Systematic and biogeographical study of Protura (Hexapoda) in Russian Far East: new data on high endemism of the group

Abstract Proturan collections from Magadan Oblast, Khabarovsk Krai, Primorsky Krai, and Sakhalin Oblast are reported here. Twenty-five species are found of which 13 species are new records for Russian Far East which enrich the knowledge of Protura known for this area. Three new species Baculentulus krabbensis sp. n., Fjellbergella lazovskiensis sp. n. and Yichunentulus alpatovi sp. n. are illustrated and described. The new materials of Imadateiella sharovi (Martynova, 1977) are studied and described in details. Two new combinations, Yichunentulus borealis (Nakamura, 2004), comb. n. and Fjellbergella jilinensis (Wu & Yin, 2007), comb. n. are proposed as a result of morphological examination. Keys to species of the genera Fjellbergella and Yichunentulus are given. An annotated list of all species of Protura from Russian Far East is provided and discussed. Widely distributed species were not recorded in this area. This may be because of the high sensitivity of Protura to anthropogenic impact and low dispersal ability of the group.


Introduction
The Protura are minute soil-dwelling arthropods with more than 800 species known so far in the world (Bu et al. 2012, Szeptycki 2007, Shrubovych 2014. They have been a group of focus in the study of the evolutionary history of Hexapoda and Arthropoda because of their basal phylogenetic position (Chen et al. 2011, Luan et al. 2005, Mallatt et al. 2010, Meusemann et al. 2010. The Russian Far East (abbreviated as RFE throughout the present paper) occupies an area of 3,016 thousand sq. km. and extends from Wrangel Island southwards to Khasan Lake (Fig. 1). Forests occupy 39% of the territory and predominate in Primorsky Krai, Amur Oblast, Sakhalin Oblast, and Khabarovsk Lrai. The insect fauna is associated with mixed broadleaved-coniferous forests in the south of RFE. About 31,500 species of insects have been recorded in the RFE so far where Eastern-Asiatic and local species make the most part of the fauna (Storozhenko et al. 2002). Eighteen species of Protura have been recorded in the RFE. Compared to the neighbouring regions, 34 species of Protura have been recorded in Northeast China (Bu et al. 2013), 20 species were found in Korea (Lee and Rim 1988) and 88 species are recorded in Japan (Kaneko et al. 2012). The only seven publications on Protura of the RFE are: Martynova who described Imadateiella sharovi (Martynova, 1977) from Magadan; Nakamura (2004) who reported eight species from Khabarovsk Krai; Shrubovych (2009Shrubovych ( , 2010Shrubovych ( , 2014 and Bernard (2012, 2013) who studied the Protura materials from different collections of Primorsky Krai and Sakhalin Island and nine species have been added to the proturan fauna of RFE.
Much of the material was collected by us during a joint Chinese-Russian expedition in autumn of 2011 which was a part of study of the biodiversity of basal Hexapoda of Pacific coast of Asia (2011)(2012). Several localities in southern RFE were searched: three locations of Primorsky Krai (Shkotovsky, Khasansky, and Lazovsky districts) and one of Khabarovsk Krai (Vaninsky district). Other materials collected by M. Potapov et al. (2009M. Potapov et al. ( -2010 were also used. Around a thousand individuals are included in our study. Based on this material in all 25 species were identified, including 3 new species and 10 species newly recorded for the RFE. For another 12 species we give the new data on their distribution. The genera Fjellbergella and Yichunentulus are revised and rediagnosed, and the keys to species of the two genera are given.

Materials and methods
The specimens were collected by Tullgren funnels using fast extraction with strong heating of samples during several hours. All specimens were mounted on slides in Hoyer's medium and dried at 60 °C. Specimens were identified and drawn with the aid of a NIKON E600 phase contrast microscope. The photos were taken by digital camera Nikon DXM1200. Type specimens are deposited in the Shanghai Entomological Museum (SEM), Institute of Plant Physiology & Ecology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, and Moscow State Pedagogical University (MSPU).
Etymology. The species is named after Krabbe Peninsula where the type specimens were collected. Distribution. Known only from type locality. Diagnosis. Baculentulus krabbensis sp. n. is characterized by extremely long sensilum b on foretarsus, sensillum a' located distal to t1, sensillum b' absent, eight A-setae on tergite VI and VII, presence of P3a on tergite VII, and special female genitalia with short basal apodeme.

