Chironomus gelhausi Bouchard, 2022

Jr, R. William Bouchard, Hayford, Barbara L. & Ferrington Jr, Leonard C., 2022, Chironomus gelhausi, a new species of surface-mating Chironomus Meigen, 1803 (Diptera: Chironomidae) from Mongolia, Zootaxa 5116 (1), pp. 123-135 : 124-133

Chironomus gelhausi Bouchard sp. nov.

Type material. Holotype: MONGOLIA, Hovsgol Aimag, Moron Soum, Tunamal Nuur, 5.5 km west of Arbulag , N 49.89920, E 99.39433, 1871 m, 7.vii.2006, leg. J.K. Gelhaus, 1 male ( UMSP).

Allotype: MONGOLIA, Hovsgol Aimag, Moron Soum, Tunamal Nuur, 5.5 km west of Arbulag , N 49.89920, E 99.39433, 1871 m, 7.vii.2006, leg. J.K. Gelhaus, 1 female ( UMSP).

Paratypes: MONGOLIA, Hovsgol Aimag, Moron Soum, Tunamal Nuur, 5.5 km west of Arbulag , N 49.89920, E 99.39433, 1871 m, 7.vii.2006, leg. J.K. Gelhaus, 14 males, 2 females ( UMSP [10 males, 1 female], ANSP [4 males, 1 female]) .

Etymology. Named for Jon K. Gelhaus, the collector of the material used for this study and a friend and colleague of the authors. Jon Gelhaus was also influential in setting the first author (RWB) on the path of studying insects and Diptera in particular.

Diagnostic characters. Males can be separated from other Chironomini by the combination of the following: fused antepronotal lobes; pulvilli present; antenna with 11 flagellomeres; well-developed inferior and superior volsellae; setae on the base of the superior volsella; inferior volsella distally and dorsoventrally broadened, but not greatly expanded as in most Kiefferulus ; and lack of median setae on anal tergite. More specifically, males can be separated from other species of Chironomus s. lat. (see treatment of taxonomy in “Remarks” section) by the combination of the following: large, conical frontal tubercles; antennae lacking typical plume; an apical truncation of the wing; AR 1.27–1.70; shortened palps; mid and hind tarsi reduced; long inferior volsellae extending well beyond gonostylus; parallel-sided anal point which rapidly constricts distally into a small point; setae present on ventral side of extension of superior volsellae; and lack of median setae on anal tergite. Females can by separated from other Chironomini by the following: squama with setae; antenna with 5 flagellomeres; palps with 5 segments; pulvilli present; front tibia with low, rounded scale; mid and hind tibia with 2 spurs; gonocoxapodeme rounded and not joined mesally; lack of setae on gonocoxite IX; gonapophyses VIII divided into dorsomesal lobe and well-developed ventrolateral lobe; cerci large; and segment X expanded forming a collar around basal half of cerci although not as well developed as in Fleuria . More specifically, females can be separated from other species of Chironomus s. lat. by the combination of the following: large, conical, frontal tubercles; reduced palps; an apical truncation of the wing; mid and hind tarsi reduced; gonocoxite IX without seta; apodeme lobe weak, without microtrichia; and segment X with more than 20 setae.

Description

Male imago (n=15, unless otherwise stated). Total length 8.40–13.47, 9.80 mm (n=14). Wing length 3.79–4.32, 4.15 mm. Total length/wing length 1.98–3.21, 2.36 (n=14). Wing length/length of profemur 3.99–6.09, 4.48 (n=14). Coloration brown to pale brown (alcohol preserved specimens), wings hyaline and without markings.

Antenna (n=6) ( Fig. 1A ). Antennae missing from most specimens. Antenna with 11 segments and antennal plume reduced; AR 1.27–1.70, 1.54. Ultimate flagellomere 629–815, 737 μm long. Longest antennal seta 183–363, 275 μm long (n=4), most setae missing in some specimens.

