02623nas a2200193 4500008004100000245015600041210006900197520182100266653002402087653003302111653002502144653001802169100001702187700002502204700001802229700002402247700002702271856013102298 2018 eng d00aExtreme call amplitude from near-field acoustic wave coupling in the stridulating water insect Micronecta scholtzi (Micronectinae)0 aExtreme call amplitude from nearfield acoustic wave coupling in 3 a

Underwater acoustic transducers, particularly at low frequencies, are beset by problems of scale and inefficiency due to the large wavelengths of sound in water. In insect mating calls, a high call volume is usually desirable, increasing the range of signal transmission and providing a form of advertisement of the signaller's quality to a potential mate; however, the strength of the call is constrained by body size and by the need to avoid predators who may be listening in. Male crickets and water boatmen avoid some of the limitations of body size by exploiting resonant structures, which produce sharply tuned species-specific songs, but call frequency and volume remain linked to body size. Recently, the water boatman Micronecta scholtzi was found to circumvent this rule, producing a louder mating call than that of similar, but much larger, Corixa. The resonant structure in Corixidae and Micronectinae is believed to be the trapped air reserves around the insect as it dives, driven by a stridulatory apparatus. However, the method by which energy is transferred from the striated area to the bubble is unknown. Here, we present modelling of a system of near-field coupling of acoustic sources to bubbles showing an exponential increase in sound power gain with decreasing distance that provides a simple solution to the stimulus of the air bubbles in Corixidae and Micronectinae and explains the discrepancy of M. scholtzi's extreme call volume. The findings suggest a possible route to engineered systems using near-field coupling to overcome size constraints in low-frequency (less than 500 Hz) underwater transducers, where the input efficiency of a piezoelectric device can be coupled through the hydrodynamic field to the high radiative efficiency of a near-ideal monopole emitter.

10aMicronecta scholtzi10anear-field acoustic coupling10aunderwater acoustics10awater boatmen1 aReid, Andrew1 aHardie, David, J. W.1 aMackie, David1 aJackson, Joseph, C.1 aWindmill, James, F. C. uhttps://royalsocietypublishing.org/doi/10.1098/rsif.2017.0768https://royalsocietypublishing.org/doi/pdf/10.1098/rsif.2017.076801753nas a2200133 4500008004100000245011400041210006900155520126000224100001801484700001801502700002701520700001901547856005301566 2011 eng d00aSo Small, So Loud: Extremely High Sound Pressure Level from a Pygmy Aquatic Insect (Corixidae, Micronectinae)0 aSo Small So Loud Extremely High Sound Pressure Level from a Pygm3 a

To communicate at long range, animals have to produce intense but intelligible signals. This task might be difficult to achieve due to mechanical constraints, in particular relating to body size. Whilst the acoustic behaviour of large marine and terrestrial animals has been thoroughly studied, very little is known about the sound produced by small arthropods living in freshwater habitats. Here we analyse for the first time the calling song produced by the male of a small insect, the water boatman Micronecta scholtzi. The song is made of three distinct parts differing in their temporal and amplitude parameters, but not in their frequency content. Sound is produced at 78.9 (63.6–82.2) SPL rms re 2.1025 Pa with a peak at 99.2 (85.7– 104.6) SPL re 2.1025 Pa estimated at a distance of one metre. This energy output is significant considering the small size of the insect. When scaled to body length and compared to 227 other acoustic species, the acoustic energy produced by M. scholtzi appears as an extreme value, outperforming marine and terrestrial mammal vocalisations. Such an extreme display may be interpreted as an exaggerated secondary sexual trait resulting from a runaway sexual selection without predation pressure.

1 aSueur, Jerome1 aMackie, David1 aWindmill, James, F. C.1 aSoares, Daphne uhttps://dx.plos.org/10.1371/journal.pone.0021089