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1 June 2016 Notes on the Tropical Andean Genus Disceratus (Orthoptera, Tettigoniidae, Pseudophyllinae), the Probable Male of D. nubiger, and Its Calling Song
Holger Braun
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Abstract

A male Disceratus specimen found in cloud forest of Podocarpus National Park in southernmost Ecuador is apparently conspecific with Disceratus nubiger Scudder 1869, known only from the female holotype, collected one and a half centuries ago on slopes of the volcano Antisana. The song of this male could be recorded, confirming the identification of field recordings as well as additional acoustic records with an ultrasound detector at the same site. This incessant calling song, a series of steadily repeated short clicks with a sharp peak at 20 kHz, easily reveals the presence of this short-legged and brachypterous katydid — it lives in bamboo thickets within cloud forest, where individuals are very difficult to find. More fieldwork and nocturnal acoustic monitoring in the tropical Andes will be essential to shed light on the distribution and life history of this practically forgotten genus and its species, some of them probably still undiscovered. Disceratus is recognized as full genus rather than a subgenus of Gnathoclita.

Introduction

The neotropical genus Disceratus Scudder 1869 comprises five species of yellowish or reddish brown, short-legged and brachypterous katydids that are distinguished by two knobs or spiniform processes on the clypeus, and elongated mandibles in males. The name seems to be derived from these hornlets (Greek fi01_01.gif = horned). While D. karschi Brunner von Wattenwyl 1895, known from a single female specimen, is supposed to be from Costa Rica, the four other species are from the Andes of Ecuador (listed according to type locality from north to south): D. anostostoma (Gorochov 2012) from Pichincha Province (Cordillera Occidental, 1970 m), D. nubiger Scudder 1869 from slopes of the volcano Antisana (Cordillera Oriental, at 3000 m), D. immanis Hebard 1924 from Chimborazo (Cordillera Occidental, at 3000 m) and D. festae Giglio-Tos 1898 from Cañar Province (separation into two distinct cordilleras complicated). All seem to be known from the type specimens only: respectively a unique male, a unique female, a male and female pair, and a female along with two nymphs of both sexes. Male sexual differences include more elongated mandibles and an upcurved rear margin of the pronotum, the latter probably providing space to move the tegmina during stridulation. In the known females the metazona is flat.

In his monograph of the large subfamily Pseudophyllinae, Beier (1960) assigned Disceratus to the new tribe Glaphyraspidini, a group of altogether five genera that ultimately needed to be renamed Homalaspidiini (Homalaspidia Uvarov 1940 is a new name for the preoccupied name Homalaspis Brunner von Wattenwyl 1885, while the unnecessary replacement name Glaphyraspis Beier 1960 is preoccupied as well, cf. Eades et al.). A recently described species of Disceratus was first placed into the new subgenus Tettohenicus Gorochov 2012 within the genus Gnathoclita Haan 1843, the latter being distinguished by strongly elongated mandibles and clypeus in males, and belonging to the tribe Eucocconotini (Beier 1960). That subgenus turned out to be a synonym of the genus Disceratus, which in turn was moved as subgenus under Gnathoclita, the respective author criticizing the “erroneous inclusion of two subgenera ... in different tribes by Beier” (Gorochov 2014).

In fact, the two genera are quite different. First, Disceratus lacks the ventral tubercles at the base of fore and middle coxae, which are considered to be diagnostic for the tribe Eucocconotini and are present in Gnathoclita (Beier 1960). As already mentioned, Disceratus has a pair of apically rounded spiniform processes on the normally-sized clypeus, which are not present on the protruding mouthparts of Gnathoclita with its prolonged clypeus. The mandible tips in Disceratus are free, while in Gnathoclita they are covered by the labrum. In Disceratus the lateral lobes of the pronotum are much longer than high, while in Gnathoclita the pronotum is fairly short. Disceratus has short and slit-like tympanal openings which are situated laterally on the base of the fore tibiae (about 1/3 of total tibial width removed from the edges of the flat dorsal surface), whereas in Gnathoclita the openings seem to be wider and coincide with the dorsal edges of the tibiae. Finally, all Disceratus species are brachypterous, with tegmina shorter than the pronotum and hind wings wanting (Scudder 1869, Beier 1960), while in the four real Gnathoclita species the tegmina are considerably longer than the pronotum or even projecting beyond the abdomen tip, with hind wings being present (Beier 1960). However, both genera probably should not be kept in two different tribes.

For a long time I thought a Disceratus species discovered in 1997 on the Eastern Andean Cordillera in the very south of Ecuador was new (Braun 2002, 2008), but apparently it belongs to D. nubiger Scudder 1869, the type species of the originally monotypic genus. It has never been reported again since its original description, based on a female from a place called Salto (perhaps a waterfall) on the slopes of the volcano Antisana, also on the Cordillera Oriental, at 10,000 feet (around 3000 m). The expedition led by naturalist James Orton, during which the specimen was collected, ascended Antisana on its western slope, reaching “a little lake called Mica” (Orton 1870). This is the Laguna de la Mica at over 3900 m (Google Earth). The new locality is 410–420 km further south. There the species seems to live in bamboo thickets in cloud forest (so the name “nubiger”, borne by the clouds, is quite appropriate). It requires the aid of an ultrasound detector and the male's distinctive and incessant calling song to detect these cryptic katydids.

