The Ander's organ: a mechanism for anti-predator ultrasound in a relict orthopteran
grig, insect, bioacoustics, predation, secondary defences, ancient
The use of acoustics in predator evasion is a widely reported phenomenon amongst invertebrate taxa, but the study of ultrasonic anti-predator acoustics is often limited to the prey of bats. Here, we describe the acoustic function and morphology of a unique stridulatory structure – the Ander's organ – in the relict orthopteran Cyphoderris monstrosa (Ensifera, Hagloidea). This species is one of just eight remaining members of the family Prophalangopsidae, a group with a fossil record of over 90 extinct species widespread during the Jurassic period. We reveal that the sound produced by this organ has the characteristics of a broadband ultrasonic anti-predator defence, with a peak frequency of 58±15.5 kHz and a bandwidth of 50 kHz (at 10 dB below peak). Evidence from sexual dimorphism, knowledge on hearing capabilities and assessment of local predators, suggests that the signal likely targets ground-dwelling predators. Additionally, we reveal a previously undescribed series of cavities underneath the organ that probably function as a mechanism for ultrasound amplification. Morphological structures homologous in both appearance and anatomical location to the Ander's organ are observed to varying degrees in 4 of the 7 other extant members of this family, with the remaining 3 yet to be assessed. Therefore, we suggest that such structures may either be more widely present in this ancient family than previously assumed, or have evolved to serve a key function in the long-term survival of these few species, allowing them to outlive their extinct counterparts.
Woodrow, C., Judge, K. A., Pulver, C., Jonsson, T., Montealegre-Z, F. (2021). The Ander’s organ: a mechanism for anti-predator ultrasound in a relict orthopteran. Journal of Experimental Biology, 224: jeb237289. https://doi.org/10.1242/jeb.237289
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