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Andrew C Mason

Publications and source records attributed to Andrew C Mason.

12 recordsLinked to original sources
PubMed2006

Measuring and quantifying dynamic visual signals in jumping spiders.

Animals emit visual signals that involve simultaneous, sequential movements of appendages that unfold with varying dynamics in time and space. Algorithms have been recently reported (e.g. Peters et al. in Anim Behav 64:131-146, 2002) that enable quantitative characterization of movements as optical flow patterns. For decades, acoustical signals have been rendered by techniques that decompose sound into amplitude, time, and spectral components. Using an optic-flow algorithm we examined visual courtship behaviours of jumping spiders and depict their complex visual signals as "speed waveform", "speed surface", and "speed waterfall" plots analogous to acoustic waveforms, spectrograms, and waterfall plots, respectively. In addition, these "speed profiles" are compatible with analytical techniques developed for auditory analysis. Using examples from the jumping spider Habronattus pugillis we show that we can statistically differentiate displays of different "sky island" populations supporting previous work on diversification. We also examined visual displays from the jumping spider Habronattus dossenus and show that distinct seismic components of vibratory displays are produced concurrently with statistically distinct motion signals. Given that dynamic visual signals are common, from insects to birds to mammals, we propose that optical-flow algorithms and the analyses described here will be useful for many researchers.

Algorithms↗
PubMed2006

Seismic signal production in a wolf spider: parallel versus serial multi-component signals.

Animal signals can consist of multiple parts within or across sensory modalities (multi-component signals or multimodal signals). While recent work has focused on multimodal signals, the production, processing and evolution of multi-component signals has received considerably less attention. Here, using synchronous high-speed video and laser vibrometer recordings followed by experimental manipulations of putative sound-producing structures, we explored the mechanisms of seismic signal production in the courtship display of Schizocosa stridulans Stratton. Two types of seismic courtship signals were observed: 'rev' and 'idle' signals. Revs consist of a high-frequency component produced by flexions of the male pedipalp (stridulation) simultaneous with a low-frequency component produced by movements of the abdomen (tremulation). This multi-component signal is produced by independent structures and represents a parallel multi-component display. By contrast, idle displays consist of a high-intensity component produced by drumming of the forelegs on the substrate (percussion) followed by a high-frequency component produced by flexions of the male pedipalp (stridulation). While the components of the idle display are also produced by independent structures, the leg drumming and palp flexions occur serially and do not overlap in time. We discuss the selective pressures that may drive the evolution of multiple sound-producing structures as well as the selective pressures that drive the evolution of parallel versus serial multi-component signals.

Animals↗
PubMed2006

Generation of extreme ultrasonics in rainforest katydids.

The calling song of an undescribed Meconematinae katydid (Tettigoniidae) from South America consists of trains of short, separated pure-tone sound pulses at 129 kHz (the highest calling note produced by an Arthropod). Paradoxically, these extremely high-frequency sound waves are produced by a low-velocity movement of the stridulatory forewings. Sound production during a wing stroke is pulsed, but the wings do not pause in their closing, requiring that the scraper, in its travel along the file, must do so to create the pulses. We hypothesize that during scraper pauses, the cuticle behind the scraper is bent by the ongoing relative displacement of the wings, storing deformation energy. When the scraper slips free it unbends while being carried along the file and its deformation energy contributes to a more powerful, higher-rate, one-tooth one-wave sound pulse, lasting no more than a few waves at 129 000 Hz. Some other katydid species make pure-tone ultrasonic pulses. Wing velocities and carriers among these pure-tone species fall into two groups: (1) species with ultrasonic carriers below 40 kHz that have higher calling frequencies correlated with higher wing-closing velocities and higher tooth densities: for these katydids the relationship between average tooth strike rate and song frequency approaches 1:1, as in cricket escapement mechanisms; (2) a group of species with ultrasonic carriers above 40 kHz (that includes the Meconematinae): for these katydids closing wing velocities are dramatically lower and they make short trains of pulses, with intervening periods of silence greater than the duration of the pulses they separate. This signal form may be the signature of scraper-stored elastic energy.

Animal Communication↗
PubMed2005

The mechanics of sound production in Panacanthus pallicornis (Orthoptera: Tettigoniidae: Conocephalinae): the stridulatory motor patterns.

