Pseudorthocladius immezensis, Moubayed-Breil & Lods-Crozet, 2021

Moubayed-Breil, Joel & Lods-Crozet, Brigitte, 2021, PSEUDORTHOCLADIUS IMMEZENSIS SP. N., A NEW RELICT SPECIES INHABITING THE MACUN HIGH-ALPINE STREAM, SWISS ALPS (DIPTERA: CHIRONOMIDAE), CHIRONOMUS Journal of Chironomidae Research 34, pp. 13-20 : 14-19

Pseudorthocladius immezensis sp. n.

http://zoobank.org/51951519-569F-44D8-B0F0- 0DB2370A1D21

Material examined. Holotype, Switzerland. 1 male adult, Malaise trap, leg. B. Lods-Crozet. Macun cirque, streamlet and rheocrenes, left shore of Immez Lake (46°43’39.678’’ N, 10°07’55.764’’E); alt. 2616 m a.s.l., 27.VII.2013. Environmental data from inlet of Immez Lake (after Lods-Crozet et al. 2012): crystalline water, conductivity 5.9 µS/cm; temperature (min-max, 3.9-19.5 °C; mean, 11.6 °C), pH 6.7.

Paratype. 1 male adult, leg. B. Lods-Crozet, same date and locality as for holotype.

Holotype (mounted on 1 slide; GBIFCH 00597051) is deposited in the collections of the ‘Musée cantonal de Zoologie, Palais de Rumine, 6 place de la Riponne, CH-1014 Lausanne (MZL), Switzerland. Paratypes, Switzerland. 1 male adult, mounted on 1 slide, is deposited in the collection of the senior author.

Etymology. The name ‘ immezensis ’ refers to the Immez Lake basin where the type-material was collected.

Diagnostic characters

P. immezensis sp. n. can easily be distinguished from other related species by the following combination of characters. Head. Base and median part of coronal suture with atypical lateral and median extensions; temporal setae 10-11; antenna 1280 µm long, last flagellomere about 300 µm long, apical seta absent, AR 0.30. Sensilla coeloconica absent on palpomere 3. Clypeus sub-trapezoidal, with 8 setae. Thorax. Lobes of antepronotum in contact; humeral pit half ellipse-like. Wing. Distal half of membrane densely covered with macrotrichia (hairy cells are: r 4+5, m 1+2, m 3+4; cells cu and an bare); squama with 5 setae. Legs. Sensilla chaetica present on tarsomeres ta 1 -ta 5 of PI-PIII. Abdomen. Tergite IX broad basally, narrowed distally. Anal point markedly enlarged at base, with 17 setae mostly located close to the lateral margin. Virga with 4 spines. Gonocoxite truncate in its inner apical margin. Superior volsella, large lobe-like. Inferior volsella double: dorsal lobe nose-like with smooth inner margin; ventral lobe low. Gonostylus without posterior projection, caudal margin rounded; crista dorsalis absent.

Description

Adult male

(n = 2; Figs 1A, D , G-H, J, I, M; 2A-H)

Small to medium sized species. Total length (TL) 2.25 mm, wing length (WL) 1.35 mm; TL/WL = 1.67 (n =1). General colouration is ranging from pale brown to dark brown; head, thorax and antenna brown; thorax brown with dark brown mesonotal stripes; legs uniformly brown; abdomen and anal segment brown.

Head (n =2). ( Fig. 1A ). Eyes bare, midline of the frontal area slightly concave, frontal tubercles low; base and median part of coronal suture with outwards and inwards extensions; coronal setae present; temporal setae 10-11 including 8-9 inner and 2 outer verticals, postorbitals absent. Palp 5-segmented, length (in µm) of segments: 15, 30, 45, 48, 55; segments 1-2 fused, segment 2 bulbous; palpomere 3 ( Fig. 1D ) with 3 sensilla clavata, sensilla coeloconica absent. Clypeus ( Fig. 1G ) subtrapezoidal, with 8 setae in 2 rows. Antenna 1280 µm long, last flagellomere about 300 µm long, apex distinctly clubbed, apical seta absent, antennal groove reaching segment 3, AR 0.30.

Thorax. Lobes of antepronotum ( Fig. 1H ) thinner basally and not gaping, lateral antepronotals 5, located apically; acrostichals 9 in 1-2 rows, starting at some distance from antepronotum; dorsocentrals 9 in 1-2 rows; prealars 4 in 1 row; supraalars absent; humeral area ( Fig. 1I ) with contrasting brownish granulation, humeral pit half ellipse-like, parapsidal fork composed of micro-granulation; scutellum ( Fig. 1J ) broad, heart-like with 6 thin setae in 1 row.

