invertebrates

The sea is actually a very noisy place. Sound is a convenient mediator of information in water, since it travels far, irrespective of daylight and visibility. This has been exploited by all sorts of animals living in the sea. However, the acoustical properties of water put special demands on sea animals trying to use sounds. This has lead to a rich variety of adaptations in both sound generators, receptors and use in the sea. Among the noisiest sea creatures is a Crustacean, the snapping shrimp Alpheus japonicus, producing a pistol shot like, broadband (<20-200 kHz) sound with their claws. They do so in connection with prey capture, resulting in the immobilizing of small fish. It is not the sound itself, but a powerful jet of water ejected through a hole in the claw, that blocks out the fish's linear system. The sound is produced when two smooth surfaces, pressed tightly in the open claw, are suddenly forced apart when the claw is closed. Less noisy are fish, mostly limiting themselves to silent, low frequency grunts used in social contexts. Sometimes the fish bladder is used as a resonance chamber, amplifying the sound. Hearing is mostly limited to the low frequency range, even if recent research shows that e.g. herrings Clupea harengus may hear up to over 10 kHz. Birds are not believed to display much underwater social behaviour, nor sounds. But loons (Gaviidae), penguins (Spheniscidae), cormorants (Phalacrocoracidae), diving ducks such as the eider duck Somateria mollissima, and auks (Alcidae) all make noise when swimming, mainly cavitation noise. All marine mammals, when they returned to a life in the sea, had to re-adapt to the acoustical properties of water. In order to be effective, both the terrestrial sound generation and reception systems had be remodelled. This has occurred to a various extent in present day marine mammals. Water dwelling Carnivores, such as the polar bear Thalarctos maritimus, may be good swimmers and divers, but have not developed special underwater adaptations in neither sound generation nor hearing. The otter Lutra lutra and the mink Mustela vison chase and catch fish under water, but then apparently rely on vision and touch (vibrissae). They too have normal terrestrial ears. Propeller-like noise from swimming minks, which is believed to be cavitation noise from the front paws, has been reported. Pinnipeds are much more adapted to life in water, although they have maintained an important link to terrestrial life in connection with reproduction. Therefore they have a sound repertoire for use both in air and in water. Their calls are low frequency, often composed of trains of pulses, but FM sounds also occur. These calls may be heard at great distances. 0ne species, the leopard seal Hydrurga leptonyx, is reported to produce ultrasonic sounds in connection with fish chasing. Often the throat region is seen to be moving and/or inflated in connection with the seals' underwater sounds, indicating that the larynx may be involved in their production, but most often no air is expelled into the water. Or cavity resonance may be involved, e.g. in the bell-like sound of walrus, which is believed to be produced the pharyngeal pouches. Seal hearing is acute and partly adapted to the water physics. The Cetaceans have cut every link to terrestrial life, with no need for compromises in their acoustical adaptations. Baleen whales use very low frequency and sometimes very intense sounds, in order to reach far with their communication signals. Their sound generation mechanism is largely unknown, but may involve resonance in the lungs and/or trachea. Their hearing shows clear morphological adaptations to underwater demands, but so far their characteristics are rather unknown. Odontocetes have gone the farthest in their acoustical adaptation, and have developed the most sophisticated sonar in the animal kingdom. In at least the Delphinids the sonar clicks are concentrated into a narrow beam pointing forward, approximately along the long axis of the rostrum. This is done by means of the melon, a fatty tissue structure in front of the blowhole. Most Delphinids also produce FM whistles in the 5-25 kHz range. The most well-known of these is the so called signature whistle, which is believed to be like an acoustical fingerprint. The sonar clicks as well as the whistles are produced by means of a new sound generation system in the nasal cavities, powered by air pressure created in the bony nares. The main part of the sonar click is purely a tissue phenomenon, whereas the whistles are produced in the air within the nares. The air used during sound production is collected in diverticula just below the blowhole, and is then pulled back to the bony nares to be used again. In its extreme, the pulsed sounds may be powerful enough to debilitate prey. This has been suggested for the sperm whale, where the large head, with the spermaceti organ, may be a huge sound amplifier. The hearing in most Delphinids is extremely acute, ranging from below 1 kHz to 150 kHz. The sounds are entering via the lower jaw, and is guided to the middle ear by mean of a special fatty tissue channel. The hearing is not affected by water depth, indicating that the air in the middle ear is not involved in the sound transmission.