To examine whether sound production in katydids relies on an escapement mechanism similar to that of crickets we investigated the functional anatomy and mechanical properties of the stridulatory apparatus in the katydid Panacanthus pallicornis. Males of this species produce sustained pulses with a sharp low frequency peak of approximately approximately 5 kHz and a broad band spectrum between 15 and 25 kHz. Simultaneous recordings of movement and sound indicate that the entire stridulatory file is used for sound production and there is nearly a 1:1 correspondence between the number of cycles in a song and the number of teeth on the file. There is an overall tendency for both the spacing of teeth to increase along the file and the velocity of wing closure to increase as the scraper traverses the file. There is considerable variation, however, in the evenness of tooth spacing and in the instantaneous velocity of wing closure during sound production. The production of sustained pulses appears to depend on resonance in the right tegmen, with the left tegmen acting primarily as a damping element. This resonance is not strongly coupled to the scraper and, unlike crickets, the timing of file-scraper interactions, and therefore the phasing of energy input to wing oscillations, is variable. Similarly, the quality of the sound spectrum varies over the course of a single stridulatory wing-stroke. Based on measurements of tooth spacing on the stridulatory file and cycle-by-cycle frequency of sound output, we predicted the velocity of wing movement that would provide consistent phasing of file-scraper interactions with respect to sound-radiating wing oscillations and compared this with measurements of wing velocity. Acceleration of wing velocity during stridulation results in a closer match to the velocity required for optimal phasing during a portion of the call, and this corresponds with higher amplitudes of radiated sound and the excitation of higher order modes of vibration (evident as distinct harmonic peaks in spectrograms). Our results suggest that in katydid stridulation, the movement of the scraper along the file is not regulated by an escapement mechanism as it is in crickets. Instead, katydids that produce pure-tone songs sweep their wings over a range of velocities, within which some portion matches file tooth spacing to give optimal phasing of energy input to excite a resonance in the right tegmen.

Acoustics↗
PubMed2005

The start of phonotactic walking in the fly Ormia ochracea: a kinematic study.

Ormia ochracea (Diptera, Tachinidae) are acoustic parasitoids of crickets that have one of the most directionally sensitive auditory systems known. We studied dynamic characteristics of walking phonotaxis in these flies in response to variations in sound source azimuth, and compared phonotaxis of flies in freely walking conditions to tethered flies walking on a treadmill. Motor patterns at the initiation of phonotaxis are not stereotyped even for similar stimulus conditions. Flies respond to directional sound sources by walking in a tight curve that combines rotation and forward translation until they are oriented towards the source direction, then continue on a straight path. Translational velocity accelerates throughout the duration of the stimulus then decelerates following stimulus offset. In contrast, rotational velocity accelerates and then decelerates within the duration of the stimulus such that flies have completed the rotational component of the response and reached their final heading before the end of the stimulus. Rotational velocity is the only response parameter that varies systematically with sound source direction (azimuth). Differences in the amplitude of rotational velocity as a function of source azimuth determine the directional orientation of phonotactic responses. The relationship between rotational velocity and source azimuth is similar to a neural measure of auditory directionality (interaural latency). There were some differences between freely walking and tethered conditions, although both showed qualitatively similar responses. Flies accelerated more slowly and attained lower maximum velocities on the treadmill, consistent with the greater inertia of the treadmill sphere relative to the flies. Also, flies tended to continue walking longer on the treadmill following cessation of the stimulus.

Acoustic Stimulation↗
PubMed2004

The physiology of insect auditory afferents.

This review presents an overview of the physiology of primary receptors serving tympanal hearing in insects. Auditory receptor responses vary with frequency, intensity, and temporal characteristics of sound stimuli. Various insect species exploit each of these parameters to differing degrees in the neural coding of auditory information, depending on the nature of the relevant stimuli. Frequency analysis depends on selective tuning in individual auditory receptors. In those insect groups that have individually tuned receptors, differences in physiology are correlated with structural differences among receptors and with the anatomical arrangement of receptors within the ear. Intensity coding is through the rate-level characteristics of tonically active auditory receptors and through variation in the absolute sensitivities of individual receptors (range fractionation). Temporal features of acoustic stimuli may be copied directly in the timing of afferent responses. Salient signal characteristics may also be represented by variation in the timing of afferent responses on a finer temporal scale, or by the synchrony of responses across a population of receptors.

Afferent Pathways↗
PubMed2004

Identified auditory neurons in the cricket Gryllus rubens: temporal processing in calling song sensitive units.

