Phonotaxis Tests Research Articles

In your CORT: Corticosterone and its receptors in the brain underlie mate choosiness in female Cope's gray treefrogs (Hyla chrysoscelis)

Selecting an attractive mate can involve trade-offs related to investment in sampling effort. Glucocorticoids like corticosterone (CORT) are involved in resolving energetic trade-offs. However, CORT is rarely studied in the context of mate choice, despite its elevated levels during reproductive readiness and the energetic transitions that characterize reproduction. Few systems are as well suited as anuran amphibians to evaluate how females resolve energetic trade-offs during mate choice. Phonotaxis tests provide a robust bioassay of mate choice that permit the precise measurement of inter-individual variation in traits such as choosiness–the willingness to pursue the most attractive mate despite costs. In Cope's gray treefrogs (Hyla chrysoscelis), females exhibit remarkable variation in circulating CORT as well as choosiness during mate choice, and a moderate dose of exogenous CORT rapidly (<1 h) and reliably induce large increases in choosiness. Here we measured the expression of glucocorticoid (GR) and mineralocorticoid (MR) receptors in the brains of females previously treated with exogenous CORT and tested for mate choosiness. We report a large decrease in GR expression in the hindbrain and midbrain of females that were treated with the moderate dosage of CORT–the same treatment group that exhibited a dramatic increase in choosiness following CORT treatment. This association, however, does not appear to be causal, as only forebrain GR levels, which are not affected by CORT injection, are positively associated with variation in choosiness. No strong effects were found for MR. We discuss these findings and suggest future studies to test the influence of glucocorticoids on mate choice.

Sensory biases in response to novel complex acoustic signals in male and female grey treefrogs, Hyla chrysoscelis.

The sensory bias hypothesis proposes that female preferences for male sexual signalling traits evolved in contexts other than mating. Individuals of both sexes may experience similar selection pressures in these contexts; thus males may have similar biases to females for variation in signal traits. We tested this prediction in the grey treefrog, Hyla chrysoscelis, in which males produce simple advertisement calls, but females are more attracted to certain novel complex stimuli. We recorded males' responses to playbacks of both simple advertisement calls and complex calls consisting of the advertisement call with an acoustic appendage (filtered noise, or heterospecific call pulses) either leading or following the call. We tested females' preferences for the same stimuli in phonotaxis tests. We found evidence for a sensory bias in both sexes: males gave more aggressive calls in response to complex stimuli and females sometimes preferred complex over simple calls. These biases were not universal and depended on both temporal order and appendage characteristics, but how these effects manifested differed between the sexes. Ultimately, our approach of studying biases of both sexes in response to novel mating signals will shed light on the origin of mating preferences, and the mechanisms by which sensory biases operate.

Mate choice decisions of female serrate-legged small treefrogs are affected by ambient light under natural, but not enhanced artificial nocturnal light conditions

Artificial light at night (ALAN) is a widespread anthropogenic stimulus that can significantly alter nocturnal animals’ behavior, from migration to foraging to vocal communication. In the present study, we tested the hypothesis that the mate choice decisions of female serrate-legged small treefrogs (Kurixalus odontotarsus) were influenced by ambient light intensity. Standard two-speaker phonotaxis tests were conducted in a sound attenuating chamber. We set four light treatments (I-IV, from low to high) based on a range of light intensities from the maximum natural light at night (i.e., full moon) to that of the actual calling sites, which had artificial light. Contrary to our prediction, female frogs showed a preference for calls on the bright side in treatment I when they were exposed to identical stimuli. However, females preferred longer calls on the dim side to shorter calls on the bright side in this treatment. In addition, there were no significant effects of choice side, light treatment or their interaction on leave time or choice time. Our results suggest that females are more attracted to mates in bright light under natural nocturnal light conditions, but the preference for longer calls is not altered in serrate-legged small treefrogs.

