Whispering to the Deaf: Communication by a Frog without External Vocal Sac or Tympanum in Noisy Environments

Atelopus franciscus is a diurnal bufonid frog that lives in South-American tropical rain forests. As in many other frogs, males produce calls to defend their territories and attract females. However, this species is a so-called “earless” frog lacking an external tympanum and is thus anatomically deaf. Moreover, A. franciscus has no external vocal sac and lives in a sound constraining environment along river banks where it competes with other calling frogs. Despite these constraints, male A. franciscus reply acoustically to the calls of conspecifics in the field. To resolve this apparent paradox, we studied the vocal apparatus and middle-ear, analysed signal content of the calls, examined sound and signal content propagation in its natural habitat, and performed playback experiments. We show that A. franciscus males can produce only low intensity calls that propagate a short distance (<8 m) as a result of the lack of an external vocal sac. The species-specific coding of the signal is based on the pulse duration, providing a simple coding that is efficient as it allows discrimination from calls of sympatric frogs. Moreover, the signal is redundant and consequently adapted to noisy environments. As such a coding system can be efficient only at short-range, territory holders established themselves at short distances from each other. Finally, we show that the middle-ear of A. franciscus does not present any particular adaptations to compensate for the lack of an external tympanum, suggesting the existence of extra-tympanic pathways for sound propagation

The Signaller's Dilemma: A Cost–Benefit Analysis of Public and Private Communication

Understanding the diversity of animal signals requires knowledge of factors which may influence the different stages of communication, from the production of a signal by the sender up to the detection, identification and final decision-making in the receiver. Yet, many studies on signalling systems focus exclusively on the sender, and often ignore the receiver side and the ecological conditions under which signals evolve.We study a neotropical katydid which uses airborne sound for long distance communication, but also an alternative form of private signalling through substrate vibration. We quantified the strength of predation by bats which eavesdrop on the airborne sound signal, by analysing insect remains at roosts of a bat family. Males do not arbitrarily use one or the other channel for communication, but spend more time with private signalling under full moon conditions, when the nocturnal rainforest favours predation by visually hunting predators. Measurements of metabolic CO(2)-production rate indicate that the energy necessary for signalling increases 3-fold in full moon nights when private signalling is favoured. The background noise level for the airborne sound channel can amount to 70 dB SPL, whereas it is low in the vibration channel in the low frequency range of the vibration signal. The active space of the airborne sound signal varies between 22 and 35 meters, contrasting with about 4 meters with the vibration signal transmitted on the insect's favourite roost plant. Signal perception was studied using neurophysiological methods under outdoor conditions, which is more reliable for the private mode of communication.Our results demonstrate the complex effects of ecological conditions, such as predation, nocturnal ambient light levels, and masking noise levels on the performance of receivers in detecting mating signals, and that the net advantage or disadvantage of a mode of communication strongly depends on these conditions

Clinic HIV-Focused Features and Prevention of Pneumocystis Carinii Pneumonia

OBJECTIVE: To examine the association of clinic HIV-focused features and advanced HIV care experience with Pneumocystis carinii pneumonia (PCP) prophylaxis and development of PCP as the initial AIDS diagnosis. DESIGN: Nonconcurrent prospective study. SETTING: New York State Medicaid Program. PARTICIPANTS: Medicaid enrollees diagnosed with AIDS in 1990–1992. MEASUREMENTS AND MAIN RESULTS: We collected patient clinical and health care data from Medicaid files, conducted telephone interviews of directors of 125 clinics serving as the usual source of care for study patients, and measured AIDS experience as the cumulative number of AIDS patients treated by the study clinics since 1986. Pneumocystis carinii pneumonia prophylaxis in the 6 months before AIDS diagnosis and PCP at AIDS diagnosis were the main outcome measures. Bivariate and multivariate analyses adjusted for clustering of patients within clinics. Of 1,876 HIV-infected persons, 44% had PCP prophylaxis and 38% had primary PCP. Persons on prophylaxis had 20% lower adjusted odds of developing PCP (95% confidence interval [CI] 0.64, 0.99). The adjusted odds of receiving prophylaxis rose monotonically with the number of HIV-focused features offered by the clinic, with threefold higher odds (95% CI 1.6, 5.7) for six versus two or fewer such features. Patients in clinics with three HIV-focused features had 36% lower adjusted odds of PCP than those in clinics with one or none. Neither clinic experience nor specialty had a significant association with prophylaxis or PCP. CONCLUSIONS: PCP prevention in our study cohort appears to be more successful in clinics offering an array of HIV-focused features