During the past few years, we used acoustic methods to investigate sound communication and to search for the presence and distribution of singing cicadas (Homoptera:  Cicadoidea) in Slovenia, Croatia, Macedonia and S.E. Asia. For detection of high pitched songs of smaller species, e.g. Cicadetta or Tettigetta the use of a bat detector - in our case Ultra Sound Advice 5-25 with the microphone mounted to a Telinga parabola - proved to be very suitable, as reported already at the IBAC conference in Potsdam. We use it mainly in the heterodyne mode with the frequency selector tuned to the lowest frequency. With such equipment it is possible to detect songs of small singing cicadas even in areas with high traffic noise and at a distance of up to about 50 m. In addition to this Telinga microphones Pro 1II and Pro V Science were used for recording in combination with the DAT recorders Sony TCD-D3, -D7, -D10 and Pioneer D-C88. The latter was used mainly in the HS mode in combination with the special version of the Pro V Science microphone, with one mic capsule sensitive also in the ultrasonic range. Such a system enabled us to make recordings in the frequency range of 20 to 44000 Hz. As a result of such investigations in Slovenia, Croatia and Macedonia in the last few years many new data about songs and distribution of single species were obtained. In addition to this, during this survey we found in Slovenia not only Cicadetta montana (Scopoli) as described by Boulard (1995) but, with the aid of the bat detector, another similar and closely related species with a different song, which still has to be identified. In Macedonia this year we were able to find, record and catch on Galicica mountain yet another unidentified species with a very characteristic song, which is also closely related to Cicadetta montana. Furthermore, it was found that the species Cicadatra hyalinata (Bru1le), considered by some authors to be only a variety of C. atra (Olivier), has a different calling song and is therefore most probably a good species. Most interesting is the discovery of Cicadatra persica (Kolenati) in the Radika Gorge, not previously known from the Balcans and detected for the first time a year before during acoustic scanning of this region. The songs of this species were previously not recorded and analyzed. A detailed description of these interesting cicadas and their songs is in preparation.

In the genus Drosophila, mating is the result of a courtship involving several sensory modalities. A key component is the production of song made by the male. These sounds, directed towards females, are produced by wing vibration. They consist of sine song and intermittent pulse trains varying in length. The pulses are separated by interpulse intervals (lPI), whose mean values are characteristic of each strain. The aim of this work is to compare the development of the species specific song in two related strains Drosophila melanogaster and D. simulans. Is there progressive maturation or a sudden establishment of the song pattern? Is the pattern common at the first stage but divergent afterwards, according to each strain? Males were placed with mature female at six precise stages of maturation (12, 17, 22, 27, 33 hours and mature (4 days)) and the courtship was recorded. In the melanogaster strain, frequencies of pulse and sine are very close to those of the mature stage as early as 12 hours but the rhythm of emission differs. It is only at 27 hours that the mature rhythm appears and consequently that males succeed in mating. In simulans, experiments are under way.

The aim of this work is to amplify the knowledge of acoustic communication in ants. Four myrmicinae species belonging to the genus Messor (i.e. M. capitatus, M. minor, M. structor and M. wasmanni) were tested. Some Messor species have already been the object of a preliminary study only on workers (Schillinger and Baroni Urbani, 1985), but in our work the ultrasonic emission of specimens belonging to the castes of queens, males and workers (minor and major) were recorded. Ultrasonic signals were acquired using a Bruel & Kjaer 2231 with a B&K 4135 transducer (frequency response up to 100 kHz) and a bat detector Ultra Sound Advice S-25. Signals were fed into an amplifier with an anti-aliasing low-pass filter to be digitally recorded and analyzed on a Pc-based Digital Signal Processing Workstation. Sampling frequencies up to 20,0000 s/sec allowed recording up to 87.5 kHz. Ants were held with a pincer and the microphone was kept at a distance of approx. 1 cm. The description and measurements of stridulatory apparata were made by means of S.E.M. (Scanning Electron Microscope Cambridge S 250 TP) analysis on the same specimens used for recordings. In all the individuals investigated, a stridulatory organ occurs in the position regarded as typical of Formicidae: the plectrum on the hind margin of the third abdominal tergite and the file of pars stridens on the pretergite of the fourth. The file is made up of very regular parallel cuticular ridges and, in all the individuals examined, extends for almost the whole length of the pretergite itself, stopping at a very short distance from the anterior margin of the pretergite. The pars stridens shows very sharp margins. Posteriorly, some long bristles occur in proximity of the margins. The hind margin of the third abdominal tergite shows, in its very central part, a thickening connected with the scraper. This thickening makes the scraping action of the tergal margin more effective by conferring rigidity upon this region. For each species it is possible to describe a common general pattern of structure and operation of the organ producing sounds and ultrasonic emission which always have values of maximum frequency higher than 41 kHz. Playback tests are in progress in order to clear up the biological role and significance of the acoustic signalling for the survival of the colony of these species.

