Holarctc Chironomus: C. 1TE

Chironomus species 1TE, from BOLD Database

Stur & Ekrem 2020 - as sp. 1TE.
Also referred to in BOLD database as C. cf. saxatilis - incorrect association (Stur & Ekrem 2020).

In BOLD Bin: BOLD:AAC0592.

It is possible that this is the species recorded as C. riparius in Greenland.

Adult:

Male
Dark species, thorax, abdomen and legs blackish brown.
Wing length about 3 mm, width about 0.8 mm, VR about 0.94; AR perhaps 3.5; LR about 1.4-1.5
About 6-9 setae on tergite IX, each in a separate patch. Anal point narrow, SV similar to C. holomelas, C. saxatilis closest to Strenzke's S(c)-type; style narrowing over posterior half.

Pupa: Not known.

Larva: (based on Greenland specimens): A small-moderate halophilus-type (males 11.7-12.2 mm), ventral tubules short, posterior pair usually longer (0.24-0.40; 0.28-0.40 mm), anal tubules long with constriction in middle, dorsal abt. 380-825 µm; abt 2-4 times longer than wide; ventral abt 400-700 µm, abt 2-4 times longer than wide).
Darkening of head capsule variable: gula pale to dark; frontclypeus dark to v. dark, sometimes with darkening outside the frontoclypeus but capsule generally yellowish brown.

Mentum (Fig. c) with 4th laterals reduced about halfway to height of 5th laterals (type I-II), central trifid tooth probably type III, but wear may make it appear as type IB or type IV.
Ventromental plates (Fig. d) separated by at least a third to half the mentum width, with about 35-48 striae, VMR 0.22-0.34. Pecten epipharyngis (Fig. a) with about 11-15 relatively broad teeth (type C).
Premandible (Fig. a) with teeth about equal in length or outer slightly longer, inner tooth about 2.5-3 times wider than outer tooth.
Distance between antennal bases slightly longer than that between the S4 setae, which are separated by about 3/4 of the width of the frontoclypeus.
Antenna (Fig. b) with A1 about 0.4-0.45 of the VHL and 3.5-4 times longer than wide, RO variable - from 0.15 to 0.36 up from base of segment; AR abt 1.75-2.51. Antennal proportions (µm) 125-150 : 32-40 : 9-11 : 13-15 ; 6-10.
Mandible (Fig. e) with 3rd inner tooth partly to fully separated and partially darkened (type II-IIIB), with about 12-13 furrows on the outer surface near the base, and 11-13 setae in the Pecten mandibularis.

Larval characters, particularly of the antenna, are quite variable. While nothing is known of the larval habitats, it is possible that this is due to ecological difference which may influence the length of the life cycle, which is known to extend up to 7 years in some high northern species (Butler 1982), i.e. there may be members of different cohorts.

Cytology: 4 polytene chromosomes with the pseudothummi arm combination AE, BF, CD, G.
Arm G with a terminal nucleolus and no clear BRs. No nucleoli in other chromosomes.
Possible inversion in arm A.
Arm A1: Inverted towards distal end cf. holomelas sequence.
Arm A2: simple inversion of about 1/3 of arm distal to middle of arm - possible it is as holomelas.
Arm B1: Puff (group 7) near distal end, with dark bands (group 8?) on proximalal side.
Arm C1: 1, 6 - 2, 7 - 10?, etc. Possibly as holomelas, saxatilis.
Arm D1: proximally possibly 16 - 24. Inverted cf. saxatilis
Arm E1: probably 1 - 3e, 10b - 3f, 10c-g, 11 - 13 i.e. as luridus, halophilus, etc.
Arm F1: ?-?, 21-23
Arm G1: Terminal nucleolus; probably BR about middle of the chromosome. May be closely paired or paired only at nucleolus.

Molecular sequence: mtCOI: Sequence for this species is in the BOLD database where it is placed in BOLD BIN AAC0592. However, the sequence for one of the available larvae shows only about 94% similarity, and is described below as a potential closely related species, Species 5h for which there is no sequence in GenBank or the BOLD database.

Another larva from Peary Land has a COI sequence most closely related to Sp. 1TE, and there are some differences in the larvae - however, the larva shows a number of malformations so is not certain just how real some of these differences are.

Larva GP8.1.1 12F: A halophilus-type larva, very similar to those of Sp. 1TE.
Length about 10.8 mm, ventral tubules shorter than those of other available specimens: anterior 0.18 mm. posterior 0.24 mm; anal tubules much shorter 300-400 µm (ventral pair longer) and about 1.9-1.8 times longer than wide. Head capsule generally dark, gula darkened over posterior 2/3. Distance between the S4 setae about the same as that between the antennal bases, but the setae are closer to the margin (80% of width of frontoclypeus between them).
Mentum (Fig. c) with 4th laterals reduced about to level of 5th laterals (type II) and central tooth probably type IB. Ventromentum (Fig. d) and Pecten epipharyngis (Fig. a) as in other larvae; Premandible not clear. Antenna (Fig. b) also essentially as in the other larvae, but A5 is the same length as A3. Mandible (Fig. e) of type IIB, and with similar number of PMan setae; with 14-15 furrows on the outer surface near the base.

Found: Northwest Territories-Aulavik National Park (73.71°N;, 119.92°W), Banks Island
Nunavut - Auyuittuq National Park (67.88°N, 65.02°W) & Sirmilik National Park (72.99°N, 81.14°W), Baffin Island; Quttinirpaaq
National Park (82.22°N, 72.22°W), Ellesmere Island.
Yukon Territory - Ivvavik National Park (69.162°N, 140.155°W).
Greenland - Nedre Midsommer Sö, Peary Land, sample GP8 (82.63°N, 32.50°W); Northeast Greenland NP.
Norway - Spits-Bergen and Jan-Mayen, Svalbard (Stur & Ekrem 2020).
Sweden - Borgholm, Barnaesuddern, Oeland (BOLD)

C. saxatilis was described by Wülker et al. (1981) with the type specimen a polytene chromosome squash. It has been suggested that it is a synonym of C. lugubris (Lindeberg, unpubl.), although this is not supported by COI sequence data. It is very similar in morphology to C. holomelas, such that Wülker et al. did not see the necessity of illustrating the male terminalia. The polytene chromosomes suggest that the present species cannot be C. saxatilis, but is closely related and does not match any cytologically studied species from the Holarctic.