Investigation area and methods.—The species was found during extensive fieldwork in Podocarpus National Park and its surroundings between August 1997 and January 2000 (Braun 2002, 2008). At that time a collecting permit was provided by the Instituto Ecuatoriano Forestal y de Áreas Naturales y Vida Silvestre (INEFAN), which in 1999 was integrated in the Ministero del Ambiente del Ecuador. The collected individual was accommodated in a dome-shaped gauze cage with a square base of 30 cm side length and a height of 15 cm. It was furnished with plant parts and provided with small cucumber pieces almost every day. Sound recordings of the caged male and of undiscoverable males in the field were made with a Laar Bridge Box XL (BVL von Laar, Klein Görnow) at 400 kHz sampling rate and stored on DAT (digital audio tape) using a Sony Walkman (TCD-D7 and TCD-D100). Temperatures were taken with a simple pocket thermometer. A Mini-3 heterodyne bat detector (Ultrasound Advice, London) was used for acoustic monitoring. Sound analysis was done with Avisoft-SASLab Pro (R. Specht, Berlin). Recordings were also stored as WAV files: originally ten times slowed down on DAT, read in with 22.05 kHz sampling rate in Cool Edit 2000 (Trial Version), and then set to 220.5 kHz. Sound recordings, additional images and a map are available on Orthoptera Species File Online (Eades et al.). Photos of type specimens of other Disceratus species and the Gnathoclita species can also be accessed there.

Fig. 1.

Male of Disceratus nubiger: Two staged photos during day; locality on western slope of Cajanuma ridge at almost 3000 m (photographed in January 2010); specimen in lateral, frontal and dorsal view, and subgenital plate in ventral view (specimen cbt016s01).

f01_01.jpg

Disceratus nubiger Scudder 1869
 urn:lsid:Orthoptera.speciesfile.org:TaxonName:465472

  • Examined specimens.— Male cbt016s01, Ecuador, Provincia de Loja, Parque Nacional Podocarpus, Cajanuma (access to park south of Loja), 2990 m, 17 October 1999, leg. H. Braun, in collection of author; another male was destroyed when it drew its powerful mandibles into the finger of a startled field assistant of F. Matt, right after it was caught by the latter in December 1997 at the same site at a slightly lower elevation: this specimen's remains were used for drawings of the cercus (Fig. 2).

  • Descriptive notes and comparison with holotype.—Most morphological details are illustrated (Figs 1, 2). In comparison with the female holotype, the mandibles are strongly elongated and the rear margin of the pronotum is upcurved (both sexual dimorphisms). On the lateral lobes of the pronotum the blackish coloration of the ventral margin and the upper rear corner is slightly more extensive. The tegmina, bearing the stridulatory apparatus, are only a little shorter than the pronotum. The legs, especially the femora, seem somewhat stouter. Prosternal spines are delicate and short (shorter than the clypeus hornlets), mesosternal lobes are pointed and erected, metasternal ones broadly rounded, and the metasternal pit is transverse, short, and deep (divided by a thin medial ridge). Fore femora bearing two ventral spines, middle femora two, and hind femora four. Only the internal genicular lobes of middle and hind femora are armed. In the female holotype the external lobes of hind femora are rounded and unarmed and “some of the internal genicular lobes are armed” (Hebard 1924).

  • Measurements.—Length of pronotum 6 mm (same in holotype), tegmina 5 mm, hind femora 11 mm (13 mm in holotype).

  • Comparison with other species.— The male of D. anostostoma has longer and more down curved clypeus hornlets (length greater than diameter of eye), cerci without dorsal spinule, its subgenital plate has a v-shaped emargination, and the distance between the styli is barely greater than half their length. The D. immanis pair each have thinner clypeus hornlets, male cerci and subgenital plate seem to be like in D. anostostoma, and the mandibles are also considerably elongated in the female, although less so than in the male. The female of D. festae has small clypeus hornlets, pronotum without black median stripe, and distally blackened abdominal tergites. The female of D. karschi has very short clypeus knobs and femora with black medial stripes.

  • Song.—Two males calling from inaccessible bamboo shrubbery were recorded at night in the field and a located and captured individual was later recorded calling caged. The song of this nocturnal species was also discovered subsequently on a recording of the little walking leaf katydid Typophyllum egregium (Fig. 3A). It makes long series of very short low-ultrasound clicks at an almost constant repetition rate (Fig. 3). At a temperature of 7°C at night in the natural habitat one click every 400–500 ms. These clicks have a loud onset and rapidly decay within 10–15 ms. Considering that loud clicks produce echoes, particularly in dense vegetation, the real signal duration might be only 1 ms (Fig. 3C). The frequency spectrogram shows a surprisingly sharp peak for such a short signal at 20 kHz (Fig. 3E). This distinctive song, reminiscent of a clockwork, can readily be detected with a bat detector. At a temperature of 18°C the caged male called much more rapidly, producing a click about every 150 ms (Fig. 3D). The carrier frequency is independent of temperature.