Wing (n = 2). ( Fig. 1M ). Brachiolum with 1 seta; subcosta reaching the fork of radius, distribution of setae on veins: R, 16-17; R 1, 11-12; remaining veins bare; costal extension about 25-30 µm; distal half of membrane densely covered by macrotrichia which are clearly visible at 125-200X; hairy cells are: r 4+5 (150-160), m 1+2 (80-85), m 3+4 (about 40); cells cu and an bare; squama with 5 setae.

Legs (n = 1). Femur of PI and PIII nearly subequal (520 and 530 µm long); length (in µm) of tibial spurs: PI, 40; PII, 35 and 40; PIII, 30 and 45; longest seta of tibial comb 35 µm long. Sensilla chaetica present only on apical part of tibia of PI-PII, are more abundant on tarsomeres ta 1 -ta 5. Length (in µm) and proportions of prothoracic (PI), mesothoracic (PII) and metathoracic (PIII) legs as in table 1.

Abdomen. Hypopygium (n = 2) in dorsal and ventral view as in Figs 2 A-B. Tergite IX ( Figs 2A, E ) about 135-140 µm maximum width at base, occupying the entire width of segment IX, large cuplike basally, distal part subtriangular and extremely narrowing; dorsal side linear and lacking hump as shown in lateral view ( Fig. 2E ); setae absent on median and posterior area. Anal point ( Figs 2A, E ) with a characteristic enlarged base, distal part distinctly subtriangular (clearly visible in lateral view, Fig. 2E ), presence of 17 setae (12 located close to the lateral margin and 5 on dorsomedian area). Laterosternite IX with 12-14 setae (6-7 on each side). Sternapodeme and phallapodeme as in Fig. 2B , transverse sternapodeme semi-circular and orally projecting, lateral expansion well developed; phallapodeme sinuous, thicker in its median part. Virga ( Figs 2A, D ) composed of 4 spines including 3 long and 1 short (located at base). Gonocoxite ( Figs 2 A-B, F) 155 µm long, 65 µm maximum width, apical part 25-30 µm wide, inner apical margin truncate. Superior volsella ( Figs 2C, F ) well-developed, large lobe-like as illustrated in dorsal ( Fig. 2A ) and lateral view ( Fig. 2F ). Inferior volsella ( Figs 2A, C, E ) about 40-45 µm long, 25 µm maximum width, consists of double lobes: dorsal one nose-like with smooth inner margin, apex distinctly bent downwards, median area with a distinct cluster of short setae; ventral one low triangular lobe. Gonostylus ( Figs 2A , G-H) 70 µm long, 20 µm maximum width, without posterior projection, posterior margin rounded bearing a distinct notch distally clearly visible when viewed at acute and right angle; crista dorsalis absent. HR = 2.22. HV = 3.22.

Female adult, pupal exuvia and larva: unknown.

Differential diagnosis

Morphological differences between P. immezensis sp. n. and morphologically similar congeners (namely P. cristagus ; P. curtistylus ; P. filiformis ; P. pilosipennis ) are highlighted in the following differential diagnosis.

Adults of P. immezensis has a head with low frontal tubercles and atypical outward and inward extensions of the coronal suture ( Fig. 1A ), different from what is observed in P. curtistylus ( Fig. 1B ) and P. sp. 1 ( Fig. 1C ) which belongs to an unnamed species known from the Mutt stream (upper Rhone basin, Switzerland, alt. 2100 m); sensilla coeloconica absent on palpomere 3 ( Fig. 1D ), present in P. curtistylus ( Figs 1 E-F); low antennal ratio (AR 0.30) compared to what is observed in P. curtistylus (0.84) and P. cristagus (about 1.40) ( Saether and Sublette 1983, Stur and Saether 2004); humeral pit formed like a half ellipse ( Fig. 1I ), absent in P. curtistylus ( Fig. 1K ); scutellum large heart-like, with 6 similar thin setae ( Fig. 1J ), is horizontal diamond-like and bearing 2 stronger (occasionally 4) median setae in P. curtistylus and P. filiformis ( Fig. 1L ); distal half of wing densely haired ( Fig. 1M ), different from wings of P. curtistylus ( Saether and Sublette 1983, Figs 27C-D), P. cristagus ( Stur and Saether 2004, Fig. 1 ) and P. pilosipennis ( Saether and Sublette 1983, Fig. 26C); cells cu and an bare, while both are setose in P. cristagus and P. pilosipennis ; basal part of anal point distinctly enlarged ( Figs 2A, E ), different from that of P. curtistylus ( Fig. 2I ), P. cristagus ( Stur and Saether 2004, Fig. 2 ) and P. pilosipennis ( Saether and Sublette 1983, Fig. 26D); virga with 4 spines ( Figs 2A, D ), is absent in P. cristagus and P. pilosipennis ( Stur and Saether 2004; Saether and Sublette 1983); inferior volsella nose-like, bent downwards apically, with a distinct cluster of short setae on median area ( Figs 2A, C ), inferior volsella is bulbous in P. cristagus ( Stur and Saether 2004, Fig. 2 ) or large lobe-like in P. pilosipennis ( Saether and Sublette 1983, Fig. 26D); posterior margin of gonostylus rounded and bearing a notch distally ( Figs 2A , G-H), gonostylus is linearly elongate and bearing a prominent outer heel in P. cristagus ( Stur and Saether 2004, Fig. 3 ); crista dorsalis absent ( Figs 2A , G-H), is large, tooth-like in P. cristagus ( Stur and Saether 2004, Fig. 3 ).

