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Dive into the research topics where H. Carl Gerhardt is active.

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Featured researches published by H. Carl Gerhardt.


Animal Behaviour | 1991

Female mate choice in treefrogs: static and dynamic acoustic criteria

H. Carl Gerhardt

Abstract Patterns of variation in the acoustic properties of advertisement calls of several species of treefrogs (family Hylidae) are related to patterns of female preferences for these same properties. Properties were unequivocally classified as static or dynamic based on within-male variability during bouts of calling. Static properties are highly stereotyped within males and between males in natural populations. Dynamic properties often change by as much as 100% during single bouts of calling; dynamic properties are usually much more variable among males in natural populations than are static properties. An analysis of the calling performance of individual males over the course of a breeding season indicated that at least one dynamic property, pulse number (or call duration) in Hyla versicolor, was sufficiently repeatable to differentiate between males. Playback experiments that employed synthetic calls showed that: (1) females exhibit patterns of preferences that should result in selection that is stabilizing or weakly directional on static properties, and highly directional on dynamic properties; and (2) the overall attractiveness of a signal is affected by variation in both static and dynamic properties. Similar results were found in laboratory and field studies of other taxa, primarily anurans and insects. Patterns of variability in call properties of males and in female preferences are discussed in terms of proximate mechanisms and theoretical models of the evolution of female choice.


Journal of Comparative Physiology A-neuroethology Sensory Neural and Behavioral Physiology | 1975

Sound pressure levels and radiation patterns of the vocalizations of some North American frogs and toads

H. Carl Gerhardt

SummarySound pressure levels of the vocalizations of 21 species of North American anurans were measured in the field. In most species the peak levels at 50 cm in front of the male exceeded 100 dBre 2×10−4 μbar (Table 2). The sound pressure levels of the calls of most individuals varied by less than 2.5 dB, but intraspecific variation was significantly higher, averaging about 8.5 dB (Tables 1, 2). Sound pressure levels of mating calls were positively correlated with body size in the toad,Bufo americanus (Fig. 2); however, interspecific differences in sound pressure levels were not clearly related to interspecific differences in body size. Measurements of directivity patterns indicated that sound fields around three males ofHyla crucifer were uniform, whereas two males ofH. chrysoscelis represented directional sound sources (Table 3).


Science | 1978

Temperature Coupling in the Vocal Communication System of the Gray Tree Frog, Hyla versicolor.

H. Carl Gerhardt

The gray tree frog mates over a temperature range of at least 9�C. Gravid females, tested at two different temperatures, preferred synthetic mating calls with temperature-dependent temporal properties similar to those produced by a male at about the same temperature as their own. Thus, the vocalization system and the temporal pattern recognition system are affected by temperature in a qualitatively similar fashion.


Evolution | 2003

REPRODUCTIVE CHARACTER DISPLACEMENT IN THE ACOUSTIC COMMUNICATION SYSTEM OF GREEN TREE FROGS (HYLA CINEREA)

Gerlinde Höbel; H. Carl Gerhardt

Abstract Interactions between species can affect the evolution of their sexual signals, receiver selectivity, or both. One commonly expected outcome is reproductive character displacement, whereby adverse consequences of mismating select for greater differentiation of communication systems in areas of sympatry than in areas of allopatry. We found evidence of reproductive character displacement in the acoustic communication system of green tree frogs (Hyla cinerea). The strength of female preferences for the spectral properties of calls that distinguish conspecific calls from those of a closely related congener, H. gratiosa, was greater in areas of sympatry with H. gratiosa than in areas of allopatry. We also found subtle differences in advertisement calls and in the heights of male calling perches when we restricted our comparisons to localities in which H. gratiosa was also breeding (syntopy) with localities where this species was absent. Hyla cinerea and H. gratiosa show only weak genetic incompatibility, but the calls representative of interspecific hybrids were unattractive to females of both parental species. Hybrids might also be at an ecological disadvantage because of different habitat preferences of the two taxa. Thus, selection against production of less fit or less attractive hybrid or backcross offspring are probably the main causes responsible for the differences documented in this paper.


Archive | 1992

Design of Playback Experiments: The Thornbridge Hall NATO ARW Consensus

Peter K. McGregor; Clive K. Catchpole; J. Bruce Falls; Leonida Fusani; H. Carl Gerhardt; Francis Gilbert; Andrew G. Horn; Georg M. Klump; Donald E. Kroodsma; Marcel M. Lambrechts; Karen E. McComb; Douglas A. Nelson; Irene M. Pepperberg; Laurene M. Ratcliffe; William A. Searcy; D.M. Weary

Playback is an experimental technique commonly used to investigate the significance of signals in animal communication systems. It involves replaying recordings of naturally occurring or synthesised signals to animals and noting their response. Playback has made a major contribution to our understanding of animal communication, but like any other technique, it has its limitations and constraints.


