‘Absolute steepness’ of ramps as an essential cue for auditory pattern recognition by a grasshopper (Orthoptera; Acrididae; Chorthippus biguttulus L.)

Male grasshoppers of the species Chorthippus biguttulus react to female songs with a characteristic turn towards the female. The probability of turning towards female song models was used to evaluate those parameters which are essential for a signal to be interpreted as female song.

1. The shape of sound pulses turned out to be most decisive; pulses with ramps rising gradually over 3 and more ms were efficient (Figs. 2, 3), whereas rectangularly modulated pulses evoked only weak responses and only when pulse intervals were between 3 and 5 ms (Fig. 2). The decline of a pulse did not influence its efficiency (Fig. 3). In particular, pulses with sudden onsets and gradual declines were as weakly effective as rectangularly modulated ones and thus remarkably less effective than pulses with ramp-like onsets (Fig. 4).
2. Intensity tuning curves suggest, that the absolute steepness of ramps (expressed as μbar/ms) is detected by the grasshopper nervous system (Figs. 6, 7), possibly by processing the delay in excitation onset of at least two receptor types differing in threshold sensitivity.
3. The sawtooth shape of pulses in female signals is suggested to be adaptive with respect to directional hearing.

     

Operational Sex Ratio and Individual Mating Frequencies in Two Bushcricket Species (Orthoptera,Tettigonioidea, Poecilimon)

During mating the male bushericket transfers a large spermatophore which is consumed by the female after copulation. Such a ‘nuptial gift' is likely to have strong effects on the mating frequency of both males and females and thus on the operational sex ratio (OSR): For the male a longer time period will be required in which he is prevented from further matings. For the female consumption may be advantageous increasing interest in matings. To quantify these effects field studies were carried out on two species of the genus Poecilimon. Both species differed widely in the mean number of matings observed per day (19% of all females in P. veluchianus compaied to 42% in P. affinis; Fig. 2) and thus in the distribution of female mating intervals (P. veluchianus 2 days, P. affinis 1 day (modes); Fig. 3). Separate experiments on the minimum male mating interval and the spermatophore weight also revealed distinct differences: the mean spermatophore weight was 26% of the male body weight in P. veluchianus and 15% in P. affinis (Fig. 6). Accordingly the refractory period was longer in P. veluchianus; 3 days after a previous mating nearh all males were ready to remate, compared to 2 days in P. affinis (Fig. 5). These differences, however, compensated one another in that the amount of spermatophylax material transferred per day was very similar in both species in relation to female body weight. Using data on female mating frequency per day and male remating ability, an upper estimate for the OSR was calculated. A lower limit for the OSR was given taking into account the most frequent female mating interval (big. 7). In both species the OSR remained relatively constant for large parts of the season. The medians (upper/lower estimate for the ratio males to females ready to mate: 2.95/1.19 in P. veluchianus; 2.22 0.88 in P. affinis) were very low, comparable to that in explosive breeding frog species. Thus in the bushcricket mating system, females may be able to demand large male mating efforts so that the operational sex ratio can come close to unity.     

European checkerspots (Melitaeini: Lepidoptera,Nymphalidae) are not aposematic – the point of view of great tits (Parus major)

相似文献   

Object classification by echolocation in nectar feeding bats: size-independent generalization of shape

The nectar-feeding bat Glossophaga can be trained to discriminate two hollow forms, a hollow hemisphere and a paraboloid with the same diameter and depth, in total darkness. During training a saturation level of about 85-90% correct choices or more can be reached within 50-100 visits. To investigate generalization abilities, the bats were tested with pairs of the same shape but of different size. Although no reward was offered, they preferred the hollow sphere (30 mm and 50 mm diameter, but not 18 mm) over the corresponding paraboloids. Thus, the bats were able to generalize some features of the rewarded form and detect them in forms of the same shape but different size. This transposition is remarkable, since the bats could not use absolute spectral characters, but had to pay attention to size-independent features common to hollow hemispheres. Possible cues are the variation of echoes in dependence of different angles of calling direction (constant in spheres, changing with position in paraboloids) and/or the "timbre" of the echoes, i.e. their spectral pattern independent of their absolute pitch     