Head ( Fig. 1B ). Temporal setae 17–35, 28 μm; including 3–8, 5 inner verticals, 6–14, 10 outer verticals, and 7–16, 13 postorbitals. Clypeus with 5–22, 16 setae. Frontal tubercle 88–153, 114 μm high, 105–170, 139 μm wide, well developed and conical shaped with apical end constricted (Fi. 1B). Frons covered in dense microtrichia with microtrichia longest on frontal tubercles. Tentorium, stipes and cibarial pump as in Figure 1C . Tentorium 230–325, 281 μm long; 55–84, 68 μm wide at sieve plate and 40–70, 55 μm wide at tentorial pit. Stipes 175–294, 267 μm long; 10–17, 14 μm wide. Palp segment lengths (n=12): 75–124, 92; 60–90, 75; 198–278, 235; 51–270, 141; 116–153, 131. Third palpomere ( Fig. 1D; n =14) with 11–19, 15 sensilla, longest 10–24, 16 μm long.

Thorax. Tubercle well developed. Antepronotum with no setae. Dorsocentrals 10–19, 15, all short and decumbent; acrostichals 6 (n=1), all short and decumbent, starting midway between antepronotum and tubercle, typically not visible when laterally mounted although two setal scars were apparent on tubercle on one specimen; prealars 7–11, 9. Scutellum with 6–15, 10 setae.

Wing ( Fig. 2A ). Apical tip of wing truncated; VR 1.02–1.11, 1.07. Brachiolum with 3–5, 4 setae; R 18–27, 24; R 1 with 0 setae; R 4+5 with 2–8, 4 setae; other veins and cells bare. Squama with 13–26, 18 setae.

Legs (Figs, 2B, C). Mid and hind legs reduced in length ( Fig 2B ). Scale of fore tibia 24–60, 43 μm long ( Fig 2C ); spur of mid tibia 29–53, 41 μm long; spur of hind tibia 30–59, 43 μm long ( Fig 2C ) although hind tibia spur reduced or missing on some specimens. Comb on mid tibia 18–31, 24 μm long, with width of combs on mid tibia similar; comb on hind tibia 18–38, 25 μm long, one comb on hind tibia much wider than the other ( Fig 2C ). Width at apex of fore tibia 145–175, 161 μm; width at apex of mid tibia 120–189, 170 μm; width at apex of hind tibia 160–213, 193 μm. Lengths and proportions of legs as in Table 1 .

Hypopygium ( Fig. 3 ). Rotated up to 180º in all specimens examined. Tergite IX covered with microtrichia, with no median setae anterior of the anal point and 39–61, 50 setae on each side of base of anal point ( Fig. 3E ); anal tergite bands forming a shallow “U” and not reaching the base of anal point ( Fig. 3A ). Laterosternite IX with 0 setae. Anal point broad, parallel-sided and rapidly constricting to a small point, 92–115, 104 μm long, 40–78, 65 μm wide at base, 59–78, 69 μm wide medially, 5–15, 11 μm wide near apex; T-shaped in cross section. Transverse sternapodeme 390–525, 468 μm long, nearly straight ( Fig. 3B ). Phallapodeme 445–636, 556 μm long. Superior volsella and 280–380, 340 μm long, 76–125, 101 μm wide at base, 24–54, 40 μm wide at apex, with 27–38, 31 setae on the ventral side and extending to approximately the midpoint of the medially directed extension; dorsal side of the superior volsella with microtrichia only present on base and ventral side with microtrichia extending approximately 2/3 of the superior volsellae ( Fig. 3C ). Median volsella absent. Inferior volsella extending beyond apex of gonostylus 662–1118, 902 μm long, 48–145, 70 μm wide at base, 66–194, 115 μm wide at apex, dorsoventrally expanded distally, and covered with numerous simple, stout setae ( Fig. 3D ). Gonocoxite 403–732, 558 μm long. Gonostylus 414–690, 538 μm long, robust, dorsoventrally expanded, and with numerous stout setae, especially on the inner margin ( Fig. 3D ). HR 0.79–1.22, 1.04. HV (n=14) 1.42–2.65, 1.87.

Female imago (n=3, unless otherwise stated). Total length 8.53–9.24, 8.79 mm. Wing length 5.02–5.24, 5.11 mm. Total length/wing length 1.64–1.84, 1.72. Wing length/length of profemur 4.32–5.07, 4.63. Coloration as in male.

Antenna (Fig. X). AR 0.51–0.67, 0.57. Flagellomere lengths (in μm): 234–264, 245; 123–130, 127; 114–121, 117; 128–143, 133; 303–400, 353. Longest antennal seta 129–170, 150 μm long.

