SOUND PRODUCTION AND SOUND EMISSION IN SEVEN SPECIES OF EUROPEAN TETTIGONIIDS PART III. DETERMINATION OF THE MECHANISM OF SOUND PRODUCTION USING CEPSTRUM ANALYSIS

ABSTRACT

The mechanism of sound production in tettigoniids is examined by applying the method of ‘cepstrum’ analysis to insect calls. The power cepstrum is defined as the inverse Fourier transform of the logarithmic power spectrum. This analysis shows that the tettigoniid sound signal is a convolution in time of probably two components. The first is caused by the initial impact of teeth of the stridulatory file on the left wing against the plectrum on the right wing (termed the input pulse); the second is caused by the oscillating properties of the tegmina (these being a function of the intrinsic frequencies of dorsal fields and mirror and their damping properties). In the cepstrum each component appears as a varying number of peaks. The tooth impacts cause a very low quefrency peak probably representing the time in which the two tegmina are in contact during each impact and high quefrency peaks representing the impulse repetition rate. The oscillating properties of the tegmina cause two major quefrency peaks which can be clearly related to the size of the dorsal fields and of the mirror respectively, and therefore to their intrinsic frequencies. The high damping factor of the tegmina together with the transient shape of the tegminal input pulse causes a strong time limitation of the impulses and is therefore responsible for the broad frequency bands occurring in the power spectra of the tettigoniid songs. The impulse generation of a synthetic tettigoniid song is discussed.     

Temporal patterns of geographic parthenogenesis in a freshwater snail

Geographic parthenogenesis describes the observation that parthenogenetic organisms tend to occupy environments different from those of their close, sexually reproducing relatives. These environments are often described as extreme or disturbed habitats. We examined whether patterns of geographical parthenogenesis persist over time, by conducting a 3-year life-history survey and comparing two very proximate habitats of the freshwater snail Melanoides tuberculata : Nahal Arugot, a desert stream naturally disturbed by flash floods, and Or Ilan, a stable freshwater pond. Both sites occur in a xeric environment and are subject to otherwise similar biotic (e.g. parasites, predators) and climatic conditions. In the stable habitat, male frequencies and snail densities were significantly higher than in the disturbed one, whereas infection levels, mean embryo counts, and water temperatures were similar at both sites. Additionally, male frequencies declined after density decreased, thereby providing evidence for geographical parthenogenesis via reproductive assurance. Infection prevalence was very low regardless of reproduction mode. Although further genetic work is required, the apparent metapopulation structure of M. tuberculata in the Judean desert may be suitable for evaluating other possible explanations of geographical parthenogenesis.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 91 , 711–718.     

Insect Melanogenesis. II. Inability of Manduca Phenoloxidase to Act on 5, 6-Dihydroxyindole-2-Carboxylic Acid1

Eumelanins in animals are biosynthesized by the combined action of tyrosinase, 3, 4-dihydroxyphenylalanine (DOPA)chrome isomerase, and other factors. Two kinds of eumelanins were characterized from mammalian systems; these are 5,6-dihydroxyindole (DHI)-melanin and 5, 6-dihydroxyindole-2-carboxylic acid (DHICA)-melanin. In insects, melanin biosynthesis is initiated by phenoloxidase and supported by DOPAchrome isomerase (decarboxylating). Based on the facts that DOPA is a poor substrate for insect phenoloxidases and DHI is the sole product of insect DOPAchrome isomerase reaction, it is proposed that insects lack DHICA-melanin. Accordingly, the phenoloxidase isolated from the hemolymph of Manduca sexta failed to oxidize DHICA. Control experiments reveal that mushroom tyrosinase, as well as laccase, which is a contaminant in the commercial preparations of mushroom tyrosinase, are capable of oxidizing DHICA. Neither the whole hemolymph nor the cuticular extracts of M. sexta possessed any detectable oxidase activity towards this substrate. Thus, insects do not seem to produce DHICA-eumelanin. A useful staining procedure to localize DHICA oxidase activity on gels is also presented.     