New data on the sound produced by Sphingonotus coerulans corsicus Chopard, 1923 and Truxalis nasuta Linneo, 1758 are given. Oscillograms of both sounds are provided for the first time, as well as their physical characteristics and other aspects of the communication between specimens. For both species sound seems to be a territorial and sexual cue; they have not been observed singing when isolated, as other Acrididae, but always when they are close to or in contact with other individuals. The song of Truxalis nasuta consists of isolated echemes composed of 7-29 syllables lasting about 0.234 seconds. The syllable repetition rate is about 2.2 syllables/sec. The main frequency of emission is between 1 and 10 kHz, with the main peak at 5 kHz. For Sphingonotus coerulans corsicus two different songs have been recorded, one for territorial behaviour and other for courtship. The territorial song consists of isolated syllables lasting about 0.350 seconds with the main frequency between 4 and 8 kHz, with a peak at 7 kHz. The courtship song consists of a syllable produced by the movement of ' the hind legs followed by several microsyllables produced by light movements of the hind legs. The syllable lasts about 0.670 seconds. Sometimes, after the sounds referred to above, the specimens produce a new syllable, always shorter than the first, and with more microsyllables, but always fewer than before. The frequency of this song lies between 3 and 5 kHz, with the main peak at 3 kHz. This communication has been partially supported by the D.G.I.C.Y.T. grant number P889-0448 of the Spanish Government.

The genus Megatrupes Zunino 1984 is up to now represented by two species, M. cavicollis mates 1887) and M. fisheri (Howden 1987), both distributed between the western Sierra Madre and the Sistema Volcànico Transversal, in Mexico. The aim of our research is to analyze the sound produced by M. cavicollis through two distinct apparatuses - thoraco-elytral and coxo-abdominal. The individuals examined were collected during the summer of 1987 at the Reserva de la Biosfera "La Michilia'', Durango, Mexico. Signals were recorded, acquired and analyzed through the program Signalize 3.12. Each emission consists of a disyllabic chirp, with two distinct sub-units separated by a pause. This is a standard situation among the Geotrupinae. Seven variables concerning duration and frequencies of the chiro have been analyzed. The sexual dimorphism, as regards the morpho-anatomy, does not appear in the acoustic context. Both apparatuses contribute to the sound production. Nevertheless, the coxo-abdominal apparatus seems to be more effective than the thoraco-elytral. Individuals deprived of the elytra emitted stridulations very similar to those usually produced by individuals not experimentally constrained, whereas individuals deprived of their hind legs emitted very thin, unrecognizable sounds. Although statistical analyses of frequencies and duration show significant differences among individuals, males and females do not appear to be separated into two distinguishable clusters.

Hearing in moths has evolved to enable them to detect and evade echolocating bats. Thus most moths are silent. Among Arctiidae click production with tymbal organs on the metathoracic episternites is fairly common, but in most species this is also part of the interaction with bats. However, a few moth species produce sound and use their hearing for intraspecific communication. Generally, the noctuid species described so far produce sound by some kind of stridulatory mechanism, often involving the wings and legs. Here we describe quite another mechanism of sound production in the male noctuid moth Pseudoips fagana (Fabricius) of the subfamily Chloephorinae, involving a ventral "tymbal'' organ centrally located on the ventral part of the basal abdominal segment. P. fagana, the green silver line, is common in northern Europe. The sound production has been detected while the moths my around the tree-tops in the dusk. The clicks sound like electric sparks to the human ear and may be heard at several meters distance. We recorded clicks from males in stationary flight in the lab. The moths would only click while flying in place. We elicited the clicks by very intense ultrasonic sound pulses. The moths produce short series of clicks each lasting around 0.3 to 0.4 ms with maximum sound energy around 30 kHz. The sound pressure level was intense, 119 do SPL at 2 cm. The sound producing organ is buried deep in a groove, but may be observed if the moth is placed ventral side up and the abdomen is bent dorsally. The hearing of P. fagana was measured by recording extracellularly from the auditory nerve. Both males and females were most sensitive around 30 kHz, with a threshold of about 35 do SPL, thus matched to the spectrum of the sounds. There are no behavioural observations on these moths, but we believe it most likely that the sounds are part of the sexual display. Research supported by the Danish National Research Foundation.

The songs of the following species are presented: Conocephalus (Xiphidion) cinereus Thunberg, 1815, C. (X.) ictus (Scudder, 1875), C. (X.) magdalenae Nascrecki, 2000, C. (Anisoptera) strictus (Scudder, 1875), Dichopetala brevihastata Morse, 1902, D. castanea Rehn & Hebard, 1914, D. pollicifera Rehn & Hebard, 1914, Phyllophyllia guttulata Stål, 1863, Stilpnochlora azteca (Saussure, 1859), Boopedon gracile Rehn, 1904, Syrbula montezuma (Saussure, 1861) and Teniopoda tamaulipensis Rehn, 1904. Considerations on distribution, taxonomy, ethology, biodiversity and conservation are given.