Head (Fig. X). Well-developed conical frontal tubercles, frontal tubercle 59–86, 76 μm high, 91–100, 96 μm wide, with conspicuous microtrichia. Frons as in male. Temporal setae 22–25, 24; including 3–4, 3 inner verticals, 9–11, 10 outer verticals, and 8–13, 10 postorbitals. Scapus setae 0–8, 5. Clypeus with 22–33, 28 setae. Tentorium 275–311, 292 μm long; 49–85, 64 μm wide at sieve plate and 31–50, 40 μm wide at tentorial pit. Stipes 270–296, 283 μm long; 10–16, 13 μm wide. Palp segment lengths (n=2; in μm): 79–104, 92; 55–80, 68; 226–275, 251; 128– 130, 129; 136–173, 155. Third palpomere (n=2) with 19–26, 23 sensilla, longest 11–15, 13 μm long.

Thorax. Tubercle well developed. Antepronotum with no setae. Dorsocentrals 13–19, 15, all short and decumbent; apparently 0 acrostichals, although they may not be visible in laterally mounted specimens as in the male; prealars 7–9, 8. Scutellum with 7–16, 11 setae, uniserial.

Wing. Apical tip of wing truncated as in male; VR 1.08–1.13, 1.10. Brachiolum with 3–4, 4 setae; R with 29–35, 32 setae; R 1 with 1–11, 5 setae; R 4+5 with 13–24, 18 setae; other veins and cells bare. Squama with 14–17, 16 setae.

Legs. Mid and hind legs reduced in length. Scale of fore tibia 33–45, 37 μm long; spur of mid tibia 40–44, 41 μm long; spur of hind tibia 31–34, 33 μm long (n=2). Comb on mid tibia 20–25, 23 μm long, with width of combs on mid tibia similar; comb on hind tibia 22–23, 23 μm long (n=2), one comb on hind tibia much wider than the other. Width at apex of fore tibia 125–135, 130 μm; of mid tibia 154–165, 158 μm; of hind tibia 179–187, 182 μm. Lengths and proportions of legs as in Table 2 .

Abdomen. Tergite VIII with 32–37, 34 setae. Sternite VIII with 122–179, 149 setae and no lateral setae.

Genitalia ( Fig. 4 ). Gonocoxite IX without setae. Tergite IX with 51–56, 53 setae. Gonocoxapodeme rounded and not joined mesally. Segment X expanded forming a collar around basal half of cerci with 64-78, 71 setae. Cercus large, expanded anteriorly and irregularly shaped, 355–424, 393 μm long. Seminal capsule 273–346, 320 μm long and 194–241, 217 μm wide. Notum 367–383, 376 μm long. Gonapophyses VIII divided into a dorsomesal lobe and well-developed ventrolateral lobe; apodeme lobe weak, without microtrichia.

Pupa: unknown

Larvae: unknown

Remarks. Currently, we lack consensus regarding the placement and status of Chironomus subgenera and closely related genera ( Cranston et al. 1989, Martin et al. 2007, Epler et al. 2013) which complicates placement of C. gelhausi . Cranston et al. (1989) recognized several subgenera (i.e., Camptochironomus, Lobochironomus, Chaetolabis, and Chironomus s. str.). Fleuria and Baeotendipes are included as separate genera in Cranston et al. (1989), but this publication also noted that these two genera are probably subordinate within Chironomus . Epler et al. (2013) treats Baeotendipes and Fleuria as part of Chironomus s. lat. although it is also noted that inclusion of Fleuria with Chironomus does not imply synonymy. In addition, Epler et al. (2013) indicated that Camptochironomus should be synonymized with Chironomus s. str which is supported by molecular studies of phylogenic relationships within the genus ( Guryev et al. 2001, Martin et al. 2007). Although a fuller description of the status of Chironomus and closely related genera is beyond the scope of this paper, it is relevant to the generic placement of C. gelhausi . Here we follow the classification of Martin et al. (2007) and Epler et al. (2013) where Chironomus s. lat. consists of the subgenera Chironomus s. str., Chaetolabis, and Lobochironomus (including Einfeldia Group C). The genus Chironomus s. lat. also includes “ Baeotendipes ” which may be part of Chironomus s. str. or a separate subgenus. The taxa Fleuria and Benthalia ( Einfeldia species group B) are considered to likely be distinct genera closely related to Chironomus .