When virginity matters: age and mating status affect female responsiveness in crickets

Behavioural assays in which animals recognize, localize or discriminate among signals are broadly useful for answering an array of biological questions, but results can be sensitive to the characteristics of individuals, including age and mating status. Researchers may prefer to use young, unmated individuals in experiments both to control for the effects of mating and because younger and unmated individuals may respond more often or more quickly. In natural contexts, virgin females are likely to behave differently than mated females, especially in animals that store sperm for future use, because the costs and benefits of mating are different for these two groups. In species in which multiple mating is common, individuals are much more likely to have mated at least once at the time of any given mating event than they are to be virgins, suggesting the use of virgin subjects in experiments is not reflective of most natural mating decisions. We conducted a literature review to sample the methods employed in empirical studies that use crickets in phonotaxis assays. Many studies draw conclusions based only on virgins, and methods vary widely with respect to the age of individual subjects. We then conducted an empirical study of the effect of mating status and age on female phonotaxis behaviour in Teleogryllus oceanicus, the Pacific field cricket. Our results show that both age and mating status affect some commonly used measures of female responsiveness in phonotaxis assays: older females begin moving more quickly in phonotaxis tests, while virgins have shorter response latencies. These findings are consistent with the idea that the cost of remaining unmated increases with age, and that virgin females benefit from an initial mating more than mated females benefit from additional matings.

Temporal information processing in gray treefrogs: Compute within frequency then integrate across frequency

In Cope’s gray treefrog (Hyla chrysoscelis), the pulse rate of advertisement calls is a species recognition cue. This temporal information is redundant across two spectral bands in the call’s bimodal spectrum that are primarily transduced by different inner ear papillae. Previous studies have shown that some neurons in the frog auditory midbrain are selective for bimodal spectra and that, compared with unimodal spectra, calls with bimodal spectra are more attractive. In addition, “interval-counting” neurons in the frog auditory midbrain are selective for conspecific pulse rates. However, it is not known whether pulse rate information is computed prior to, or subsequent to, spectral integration. We conducted behavioral experiments to investigate the serial order of pulse rate computations and spectral integration. In phonotaxis tests that used bimodal and unimodal stimuli with variable pulse rates, we tested the hypothesis that spectral information is integrated prior to pulse rate computations versus the alternative hypothesis that pulse rate can be computed independently in different frequency channels prior to spectral integration. Our results support the latter hypothesis, and suggest pulse rate can be computed independently in separate frequency channels. These results give insight into the mechanisms of temporal processing underlying the perception of key biological information.

Male-male competition and female choice are differentially affected by male call acoustics in the serrate-legged small treefrog, Kurixalus odontotarsus.

BackgroundThe evolution of exaggerated vocal signals in anuran species is an important topic. Males and females have both evolved the ability to discriminate communication sounds. However, the nature of sexual dimorphism in cognition and sensory discrimination and in the evolution and limitation of sexual signal exaggeration remain relatively unexplored.MethodsIn the present study, we used male calls of varied complexity in the serrate-legged small treefrog, Kurixalus odontotarsus, as probes to investigate how both sexes respond to variations in call complexity and how sex differences in signal discrimination play a role in the evolution of sexual signal exaggeration. The compound calls of male K. odontotarsus consist of a series of one or more harmonic notes (A notes) which may be followed by one or more short broadband notes (B notes).ResultsMale playback experiments and female phonotaxis tests showed that increasing the number of A notes in stimulus calls elicits increased numbers of response calls by males and increases the attractiveness of the stimulus calls to females. The addition of B notes, however, reduces male calling responses. Moreover, call stimuli which contain only B notes suppress spontaneous male calling responses. Phonotaxis experiments show that females prefer calls with greater numbers of A notes and calls containing both A notes and B notes, but do not prefer calls with only B notes.DiscussionMale-male competition and female choice appear to have played different roles in the evolution and limitation of signal complexity in K. odontotarsus. These results provide new insights into how exaggerated compound signals evolve and how signal complexity may be limited in anurans.

Frequency channel-dependent selectivity for temporal call characteristics in gray treefrogs, Hyla versicolor.

Sensory receptors transmit information on multiple stimulus dimensions. Much remains to be understood about how the processing of different signal characteristics is partitioned and integrated in different areas of the nervous system. Amphibian hearing involves two morphologically distinct inner-ear organs that process different components of the frequency spectrum. Many anuran signals contain two frequency peaks, each one matching the sensitivity of one of these two organs. We hypothesized that the processing of temporal characteristics of acoustic signals would differ in these two frequency channels, perhaps because of differences in the response properties of the two inner-ear organs. We tested this hypothesis in the gray treefrog, Hyla versicolor; male advertisement calls of this species contain a bimodal frequency spectrum. We generated synthetic male advertisement calls in which we independently manipulated the pattern of amplitude modulation in the low-frequency peak or the high-frequency peak and measured the attractiveness of these stimuli to females in single-speaker and two-speaker phonotaxis tests. We obtained multiple lines of evidence that females were more selective for fine-temporal characteristics in the high-frequency peak. We discuss the potential implications of frequency channel-dependent temporal processing for signal evolution and suggest that additional neurophysiological investigations of the anuran auditory periphery will give important insights into how the nervous system partitions the encoding of multiple characteristics of complex signals.

