Yalongaphaenops erwini gen. et sp. nov., the world's most high-altitude hypogean trechine beetle from China (Coleoptera, Carabidae, Trechinae) Author Belousov, Igor A. All-Russian Institute of Plant Protection, Podbelskogo 3, 189620, St. Petersburg, Pushkin, Russia ibelous@yandex.ru Author Kabak, Ilya I. https://orcid.org/0000-0002-5549-6539 All-Russian Institute of Plant Protection, Podbelskogo 3, 189620, St. Petersburg, Pushkin, Russia text ZooKeys 2021 2021-06-16 1044 197 220 http://dx.doi.org/10.3897/zookeys.1044.62572 journal article http://dx.doi.org/10.3897/zookeys.1044.62572 1313-2970-1044-197 D6810E58261E4852887B167E07A68A9C 637074ECD8D7523A90E56E022BF1B99C Yalongaphaenops erwini sp. nov. Figures 1 , 2-6 , 7, 8 , , 9 Material examined. Holotype : China • 1(1) male, with label data " China , Sichuan Province , SW Mianning Town ; 28°15'27"N , 101°43'51"E ; H = 3805 m a.s.l. ; 11.07.2011 ; Belousov & Kabak leg." (ZIN). Paratypes . 2(1) males (one male teneral) with same data as holotype (CBK). Diagnosis. Since Y. erwini gen. et sp. nov. is the only known species of the genus, and it is difficult, for the moment, to give a consistent species diagnosis different from that of the genus. However, the combination of the highly specialized, barrel-like shape of pronotum with rather short appendages (antennae only marginally longer than elytra), and only one pair of pronotal setae may be of major importance for species identification. Description. Body length 5.15-5.21 mm. Forebody narrow, head slightly narrower and much longer than pronotum, elytra rather large, with distinct humeri and subconvex disk (Fig. 1 ). Legs and antennae thin and rather long. Amber-reddish with paler testaceous elytra and three or four distal antennomeres; 4-6 basal antennomeres rather dark. Legs reddish amber, with vaguely obscured femora; first tarsomere of all legs noticeably darker than the ultimate one, which is rather pale yellowish. Microsculpture of dorsum distinct, surface matte. Mesh pattern of microsculpture strongly varying on different parts of head from large shallow isodiametric cells on convex parts of frons and occiput (Fig. 4 ), to markedly transverse coarse cells in impressed portions of head. Pronotum with rather regular microsculpture consisting of clearly transverse meshes (Fig. 5 ). Microsculpture of elytra (Fig. 6 ) more irregular, consisting of shallow very transverse cells, strongly varying in shape depending on their location in respect to striae and setiferous pores. Microsculpture of underside rather shallow, consisting of transverse meshes. Proportions of the body are given in Table 1 . Table 1. Morphometric characteristics of Yalongaphaenops erwini gen. et sp. nov. Abbreviations: AL - length of antennae; BH - height of body, i.e., maximum thickness of abdomen with elytra in lateral view; EL - length of elytra; EW - width of elytra; HW - width of head; L2 - length of antennomere 2; L3 - length of antennomere 3; PA - width of pronotum between anterior angles; PB - width of pronotum at base; PL - length of pronotum; PW - maximum width of pronotum; TaL - length of hind tarsus; TiL - length of hind tibia; W3 - width of antennomere 3; PSa - distance from anterior margin of pronotum to anterior lateral seta of pronotum; D1 - distance from the scutellum apex to level of anterior discal setiferous pore of the left elytron; D2 - distance from the scutellum apex to the level of posterior discal setiferous pore of the left elytron; D3 - distance from the scutellum apex to the level of preapical setiferous pore of the left elytron; U1-8 - distance from the scutellum apex to the level of the corresponding umbilicate pore of the left elytron.