In addition to our lack of consensus regarding the placement and status of Chironomus subgenera and closely related genera, the placement of C. gelhausi is complicated by several morphological characteristics which are apparently unusual due to its surface-mating habit. It has been demonstrated that in other surface mating Chironomidae taxa with highly specialized morphology, placement into a genus using only morphology can be problematic (e.g., Andersen et al. 2016, Qi et al. 2018). However, the morphology in C. gelhausi is not so specialized for surface mating to make generic placement ambiguous, particularly within the broader concept of Chironomus s. lat. (sensu Epler et al. 2013). As such, C. gelhausi fits reasonably well within the diagnosis for the genus Chironomus . The following characters for C. gelhausi are consistent with the adult male diagnosis for Chironomus s. lat. in Cranston et al. (1989): 11 flagellomeres; fused antepronotal lobes; pulvilli present; well-developed inferior and superior volsellae; and setae on the base of the superior volsellae. This species differs from the Chironomus s. str. diagnosis in Cranston et al. (1989) in that setae are present on the ventral side of the extension of the superior volsella which is bare in other Chironomus s. str. species. Although superior volsellae differ in shape between C. gelhausi and Chironomus (Chaetolabis) , both taxa possess setae on the ventral side of the superior volsellae indicating that this character occurs within Chironomus s. lat. In addition, median anal tergite setae are absent in C. gelhausi which is unusual in Chironomus s. lat.; however, these setae are also absent in some surface-mating Chironomus s. str. species (e.g., Chironomus pallidivittatus Malloch and Chironomus tepperi Skuse ) ( Cranston et al. 1989, Martin 2022). The mean antennal ratio for males of C. gelhausi was only 1.54 which differed from the diagnostic antennal ratios for Chironomus s. lat. (greater than 2.0; Cranston et al 1989) and “ Baeotendipes ” (approximately 2.0; Cranston et al. 1989). However, the lower antennal ratio is also observed in other surfacing mating taxa (e.g., Fleuria antennal ratio = 0.64; Song et al. 2017). Thus, there is no discrepancy placing C. gelhausi in Chironomus s. lat. if the lower antennal ratio in C. gelhausi can be attributed to its surface-mating habit. Similarly, C. gelhausi differs from the diagnoses for most other Chironomus species ( Cranston et al. 1989) by possessing reduced palps, reduced mid and hind legs, and a robust gonostylus densely covered with setae on the inner margin. However, some or all of these characters are also observed in some Chironomus s. str. and “ Baeotendipes ” species and can presumably be attributed to surface mating.

The species C. gelhausi shares several morphological characteristics with Fleuria including truncated wings, large and conical frontal tubercles, reduced palps and mid and hind legs, lack of median anal tergite setae, and robust gonostylus densely covered with setae on the inner margin. However, these characters are likely to be homoplastic and related to the shared surface-mating habit of these taxa. In addition, the hypopygia of these two taxa are very different with Fleuria possessing a globular hypopygium with short, wide superior and inferior volsellae and a short, kidney-shaped gonostylus ( Cranston et al. 1989). However, the distinctive hypopygial characters in Fleuria may represent strongly modified morphology associated with surface-mating and therefore is possibly autapomorphic within the species. Another species which may represent a second species of Fleuria with a more typical hypopygium, Chironomus natchitocheae Sublette ( Cranston et al. 1989) , also does not have hypopygial characters which would indicate affiliation with C. gelhausi . Placement of C. natchitocheae within Benthalia ( Einfeldia Group B) has also been suggested (J. Martin pers. com., Epler 2019) based on the presence of a longitudinal row of median setae on the anal tergite. However, C. gelhausi lacks median anal tergite setae which indicates that it does not belong within Benthalia . The species C. gelhausi shares some characters with Kiefferulus including the presence of setae on the ventral side of the extension of the superior volsella and the lack of median setae on the anal tergite in some species. However, in males of C. gelhausi , the inferior volsella is not as strongly expanded distally and in the female there are no apically pointed scales on the dorsomesal lobe ( Cranston et al. 1990). Overall, morphological characters do not indicate that C. gelhausi should be placed in Fleuria , Benthalia , or Kiefferulus .