An exception to the matched filter hypothesis: A mismatch of male call frequency and female best hearing frequency in a torrent frog.

The matched filter hypothesis proposes that the tuning of auditory sensitivity and the spectral character of calls will match in order to maximize auditory processing efficiency during courtship. In this study, we analyzed the acoustic structure of male calls and both male and female hearing sensitivities in the little torrent frog (Amolops torrentis), an anuran species who transmits acoustic signals across streams. The results were in striking contradiction to the matched filter hypothesis. Auditory brainstem response results showed that the best hearing range was 1.6–2 kHz consistent with the best sensitive frequency of most terrestrial lentic taxa, yet completely mismatched with the dominant frequency of conspecific calls (4.3 kHz). Moreover, phonotaxis tests show that females strongly prefer high‐frequency (4.3 kHz) over low‐frequency calls (1.6 kHz) regardless of ambient noise levels, although peripheral auditory sensitivity is highest in the 1.6–2 kHz range. These results are consistent with the idea that A. torrentis evolved from nonstreamside species and that high‐frequency calls evolved under the pressure of stream noise. Our results also suggest that female preferences based on central auditory system characteristics may evolve independently of peripheral auditory system sensitivity in order to maximize communication effectiveness in noisy environments.

Multitasking males and multiplicative females: dynamic signalling and receiver preferences in Cope's grey treefrog

The ‘multitasking hypothesis’ for complex signal function predicts performance trade-offs between signal components that negatively covary (e.g. due to energetic or mechanical constraints) and receiver preferences for more extreme values of the negatively covarying components that are difficult to produce simultaneously. We tested these two predictions in Cope's grey treefrogs, Hyla chrysoscelis. In a field study, we recorded and analysed 1000 advertisement calls from males calling in breeding choruses to test the prediction that two signal components important in female mating decisions (call rate and call duration) negatively covary under natural conditions. In a laboratory study, we conducted phonotaxis tests with female subjects to test the prediction that females prefer calls with higher overall ‘call efforts’ (the product of call rate × call duration). Consistent with predictions of the multitasking hypothesis, call rate and call duration were significantly negatively related and females preferred calls produced with higher call efforts, manifested through preferences for greater values of both call rate and call duration. We conducted an additional playback experiment to test the hypothesis that males increase their call effort in competitive situations to maximize their attractiveness to females. Compared to quiet conditions, male subjects increased their call duration and decreased their call rate, but did not alter call effort, in response to a simulated calling neighbour or broadcasts of chorus noise. Together our data have implications for understanding the function of multicomponent signals when signallers must balance performance trade-offs in mate attraction with dynamic signal modifications in other social contexts.

An Investigation of the Functional Significance of Responses of the Gray Treefrog (Hyla versicolor) to Chorus Noise

Abstract We evaluated the hypothesis that adjustments in call duration made by male Gray Treefrogs render their calls less easily masked in noise and so facilitate communication with females in choruses. We also tested whether shifts in male call duration and rate can be elicited through changes in the level of filtered background noise. We found that males increased the number of pulses in their calls while lowering call rate with elevations in noise level in a fashion similar to that reported during broadcasts of calls. In phonotaxis tests with females using unmodulated or modulated background noise and calls (10, 20, 30, or 40 pulses long) presented at either unequal or equal rates, we failed to find significant differences in noise levels at call recognition thresholds for calls of different duration. However, calls were detected more easily (i.e., noise levels at recognition thresholds were higher) when the noise background was modulated as compared to unmodulated. Our results and those of an earlier...

Signal recognition by green treefrogs (Hyla cinerea) and cope’s gray treefrogs (Hyla chrysoscelis) in naturally fluctuating noise.