Index	Range	Index	Range	Index	Range
PW/HW	1.08-1.09	L3/L2	2.01-2.11	(U1/EL) x 100	11.9-13.0%
EW/HW	2.30-2.36	EL/BH	2.70-2.82	(U2/EL) x 100	17.0-18.3%
PL/PW	1.18	TiL/TaL	1.42-1.51	(U3/EL) x 100	21.4-24.0%
(PSa/PL) x 100	19.6-22.8%	EL/EW	1.64-1.66	(U4/EL) x 100	31.6-34.6%
PW/PB	1.47-1.50	EW/PW	2.13-2.16	(U5/EL) x 100	60.3-62.0%
PA/PB	1.05-1.12	(D1/EL) x 100	22.1-23.4	(U6/EL) x 100	69.1-70.2%
AL/EL	1.14-1.15	(D2/EL) x 100	51.9-52.3	(U7/EL) x 100	82.2-83.2%
L3/W3	3.65-4.10	(D3/EL) x 100	83.2-84.2	(U8/EL) x 100	90.0-90.1%

Head (Fig. 2 ) very large, subparallel-sided, with maximum width markedly before mid-length, gradually narrowed posteriad. Frontal furrows incomplete, reaching approximately level of posterior supraorbital setae, unevenly arcuate and impressed, becoming deeper near clypeal and parietal impressions, the latter distinct. Usually two supraorbital pores on each side of head, in the holotype: two posterior supraorbital pores on the right side (thus, three pores on one side and two on the other); anterior supraorbital pore moderately foveolate, posterior one slightly so, located in lines barely convergent posteriorly (Figs 7 , 8 ). Labrum subrectangular, distinctly transverse, its anterior margin nearly straight (lateral lobes barely produced), six setae. Mandibles rather short compared to head, more distinctly curved apically, tooth on the right one with rather long base, with proximal denticle much larger than others (Fig. 3 ). Maxillary palpi long and slender, penultimate segment more than 1.5 times longer than two adjacent segments. Antennae long. The second antennomere is shortest, the third one the longest; antennomeres 4-10 becoming gradually shorter, beginning with antennomere 8 not longer than the first segment (scapus); antennomere 11 approximately as long as each of antennomeres 4 and 5 and clearly longer than antennomere 10. For ratios of second and third antennomeres see Table 1 . Pronotum (Fig. 2 ) clearly longer than wide, moderately constricted to base, with lateral margins shortly rounded in apical fifth, then rectilinearly convergent posteriad, though more or less regularly undulated for most of their length, without distinct sinuation before hind angles. Basal margin rectilinear or slightly concave medially, obliquely truncate laterally. Front angles broadly rounded, barely produced beyond anterior margin, the latter nearly straight or slightly concave medially. Hind angles of pronotum not large but distinct, pointed apically, directed outwards and occasionally posteriad. Both lateral groove and lateral border continuous, becoming very subtle behind anterior lateral seta and slightly widened again toward hind angles (in posterior 4/10 of the length). Anterior lateral seta located at broadest point of pronotum, approximately in anterior fifth of length. Posterior seta absent (Figs 7 , 8 ). Prebasal transverse impression rather shallow, especially so in median part, more sharply engraved in basal foveae which are rather small, clearly outlined and well impressed. Base of pronotum smooth, with a few shallow and irregular wrinkles. Apical transverse impression vague and shallow. Median line distinct, becoming much deeper at level of both apical and prebasal transverse impressions. Elytra not large, but rather wide, with well-developed humeri and broadly rounded apex, their maximum width slightly behind mid-length. Preapical sinuation distinct. Lateral margins markedly reflexed, marginal groove rather wide. Basal slope of elytra with only first elytral stria well impressed. Parascutellar striole rudimentary, very short. Discal striation reduced: only striae 1 and 2 rather complete, stria 3 only partially traceable, usually more or less distinct between two discal setiferous pores, clearly extending beyond level of the second discal setiferous pores in one specimen, smooth or vaguely punctate. All interspaces flat. Anterior discal setiferous pore located at level slightly behind umbilicate pore 3 while the second one clearly before umbilicate pore 5 (Figs 7 , 8 ). Preapical pore located in the apical cross at level near or behind umbilicate pore 7. Exterior pore of apical triangle markedly shifted inward and forward, being located at level near middle of the apical striole and equidistant between the latter and angulo-apical pore which is attached to marginal border and subequally distant from elytral suture and apical margin. Inner side of the apical triangle (formed by three apical pores including