SOUND PRODUCTION AND SOUND EMISSION IN SEVEN SPECIES OF EUROPEAN TETTIGONIIDS. PART I. THE DIFFERENT PARAMETERS OF THE SONG; THEIR RELATION TO THE MORPHOLOGY OF THE BUSHCRICKET

Abstract

Comparative studies of sound production and sound emission in seven species of European tettigoniids have been carried out. The species chosen were two Tettigoniines (Tettigonia cantans, Tettigonia viridissima), two Ephippigerines (Ephippiger discoidalis, Ephippiger ephippiger), and three Decticines (Decticus albifrons, Decticus verrucivorus, Psorodonotus illyricus). The factors which determined the choice of species were the different morphology (for example body shape and weight, and wing size) of the three subfamilies. The parameters of the different songs (e.g. dominant frequency, intensity) are normally not correlated to any of the investigated morphological characteristics of the animals. In the brachypterous species intraspecific correlations exist between wing size and the dominant low frequency band of the call. This frequency band is also observable at related higher frequencies in the ultrasonic range (20–60 kHz), the observed band width increasing with frequency. Sound emission in all species is to some extent directional. This directionality is related to body size and wing structure. The song structure of the different species does not appear to be related to any observable characteristic of the habitat of die animals. A possible exception may be the song of Psorodonotus illyricus with a particularly low dominant frequency band. The phylogenetic development of the songs seems to be determined by relationships between the different species rather than to any factors contributed by the habitat.     

SOUND PRODUCTION AND SOUND EMISSION IN SEVEN SPECIES OF EUROPEAN TETTIGONIIDS. PART II. WING MORPHOLOGY AND THE FREQUENCY CONTENT OF THE SONG

ABSTRACT

Sound production in seven species of bush crickets (Tettigonia cantans, T. virridissima, Decticus verrucivorus, D. albifrons, Psorodonotus illyricus, Ephippiger ephippiger, E. discoidalis) has been investigated. Aspects of wing morphology have been compared and show that areas of the dorsal fields and the mirror are correlated with the dominant frequencies of the songs. Tooth removal from the pars stridens produces gaps in the time structure of single syllables but no change in the song power spectra. The removal of the tegminal lateral field in long- and medium-sized wing species (T.c., T.v., D.a., D.v.) produces an increase in the ultrasonic components of caudally-emitted sound. This suggests an absorbing function for the lateral fields in intact animals. In all species removal of a small portion of the mirror frame or of the mirror membrane attenuates the whole stridulatory signal, but especially the ultrasonic components. The mirror therefore functions as an amplifier, especially for high frequencies. Manipulation of the dorsal fields of long- and medium-winged species, or the distal edges of tegmina of brachypterous species, deletes or shifts the songs' dominant frequency. Thus the different tegminal structures (and especially the dorsal fields) contribute to the time structures and power spectra of the stridulatory songs of these species.     

A Race for Space? How Sphagnum fuscum stabilizes vegetation composition during long‐term climate manipulations

Strong climate warming is predicted at higher latitudes this century, with potentially major consequences for productivity and carbon sequestration. Although northern peatlands contain one‐third of the world's soil organic carbon, little is known about the long‐term responses to experimental climate change of vascular plant communities in these Sphagnum‐dominated ecosystems. We aimed to see how long‐term experimental climate manipulations, relevant to different predicted future climate scenarios, affect total vascular plant abundance and species composition when the community is dominated by mosses. During 8 years, we investigated how the vascular plant community of a Sphagnum fuscum‐dominated subarctic peat bog responded to six experimental climate regimes, including factorial combinations of summer as well as spring warming and a thicker snow cover. Vascular plant species composition in our peat bog was more stable than is typically observed in (sub)arctic experiments: neither changes in total vascular plant abundance, nor in individual species abundances, Shannon's diversity or evenness were found in response to the climate manipulations. For three key species (Empetrum hermaphroditum, Betula nana and S. fuscum) we also measured whether the treatments had a sustained effect on plant length growth responses and how these responses interacted. Contrasting with the stability at the community level, both key shrubs and the peatmoss showed sustained positive growth responses at the plant level to the climate treatments. However, a higher percentage of moss‐encroached E. hermaphroditum shoots and a lack of change in B. nana net shrub height indicated encroachment by S. fuscum, resulting in long‐term stability of the vascular community composition: in a warmer world, vascular species of subarctic peat bogs appear to just keep pace with growing Sphagnum in their race for space. Our findings contribute to general ecological theory by demonstrating that community resistance to environmental changes does not necessarily mean inertia in vegetation response.     