Animal Behaviour | 2001

Neighbour–stranger discrimination by territorial male bullfrogs (Rana catesbeiana): II. Perceptual basis

Mark A. Bee; H. Carl Gerhardt

Some territorial animals discriminate among neighbours and strangers based on individual differences in acoustic signals. Male North American bullfrogs, Rana catesbeiana, display this form of discrimination based on individual variation in advertisement calls. In this study, we investigated the acoustic basis of neighbour–stranger discrimination to determine how individual identity might be encoded by particular properties of bullfrog advertisement calls. We analysed patterns of within-male and between-male variability in 1078 bullfrog advertisement calls recorded from 27 territorial males. All call properties that we examined varied significantly among males. However, fundamental frequency and dominant frequency showed the lowest within-male variation and the highest repeatability between two recording sessions, and both properties were highly correlated with the first canonical root from discriminant function analyses, which typically accounted for 70–80% of the variability between males. We suggest that neighbour–stranger discrimination in bullfrogs is partially mediated by between-male differences in the spectral or fine temporal properties of advertisement calls.


Behavioral Ecology and Sociobiology | 2001

Female mate choice in the gray treefrog (Hyla versicolor in three experimental environments

Joshua J. Schwartz; Bryant W. Buchanan; H. Carl Gerhardt

Abstract. We studied female mate choice by Hyla versicolor in three venues to examine how acoustic and spatial complexity, background noise, and the calling behavior of males might influence preferences manifest in previous laboratory two-stimulus choice tests. Our laboratory-based two-stimulus choice tests with and without broadcasts of chorus noise demonstrated that females prefer long calls relative to short calls when calling efforts of alternatives are equivalent. Background noise impaired the ability of females to discriminate in favor of longer over shorter calls, but the magnitude of the effect was small. Captures of females at eight speakers broadcasting 6- to 27-pulse calls at the edge of a pond revealed strong discrimination against only the shortest call variant. In natural choruses, females may only rarely encounter males using such unattractive vocalizations. Female phonotaxis at an artificial pond with caged and electronically monitored calling males also indicated that consequences of female preferences for temporal aspects of calling observed in two-stimulus choice tests are much attenuated in choruses and explain only small portions (<10%) of the variation in male mating success. Nevertheless, relatively high call duration and calling effort increased male attractiveness. Acoustic interference emerged as another significant factor influencing male mating success and possibly the differences in female choice observed in laboratory and chorus settings. We suggest that the bias of females against both overlapped and very short calls may help explain why males lengthen their calls but lower their rate of delivery in response to increases in chorus size.


Journal of Comparative Physiology A-neuroethology Sensory Neural and Behavioral Physiology | 1988

Acoustic communication in the gray treefrog, Hyla versicolor: evolutionary and neurobiological implications

