Peter M. Narins

Bimodal signal requisite for agonistic behavior in a dart-poison frog, Epipedobates femoralis

Animal acoustic signals play seminal roles in mate attraction and regulation of male spacing, maintenance of pairbonds, localization of hosts by parasites, and feeding behavior. Among vertebrate signals, it is becoming clear that no single stereotyped signal feature reliably elicits species-specific behavior, but rather, that a suite of characters is involved. Within the largely nocturnal clade of anuran amphibians, the dart-poison frog, Epipedobates femoralis, is a diurnal species that physically and vigorously defends its calling territory against conspecific intruders. Here we report that physical attacks by a territorial male are provoked only in response to dynamic bimodal stimuli in which the acoustic playback of vocalizations is coupled with vocal sac pulsations, but not by either unimodal cues presented in isolation or static bimodal stimuli. These results suggest that integration of dynamic bimodal cues is necessary to elicit aggression in this species.

Hearing and sound communication in amphibians

Hearing and Sound Communication in Amphibians: Prologue and Prognostication.- An Integrative Phylogeny of Amphibia.- The Behavioral Ecology of Anuran Communication.- Call Production and Neural Basis of Vocalization.- Recognition and Localization of Acoustic Signals.- Pathways for Sound Transmission to the Inner Ear in Amphibians.- Anatomy, Physiology, and Function of Auditory End-Organs in the Frog Inner Ear.- Central Auditory Pathways in Anuran Amphibians: The Anatomical Basis of Hearing and Sound Communication.- Function of the Amphibian Central Auditory System.- Plasticity in the Auditory System across Metamorphosis.- Sound Processing in Real-World Environments.

Acoustically induced call modification in the white-lipped frog, Leptodactylus albilabris

The vocalization behaviour of Leptodactylus albilabris was investigated using field playback experiments. To assess the response of males to pre-recorded natural ‘chirp’ (advertisement call) and natural ‘chuckle” (aggressive call) stimuli of gradually increasing broadcast intensity, three parameters (intensity, dominant frequency and repetition rate) of the chirp call were analysed. Of the males tested, 69% showed a significant increase in chirp intensity with increased levels of both stimulus types. In response to playback of the chirp stimulus, males actively modified the dominant frequency of their chirp calls over a mean range of 91·42 Hz, and in one case as much as 400 Hz. Moreover, 12 of 17 males shifted the frequency of their call towards the dominant frequency of the chirp stimulus (2175 Hz) by either increasing or decreasing the dominant frequency of their chirp calls. In response to the natural chuckle stimulus, 83% of the males showed either a decrease or no significant change in the dominant frequency of their chirps. All eight males for which both the chirp frequency and intensity were analysed and that showed an increase in chirp intensity also showed a concomitant increase in chirp dominant frequency. These results are the first to document quantitatively the plasticity of advertisement call intensity and dominant frequency in an anuran. The possible effects of advertisement call modification on male mating success in L. albilabris is discussed.

Old World frog and bird vocalizations contain prominent ultrasonic harmonics

Several groups of mammals such as bats, dolphins and whales are known to produce ultrasonic signals which are used for navigation and hunting by means of echolocation, as well as for communication. In contrast, frogs and birds produce sounds during night- and day-time hours that are audible to humans; their sounds are so pervasive that together with those of insects, they are considered the primary sounds of nature. Here we show that an Old World frog (Amolops tormotus) and an oscine songbird (Abroscopus albogularis) living near noisy streams reliably produce acoustic signals that contain prominent ultrasonic harmonics. Our findings provide the first evidence that anurans and passerines are capable of generating tonal ultrasonic call components and should stimulate the quest for additional ultrasonic species.

Do frogs communicate with seismic signals

Male white-lipped frogs exhibit conspicuous behavioral responses to calling conspecific males that are nearby but out of view. Since the calls often are accompanied by strong seismic signals (thumps), and since the male white-lipped frog exhibits the most acute sensitivity to seismic stimuli yet observed in any animal, these animals may use seismic signals as well as auditory signals for intraspecific communication.