The female of C. gelhausi also fits within Chironomus s. lat. although some characters are not consistent with the diagnosis in Saether (1977). For example, the apodeme lobe in C. gelhausi does not appear to bear microtrichia although this may be consistent with some Chironomus . For example, microtrichia are not shown on the illustration of the apodeme lobe Chironomus aprilinus Meigen (as Chironomus halophilus Kieffer ) in Saether (1977). Segment X also has large extensions which bear more than 20 setae on each side in C. gelhausi . However, in C. gelhausi the apodeme lobe is not fused with the dorsomesal lobe and the extensions on segment X are not expanded to the extent observed in Fleuria . The expanded segment X and the lack of setae on gonocoxite IX could be associated with surface mating although we are not aware of previous discussions regarding how these genitalic characters may be advantageous for surface-mating species. In general, additional comparative analyses of the females between Chironomus and related genera is needed.

Although C. gelhausi fits reasonably well into the genus Chironomus , it may not key out correctly in existing keys for adult males and females (e.g., Cranston et al. 1989, Saether 1977) due the apically truncated wing, reduced palps, reduced mid and hind tarsi, and other characters associated with surface mating. In both Cranston et al. (1989) and Saether (1977), C. gelhausi will likely key out as Fleuria , although for both the male and female, these couplets do not match all of the characters used in the couplets for Fleuria . As a solution, we suggest, the following amendment to the dichotomous key in Cranston et al. (1989):

2. Wing apically with angled truncation and antenna with fewer than 10 flagellomeres (Fig. 10.22).......... Fleuria (p. 379)

- Wing apically rounded. Antenna with 11–13 flagellomeres ( Acalcarella exceptionally has 9 flagellomeres). If wing apically with angled truncation then antenna with 11 flagellomeres..................................................... 3

For the female, the dichotomous key in Saether (1977) would need to be amended in several locations and we do not suggest those here. An update to the key in Saether (1977) including the addition of taxa and to reflect changes in taxonomy would be an opportunity to incorporate amended characters in Chironomus .

Despite some characters which differ from the diagnosis, C. gelhausi fits best within Chironomus s. lat. and atypical characteristics can be attributed to its surface-mating habit as in some other Chironomus s. str. species ( Hein & Schmulbach 1971) and possibly “ Baeotendipes ”. Due to uncertainty regarding the relationship and status of Chironomus subgenera and closely related taxa, we opt not to propose subgeneric placement for C. gelhausi . In general, additional study, including examination of the larva and pupa as well as cytological and molecular evidence will be needed to determine relationships between this species and other species of Chironomus s. lat.

Distribution and ecology. The habitat from which C. gelhausi was collected is used here to describe its ecological requirements and possible distribution for this species. Chironomus gelhausi is known from a single lake in Mongolia, Tunamal Nuur (nuur = lake; Fig. 5A ). Interestingly, another surface-mating species was collected at this locality, a skating trichopteran, Agrypnia hayfordae Morse & Chuluunbat (Morse & Chuluunbat 2007). This lake is small, approximately 8 hectares, with a muddy and rocky shoreline, and is surrounded by steppe ( Fig. 5 ). At the time of sampling, this lake lacked emergent vegetation and floating algae ( Fig. 6 ) and had black, anoxic sediments indicating high levels of nutrient enrichment. Many species of Chironomus occur in and are in fact characteristic of eutrophic and hypereutrophic lakes. Based on physical descriptions of this lake, C. gelhausi occupies a habitat which is characteristic of many species in this genus. Some species of Chironomus are also tolerant of elevated salinity ( Cranston et al. 1989) and many lakes in western Mongolia are considered subsaline, hyposaline, mesohaline, and hypersaline (Bouchard et al. in press). However, salinity measurements for Tunamal Nuur were not available and we cannot determine at this time if this species is halophilic. Although this species is known from a single lake, it is possible that this species occurs in other lakes in the region given that lakes are relatively common within the Great Lakes region of Mongolia. Unfortunately, it is possible that habitat for this species is shrinking because lakes in this region face threats from overgrazing and climate change which is decreasing lake sizes and degrading water quality ( Laurie et al. 2010, Hilker et al. 2014, Tao et al. 2015).

