bioRxiv preprint doi: https://doi.org/10.1101/429209; this version posted October 1, 2018. The copyright holder for this preprint (which was not certified by peer review) is the author/funder. All rights reserved. No reuse allowed without permission. Antlions are sensitive to subnanometer amplitude vibrations carried by sand substrates Vanessa Martineza,c, Elise Nowbaharia, David Sillam-Dussèsa,b, and Vincent Lorentc, aLaboratoire d’éthologie expérimentale et comparée, Université Paris 13, Sorbonne Paris Cité, 99 av. J-B Clément, 93430 Villetaneuse, France bIRD - Sorbonne Universités, iEES-Paris, U 242, Bondy, France cLaboratoire de physique des lasers, Institut Galilée, Université Paris 13, Sorbonne Paris Cité, CNRS, 99 av J-B Clément, 93430 Villetaneuse, France European pit-building antlions (Myrmeleon inconspicuus / Ram- avalanche alerting the antlion hiding below a layer of sand at bur 1842) are studied in their capacity to detect vibrations gen- the bottom of the trap. The avalanche is maintained by the erated by the locomotion of an ant (Cataglyphis cursor) outside antlion tossing sand towards the prey by the intermediate of the pit. These locomotions have been recorded by laser ve- his eventually closed mandibles. The probability for a prey locimetry and copied in detail in their time sequences. The se- to escape from the pit is very low. quences are replicated by micro-controllers digital outputs act- Since the senses of vision and chemoreception can be dis- ing on piezoelectric transducers placed several centimeters out- side the peripheries of the pits: their actions on the surface of carded (see D. Devetak in (3) chapter 16), we can associate a sand media create surface waves with particle accelerations the prey reception to sand movements either by avalanche or that are 3 orders of magnitude less than g, alleviating any pos- vibrations. The study explained hereafter focuses on vibra- sibility of sand avalanche towards the bottom of the pit. De- tion reception only. It is mostly inspired by the works of Le pending on the amplitude of the vibrations, the antlions answer Faucheux (4), Fertin and Casas (5) and Mencinger-Vrackoˇ back, generally by sand tossing. One remarkable feature is the and Devetak (6) who identified the tufts of bristles around time delay from the start of the cue and the aggressive behavior the body of the antlion as possible mechanoreceptive sensors. induced by this cue. This time delay is studied versus the cue While the seminal work of Le Faucheux concentrate in iden- amplitude. The result of this work is that anlions answer back tifying the bristles as mechanoreceptors by selectively ablat- within minutes to cues with amplitudes between 1 to 2 nanome- ing those, the independent studies in the groups of Casas and ters at the level of their mechanosensors, and within seconds to Devetak demonstrated the ability of the antlion to localize its these same cues if they are preceded by a sequence of signals at the Ångström amplitude. This induced aggressive behaviour prey in evidencing the strong correlation of sand tossing di- evidences the sensitivity to vibrations at extremely low level. rection and prey direction. Our study is made with no interference with the behavioural arthropod sensors | behaviour physiology | vibration propagation in granular media | biomechanics repertoire of the antlion, whereas the preys are replaced by Correspondence: [email protected] artificial cues with a total control of the amplitude of the vi- bration: the vibration induced are far from originating any avalanche leaving only vibrations as a signalization of the 1. Introduction presence of a prey. In this framework we specifically address The question of vibrational communication intermediated by the question of a threshold in the perception of vibration. mechanoreceptors in arthropods has received many attentions particularly in arachnids. Spiders have been the object of 2. Material and Methods an extensive study (for a complete overview seeDRAFT the book of Friederich G. Barth (1)). The seminal work of Philip H. (a) Choice of animal model. The ecology of antlions in- Brownell (2) in the seventies was devoted to the study of forms us that 10 % of the species (7) are digging a pit in how desert scorpions locate their prey. The desert scorpions the sand or in a similar granular media. Once this construc- are poorly equipped with visual auditory and olfactory senses tion done, the antlion waits at the bottom of the trap for a and hence their prey detection is by a large extend due to the prey to descend the slope of this funnel. Depending of the vibration reception through their sensilla located at the tarsi. size and weight of the prey, this last one might eventually be In terms of sensory systems, the antlion larvae is similar to able to climb up the sand slope (8). On the other hand, the the desert scorpion in its