Bioacoustics of Eneoptera caliginosa

Taxonomic discussion. Chopard (1931a) mentioned that Platydactylus caliginosus differs from E. surinamensis in the study describing the species E. guyanensis . However, in his 1968 catalogue, he considered P. caliginosus as a synonym of E. surinamensis , with no further explanation ( Chopard, 1968 ). The name was later treated by Robillard & Desutter-Grandcolas (2005) as having an unclear status ( E. caliginosus ?) in their revision of Eneoptera and did not study the type specimen. Here, we compared the type specimens of E. caliginosa and E. gracilis , which revealed that despite minor differences, the two species are very similar in terms of external morphology and male genitalia ( Figs 1 , 3 ). Original descriptions by Walker (1869) are very brief, and E. gracilis was described without prior examination of the type of P. caliginosus ; in this context, it is likely that E. gracilis , described from Colombia ( Fig. 1E–G ), could correspond to P. caliginosus , described from Guyana ( Fig. 1A–D ). Our comparisons of specimens from various localities from French Guiana, Brazil , Colombia , Venezuela , Suriname and Bolivia support this hypothesis, as there are only minor and inconsistent differences among these localities that could be either explained by intraspecific variation within a given series, or by the wide geographic range. While no detailed molecular data is available yet to test the similarity between the two species, acoustic data are clearly supporting it: the call of E. gracilis has first been described by Zefa et al. (2022) based on the recording of specimens from Brazil . Interestingly, despite the fact that E. gracilis was previously known only from Colombia , Zefa et al. (2022) identified their specimens as E. gracilis , the only species likely matching the morphology and male genitalia of their recorded males. The male that we recorded here from the type locality of E. gracilis in Colombia is similar to the call described by Zefa et al. (2022) ( Figs 4A , 5 ). It supports the hypothesis that the specimens from western ( Colombia ) and eastern ( Brazil ) South America belong to one species. Based on these pieces of evidence, and rule of priority, we synonymize E. gracilis Robillard, 2005 under Eneoptera caliginosa ( Walker, 1869 ) stat. nov. as junior synonym ( syn. nov. ).

Redescription Size average to small for the genus, shape slender ( Fig 1 ), variable in coloration (see below), but dorsum generally lighter than rest of body, dark brown. Fastigium (rostrum) rounded dorsally and apically, giving a more globular aspect to head than in other congeners ( Fig. 2A ). Vertex rounded, with three wide, well-marked longitudinal black bands. FWs dull brown in both sexes ( Fig. 1 ). Hind legs elongated, FIII with a straight apical part before knee. Coloration variable, encompassing most color patterns documented in congeners, some specimens being light cream, some dark brown, almost black, with or without orange band on hind knee characteristic of E. guyanensis . Male. Stridulatory file with 51 to 59 simple teeth (mean 55, n=5; Table 2 ). Harp veins straight, parallel on their whole length ( Fig. 11A ). Male genitalia. ( Fig. 3A–E ) Pseudepiphallic sclerite triangular. Lophi as long as rest of pseudepiphallic sclerite, but shorter and less sclerotised than in E. surinamensis , their membranous part visible both ventrally and dorsally. Pseudepiphallic sclerite setose dorsally. Distal lobe of pseudepiphallic parameres short and rounded; median lobe oriented innerly; basal lobe membranous. Ectophallic fold short, almost triangular. Female. FW ( Figs 1B , 2 ) with black triangular area of lateral field made of cells slightly wider than long (about 10 cells in the widest part), their delimiting veins underlined with yellow ( Fig.2A ). Ovipositor shorter than FIII . Female genitalia. ( Fig. 3F ) Copulatory papilla well sclerotised, shorter than in E. surinamensis and diamond-shaped; its distal part enlarged, bifid and membranous. Calling song. ( Figs 4A , 5 , Table 1 ) The call has first been described by Zefa et al. (2022) who studied specimens from Brazil .We describe here the call of a specimen from Menegua, Pto Lopez, Colombia ( type locality of E.gracilis ), which shows similar parameters as reported by Zefa et al. (2022) . The calling song is a continuous trill without amplitude modulation as in the other species of the genus. Syllable duration is 8.1±0.9 ms, for a period of 24.7±1.4 ms, which involves a syllable duty cycle of 33.3%. The dominant frequency is 3.58±0.04 kHz and corresponds to the fundamental peak of the spectrum; the calling song of E. caliginosa does not have any particularity in terms of frequency spectrum, except that the harmonics are powerful, as in other non-Lebinthini eneopterines ( Fig. 5 ), but they never co-dominate the spectrum as observed in the “low frequency” part of the calling song of E. guyanensis ( Robillard et al. , 2015 ) . Sound-production mechanism. ( Fig. 11B , Table 2 ) Males of Eneoptera caliginosa possess ca. 64 teeth, but only 26 are functional teeth arranged along the straight part of the stridulatory file, as typically observed in crickets. The mean inter-tooth distance of the functional part is 35.66 μm (tooth density = 35.4±1.4 teeth/mm). The global speed of stridulation derived from the syllable duration and file length is ca. 109 mm /s, which matches the tooth strike rate that generates the fundamental peak of the spectrum.