We use observations of the behavior of C. gelhausi in the field and morphological characteristics to describe possible strategies used by this species to exploit the harsh environment in which they occur. During collection of this species, individuals were observed aggregating on exposed rocks near the shore in groups largely consisting of males. Some individuals were observed skating using their wings for propulsion on the water’s surface. Active adults were observed skating out toward the middle of the lake, but no aggregations on the water’s surface were observed. Although copulation was not observed in the field, the hypopygium was inverted up to 180º in all preserved male specimens examined for this study. This indicates that these individuals had mated and that the hypopygium remained in the inverted position following mating. This attribute can be used to provide insight into the mating behavior of C. gelhausi . Torsion of the male abdomen (i.e., hypopygium inversum) has been observed in several surface-mating dipterans including chironomids (e.g., Chironomus tepperi Skuse , Fleuria Kieffer , Oliveridia hugginsi Ferrington & Saether , Dicrotendipes sinicus Qi & Lin ) and tipulids ( Phantolabis lacustris (Alexander)) (Martin & Porter 1977, Cranston et al 1989, Ferrington & Saether 1987, Qi et al 2018, Bouchard & Gelhaus 2020). In these taxa, torsion of the abdomen occurs when the mating pair changes to an end-to-end position while coupled ( Neumann 1976). In this position, either the male or female may transport the opposite sex away from competitors or to the oviposition site. The torsion of the male abdomen suggests that in C. gelhausi coupling begins with a faceto-back position with dorsal flexion of the male’s abdomen (see Neumann 1976). Once coupled, the position likely changes to an end-to-end position with 180º torsion of the male’s abdomen. However, it is not known if this species mates on substrates or on the water’s surface.

Observations of the behavior and morphology of C. gelhausi indicated that morphological features associated with surface mating are not as extreme in this species as in some other surface-mating species of Chironomidae (e.g., Clunio Haliday , Pontomyia Edwards, Zealandochlus Brundin ). Field notes also indicated that this species could both skate on the water’s surface as well as fly short distances. This species was also observed flying to light traps. This intermediate degree of adaption to surface-mating where adults can skate as well as fly has been documented in other chironomids which have or are presumed to have lost the behavior of aerial swarming including Fleuria Kieffer and Goeldichironomus amazonicus (Fittkau) ( Fittkau 1968, Wirth 1979, Fedorova & Zhantiev 2009). Such a strategy would presumably be beneficial in ensuring that adults are not displaced from the mating site while also maintaining the ability to rapidly disperse to new habitats. We can hypothesize that such a strategy is advantageous on the Mongolian steppe where there is limited tall vegetation to provide shelter for aerial swarms and suitable habitats can be sparsely distributed in the landscape. We conclude that C. gelhausi is a Chironomus species which has independently evolved surface-mating behavior and concomitant morphological characteristics that impart advantages in a harsh environment.

Figures

FIGURE 1. Chironomus gelhausi n. sp. male. A—antenna; B—head; C—cibarial pump; D—distal end of third palpomere.

FIGURE 2. Chironomus gelhausi n. sp. male. A—wing; B—fore, mid, and hind tarsi; C—apex of fore, mid, and hind tibiae.

FIGURE 3. Chironomus gelhausi n. sp. male. A—hypopygium, dorsal view; B—hypopygium with anal point and tergite IX removed, dorsal aspect to the left and ventral aspect to the right; C—ventral view of superior volsella; D—lateral view of gonostylus (left) and inferior volsella (right); E—anal point, lateral view.

FIGURE 4. Chironomus gelhausi n. sp. female genitalia, A—ventral view; B—lobes of gonapophyses VIII (VIL = ventrolateral lobe; ApL = apodeme lobe; DmL=dorsomesal lobe).

FIGURE 5. Wide view of the type locality (Tunamal Nuur) of Chironomus gelhausi n. sp. (photo credit: C. Riley Nelson).

FIGURE 6. Shoreline habitat of the type locality (Tunamal Nuur) of Chironomus gelhausi n. sp. (photo credit: C. Riley Nelson).