low ability in seeing and high sen- antlion, alerted by the sand avalanche and/or the sand vibra- sitivity in vibration detection. In term of biotope, the antlion tion, tosses sand in the direction of the prey to aggravate the shares also similarities with the desert scorpion, at least for falling of the prey. We concentrate our study to the perception the perception of the vibrations: in both cases, those vi- of vibrations by the antlion, alleviating any chance that this brations are propagated through a granular media. Unlike antlion is alerted by sand avalanche. Euroleon nostras has the desert scorpion, the hunting strategy of the sand dig- been studied extensively in the context of the mechanorecep- ging antlion is to sit and wait for its prey. A funnel conical tors physiology (4,6,9) and in the context of environmental shape built by the antlion inside a granular media (generally factors and conditioning (10–12). Among the sit and wait sand) serves as a trap for any arthropod of reasonable size antlions, Euroleon nostras and Myrmeleon inconspicuus are adventuring into it. Usually the presence of a prey creates an very similar in their behavior (13) therefore we considered V Lorent et al. | bioRχiv | October 1, 2018 | 1–10 bioRxiv preprint doi: https://doi.org/10.1101/429209; this version posted October 1, 2018. The copyright holder for this preprint (which was not certified by peer review) is the author/funder. All rights reserved. No reuse allowed without permission. that Myrmeleon inconspicuus antlions collected in the for- (Fig.1). The ant crawls over a 10 cm × 5 cm paper surface est of Fontainebleau to be a good model for the studies con- centrated to the mechano-perception of preys. The antlions selected for the study have been characterized in size and weight (see Supplementary Note-Subjects Table SN1). (b) Analysis of a natural cue inducing an agonistic behaviour of the antlion. It is usually evidenced that the antlion attacks the prey while it falls into its pit, and there is generally no such a behaviour when the prey is outside the pit. An agonistic behaviour is usually not demonstrated when the prey is outside the pit but some antlions, while they are in the process of digesting their prey nevertheless pay attention to their environment. It has been evidenced that an antlion is violently throwing away the caught prey if another ant is crawling at some distance (a distance up to 20 cm away from the border of the pit has been noticed in the laboratory). This last behaviour gives an hint about the mechano-sensory per- formance of an antlion. A first approach to quantify the am- plitude of the signal received by the antlion would then be to Fig. 1. The figures above displays the transverse velocity of a 10 cm × 5 cm paper measure the vibration signal propagating through the surface surface measured by laser velocimetry. This surface acts as a drumhead while a −1 of the sand when this vibration is induced by an ant passing Cataglyphis cursor ant is walking on it. The vertical scale is in ms . The figure above is a velocimetry recording during 22 s. The figure below is a detail of this by. We made an attempt to measure these vibration in the fol- recording during 40 ms. lowing procedure: a Cataglyphis cursor ant, weighting 4 mg was placed around the pit of an antlion, while the antlion re- illuminated from beneath by the laser beam of a commercial moved. At the bottom of the pit there is a 5 mm2 reflective laser velocimeter (Polytech pdv-100). Velocimetry data has stamp, adhesive on one side (that makes it embedded with been acquired in conjunction with video screening in order the surface sand). The laser beam of the velocimeter strikes to exclude data resulting from the eventual contact of the ant upon that small stamp. One films the ant in synchroniza- with the boundaries of the paper drumhead. Hereafter the se- tion with the velocimetry recording. Given the noise level 1 lected velocimetry data has been replicated in the time inter- , no velocimetry signal can be retrieved while the ant is out- vals. A microprocessor board (Arduino Uno) is then coded to side the pit. Inside the pit, two different types of signals are produce a 5 volt digital output pulse of 350 microseconds du- recorded, identified mainly by their amplitudes: while the ant ration replicating these recorded time lapses. Whereas Fertin crawls back to exit the pit some avalanches are created with and Casas (5) choose to produce signals based on regular amplitudes in the 1 µm − 10 µm scale and signals of ampli- pulses of fragmented 4 kHz sinusoidal of 350 microsecond tudes between 0.05 µm to 0,5 µm with frequencies around duration, we choose to apply 350 microsecond square pulses 1200 Hz, typical of the vibration propagation induced by a on the surface of the sand trough the action of the active sur- stepping function or an impulse on a sand surface.