the preapical pore as a front summit) markedly convergent to the elytral suture posteriad. Apical slope with striae reduced: only stria 1 traceable though shallow, sometimes stria 2 extended posteriad beyond level of the preapical pore. Apical recurrent striole short, nearly straight, directed anteriad, without clear connection with any of discal striae. Umbilicate pore 1 located approximately at level of humerus. For detailed data on position of umbilicate pores see Table 1 . Metepisternite clearly longer than wide. Abdominal ventrites shortly pubescent, each with two long paramedian setae (one on each side) and occasionally with still few shorter setae. Legs long and thin; front tibiae barely S-curved; middle tibiae nearly straight, only slightly curved near femoral joint; hind tibiae distinctly S-curved; all tibiae densely pubescent in distal third, middle and hind tibiae on inner surface, front tibiae on anterior and exterior surfaces. First tarsomere of posterior legs very long, not shorter than three following segments combined. Tarsomere 4 on pro- and mesotarsi possess a well-developed ventral tubercle furnished with hyaline appendage, the latter is narrow, curled apically, not reaching the apex of tarsomere 5. Male protarsi with two basal segments dilated: first tarsomere markedly elongate, with inner tooth not large but distinct, second tarsomere subquadrate, approximately as long as wide, with very small inner tooth. Both dilated basal segments of male protarsi with small and pairwise adhesive appendages beneath which are clearly shifted inwards and distally in first tarsomere and inwards and proximally in the second. Aedeagus (Fig. 9 ) not large (especially compared with the body size), markedly curved, with elongate apical portion, curved ventrally. Sagittal crest small and poorly sclerotized. Basal orifice moderately emarginate. Endophallus armature well developed, heavily sclerotized, with a distinct mesh. Parameres slender, with rather narrow distal portions, left one slightly longer, with a small ventral apophysis, each paramere bearing 4 apical setae. Female : unknown. Distribution. China, Sichuan Province, mountains on the right bank of the Yalongjiang River, in its largest bend located SW of Mianning City (Map 1 ). Map 1. Type locality of Yalongaphaenops erwini gen. et sp. nov. (yellow pushpin). Bionomics. The species was found under deeply buried boulders and by splitting rocks near the entrance to a small cave with a creek flowing into it, in the upper forest zone (mostly coniferous tree species and deciduous shrubs) just below the treeline at an elevation of 3805 m a.s.l. (Fig. 10 ). Yalongaphaenops erwini gen. et sp. nov. is the most high-altitude specialized semi-aphaenopsoid trechine beetle known so far. The area where it was collected shows many signs of carbonate lithology. Apart from the above species, some other depigmented carabids with partially reduced eyes were found here, including members of the genus Pterostichus Bonelli, 1810 and one new cryptophilic species of Agonotrechus Jeannel, 1923. Based on both its appearance and the habitat, Yalongaphaenops erwini sp. nov. is a true hypogean species. In this respect, we prefer to follow S.-I. Ueno (1995) in his general approach to hypogean insects as well as M. Giachino and D. Vailati (2017) in avoiding, where possible, speleocentric terms like "troglobitic" . It is particularly the case of the species in question, which was collected rather close to the soil surface but at a high altitude and under humid, low-temperature conditions of the monsoon season. From the ecological standpoint, this finding is in line with our previous observations on the hypogean carabids in the Caucasus. Figure 10. Typical biotope of Yalongaphaenops erwini gen. et sp. nov. Notes. It was quite unexpected to find a highly specialized hypogean semi-aphaenopsoid species at an elevation exceeding 3800 m. Usually hypogean species are much more common at lower elevations, for example, the sweet spot of their biodiversity in the Caucasus is confined between 700 and 1300 m ( Belousov 1998 ). Much more seldomly, some hypogean species can be found there at lower or higher elevations. In the latter case, there are some taxa known so far exclusively from high elevations: the genus Taniatrechus Belousov & Dolzhanski, 1994 (entrances to the caves populated by this species are located clearly above treeline), Meganophthalmus kravetzi Komarov, 1993, Nannotrechus (Abasorites) gracilipes