Review Article |
Corresponding author: Wilbur L. Hershberger ( wilhershberger@mac.com ) Academic editor: Klaus-Gerhard Heller
© 2021 Wilbur L. Hershberger.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Hershberger WL (2021) Substrate-borne vibrations used during acoustic communication and the existence of courtship songs in some species of the genus Anaxipha (Saussure) (Orthoptera: Trigonidiidae: Trigonidiinae). Journal of Orthoptera Research 30(2): 185-191. https://doi.org/10.3897/jor.30.70990
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Anaxipha (Saussure, 1874) are small, swordtail crickets found in much of eastern North America. Many species within the genus Anaxipha were only recently described and their calling songs characterized. However, little is known about their courtship songs or use of substrate-borne communication (drumming). This study is the first documentation of the existence of courtship songs and substrate-borne vibrational communication in the genus. Courtship songs and substrate-borne vibrational communication were first detected in the following species: Anaxipha exigua (Say, 1825), A. tinnulacita Walker & Funk, 2014, A. tinnulenta Walker & Funk, 2014, and A. thomasi Walker & Funk, 2014. When in the presence of a conspecific female, males of all four species perform courtship songs that are distinctly different in pattern of echeme delivery and syllable details compared to their respective calling songs. Additionally, males of all four species exhibited drumming behavior during courtship singing and variably during calling songs. Examination of video recordings of males drumming during courtship singing showed that they are apparently using the sclerotized portion of their mandibles to impact the substrate on which they are perched to create vibrations. Courtship song and drumming bout characteristics were statistically different among the four species studied here, although A. tinnulacita and A. tinnulenta were similar in some measurements. Drumming during calling songs was common only in A. tinnulacita, where drumming occurs predominately during the first forty percent and last twenty percent of the long echemes of calling songs. Additional study is needed to further explore the use of substrate-borne vibrational communication in this genus.
communication, courtship, courtship song, drumming, echeme, substrate-borne vibrations, vibration
Large numbers of species of small insects use substrate-borne vibrations for near-field communication with conspecifics (
All the species of Anaxipha (Saussure, 1874) in this study are tiny insects, less than 8 mm in length, and occur on a wide variety of plants and plant structures in North America (
Males and females of A. exigua (Say, 1825), A. tinnulacita Walker & Funk, 2014, A. tinnulenta Walker & Funk, 2014, and A. thomasi Walker & Funk, 2014 were collected in August and September during the years of 2019 and 2020 from appropriate habitats (shrubs, coarse weeds, and grasses at the edges or the understory of deciduous woods) in Berkeley and Jefferson Counties in West Virginia, USA. As in
Acoustic terminology follows
Courtship songs were recorded by placing a female into the cage with the male, placing the cage in a dimly lit anechoic room, and allowing the insects to interact. A minimum of three different males were used for capturing courtship songs for each species. Three to four females were used for different courtship sessions. The recordings were made using the same equipment and techniques described for recording calling songs.
Videos of courtship behavior were made by placing a male and female of the same species into a clear, plastic container with a removable lid. A hole was cut into the lid and covered with no-see-um netting. Video was captured through the side of the clear enclosure using a Canon 5DSR digital camera with a Canon 180 mm macro lens with or without a 22 mm extension tube (Huntington, NY, USA). Lighting was provided by a table lamp with a 40-watt-equivalent LED bulb (to reduce heat). Audio was simultaneously recorded using the Sound Devices 702 digital audio recorder and a Sennheiser ME62 electret-condenser microphone (Solrød Stand, Denmark) placed within a few millimeters of the netting-covered hole of the enclosure. Video was edited in Final Cut Pro X (Apple Corp., Cupertino, CA, USA). All audio and video files are archived at the Macaulay Library, Cornell Laboratory of Ornithology (audio files are ML numbers 305982-306011. Video files are ML number 488780-488784).
Calling songs and courtship songs were processed in Adobe Audition to amplify the frequency band from 0–2 kHz by 10–30 dB to make it easier to detect the drumming bouts in Raven Pro 1.6.1. Drumming bouts were selected by hand from the middle of the first tap’s signature through the middle of the last tap’s signature in each tapping bout (Fig.
All four species produced calling songs consistent with the descriptions in
A typical drumming bout showing the low-frequency and brief nature of these sounds. The figure is the selection of a drumming bout from a courtship song of A. thomasi showing the selection window spanning from the middle of the first tap to the middle of the last tap. This tapping bout consists of 12 taps.
Occurrence of drumming within calling songs of Anaxipha species (average ± SD).
Species | Taps/bout | Taps/s | Syllables/s | Temp. (°C) | n |
---|---|---|---|---|---|
A. exigua | ND | ND | 39.35 ± 0.834 | 22.6 | 9* |
A. tinnulacita | 4.27 ± 1.500 | 18.00 ± 1.525a | 11.20 ± 0.233 | 24.1 | 530 |
A. tinnulenta | 2.83 ± 0.578 | 17.36 ± 2.829ab | 4.82 ± 0.045 | 22.7 | 12 |
A. thomasi | 7.28 ± 0.813 | 17.39 ± 0.504b | 17.90 ± 0.071 | 22.1 | 34 |
Range of the number of taps per drumming bout by song type. ND = not detected.