Echolocation range and wingbeat period match in aerial-hawking bats

Aerial-hawking bats searching the sky for prey face the problem that flight and echolocation exert independent and possibly conflicting influences on call intervals. These bats can only exploit their full echolocation range unambiguously if they emit their next call when all echoes from the preceding call would have arrived. However, not every call interval is equally available. The need to reduce the high energetic costs of echolocation forces aerial-hawking bats to couple call emission to their wingbeat. We compared the wingbeat periods of 11 aerial-hawking bat species with the delays of the last-expected echoes. Acoustic flight-path tracking was employed to measure the source levels (SLs) of echolocation calls in the field. SLs were very high, extending the known range to 133 dB peak equivalent sound pressure level. We calculated the maximum detection distances for insects, larger flying objects and background targets. Wingbeat periods were derived from call intervals. Small and medium-sized bats in fact matched their maximum detection range for insects and larger flying targets to their wingbeat period. The tendency to skip calls correlated with the species' detection range for background targets. We argue that a species' call frequency is at such a pitch that the resulting detection range matches their wingbeat period.     

Validation of a non-invasive blood-sampling technique for doubly-labelled water experiments

Two techniques for bleeding small mammals have been used in doubly-labeled water (DLW) studies, including vena puncture and the use of starved nymphal stages of hematophagous reduviid bugs (Reduviidae, Hemiptera). In this study, we tested the validity of using reduviid bugs in doubly-labeled water experiments. We found that the isotope enrichment in initial blood samples collected with bugs was significantly lower compared to isotope enrichment in blood samples obtained using vena puncture. We therefore used the desiccation method for estimating total body water (TBW) in DLW experiments because TBW calculated using the isotope dilution method was overestimated when blood samples were collected using reduviid bugs. In our validation experiment with nectar-feeding bats (Glossophaga soricina), we compared estimates of daily energy expenditure (DEE) using DLW with those derived from the energy balance method. We considered Speakman's equation (controlling for 25% fractionated water loss) as the most appropriate for our study animal and calculated DEE accordingly. On average, DEE estimated with DLW was not significantly different from the mean value obtained with the energy balance method (mean deviation 1.2%). We conclude that although bug hemolymph or intestinal liquids most likely contaminate the samples, estimates of DEE are still valid because the DLW method does not depend on absolute isotope enrichments but on the rate of isotope decrease over time. However, dilution of blood with intestinal liquids or hemolymph from a bug may lead to larger variation in DEE estimates. We also tested how the relative error of DLW estimates changed with varying assumptions about fractionation. We used three additional equations for calculating DEE in DLW experiments. The basic equation for DLW experiments published by Lifson and McClintock (LM-6) assumes no fractionation, resulted in an overestimate of DEE by 10%. Nagy's equation (N-2) controls for changes in body mass but not for fractionation. Using Nagy's equation, DEE was overestimated by 8%. Under the assumption that 50% of total water flux fractionates, the alternative equation by Lifson and McClintock (LM-35) DEE was underestimated by 5%. The best fit between estimates of DEE based on DLW and energy balance measurements was derived by assuming that 32% of total water flux (TWF) is fractionated. We conclude that the outcome of DLW experiments is sensitive to assumptions regarding evaporative water loss, and thus recommend Speakman's equation 7.17 for use with bats.     

Bat Pollination of Weberocereus tunilla, an Epiphytic Rain Forest Cactus with Functional Flagelliflory

Abstract: We studied the pollination of the epiphytic cactus Weberocereus tunilla (Weber) Britton and Rose at the La Selva Biological Station in the Atlantic lowland rain forest of Costa Rica. The large, night-blooming, unpleasantly-smelling flowers were suspended on elongated main stems that hang down as much as 2 m below canopy tree branches, resulting in a unique form of flagelliflory. The only visitors to flowers were three species of glossophagine bats: Glossophaga commissarisi, Hylonycteris underwoodi and Lichonycteris obscura. Patterns of nectar secretion and concentration were found to be typical for bat-pollinated flowers. Flowering phenology and the occurrence of pollen on bats were recorded during a 1-yr period. Preliminary observations suggest that at least two other Costa Rican species of Weberocereus, W. biolleyi and W. trichophorus and possibly other species of the tribe Hylocereeae, are also pollinated by glossophagine bats.     