H. Carl Gerhardt; John A. Doherty

Summary1.Acoustic communication in the gray treefrog,H. versicolor, was studied by analyzing the vocalizations of males and observing the phonotactic behavior of gravid females in response to pairs of synthetic stimuli, which usually simulated choices between calls of conspecific males at different temperatures or choices between calls of conspecific males and those of a sibling species,H. chrysoscelis. Calls ofH. chrysoscelis were also analyzed acoustically.2.Pulse duty cycle (pulse duration divided by pulse period) averaged about 0.50 in the calls of both species over a wide range of temperature (Table 1). Pulse rise-time (as a percentage of pulse duration), which was also temperature-independent, was significantly longer inH. versicolor than inH. chrysoscelis (Table 1). The species difference in pulse shape was evident at a distance of 10 m from calling frogs (Fig. 1).3.Females strongly preferred a linear approximation to the pulse shape (rise-time) typical of conspecific calls to an approximation of the pulse shape typical ofH. chrysoscelis (Figs. 1, 2A). Females did not show a preference between linear and exponential approximations of the conspecific pulse shape (Figs. 1, 2B).4.When offered choices between synthetic calls that differed in pulse rate (pulses per s=p/s), females were usually very selective, choosing a stimulus with a pulse rate typical of a conspecific male at the test temperature over alternatives that differed by as little as 25% (Figs. 4–6). When both the call rate and pulse rate of synthetic calls were changed (Fig. 3), females showed temperature-dependent reversals in preference between 16 and 24°C (16 p/s vs 25 p/s) and between 16 and 20°C (15 p/s vs 20 p/s), but not between 20 and 24°C (20 p/s vs 25 p/s) (Table 2A–C).5.When the call rates of alternative stimuli were the same, the pulse rate selectivity of females at 20°C was biased toward stimuli with low pulse rates (Table 2F). Females tested at 16°C rejected strongly alternatives with a high pulse rate, but females tested at 24°C did not reject strongly alternatives with a low pulse rate (Table 2E). Females tested at 24°C were also less selective than females tested at 20°C in rejecting alternatives with a high pulse rate, in the range ofH. chrysoscelis (Table 2D). Females tested at 24°C did, however, strongly reject an alternative with both a pulse rate and pulse shape typical ofH. chrysoscelis (Fig. 6).6.Call duration and call rate were also relevant properties; changes in these variables modified preferences based on differences in pulse rate, provided that the pulse rates of both alternatives were within the range of variation produced by conspecific males over the normal range of breeding temperatures (Figs. 4–6).7.Females showed a weak preference for synthetic calls with a bimodal spectral structure typical of conspecific males (1.1 kHz [−6 dB]+2.2 kHz) to a synthetic call with a single spectral component of 2.2 kHz. In tests of single-component stimuli of 1.9 or 2.2 kHz against alternatives of lower and higher frequencies, female preferences indicated a pattern of relative frequency sensitivity (Fig. 7) that was similar to that of an audiogram based on evoked potentials in the midbrain over the same range of frequency.8.About 50% of the females tested responded phonotactically to a recorded call ofH. chrysoscelis when they had no other choice (Table 3). Thus, heterospecific signals were not only audible, but also behaviorally effective in the context of courtship.9.Pattern of female preferences with respect to pulse shape and pulse rate suggest that the potential for mismating with males ofH. chrysoscelis has been an important selective force in the evolution of acoustic pattern discrimination inH. versicolor.10.Results of this study are compared with those of other anurans and acoustic insects. Temperature-dependent shifts in temporal pattern preference, similar but less pronounced than those reported here for both fine temporal and gross temporal properties, were found in some species but not in others.11.The pulse rate of the males call increases linearly over a wide range of temperature (9–34°C; Gayou 1984), but female selectivity for pulse rate differs within the range of 16–24°C and is biased toward low pulse rates (Table 2). Thus, it is unlikely that both the temporal patterning of the males call and temporal pattern recognition by the female are controlled rigidly and linearly by the same neural circuitry.12.We discuss neurophysiological studies of temporal pattern selectivity in acoustic insects and anurans. There are several neural correlates of behavioral selectivity in gray treefrogs, but no published data concerning a neural correlate of the asymmetry in the strength of pulse rate preferences in gray treefrogs.


Evolution | 1994

SPECIATION BY POLYPLOIDY IN TREEFROGS: MULTIPLE ORIGINS OF THE TETRAPLOID, HYLA VERSICOLOR

Margaret B. Ptacek; H. Carl Gerhardt; Richard D. Sage

Speciation by polyploidy is rare in animals, yet, in vertebrates, there is a disproportionate concentration of polyploid species in anuran amphibians. Sequences from the cytochrome b gene of the mitochondrial DNA (mtDNA) were used to determine phylogenetic relationships among 37 populations of the diploid‐tetraploid species pair of gray treefrogs, Hyla chrysoscelis and Hyla versicolor. The diploid species, H. chrysoscelis, consists of an eastern and a western lineage that have 2.3% sequence divergence between them. The tetraploid species, H. versicolor, had at least three separate, independent origins. Two of the tetraploid lineages are more closely related to one or the other of the diploid lineages (0.18%–1.4% sequence divergence) than they are to each other (1.9%–3.4% sequence divergence). The maternal ancestor of the third tetraploid lineage is unknown. The phylogenetic relationships between the two species and among lineages within each species support the hypothesis of multiple origins of the tetraploid lineages.


Journal of Comparative Physiology A-neuroethology Sensory Neural and Behavioral Physiology | 1979

Accuracy of phonotaxis by the green treefrog (Hyla cinerea)

Jürgen Rheinlaender; H. Carl Gerhardt; David D. Yager; Robert R. Capranica

Summary1.Phonotactic approaches (N=156) of 42 female green treefrogs (Hyla cinerea) were videotaped over a distance of 3.75 m in response to synthetic mating calls (0.9 kHz and 0.9, 2.7 and 3.0 kHz).2.To quantify the accuracy of phonotaxis, jump anglesγ and head orientation angles α were measured (Fig. 2) when the animals were 1 m or farther from the sound source.3.Phonotaxis was extremely accurate in response to the 3-component call, which is behaviorally equivalent to the males natural mating call. The mean jump angle was

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Gerlinde Höbel

University of Wisconsin–Milwaukee

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Mark A. Bee

University of Minnesota

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