Abstract
ABSTRACTThe 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.
Highlights
Invertebrates have evolved a remarkable array of modes of communication, from chemical markers and aposematic colours to acoustic, vibrational and behavioural cues
Insects have evolved a vast array of secondary defence mechanisms that fulfil an important role in avoiding predation (Belwood, 1990)
Various hypotheses were made from his morphological description which we here investigated; namely that sounds are generated during organ use and proving that the contraction of the abdomen forms the more significant motion in acoustic signal generation
Summary
Invertebrates have evolved a remarkable array of modes of communication, from chemical markers and aposematic colours to acoustic, vibrational and behavioural cues. Insects have evolved a vast array of secondary defence mechanisms that fulfil an important role in avoiding predation (Belwood, 1990) These defences include the more characteristic traits of insects such as the hymenopteran sting, the spray of bombardier beetles (Eisner, 1958) and the saliva of assassin bugs (Edwards, 1961), and often function as a composite of behavioural, physical and chemical elements. Acoustic secondary defences have driven studies of predator–prey dynamics ever since early studies of invertebrate communication (Dumortier, 1963) In this context, sounds have been found to facilitate predator startle responses (Hoy et al, 1989), aposematic (Batesian) mimicry (Connor, 2014) and even signal jamming of echolocating predators (Connor, 2014)
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