Species | Song Type | |
---|---|---|
Calling | Courtship | |
A. exigua | ND | 4–10 (33) |
A. tinnulacita | 2–8 (1502) | 3–9 (21) |
A. tinnulenta | 2–4 (12) | 4–9 (98) |
A. thomasi | 6–9 (31) | 3–14 (92) |
A. tinnulacita
produced numerous drumming bouts during calling songs. Analysis of the different drumming bout types (number of taps per bout) used during calling songs showed that A. tinnulacita uses the three, four, and five taps per bout tap-type most of the time (Fig.
When males were placed in the same container with a conspecific female, all four species performed courtship songs. The males for the species in this study held their wings up, nearly perpendicular to their bodies, during calling and courtship singing. The courtship songs were different from calling songs in their overall amplitude and the amplitude envelope over time. Courtships songs were also broken into smaller echemes, particularly after the first several seconds of song during any particular courtship song bout (Fig.
All four species in this study also produced numerous drumming bouts during courtship songs. The range of the number of taps per drumming bout was higher in courtship songs than in calling songs, with A. exigua giving 4–10 taps/bout, A. tinnulacita giving 3–9 taps/bout, A. tinnulenta giving 4–9 taps/bout, and A. thomasi giving 3–14 taps/bout (Table
During courtship songs, tapping within any particular drumming bout increases in peak amplitude in all four species, with the ending of a drumming bout being statistically louder than the beginning, with a p-value of < 0.0001 for each comparison (Fig.
Mean number of drumming bouts performed during different portions of calling songs in A. tinnulacita showing standard error of the means. The occurrence of drumming was variable from one calling song to the next. Consistently, more drumming bouts were given during the first 40 percent and the last 20 percent of the major echemes of calling song (n = 14 songs, 1218 drumming bouts total).
Oscillograms of the calling and courtship songs of the four species of Anaxipha. A1. A. exigua calling song; A2. A. exigua courtship song; B1. A. tinnulacita calling song; B2. A. tinnulacita courtship song; C1. A. tinnulenta calling song; C2. A. tinnulenta courtship song; D1. A. thomasi calling song; D2. A. thomasi courtship song. All audio files were normalized to -3 dBFS for comparison. Y-axis represents amplitude and is analogous to dBFS (full scale).
Audio spectrograms of three seconds of calling and courtship songs of the four species of Anaxipha. A1. A. exigua calling song; A2. A. exigua courtship song; B1. A. tinnulacita calling song; B2. A. tinnulacita courtship song; C1. A. tinnulenta calling song; C2. A. tinnulenta courtship song; D1. A. thomasi calling song; D2. A. thomasi courtship song. Compared to calling song, the individual syllables of courtship songs are shorter, patterned differently, with more sounds associated with wing-opening movements (wing-dragging).
Syllable duration comparison between song types (average ± SD). The syllable duration is statistically significantly shorter in courtship songs across the four species in this study. Numbers in parentheses are the number of syllables analyzed from each song type. Due to the significant skewness of the raw data, p-values were calculated from t-tests of Log10 transformed data comparing the sample means.
Species | Syllable Duration (ms) | p-value | |
---|---|---|---|
Calling | Courtship | ||
A. exigua | 17.61 ± 2.662 (961) | 2.83 ± 0.468 (102) | < 0.00001 |
A. tinnulacita | 28.06 ± 0.875 (480) | 12.63 ± 4.764 (480) | < 0.00001 |
A. tinnulenta | 36.11 ± 1.967 (583) | 5.34 ± 1.805 (103) | < 0.00001 |
A. thomasi | 16.85 ± 1.625 (540) | 13.61 ± 5.655 (362) | < 0.00001 |
Average taps/bout and taps/s within courtship songs of the four Anaxipha species compared to the average syllable rate of their respective courtship song during these tapping bouts (± SD).
Species | Taps/bout | Taps/s | Pulses/s | Temp. (°C) | n |
---|---|---|---|---|---|
A. exigua | 6.61 ± 1.340a | 19.91 ± 0.941 | 39.15 ± 0.952 | 22.6 | 33 |
A. tinnulacita | 6.19 ± 1.540a | 20.67 ± 0.667 | 13.21 ± 0.067 | 23 | 21 |
A. tinnulenta | 6.93 ± 0.865a | 17.58 ± 1.130 | 4.63 ± 0.053 | 22.1 | 98 |
A. thomasi | 8.41 ± 3.210 | 23.15 ± 0.715 | 20.04 ± 0.221 | 23.5 | 92 |
Audio spectrograms of courtship songs of four species of Anaxipha showing drumming bouts (below 2 kHz) and tegminal sounds (above 4 kHz). Low frequencies (below 2 kHz) were enhanced to better show the low-frequency drumming bouts. A. Anaxipha exigua, dark areas below 1 kHz are drumming bouts; B. Anaxipha tinnulacita, fine, dark lines after 1:05 (min:sec) are the drumming bouts; C. Anaxipha tinnulenta, the dark areas after 5 sec and below 2 kHz are the drumming bouts; D. Anaxipha thomasi, the compact dark areas below 2 kHz are the drumming bouts. The clustered, individual taps between drumming bouts are sounds made by the insect jumping repeatedly and rapidly between echemes during the courtship display. Note that the time scales for each courtship song are different, as each species courtship song length is different and variable.