This study characterizes aspects of the anatomy and physiology of auditory receptors and certain interneurons in the cricket Gryllus rubens. We identified an 'L'-shaped ascending interneuron tuned to frequencies > 15 kHz (57 dB SPL threshold at 20 kHz). Also identified were two intrasegmental 'omega'-shaped interneurons that were broadly tuned to 3-65 kHz, with best sensitivity to frequencies of the male calling song (5 kHz, 52 dB SPL). The temporal sensitivity of units excited by calling song frequencies were measured using sinusoidally amplitude modulated stimuli that varied in both modulation rate and depth, parameters that vary with song propagation distance and the number of singing males. Omega cells responded like low-pass filters with a time constant of 42 ms. In contrast, receptors significantly coded modulation rates up to the maximum rate presented (85 Hz). Whereas omegas required approximately 65% modulation depth at 45 Hz (calling song AM) to elicit significant synchrony coding, receptors tolerated a approximately 50% reduction in modulation depth up to 85 Hz. These results suggest that omega cells in G. rubens might not play a role in detecting song modulation per se at increased distances from a singing male.

Acoustic Stimulation↗
PubMed2004

The effect of substrate on the efficacy of seismic courtship signal transmission in the jumping spider Habronattus dossenus (Araneae: Salticidae).

The jumping spider Habronattus dossenus Griswold 1987 (Salticidae) communicates using seismic signals during courtship and can be found on rocks, sand and leaf litter. We examined the filtering properties of, and tested the efficacy of male courtship signals on, these natural substrates. These substrates have drastically different filtering properties at the distances at which the males court. Rocks sharply attenuated all frequencies, with considerable variability among different rocks. Desert sand showed band-pass properties, attenuating frequencies contained in the animal's signal. Leaf litter passed all frequencies and was the most favourable signalling environment. In behavioural trials, the proportion of males mating successfully was significantly higher on leaf litter than on rocks or desert sand. Males did not modify their courtship behaviour on different substrates. Therefore, the effectiveness of male courtship seismic signals appears to be strongly constrained by the available substratum resources.

Animal Communication↗
PubMed2003

Temporal trends (1973-1997) in survival of patients with esophageal adenocarcinoma in the United States: a glimmer of hope?

OBJECTIVE: The incidence and mortality related to esophageal adenocarcinoma (EAC) has been rising in the United States. Meanwhile, the number of diagnostic and therapeutic procedures has increased in number and improved technologically. However, the impact of these advances on the survival of EAC in clinical practice remains unknown. METHODS: Patients with histologically proven EAC between 1973 and 1997 were identified in registries of the Surveillance, Epidemiology, and End Results database, and analyzed in 5-yr time periods. The observed and relative survival rates were calculated. The joint influence of the time of diagnosis, stage and grade of cancer, demographic features, surgical therapy, and radiotherapy were assessed in Cox proportional hazard survival analyses. RESULTS: Between 1973 and 1997, we identified 4835 patients with EAC. The 1-yr and 5-yr observed survival rates increased from 34% and 5% during 1973-1977 to 44% and 13% during 1993-1997 (p < 0.05). In the Cox survival analysis, the more recent year of diagnosis, early stage of tumor, younger age at presentation, receiving radiotherapy or surgery were independent predictors of reduced risk of mortality. The proportion of patients with in situ EAC and those with local spread increased progressively from 0.3% and 17.7% in 1973-1977 to 2.3% and 25.3%, respectively, in 1993-1997 (p < 0.05). The proportion of patients receiving radiation therapy either before or after surgery has increased from 7% in 1973-1977 to 16% in 1993-1997 (p < 0.05). CONCLUSIONS: The short- and long-term survival of patients with EAC has improved slightly in the United States over the past 25 yr. Some of the improvement may be related to an increase in the number of younger patients, and in cases with in situ and localized cancers. However, the overall survival of patients with EAC remains dismal.

Adenocarcinoma↗
PubMed2003

Seismic signals in a courting male jumping spider (Araneae: Salticidae).

Visual displays in jumping spiders have long been known to be among the most elaborate animal communication behaviours. We now show that one species, Habronattus dossenus, also exhibits an unprecedented complexity of signalling behaviour in the vibratory (seismic) modality. We videotaped courtship behaviour and used laser vibrometry to record seismic signals and observed that each prominent visual signal is accompanied by a subsequent seismic component. Three broad categories of seismic signals were observed ('thumps', 'scrapes' and 'buzzes'). To further characterize these signals we used synchronous high-speed video and laser vibrometry and observed that only one seismic signal component was produced concurrently with visual signals. We examined the mechanisms by which seismic signals are produced through a series of signal ablation experiments. Preventing abdominal movements effectively 'silenced' seismic signals but did not affect any visual component of courtship behaviour. Preventing direct abdominal contact with the cephalothorax, while still allowing abdominal movement, only silenced thump and scrape signals but not buzz signals. Therefore, although there is a precise temporal coordination of visual and seismic signals, this is not due to a common production mechanism. Seismic signals are produced independently of visual signals, and at least three independent mechanisms are used to produce individual seismic signal components.

Abdomen↗