chekhov peak, litter on top, 16.vi.2017, coll. A. Kuprin; Khabarovsky Krai, Sikhote-Alin Range, Nanaisky District, ~ 15 km N road Khabarovsk-Sovetskaya Gavan, Golaya mount. massif, Studeny Pass, coniferous forest, rotten wood, 28. vi– 07.vii.2017, coll. A. Brinev; Sikhote-Alin Range, Vaninsky District, nearby Vysokogorny, valley of Mulinka River, rotten wood, ~ 600 m alt., 29.ix.2011, coll. M. Potapov; Vaninsky District, nearby Datta, coastal larch-wood, 28.ix.2011, coll. M. Potapov; Kamchatka, Elizovsky District, vicinities of Malki, 53.3219°N, 157.5502°E, 260 m alt., Betula ermanii forest, litter and rotten wood, 26.vi.2012, coll. M. Potapov and N. Kuznetsova.

Additionally, specimens from 32 localities, i.e. Ukraine (Skolevskiye Beskids), Bosnia (Perucica), Germany (Helgoland Isl., Zittau Mts, and Bavarian Alps), France (Mont Blanc), Russia (Komi, Middle Ural Mts.), Caucasus (Teberda, Guzeripl, Tsey, Khosta, Krasnaya Polyana, Lagonaki, and several other locations in Western part of North Caucasus), Armenia (Dilizhan), Georgia (Batumi, Kutaisi), Turkey (one unprecise locality, coll. L. Deharveng), Kazakstan (West Altai), Russia, West Siberia (Altai Mts.) and East Siberia (Podkamennaya Tunguska, Shira, W Sayan Mts), were examined.

Description.

Body stout, very characteristic, head massive, with swollen front (Fig. 81) and brown robust mouth parts. Size from 0.9 to 1.7 mm. Without pigmentation. Cuticle with fine hexagonal primary granulation. PAO slender, usually constricted, often with small "inner denticles" (Figs 83-85) (see also the Discussion part). PAO length 1.1-1.7 as long as width of Ant.I and 1.3-2.1 as long as inner unguis length. Labium complete, guard setae e7 present, three proximal and four basomedian setae. Mandible and maxillary head strongly sclerotized. Ventral side of head with 4+4 postlabial setae. Ant.I with 13-15 common setae, two ventral s-setae (s) and three basal short micro s-setae (bms). Ant.II with three bms and one latero-distal s, Ant.III with one bms and with five distal s (including one lateral), without additional s-setae.

Common setae short. Sensillary formula as 43/22235 (s). Micro s-setae as 10/100 (ms). Tergal s-setae short and distinct. Medial s-setae on Th. II–III in front of p-row, on Abd. I–III in posterior position, between Md and Mdl. Abd.V with five s-setae arranged as three short (as, accp1, accp2), one lateral long and tubular, and one latero-ventral, short ( ‘3+1+1’ pattern) (Fig. 82), accp3 s-setae much longer than accp2 (accp2:accp3=0.5-0.9). Macrosetae smooth and short, 2,2/3,3,3, medial ones on Abd.V shorter than dens, with the whole range of ratio Mac: dens as 0.6-1.1, and 1.9-3.1 times longer than mucro. Foil setae at the tip of abdomen absent. Thorax with 2 –4+2– 4 subequal setae at ventral line.

Unguis of normal shape, without lateral and inner teeth. Empodial appendage usually longer than half of unguis (0.5-0.7). All tibiotarsi with additional setae: 23-27 setae on legs I–II and>30 setae on leg III, as a whole. Upper and lower subcoxae of legs I–III with 0,1/5 –7,8–12/7–9,8– 10 setae, respectively. Coxae of leg I with two front setae. Ventral tube with 4 –5+4– 5 latero-distal and 6-7 posterior setae (with four in distal transversal row), anteriorly without setae. Tenaculum with 4+4 teeth and one or two setae. Anterior furcal subcoxae with 11-16, posterior one with four setae. Anterior side of manubrium with 2+2 setae (rarely 2+3 or 1+2). Posterior side of manubrium with 4 –5+4– 5 latero-basal, two apical setae (ap), 2+2 setae in distal transversal row, pair of lateral setae present or absent (see the Discussion part), and 4 –5(3–6)+4–5(3– 6) in central part. Dens normally with 10-14 anterior setae (the whole range is 8-16). Posterior side of dens crenulated and with four setae: three (very rarely two) basal and one at the middle, no subapical setae. Mucro bidentate. Ratio of manubrium: dens: mucro = 3.1-4.9: 2.4-4.3: 1.

Remarks.