Belousov, 1998 and eastern species of the subgenus Archinannotrechus Belousov, 1998 of the genus Nannotrechus Winkler, 1926; all these taxa were found either in the upper forest belt not far from the treeline or even slightly above ( Belousov 1998 ). Likewise, in China, the highest biodiversity of hypogean Trechini is recorded for lower mountains of southern China (e.g., Tian et al. 2016 ). In this ecological context, the discovery of Y. erwini gen. et sp. nov. not far from treeline is consistent with the above data, except that the upper limit of the forest zone is located in the Tibetan plateau, including the Hengduan mountains as its eastern periphery, much higher than elsewhere in the Northern Hemisphere, with an impressive record of 4900 m documented for the southern part of Tibet ( Miehe et al. 2007 ). In the area where Y. erwini gen. et sp. nov. was collected, the upper limit of the forest varies from 3600 to 4100 m a.s.l. (Map 2 ). Given the potential impact of livestock grazing and based on the uppermost tree stands forming part of the treeline ecotone ( Miehe et al. 2014 ), the treeline here is supposed to be equal to approximately 4100 m a.s.l.. However, the type locality of Y. erwini gen. et sp. nov. is situated only 50 m from (Map 2 ) and 20-30 m below the adjacent timberline and the latter seems to be naturally bordered by a steep rocky ridge completely deprived of tree stands. Map 2. Relief map of the area nearby the type locality of Y. erwini gen. et sp. nov. The yellow line shows the closest distance to the upper forest limit On the other hand, the treeline does not directly impact the distribution of soil-dwelling, let alone hypogean carabid species. This is particularly true for the above-mentioned highest treelines composed mostly of Juniperus species ( Miehe et al. 2007 ) in southern Tibet. These tree species do not provide shade enough to harbor communities of mesophile carabids. In this regard, the fir forests and even broadleaved Rhododendron shrubs are much more important in creating a suitable environment for many epigean carabid species. This influence is much less evident in relation to hypogean species, but it seems very likely that the latter occur closer to the soil surface under more humid conditions. Such types of forests depend mostly on the amount of precipitation and, in the Hengduan mountains, are typical to the east-exposed slopes which are more influenced by the monsoon. That is just the case of the area under consideration. Interestingly, the tall fir forest in the immediate vicinity of the type locality of Y. erwini gen. et sp. nov. (Fig. 11 ) disintegrates very rapidly (over vertical limits of a few dozen meters) into small individual trees just as noted by Miehe et al. (2007) for the inner Himalayas of Bhutan. Figure 11. Fir forest near collecting site of Yalongaphaenops erwini gen. et sp. nov. However, tall fir trees near the type locality of Y. erwini gen. et sp. nov. met landscapes of the alpine zone in a sharp line and were directly exposed to clouds coming from open areas, catching moisture from the air as do screes and stony slopes in high mountains. The drip of the trees was particularly intensive in a narrow band along boundary of the forest resulting in a kind of permanent rain. The analogy with stony habitats was unexpectedly confirmed by the spatial distribution of some petrophilous and riparian carabids including members of Nebria Latreille, 1802 and the highly specialized Leistus Froelich , 1799 which were abundant on tree trunks in this band and completely missing elsewhere, even in stony biotopes and in the valley of a small creek. In a sense, both the high-altitude occurrence of Y. erwini gen. et sp. nov. and its ecosystem association could be interpreted in terms of the lee and mass elevation effects greatly influencing the vertical distribution of carabid beetles throughout the world ( Liebherr and Zimmerman 2000 ; Schmidt et al. 2017 ). The discovery of Y. erwini gen. et sp. nov. significantly expands both the area and the altitudinal range where subterranean trechines are likely to be found, and suggests more field work is needed to explore their diversity in the entire Tibetan region within a wide range of altitudes. Etymology. The species is named after Terry Erwin, the great American entomologist in recognition of his invaluable contribution to our knowledge of insect biodiversity as well as taxonomy, ecology, and evolution of carabid beetles.