Remarks.
We placed the present new species in the genus Baculentulus because the baculiform sensillum t1 on foretarsus, reduced labial palpus with three setae and one sensillum, smooth calyx of maxillary gland, reduced striate band, two pairs of anterior setae on mesonotum and metanotum, abdominal appendages II and III each with two setae of different length, and only 4 setae on sternite VIII. It is similar to B. samchonri (Imadaté & Szeptycki, 1976) from North Korea in having eight A-setae on both tergites VI and VII, absence of sensillum b' and extremely long sensillum b on foretarsus. They can be distinguished by the posterior setae on tergite VII (9 pairs of P-setae with P3a present in B. krabbensis sp. n. vs. 8 pairs of P-setae with P3a absent in B. samchonri), the anterior setae on tergite I (6 A-setae in B. krabbensis sp. n. vs. 4 in B. samchonri), the length of sensillum f (extremely long and surpassing the base of claw in B. krabbensis sp. n. vs. short and not reaching base of claw in B. samchonri), and the shape of female squama genitalis (basal apodeme very short in B. krabbensis sp. n. vs. basal apodeme in moderate length in B. samchonri).
Etymology. The species is named after Lazovsky Nature Reserve where the type specimens were collected. Distribution. Known only from type locality. Diagnosis. Fjellbergella lazovskiensis sp. n. is characterized by three pairs of anterior setae on tergites II-V which is different to any other members of the genus, four pair of anterior setae, nine pairs of posterior setae on tergite VII, foretarsal sensilla b, c and d located in subequal level, b shorter than c, and tergite IX and X with 14, 12 setae respectively.
Remarks. The present species is located in the genus Fjellbergella because three setae on abdominal legs, labial palpus with two-branched terminal tuft of setae, claviform sensillum t1 on foretarsus, reduced striate band, two pairs of anterior setae on mesonotum and metanotum, and 4/2 setae on sternite VIII. Fjellbergella lazovskiensis sp. n. is similar to F. tuxeni Nosek, 1980 from Alaska in having 8 A-setae on tergite VII and presence of P1a on tergite I-VII. They can be distinguished by the chaetotaxy of tergite IX and X (14 and 12 setae in F. lazovskiensis sp. n. respectively vs. 12 and 8 setae in F. tuxeni), length and location of foretarsal sensilla b and c (b shorter than c and they located at the same level in F. lazovskiensis sp. n. vs. b and c subequal in length and c located lower than b distinctly in F. tuxeni), shape and length of sensillum a' (broad and reaching base of sensillum b' in F. lazovskiensis sp. n. vs. slender and far surpassing base of sensillum b' in F. tuxeni), and shape of claw of foreleg (absence of inner flap in F. lazovskiensis sp. n. vs. presence in F. tuxeni). In addition, the new species has only 6 anterior setae on tergites II-V contrary to two other members of this genus, which have 8 anterior setae. Description. Adult body length 1200-1350 µm (n=5). Head (Fig. 6A). Ovate, length 120-130 µm, width 70-80 µm. Setae d6 present, sd4 and sd5 short sensilliform. Setae d6 11 µm, d7 10 µm and sd7 18 µm in length. Clypeal pore cp and frontal pore fp present. Pseudoculus round, length 7-8 µm, with short posterior extension, PR=16 (Fig. 6B). Calyx of maxillary gland smooth, without any appendix, blind end split into two leaves, posterior filament 16-17 µm, CF=7-8 (Fig. 6C). Maxillary palpus with two tapering sensilla, dorsal snsillum is evidently longer than lateral one (Fig. 6D). Labial palpus completed, with one-branched terminal tuft of setae, with three setae and one lanceolate basal sensillum (Fig. 6E).  (16 µm), not reaching base of γ3, c reaching base of f and in subequal level to b, d located higher than b and c, e long and reaching base of claw (30 µm), f slender, g broad and short (18 µm). Interior sensilla a' broad, b' slender and reaching base of α6, c' nearly reaching base of claw. Relative length of sensilla:
Tergites I and VIII with pores psm only, II-V with pores psm and al, VI-VII with pores psm, al and psl, IX-XI without pores, XII with single medial pore. Sternites I-IV without pores, V and VI each with 1+1 posterior pores anterior to seta P1 and 1+1 anteromembranal pores, VII with single posterior pore asymmetrical located left or right and 1+1 anteromembranal pores, VIII-XI without pores, XII with 1+1 pores al.
Etymology. The species is named after Dr. V. Alpatov who accompanied us during our scientific trips.
Distribution. Known only from type locality. Diagnosis. Yichunentulus alpatovi sp. n. is characterized by the presence of sensillum b' on foretarus and short sensilum b on foretarsus, 6 anterior seate on tergites IV-V, swelled sensillum a', presence of pores psl only on tergites VI and VII, and female squama genitalis with moderate basal apodeme and pointed acrostyli.
Remarks. The present species is located in the genus Yichunentulus because the labial palpus with one-branched terminal tuft of setae, with three setae and one lanceolate basal sensillum, the baculiform sensillum t1 on foretarus, reduced striate band, two pairs of anterior setae on mesonotum and metanotum, 4/2 setae on sternite VIII, and abdominal appendages II and III each with two setae of different length. Yichunentulus alpatovi sp. n. is close to the type species Yichunentulus yichunensis Yin, 1980 in having short sensillum b and identical body chaetotaxy. However, it can be easily distinguished from Y. yichunensis and Y. borealis (Nakamura, 2004), comb. n. by the presence of sensillum b' on foretarsus. It also differs from Y. yichunensis in the length of sensillum e (extremely long in Y. alpatovi sp. n. vs. short in Y. yichunensis) and sensilla c' (long and surpassing base of δ6 in Y. alpatovi sp. n. vs. short and only reaching base of β7 in Y. yichunensis). It differs from Y. borealis in the chaetotaxy of tergites IV-V (each with 6 A-setae in Y. alpatovi sp. n. vs. 8 in Y. borealis), shape of sensillum a' (slightly broad and as long as sensillum a in Y. alpatovi sp. n. vs. distinctly swell and shorter than sensillum a in Y. borealis), and the body porotaxy (pore psl present on tergites VI and VII only and sternites I-IV without pores in Y. alpatovi sp. n. vs. psl present on tergites III-VII and sternites II and IV each with 1+1 anteromembranal pores in Y. borealis).
Diagnosis. Abdominal appendages II and III each with 3 setae, mesonotum and metanotum each with two pairs of anterior setae, foretarsal sensillum t1 claviform, sensillum b' present, t3 willow-leaf shaped, sensillum b' present, labial palpus with terminal tuft of setae, striate band on abdominal segment VIII well developed, and sternite VIII with 4/2 setae or with 4 setae only.
Remarks. The genus Acerentulus has 47 species described in the world and most from Europe (Szeptycki 2007;, and only five species (A. kisonis Imdadaté, 1961, A. keikoae keikoae Imdadaté, 1988, A. keikoae capillatus Imdadaté, 1988, A. omoi Imdadaté, 1988and A. sinensis Wu & Yin, 2007 were recorded in East Asia so far. Acerentulus kisonis Imdadaté, 1961 is new to RFE and very rare in the samples like in Japan (Imdadaté 1988), which has single individual present in hundreds of specimens.  Nosek, 1980. Diagnosis. Mesonotum and metanotum each with two pairs of anterior setae, labial palpus with two-branched terminal tuft of setae, sensillum d located near t2 insertion, abdominal appendages II and III each with three setae, foretarsal sensillum t1 claviform, sensillum b' present, striate band on abdominal segment VIII reduced and sternite VIII with 4/2 setae.