Conchometrics, systematics and distribution of Melanopsis (Mollusca: Gastropoda) in the Levant

In this conchometric study, the systematics and distribution of the freshwater gastropod Melanopsis in the Levant are described. Of the ten species found, three are widespread, two have narrow distributions and five are known only from their type locality. Five smooth‐shelled species are recognized (buccinoidea, ammonis, dircaena, khabourensis and meiostoma). Within M. buccinoidea, Jordan Valley populations may belong to a separate subspecies. M. ammonis is clearly differentiated from buccinoidea of the nearby Jordan Valley, but less so from buccinoidea of more distant sites; differences between ammonis and meiostoma are significant but not diagnostic. Five species have ribbed shells. Within costata, four subspecies are recognized (in the northern Orontes, upper Jordan, Sea of Galilee, and in southernmost parts of the Levant). Throughout the Levant, M. buccinoidea frequently hybridizes with M. costata and fossil evidence suggests that these species have been hybridizing for the last 1.5 Myr. M. saulcyi differs from M. costata in its narrower shell and shorter, bumpier ribs and frequently hybridizes with M. buccinoidea throughout the Levant. Specimens from Homs differ from those of the Jordan Valley in their higher figurativity index, fewer ribs and lower rib density. M. germaini differs from M. costata in its more numerous ribs, M. pachya in its shorter ribs, and M. infracincta in its bumpy shell in which each rib has huge tubercles, with a pronounced ridge flanking the columella. Our conclusion that there are ten species in the Levant differs from previous studies that suggested only two subspecies of one species (or superspecies). This difference could stem from (1) our use of nonstandard as well as standard conchometrics, (2) a reappraisal of the importance of the shell vs. the radula in intrageneric systematics, and (3) differences of opinion on the subspecies concept. © 2005 The Linnean Society of London, Zoological Journal of the Linnean Society, 2005, 144 , 229?260.     

The Mediterranean Sea as a ‘cul‐de‐sac’ for endemic fishes facing climate change

The Mediterranean Sea is a hotspot of biodiversity, and climate warming is expected to have a significant influence on its endemic fish species. However, no previous studies have predicted whether fish species will experience geographic range extensions or contractions as a consequence of warming. Here, we projected the potential future climatic niches of 75 Mediterranean Sea endemic fish species based on a global warming scenario implemented with the Mediterranean model OPAMED8 and a multimodel inference, which included uncertainty. By 2070–2099, the average surface temperature of the Mediterranean Sea was projected to warm by 3.1 °C. Projections for 2041–2060 are that 25 species would qualify for the International Union for the Conservation of Nature and Natural Resources (IUCN) Red List, and six species would become extinct. By 2070–2099, 45 species were expected to qualify for the IUCN Red List whereas 14 were expected to become extinct. By the middle of the 21st century, the coldest areas of the Mediterranean Sea (Adriatic Sea and Gulf of Lion) would act as a refuge for cold‐water species, but by the end of the century, those areas were projected to become a ‘cul‐de‐sac’ that would drive those species towards extinction. In addition, the range size of endemic species was projected to undergo extensive fragmentation, which is a potentially aggravating factor. Since a majority of endemic fishes are specialists, regarding substratum and diet, we may expect a reduced ability to track projected climatic niches. As a whole, 25% of the Mediterranean Sea continental shelf was predicted to experience a total modification of endemic species assemblages by the end of the 21st century. This expected turnover rate could be mitigated by marine protected areas or accelerated by fishing pressure or competition from exotic fishes. It remains a challenge to predict how these assemblage modifications might affect ecosystem function.     

Sex versus parasitism versus density

The Red Queen hypothesis predicts that sexual reproduction should be favoured when the risk of infection by parasites is high. However, this prediction may also be achieved independently by means of the reproductive assurance and the density-dependent transmission hypotheses because higher densities increase the chances of fertilization (i.e. mates are easier to find) and increase the risk of infection. Additionally, the Red Queen hypothesis makes a long-term prediction that infection should be genotype-specific, with time-lagged dynamics. In the present study, we attempt to consolidate these two predictions by investigating whether sexuality and parasitism alternate in a time-lagged fashion on an ecological time-scale. In a 3-year study, we examined the time-lagged dynamics between male frequencies, infection levels (by Centrocestus sp.), and snail densities of four natural populations of sexual and asexual Melanoides tuberculata snails. The results obtained provide no evidence of either prediction of the Red Queen hypothesis. We found partial support for reproductive assurance in a single population, and could not discriminate between the three hypotheses in another population. The remaining two populations did not support any of the hypotheses in question.  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 93 , 537–544.