Examination of the means of the average power of the combined first two and the combined last two taps of drumming bouts in courtship songs ±SD. In nearly all instances, tapping becomes louder during an individual drumming bout within courtship songs across all four species. Numbers closer to the abscissas are louder. a = average of the first two taps, b = average of the last two taps in bouts of four taps or more. * = t-tests comparing the means of first two taps to the last two taps, within each species, showed the p-values were all < 0.0001, showing that the taps are significantly louder at the end of drumming bouts (A. exigua n = 5 songs, 45 drumming bouts; A. tinnulacita n = 4, 29; A. tinnulenta n = 4, 98; A. thomasi n = 5, 75).
Average of the peak frequencies in Hz of highest amplitude frequency of taps of drumming bouts for the specific container type in which these insects were kept.
Species | Peak Frequency ± SD | n |
---|---|---|
A. exigua | 89.8 ± 35.59 | 5, 48 |
A. tinnulacita | 277.0 ± 58.12ab | 5, 33 |
A. tinnulenta | 266.5 ± 27.84a | 5, 73 |
A. thomasi | 287.8 ± 55.96b | 5, 72 |
A. thomasi
was the only species in this study that performed jumping motions during the silent periods between echemes within courtship songs. The male would repeatedly jump backwards slightly, with irregular, rapid motions creating sounds when coming to rest on the substrate. These motions created low-frequency sounds similar in carrier frequency to those in typical tapping bouts, but the pattern of these sounds was very different from the tapping bouts given during courtship or calling song echemes (Fig.
Also noted during close examination of these species’ courtship interactions were palp-drumming sessions performed by the males typically during non-singing portions of the courtship interactions when the male and female were in close proximity (video files of this behavior are at ML488780, ML488782, and ML488784). These palp-drumming sounds were of extremely low amplitude and required significant amplification of the audio to hear them; they were not studied further here.
This is the first report showing that members of the genus Anaxipha use substrate-borne vibrations as a possible method of communication and the first to demonstrate that these trigs produce courtship songs that are distinctly different from their typical calling songs. The use of courtship songs in other Gryllidae is well known (
The high amplitude of calling songs would seem to make it harder for females to locate a displaying male in the tangle of vegetation typical of the habitat types used by these insects. The use of substrate-borne vibrations (drumming) certainly would make it easier for searching females to find courting males (
Three of the species studied here used drumming during calling songs. While these substrate-borne vibrations would certainly aid searching females looking for a perspective mate, it is unclear why A. exigua did not appear to perform drumming during calling song bouts, while drumming bouts were readily detected in the other three species studied here. Also, it is interesting that drumming bouts were easily detected in the courtship songs of A. exigua. Further study of A. exigua’s calling songs in a different container type would be illuminating to ensure that some aspect of the structure of the singing cages used here was not preventing the insect from producing these particular sounds.
It appears that the combination of calling song syllable rate, courtship song syllable rate, and the tapping rate in drumming bouts would clearly define each of these four species as distinct and separate to listening females. The change in the syllable length and syllable loudness in courtship songs along with the enhanced use of wing-closing sounds, the change in the pattern and amplitude envelope, and the increase in production of longer drumming bouts (more taps/bout) would clearly signal to the female the presence of a receptive male of the correct species.
Additional maneuvers and vibrations were only observed in A. thomasi, with males jumping (irregular, rapid, backward motions) during the silent portions of courtship encounters. It appeared that the sounds were created by his feet hitting the substrate as he lands from the jumping motions. These jumping sessions were only performed when he was not creating sounds with his tegmina. Also, males did not appear to drum during these jumping displays. The significance of these additional displays requires further investigation.
In all the species in this study that were videoed during courtship displays, males were observed to perform palp-drumming during quiet portions of the courtship display. These sounds were extremely faint. Future study of palp-drumming will require very sensitive equipment, such as laser-vibrometry, to fully detect what the males and the females are communicating to one another during these easily overlooked courtship interactions.
I am grateful to the Potomac Valley Audubon Society for granting me permission to study these species at their preserve and for the permits to collect specimens. I am grateful to Dr. Thomas J. Walker, Professor Emeritus, University of Florida, for his generous sharing of his knowledge and data. I would like to thank Dr. David Funk for sharing information and comments about these species and their songs. I am thankful to the Orthoperists’ Society for providing funding to publish this paper. Thanks also to the anonymous referees. I am also grateful for the assistance of Dr. Tracy Leskey and the JOR editor for invaluable improvements to this manuscript. All audio recordings associated with this project are archived at the Macaulay Library, Cornell Laboratory of Ornithology, ML numbers 305982-306011 and 488780-488784.