Daily Signaling Rate and the Duration of Sound per Signal are Negatively Related in Neotropical Forest Katydids

Abstract

Researchers have long examined the structure of animal advertisement signals, but comparatively little is known about how often these signals are repeated and what factors predict variation in signaling rate across species. Here, we focus on acoustic advertisement signals to test the hypothesis that calling males experience a tradeoff between investment in the duration or complexity of individual calls and investment in signaling over long time periods. This hypothesis predicts that the number of signals that a male produces per 24 hours will negatively correlate with 1) the duration of sound that is produced in each call (the sum of all pulses) and 2) the number of sound pulses per call. To test this hypothesis, we measured call parameters and the number of calls produced per 24 hours in 16 species of sympatric phaneropterine katydids from the Panamanian rainforest. This assemblage also provided us with the opportunity to test a second taxonomically-specific hypothesis about signaling rates in taxa such as phaneropterine katydids that transition from advertisement calls to mating duets to facilitate mate localization. To establish duets, male phaneropterine katydids call and females produce a short acoustic reply. These duets facilitate searching by males, females, or both sexes, depending on the species. We test the hypothesis that males invest either in calling or in searching for females. This hypothesis predicts a negative relationship between how often males signal over 24 hours and how much males move across the landscape relative to females. For the first hypothesis, there was a strong negative relationship between the number of signals and the duration of sound that is produced in each signal, but we find no relationship between the number of signals produced per 24 hours and the number of pulses per signal. This result suggests the presence of cross-taxa tradeoffs that limit signal production and duration, but not the structure of individual signals. These tradeoffs could be driven by energetic limitations, predation pressure, signal efficacy, or other signaling costs. For the second hypothesis, we find a negative relationship between the number of signals produced per day and proportion of the light trap catch that is male, likely reflecting males investing either in calling or in searching. These cross-taxa relationships point to the presence of pervasive trade-offs that fundamentally shape the spatial and temporal dynamics of communication.

Satellite remote sensing of environmental variables can predict acoustic activity of an orthopteran assemblage

“…1 , solid lines; Katydid4, Katydid5) maintain constant activity levels throughout the night. Previous studies found a negative relationship between calling signal duration and daily signaling rate in Neotropical katydids as result of acoustic trade-offs ( Symes et al, 2021 ), our data suggests that there might be a positive relationship between the dominant frequency and the daily acoustic activity as well. In addition, although we did not measure body size or specific size and properties of the producing sound structures for the species in our assemblage, crickets were overall smaller than katydid species, thus our observation might be contrary to the predictions of the morphological adaptation hypothesis ( Farina, 2014 ), previously proven in birds ( Wallschläger, 1980 ), mammals ( Fletcher, 2004 ), and frogs ( Boeckle, Preininger & Hödl, 2009 ).…”

“…In addition, we explored the relationship of acoustic activity of each species with environmental variables extracted from satellite remote sensing data. We experienced difficulties in collecting canopy dwellers, for which we recommend the use of specialized methods such as fogging ( Montealegre-Z et al, 2014 ), light trapping ( e.g ., Symes et al, 2021 ), or specialized manual tracking ( Diwakar & Balakrishnan, 2007b ) for future studies. As studies on environmental effects on insect acoustic communities are still rare, our study is an important precedent, and serves as a good example on how satellite remote sensing data can be used along with acoustic monitoring schemes in areas with low accessibility to ground-based methods of environmental measurement, such as weather stations.…”

“…Further research is required to test this hypothesis, as the effect of forest stratification over signal interference in insects remains unclear ( Schmidt & Balakrishnan, 2015 ). In addition, measurements of smaller scale time features could help to confirm temporal masking avoidance at smaller scales ( Symes et al, 2021 ), as Katydid4 and Katydid5 pulse rates and syllable duration seem to differ greatly.…”

Acoustic signalling in Orthoptera

“…Examples include the tree cricket Oecanthus henryi (Torsekar and Balakrishnan, 2020) and the field crickets Teleogryllus oceanicus (Bailey et al, 2010;Balenger and Zuk, 2015) and Gryllus texensis ; for other examples see Robinson and Hall (2002). A study of 16 Panamanian species of katydid showed a trade-off across species between the number of calling songs produced per day and the number of males silently searching (Symes et al, 2021). In duetting species, males may eavesdrop on duetting pairs and perform phonotaxis towards the responding female without singing themselves, as in the phaneropterine bushcrickets Caedicia (Hammond and Bailey, 2003) and Scudderia pistillata (Villarreal and Gilbert, 2014).…”

“…However, there are some exceptions to this pattern: a few species in the Conocephalinae produce very short songs at long intervals, and some species in the Phaneropterinae produce relatively long songs of 1-6 s in duration, or sing frequently. A study of 16 Panamanian species of katydid showed a trade-off across species between the number of signals per day and the duration of sound in each signal (Symes et al, 2021). Symes et al (2016) looked at the singing patterns of eight neotropical katydids.…”