  • Distribution and habitat.—Cordillera Oriental in Ecuador, known from western slopes of Antisana around 3000 m and the western slope of the cordillera in Podocarpus National Park 2750 – 3000 m. Living in cloud forest up to tree line, apparently associated with bamboo (including the collected individual 17 calling males were heard with an ultrasound detector in October 1999 — no monitoring occurred below 2750 m, so that the lower limit of altitudinal distribution is uncertain).

  • Fig. 2.

    Male of Disceratus nubiger: habitus, head in frontal view, subgenital plate in ventral view (after specimen cbt016s01), dried left cercus in dorsal view (shrunk, originally more cylindrical over entire length) and external lateral view (after destroyed specimen from December 1997, all pencil drawings from October 2003).

    f02_01.jpg

    Fig. 3.

    Song of Disceratus nubiger: A. accidental recording with call of the leaf-mimicking katydid Typophyllum egregium (two conspicuous syllables in the middle) and Disceratus calling in background (six clicks visible, another one hidden by second syllable of Typophyllum), 11°C, October 1997, 2750 m (recording cbt016×01r01); B. undiscoverable male calling continuously from bamboo shrubbery, 7°C, 17 October 1999 (cbt016×03r01); C. single click from B, below onset in higher resolution; D. collected individual calling like crazy at 18°C in cage (cbt016s01r01); E. linear spectrogram taken from B.

    f03_01.jpg

    Discussion

    Species identity and acoustic monitoring.—It cannot be entirely excluded that the female holotype of Disceratus nubiger and the newly-discovered male belong to different species. It would be necessary to find a male from the type locality to compare it with both the holotype and the male presented in this paper. At present it seems advisable to treat the latter as conspecific rather than to describe it as new species. A possible search on Antisana and at other montane rainforest areas on the Eastern Andean Cordillera in Ecuador should include listening after dusk with an ultrasound detector tuned to 20 kHz. This is a good example of a species with a cryptic lifestyle that can easily be detected acoustically. Without first noticing its conspicuous calling song and then tracking down the two male individuals, this katydid would have gone unnoticed at the new site. There it apparently occurs only on the western slope of the cordillera, whereas the distinctive song could not be detected on the eastern slope at the same elevation range with similar types of habitat. So the distribution of D. nubiger seems to be restricted to the inter-Andean slope.

    Elongated mandibles and systematic issues.—The elongated mandibles in males of Disceratus as well as Gnathoclita could indicate that both genera are closely related (Gorochov 2014), but it could also be the result of convergent evolution. Very similarly elongated mandibles occur in males of the Orthoptera family Anostostomatidae (in particular genus Anostostoma). Henicus monstrosus (Herbst 1803) from South Africa additionally even sports forward-directed processes on the genae, recalling the clypeal hornlets in Disceratus. The similar shape of male cerci is suggested as another indication for the possible relatedness of Gnathoclita and Disceratus (Gorochov 2014). But such stout cylindrical cerci with broadly rounded tips occur in other genera of Eucocconotini (Ottotettix and apparently Panoploscelis) and Homalaspidiini (Arrhenotettix, Homalaspidia, and Jimenezia). They appear to be prone to substantial shrinkage: the turgescence seems totally lost in dried specimens (Fig. 2 here, Fig. 1 in Braun 2011, well preserved in Figs 202, 204 in Gorochov 2014). At the moment it is perhaps practical to include Disceratus along with Gnathoclita in Eucocconotini instead of moving it back to Homalaspidiini, despite the smooth rather than granulated surface of the pronotum in some species (including D. nubiger), the obtuse-angled and not square anterior corners of its lateral lobes, and the missing ventral tubercles at the base of fore and middle coxae (also practically absent in specimens of a new Myopophyllum species from southern Ecuador, pers. obs.). Includingboth genera in the not very well defined Homalaspidiini appears less appropriate.

    Coming back to the enlarged mandibles: in Anostostomatidae they are used in combat between males, e.g. to control tree cavities where females find refuge during the day (e.g. Kelly 2004). An adaptation for aggressive behavior was also assumed for Gnathoclita sodalis Brunner von Wattenwyl 1895 (Montealegre & Morris 1995). However, males of this species seem to use tremulation signals to chase off smaller rivals (De Souza et al. 2011). Apparently there are no observations in the wild. The population density of Disceratus nubiger found at the new site, with 17 males calling in one night between 2780 m and 3000 m, is rather low for possible male-male interactions.

    Acknowledgements

    The bat specialist Felix Matt first noticed the ultrasound song of this katydid and managed to track down and capture the first specimen back in 1997. Klaus-Gerhard Heller and Glenn Morris provided useful comments concerning the song, and Glenn also offered suggestions for improving the wording.

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    Holger Braun "Notes on the Tropical Andean Genus Disceratus (Orthoptera, Tettigoniidae, Pseudophyllinae), the Probable Male of D. nubiger, and Its Calling Song," Journal of Orthoptera Research 25(1), 1-5, (1 June 2016). https://doi.org/10.1665/034.025.0102
    Published: 1 June 2016
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