Bioacoustics of Chironomus gelhausi

discussion · Plazi

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) :

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