Folsomia inoculata is a rather peculiar species due to several characteristics. On Abd.V the differentiation of s-setae is unique: accp3-s is well-marked, tubular, and longer than three shortened and thin s-setae of "dorsal triplet" (shown in detail on fig.14 in Potapov and Greenslade 2010). The furca is of middle size, in an intermediate position between short-furcated ' tatarica ' and long-furcated ' macrochaetosa ' subgroups; posterior chaetotaxy of the dens is uncommon: seta at the middle present whereas subapical one normally absent (fig. XIV, 6 in Stach, 1947), the latter, although often small, is present in all other species of the ' inoculata ' group. Appearance of the species is rather specific enabling its recognition under low magnification (Fig. 81).

Available vast material on this species shows a wide variation in several characters (chaetotaxy of manubrium and dens, shape of PAO, body length) which, however, are individual or population-dependent and does not indicate several species.

According to the original description, PAO is not constricted in F. inoculata , which was also shown in associated figures by Stach (1947, figs XIV, 7 and XIV, 8). This peculiarity was a reason for Niijima and Hasegawa (2011) to retain F. ezoensis Yosii, 1965 (described from Japan, PAO constricted) and F. inoculata Stach, 1947 (described from Poland, PAO not constricted) as two separate species. In our material, PAO is normally constricted in both western and eastern Palearctic (incl. Japan) while the character continuously varies depending on the specimen being, in fact, not constricted in an extreme variant (Fig. 83). A constricted PAO that is unlike the original description was also indicated for European populations by Martynova (1973), Schulz (1999), and Fjellberg (2007).

The modern detailed description of the species is given in Fjellberg (2007). Among other characteristics, a reduction of dorsal chaetom of manubrium was stressed, particularly lateral pair (l2) lost, only one pair of setae was shown in pr- and m-groups (fig. 23 B–C in Fjellberg 2007). Such chaetotaxy was found by us only in specimens from Helgoland (NW Germany, coll. J. Schulz) (Fig. 86). Specimens from other localities normally have a pair of lateral setae and two or more pairs of setae at least in pr-group (Fig. 88). The presence of lateral setae l2 is not stable; few individuals missing them on both sides (sometimes asymmetrically) were recorded by us in the North Caucasus (Fig. 87), Germany, France, and Japan. Thus, a wide variation of chaetotaxy of posterior side of manubrium can be concluded for F. inoculata .

Size of the body ranges between 0.9 and 1.7. Specimens from eastern populations appears to be smaller than in western ones, but the whole variation is strongly overlapping (0.9-1.5 vs 1.1-1.7 mm, respectively).

The performed multivariate analysis of metric morphology did not reveal any irregularities, and noticeable differences between eastern and western populations were not detected (Fig. 89). Nevertheless, individuals of a particular population often resemble each other and this may be partly explained by the same phenological condition.

The species is facultatively parthenogenetic and its populations mostly consist of females. Males were seen by us only in four “central” localities: in Middle Ural mountains (upper flow of Pechora River), East Siberia (Podkamennaya Tunguska), Caucasus (Aibga Range), Turkey, and Kazakstan (West Altai).

Distribution and ecology.

The species is widely distributed in the region (Fig. 90) and was listed in catalogues of Japanese Collembola ( Yosii 1977; Furuno et al. 2000), often as its junior synonym F. ezoensis . Known from Osaka ( Natuhara et al. 1994), Tokyo ( Iwanami et al. 1980), Hokkaido ( Yosii 1965, Suma 1997, Hishi et al. 2012), Shigayama ( Tamura and Chiba 1977), Kyoto ( Takeda 1995; Fujii and Takeda 2012), Aomori Pref. ( Yamauchi and Suma 1999, 2009). For Russia, F. inoculata was recorded in Sakhalin ( Kurcheva 1977; Solntseva and Molodova 1979), Ussuriyski Reserve and Kaimanovka ( Kutyreva 1979, 1984, as F. ezoensis ), Ussuriysk ( Kutyreva 1988), and Kunashir Island ( Potapov and Marusik 2000). In the revision of Folsomia of Russia the species was recorded in the Caucasus and the south of West Siberia ( Martynova 1973).

Distributional range of F. inoculata appears to be restricted to the Holarctic. In the Palearctic we still have not seen specimens from the eastern areas of East Siberia, such as Buryat Republic and Amurskaya District, despite intensive collections in appropriate sites. Thus, all populations can probably be divided to ‘western’ and ‘eastern’ which are inseparable by morphology for the present. In Scandinavia and the westernmost part of Europe F. inoculata is very rare and appears to be an alien species (absent, for example, in the Iberian Peninsula). In the Nearctic, the species is also infrequent although it occurs at least on the Pacific coast of USA (Oregon, Cascade Range, coll. A. Smolis, our identification, new record). Folsomia inoculata does not occur in the Arctic; the northernmost record is north-east corner of Komi Republic (67.50°N, NE European part of Russia) ( Babenko et al. 2017).

The species often occurs in forest litter while apparently preferring rotten wood where it can be very abundant. Folsomia inoculata is the most dendrophilous species of the ' inoculata ' group and, very likely, in the genus, having associated shape of body and crushing mouth parts. The species is also sporadically recorded in specific sites enriched by organic matter.