Genus
Remarks. The genus Fjellbergella containes only two species so far: Fjellbergella tuxeni Nosek, 1980from Alaska and F. uteorum Shrubovych & Bernard, 2013from Colorado (Nosek 1980Shrubovych and Bernard 2013). Except that, one species of the similar form Brasilidia jilinensis Wu & Yin, 2007 was also found from Northeast China. However, the species of genus Brasilidia has reduced labial palpus without tuft, and all of them occurred in tropical area (South America and India). After recheck the type specimens, we confirmed that Brasilidia jilinensis has reduced striate band, the labial palpus with reduced tuft (two-brunched), and three setae on abdominal appendages II and III which indicate it is a member of Fjellbergella. Thus we transfer B. jilinensis to the genus Fjellbergella as a new combination Fjellbergella jilinensis (Wu & Yin, 2007), comb. n. Plus the new species described in present paper, the genus Fjellbergella contains 4 species. They can be distinguished by the following key.  Yin, 1980. Diagnosis. Mesonotum and metanotum each with two pairs of anterior setae, abdominal appendages II and III each with two setae, labial palpus with one-branched terminal tuft of setae, with 3 setae and 1 sensillum, foretarsal sensillum t1 baculiform, sensillum b' absent or present, sensillum a' located distal to t1, maxillary gland simple and without appendages, sternite VIII with 4/2 setae, striate band on abdominal segment VIII reduced, and sternites II-VI each has 1+1 membranal pores.