The Acoustic Periphery of Amphibians: Anatomy and Physiology

According to current classification, the living amphibians are distributed among three orders—Caudata (newts and salamanders, or urodeles), Gymnophiona (caecilians), and Anura (frogs and toads)—which often are grouped in a single subclass—Lissamphibia. A current summary of the biology of the Lissamphibia is found in Duellman and Trueb (1994). Among the morphological features common to the three orders of Lissamphibia, but lacking in fish, are four evidently related to acoustic sensing (see Bolt and Lombard 1992; Fritzsch 1992 for recent reviews): (1) a hole (the oval window) in the bony wall of the otic capsule; (2) the insertion of one or two movable skeletal elements, the columella and the operculum, into that hole from its lateral side; (3) a periotic labyrinth, part of which projects into the hole from its medial side; and (4) two extraordinarily thin membranes (contact membranes), comprising locally fused epithelial linings of the periotic and otic labyrinths, each contact membrane forming part of the wall of a separate papillar recess in the otic labyrinth. The two papillae themselves may be homologues of two sensors found in fish—the macula neglecta and the basilar papilla. In amphibians, the putative homologue of the macula neglecta is called the amphibian papilla. Among fish, the basilar papilla has been found only in the coelacanth fish, Latimeria (Fritzsch 1987).

The vertebrate ear as an exquisite seismic sensor.

The neotropical frog Leptodactylus albilabris exhibits the greatest sensitivity to substrate-borne vibrations (seismic stimuli) reported to date for any terrestrial animal. Nerve fibers from the source of this extraordinary sensitivity in the ear show clear stimulus-evoked modulations of their resting discharge rates in response to sinusoidal seismic stimuli with peak accelerations less than 0.001 cm/s2 (10(-6) g). Evidence indicates that its source is the saccule, an organ of hearing in fish and of balance in man. We report that single vibration-sensitive fibers in the white-lipped frog saturate at (whole animal) displacements of 10 A peak to peak [Fig. 1(b)]. Assuming a conservative 20-dB dynamic range for these fibers, the in vivo frog saccule and the mammalian cochlea exhibit roughly equal sensitivities to displacement.

Chorus dynamics of a neotropical amphibian assemblage: comparison of computer simulation and natural behaviour

Abstract The high population density of vocalizing males of the Puerto Rican treefrog Eleutherodactylus coqui in their natural habitat can lead to call overlap, which may interfere with the function of the call. Simulations of groups of calling males suggest that a given male can maximize the effectiveness of each call by actively avoiding acoustic overlap with at most two of its nearest neighbours. Analysis of vocal patterns of natural groups of frogs support this hypothesis: 14 of the 18 frogs tested actively avoided acoustic overlap with no more than two neighbours (one avoided acoustic overlap with three neighbours) while three frogs exhibited active call-jamming with one of their neighbours. Moreover, cross-correlograms of calling patterns between all pairs of frogs in a group were used to infer dynamic chorus structure. Overlap avoidance behaviour is discussed in terms of reproductive success and predator evasion.

Effects of masking noise on evoked calling in the Puerto Rican coqui (Anura: Leptodactylidae)

Summary1.When appropriate synthetic call notes were broadcast to calling maleEleutherodactylus coqui in their natural habitat, the frogs responded by dropping the second note of their advertisement call. Broadband noise was used to mask the synthetic call notes, enabling an ‘effective critical ratio’ (ECR) to be derived.2.Two classes of masking functions were found: monotonically decreasing masking functions and peaked masking functions. Two hypotheses are presented to account for the existence of these distinct functional classes.3.The ECR forE. coqui was a function of the stimulus tone level used for its determination. At the lowest level (65 dB SPL), the ECR at 1 kHz was 31 dB.4.Synthetic call notes were presented in noise of various bandwidths but of constant total power. The ‘effective critical band’ (ECB) at 1 kHz forE. coqui in its natural habitat was estimated to be 500 Hz.5.These results are discussed in relation to the adaptations ofE. coqui for species-specific communication in a highly noisy environment.

The use of seismic signals by fossorial southern african mammals : A neuroethological gold mine

Behavioral adaptations exhibited by two African fossorial mammals for the reception of vibrational signals are discussed. The Namib Desert golden mole (Eremitalpa granti namibensis) is a functionally blind, nocturnal insectivore in the family Chrysochloridae that surface forages nightly in the Namib desert. Both geophone and microphone recordings in the substrate suggest that the golden mole is able to detect termite colonies and other prey items solely using seismic cues. This animal exhibits a hypertrophied malleus, an adaptation favoring detection of low-frequency signals. In a field study of the Cape mole-rat (Georychus capensis), a subterranean rodent in the family Bathyergidae, both seismic and auditory signals were tested for their propagation characteristics. This solitary animal is entirely fossorial and apparently communicates with its conspecifics by drumming its hind legs on the burrow floor. Auditory signals attenuate rapidly in the substrate, whereas vibratory signals generated in one burrow are easily detectable in neighboring burrows. The sensitivity to substrate vibrations in two orders of burrowing mammals suggests that this sense is likely to be widespread within this taxon and may serve as a neuroethological model for understanding the evolution of vibrational communication. Neuroethological implications of these findings are discussed.