It is not feasible to provide a key to known male adult Pseudorthocladius from Europe until sufficient material of all species has been examined and compared.

Ecology and geographical distribution

Only one, not associated larva of the genus Pseudorthocladius was collected in the inflow area of Lake Immez, where bryocolous and hygropetric habitats seem to represent the most favourable aquatic microhabitat for the larval populations. The new species likely belongs to the crenophilous community of species as documented by Lindegaard (1995) as no Pseudorthocladius larvae were found during extensive sampling in the lake Immez and other small lakes in the area (Lods-Crozet unpublished data; Lods-Crozet et al. 2012). Such pristine lotic habitats are considered to be microrefugia and hotspots of diversity and therefore deserve much greater consideration, protection and preservation.

Geographical distribution of the new species is currently restricted to the Alpine Swiss glacial catchments including streams and lakes delimited by the Macun cirque (Swiss National Park, eastern Swiss Alps, alt. 2616 m, Fig. 3 ), but P. immezensis sp. n. can be expected to occur in other similar mountainous areas situated in Switzerland and neighbouring countries (Italy, France, Germany, Austria, Poland).

Chironomid species encountered in the same area, and listed by Lods-Crozet et al. (2012), Lods-Crozet (2014, unpublished data, report to the scientific commission of the Swiss National Park) and Moubayed and Lods-Crozet (2018) include: Zavrelimyia melanura (Meigen, 1804) ; Diamesa bertrami Edwards, 1935 ; D. cinerella Meigen, 1835 ; D. nowickiana Kownacki & Kownacka, 1975 ; D. vaillanti Serra-Tosio, 1972 ; Protanypus caudatus Edwards, 1924 ; Pseudodiamesa branickii (Nowicki 1873) ; Pseudodiamesa nivosa (Goetghebuer, 1928) ; Pseudokiefferiella parva (Edwards, 1932) ; Chaetocladius castellai Moubayed-Breil, 2018 ; C. macunensis Moubayed-Breil, 2018 ; C. longivirgatus Stur & Spies, 2011 ; C. lodscrozetae Moubayed-Breil, 2018 ; C. suecicus (Kieffer 1916) ; Heleniella helvetica Moubayed-Breil and Lods-Crozet, 2016; H. ornaticollis (Edwards, 1929) ; Corynoneura arctica Kieffer, 1923 ; E. minor (Edwards, 1929); Orthocladius frigidus (Zetterstedt, 1838) ; Parorthocladius nudipennis (Kieffer, 1908) ; Tokunagaia rectangularis (Goetghebuer, 1940) ; Micropsectra radialis Goetghebuer, 1939 ; Paratanytarsus austriacus (Kieffer, 1924) .

The presence of P. immezensis sp. n. in high mountain Alpine ranges in the Swiss Alps (above 2600 m a.s.l.) highlights and confirms that some cold and glacial high mountain enclaves can contain diversity previously unknown to science. Documentation and knowledge of this fauna is important to monitor diversity and community changes caused by global warming and climate change.

Figures

Figure 1. Male imago of Pseudorthocladius spp. A) Head (left side, dorsal), frontal area, vertex and temporal setae of: A) P. immezensis sp. n.; B) P. curtistylus; C) P. sp. 1. D) P. immezensis sp. n., palpomeres 2-3. E-F) P. curtistylus: palpomere 3 and sensilla coeloconica. P. immezensis sp. n.: G) clypeus; H) lobes of antepronotum; I) humeral area; J) scutellum. P. curtistylus: K) humeral pit; L) scutellum. P. immezensis sp. n.: M) wing. The arrows indicate some distinguishing characters.

Figure 2. Male imago of Pseudorthocladius spp. P. immezensis sp. n.: A-B) hypopygium in dorsal and ventral view; C) superior and inferior volsella; D) virga; E) tergite IX and anal point, lateral; F) gonocoxite, lateral; G) gonostylus at right angle; H) gonostylus, lateral. P. curtistylus: I) tergite IX and anal point, lateral. The arrows indicate some distinguishing characters.

Figure 3. Malaise trap set up close to the inlet of the Immez Lake (Macun cirque, Eastern Alps, Swiss National Park; photo J.L. Lods). The arrow indicates the larval habitat of P. immezensis sp. n.