Key to the species of the genus
Remarks. The genus Yichunentulus Yin, 1980 has only one species described from Heilongjiang, Northeast China (Yin 1980). After compare Baculentulus borealis Nakamura, 2004 with congeners, we find two important characters of this species: presence of one-branched terminal tuft of setae and 3 seate on labial palpus and 4/2 setae on sternite VIII are different to any other species of the genus Baculentulus. On the contrary, those two characters match well with genus Yichunentulus. Two specimens of B. borealis newly collected from type locality are also studied. We proposed to transfer Baculentulus borealis to the genus Yichunentulus as a new combination Yichunentulus borealis (Nakamura, 2004), comb. n. The three species of the genus Yichunentulus can be distinguished by the following key. Notes. Body length 1300-1380 µm, foretarsus length 110 µm. We studied the new materials of Y. borealis collected from type locality and redescribe the head chaetotaxy and body porotaxy. Head with d6 seta present, sd4 and sd5 sensilliform. Pronotum and prosternum without pores. Mesonotum with pores sl and al, metanotum with pores sl only. Mesosternum and metasternum each with single medial pore. Tergites I and VIII with pores psm only, II with pores psm and al, III-VII with pores psm, al and psl, IX-XI without pores, XII with single medial pore. Sternites I with single medial pore, II-IV without 1+1 anteromembranal pores, V and VI each with 1+1 posterior pores anterior to seta P1 and 1+1 anteromembranal pores, VII with single posterior pore asymmetrical located left or right, VIII-XI without pores, XII with 1+1 pores al.

Abdomen. Abdominal chaetotaxy given in
Tergites I and VIII with pores psm only, II-VII with pores psm and al, IX-XI without pores, XII with single medial pore. Sternites I and VI without pores (Fig. 8H, L), II-V each with single medial pore (Fig. 8I, J), VII with single anterior pore asymmetrical located left or right on the line (Fig. 8M), VIII-XI without pores, XII with 1+1 pores al.

Segment
Remarks. Imadateiella sharovi (Martynova, 1977) is the first species of Protura described in RFE. We give the redescription of Imadateiella sharovi basing on our vast material since it shows minor differences from the redescription of Shrubovych (2014) (labial palpus , length of sensilla b, e and t2 on fortarsus and pores on sternite I). The male squama genitalis is also described for the first time. The variation on labial palpus is also uncommon -15 specimens from samples 27 and 24 have labial palpus with reduced terminal tuft of setae (Figs 7D, 8B) while other 5 specimens from samples 26, 30 and 32 have it well developed (Figs 7E, 8C). According to the redescription of Shrubovych (2014), the type specimens have well developed labial palpus. We treat all our populations as belonging to one variable species.
The description is given above.

Fjellbergella lazovskiensis sp. n.
The description is given above.

Yichunentulus borealis
The description is given above.

Family Nipponentomidae Yin, 1996
Callientomon chinensis Yin, 1980 Material examined. Distribution. Japan; Korea; Russia (Far East: Khabarovsk Krai; Prmorsky Krai). It was already recorded from Ussuriysky and Shkotovsky areas by Shrubovych and Bernard (2012) and we found it also occurred in Khabarovsk Krai. (Martynova, 1977) The description of the new material from Russian Far East is given above.