Selective phonotaxis in Tettigonia cantans and T. viridissima in song recognition and discrimination

The selectivity of female phonotaxis in Tettigonia cantans and T. viridissima was investigated on a Kramer treadmill, with respect to the specific differences in temporal pattern and spectrum of the songs of both species. In choice situations, both species preferred the conspecific song over the heterospecific one. The courses of both species were deflected by about 15–20° from the position of the conspecific song, that of T. viridissima being away from, that of T. cantans in the direction of the heterospecific song. In no-choice situations, song models with the temporal pattern of T. cantans did not attract T. viridissima. Models with the conspecific time pattern but heterospecific spectrum were as attractive as the conspecific model. In contrast, T. cantans was attracted by T. viridissima song presented alone. In choice situations, either spectral or temporal differences were sufficient for discrimination. The preference for the conspecific model gradually disappeared with stepwise reduction of its intensity and was reversed at −12 dB. Acoustic communication alone can serve species isolation in T. viridissima; however, premating isolation in T. cantans must involve other mechanisms. The orientation during the choice situations suggests a serial processing of song recognition and localization for the Tettigonia species. Accepted: 13 December 1997     

ONTOGENETIC NICHE SHIFT IN THE BRACHIOPOD TEREBRATALIA TRANSVERSA: RELATIONSHIP BETWEEN THE LOSS OF ROTATION ABILITY AND ALLOMETRIC GROWTH

Abstract: Many articulated brachiopods experience marked life habit variations during ontogeny because they experience their fluid environment at successively higher Reynolds numbers, and they can change the configuration of their inhalant and exhalant flows as body size increases. We show that the extant brachiopod Terebratalia transversa undergoes a substantial ontogenetic change in reorientation governed by rotation around the pedicle. T. transversa′s reorientation angle (maximum ability to rotate on the pedicle) decreases during ontogeny, from 180 degrees in juveniles to 10–20 degrees in individuals exceeding 5 mm, to complete cessation of rotation in individuals larger than 10 mm. Rotation ability is substantially reduced after T. transversa achieves the adult lophophore configuration and preferred orientation with respect to ambient water currents at a length of 2.5–5 mm. We hypothesize that the rotation angle of T. transversa is determined mainly by the position of ventral and dorsal points of attachment of dorsal pedicle muscles relative to the pedicle. T. transversa shows a close correlation between the ontogenetic change in reorientation angle and ontogeny of morphological traits that are related to points of attachment of dorsal pedicle muscles, although other morphological features can also limit rotation in the adult stage. The major morphological change in cardinalia shape and the observed reduction of rotation affect individuals 2.5–10 mm in length. The position of ventral insertions of dorsal pedicle muscles remains constant, but contraction of dorsal pedicle muscles is functionally handicapped because dorsal insertions shift away from the valve midline, rise above the dorsal valve floor, and become limited by a wide cardinal process early in ontogeny (<5 mm). The rate of increase of cardinal process width and of distance between dorsal pedicle muscle scars substantially decreases in the subadult stage (5–10 mm), and most of the cardinalia shell traits grow nearly isometrically in the adult stage (>10 mm). T. transversa attains smaller shell length in crevices than on exposed substrates. The proportion of small‐sized individuals and population density is lower on exposed substrates than in crevices, indicating higher juvenile mortality on substrates prone to grazing and physical disturbance. The loss of reorientation ability can be a consequence of morphological changes that strengthen substrate attachment and maximize protection against biotic or physical disturbance (1) by minimizing torques around the pedicle axis and/or (2) by shifting energy investments into attachment strength at the expense of the cost involved in reorientation.     

Acoustic pattern recognition and orientation in orthopteran insects: parallel or serial processing?

In grasshoppers the acoustic information for pattern recognition and directional analysis is processed via parallel channels and not serially. This can be concluded from the following results established by behavioural experiments:

1. For pattern recognition the inputs from both sides are added internally. This implies that directional information is lost on this channel and must be processed in parallel.
2. The location of a female song can be influenced by introducing short clicks from both sides, forcing the grasshopper to turn to the louder resp. leading side. Also, when given a choice between two patterns of different efficiency, the grasshoppers turned towards the side with the stronger directional cues and not to the side with the more efficient pattern.
3. The parallel processing of acoustic information in grasshoppers corresponds to the evolution of acoustic communication in Acridids, as song evolved only when the ability of hearing and localization was already present. This is in contrast to crickets where the close evolutionary coupling of singing and hearing in the context of mate finding possibly favoured a serial processing of song recognition and localization.