Discussion
The 31 species of Protura recorded from RFE so far are listed in Table 5. They belong to 12 genera and 4 families Berberentulidae, Acerentomidae, Nipponentomidae and Eosentomidae, half the species are known only from the RFE. The most species are representatives of Acerentomidae and Nipponentomidae, each with 11 species (70%). The family Eosentomidae is rare and consists of only 3 species. Palearctic genera Yamatentomon, Imadateiella, Yichunentulus, Callientomon and Holarctic genera Filientomon, Fjellbergella, Nipponentomon, Tuxenentulus, Verrucoentomon are the dominant taxa composing 66% of all species.
Compared with neighbouring regions, the Protura fauna of RFE is closely related to the fauna of Northeast China, Korea, and Japan, sharing 11, 7, and 11 species with each respectively (Bu et al. 2013, Imadaté 1974, Lee and Rim 1988, Szeptycki 2007, Yin 1999 (Table 5).
The biogeographical composition of Russian Far East, including Primorsky Krai and Khabarovsk Krai, has been described for many arthropods (Belyaev 2011, Kupyanskaya 2011, Loktionov 2011, Mutin 2011, Nemkov 2011, Proshchalykin 2011, Ryabinin 2009, Storozhenko 2011, Teslenko 2007, Wang et al. 2009). Strict detailed comparison of different taxa is not possible since the authors usually used different although similar chorological nomenclatures. Generalizing the published data mentioned above, the Primorsky Krai, the region in which the Protura was mostly studied by us, shows a high portion of species
exact biogeographical state of them can not be understood for now, especially in group of "local" species (see above). At a species level, the unexpected thing is that neither Holarctic nor Palearctic species of Protura is found by us. In invertebrates the Holarctic and trans-Palearctic groups of species take the considerable portion, from 10 to 55% (Table 6). Figure 10. Distribution of typical East-Palearctic species of RFE. In addition to locations listed in the text, other records are used after Imadaté (1974), Lee and Rim (1988), Szeptycki (2007) and Yin (1999). Only three widely distributed species of Protura are known so far: Acerentulus confinis (Berlese, 1908), Berberentulus capensis (Womersley, 1931), and Gracilentulus gracilis (Berlese, 1908). These species are cosmopolitans in the broad sense, but their distribution is not fully understood (Szeptycki 2007). Two of them (A. confinis and G. gracilis) are recorded from many European countries and, more rarely, from few other regions (Africa, North America, Australia, and New Zealand). Berberentulus capensis is scarcely recorded in warmer regions of the whole world. The reliable records of these species are unknown in Eastern Asia and, particularly, in RFE, but their presence is possible.
Several reasons can be proposed to explain the absence of the Holarctic and Palearctic species of Protura: -High sensitivity of Protura to anthropogenic impact (Andrés 1999, Hågvar and Abrahamsen 1990, Niijima 1976, Parisi et al. 2005, Rusek 2007). The species preferring the disturbed sites are unknown in this group of animals. As a rule, in disturbed sites the portion of wider distributed and generalist species is greater while the endemic species decline, thus we can expect higher portion of endemic species in fauna of Protura. Strong negative effect of human practices on endemic species was shown, for instance, for the Collembola, the group of arthropods closely related to Protura (Cassagne et al. 2006, Deharveng 1996. -In the Northern hemisphere, this group sharply declines at higher latitudes. In many groups of animals the portion of endemic species increases southwards in Eurasia (Chernov 1975) therefore we can assume higher endemism in Protura. The sharp decline from south to north along global transect of RFE is, however, shown for the most taxa of animals -for example, according to generalized analysis of Chernov et al. (2011) number of species of all insects in Chukotka (the most northern region) is about 20 times less than in Primorsky Krai (the most southern region).
-Low dispersal ability of Protura. This reason is possible but could not be substantiated since widely distributed species are known in other groups with low active movement but with high possibility of passive carriage (Coulson et al. 2002, Thibaud 2007. The passive carriage is unknown in Protura but only supposed by Yin et al. (1994).
In conclusion, the Protura appear to be a group with a low level of biogeographical "noise" (ruderal species), with high endemism and are candidate organisms for more detailed biogeographical analysis when more information is available for other regions.