This study tested three hypotheses about the ability of female frogs to exploit temporal fluctuations in the level of background noise to overcome the problem of recognizing male advertisement calls in noisy breeding choruses. Phonotaxis tests with green treefrogs (Hyla cinerea) and Cope's gray treefrogs (Hyla chrysoscelis) were used to measure thresholds for recognizing calls in the presence of noise maskers with (a) no level fluctuations, (b) random fluctuations, or level fluctuations characteristic of (c) conspecific choruses and (d) heterospecific choruses. The dip-listening hypothesis predicted lower signal recognition thresholds in the presence of fluctuating maskers compared with nonfluctuating maskers. Support for the dip-listening hypothesis was weak; only Cope's gray treefrogs experienced dip listening and only in the presence of randomly fluctuating maskers. The natural soundscapes advantage hypothesis predicted lower recognition thresholds when level fluctuations resembled those of natural soundscapes compared with artificial fluctuations. This hypothesis was rejected. In noise backgrounds with natural fluctuations, the species-specific advantage hypothesis predicted lower recognition thresholds when fluctuations resembled species-specific patterns of conspecific soundscapes. No evidence was found to support this hypothesis. These results corroborate previous findings showing that Cope's gray treefrogs, but not green treefrogs, experience dip listening under some noise conditions. Together, the results suggest level fluctuations in the soundscape of natural breeding choruses may present few dip-listening opportunities. The findings of this study provide little support for the hypothesis that receivers are adapted to exploit level fluctuations of natural soundscapes in recognizing communication signals.

Dip listening or modulation masking? Call recognition by green treefrogs (Hyla cinerea) in temporally fluctuating noise

Despite the importance of perceptually separating signals from background noise, we still know little about how nonhuman animals solve this problem. Dip listening, an ability to catch meaningful 'acoustic glimpses' of a target signal when fluctuating background noise levels momentarily drop, constitutes one possible solution. Amplitude-modulated noises, however, can sometimes impair signal recognition through a process known as modulation masking. We asked whether fluctuating noise simulating a breeding chorus affects the ability of female green treefrogs (Hyla cinerea) to recognize male advertisement calls. Our analysis of recordings of the sounds of green treefrog choruses reveal that their levels fluctuate primarily at rates below 10Hz. In laboratory phonotaxis tests, we found no evidence for dip listening or modulation masking. Mean signal recognition thresholds in the presence of fluctuating chorus-like noises were never statistically different from those in the presence of a non-fluctuating control. An analysis of statistical effects sizes indicates that masker fluctuation rates, and the presence versus absence of fluctuations, had negligible effects on subject behavior. Together, our results suggest that females listening in natural settings should receive no benefits, nor experience any additional constraints, as a result of level fluctuations in the soundscape of green treefrog choruses.

Sound level discrimination by gray treefrogs in the presence and absence of chorus-shaped noise

An important aspect of hearing and acoustic communication is the ability to discriminate differences in sound level. Little is known about level discrimination in anuran amphibians (frogs and toads), for which vocal communication in noisy social environments is often critical for reproduction. This study used two-choice phonotaxis tests to investigate the ability of females of Cope's gray treefrog (Hyla chrysoscelis) to discriminate between two advertisement calls differing only in sound pressure level by 2, 4, or 6 dB. Tests were conducted in the presence and absence of chorus-shaped noise (73 dB) and using two different ranges of signal levels (73-79 dB and 79-85 dB). Females discriminated between two signals differing by as little as 2-4 dB. In contrast to expectations based on the "near miss to Weber's law" in birds and mammals, level discrimination was slightly better at the lower range of signal amplitudes, a finding consistent with earlier studies of frogs and insects. Realistic levels of background noise simulating a breeding chorus had no discernable effect on discrimination at the sound level differences tested in this study. These results have important implications for studies of auditory masking and signaling behavior in the contexts of anuran hearing and sound communication.

Sound source localization in noise: Open-loop and closed-loop tests with Cope’s gray treefrog (Hyla chrysoscelis)

Event Abstract Back to Event Sound source localization in noise: Open-loop and closed-loop tests with Cope’s gray treefrog (Hyla chrysoscelis) Michael S. Caldwell1 and Mark A. Bee1, 2* 1 University of Minnesota, Department of Ecology, Evolution and Behavior, United States 2 University of Minnesota, Graduate Program in Neuroscience, United States At breeding choruses, female frogs must assess and locate a calling male among a background of competing sounds from other signalers and abiotic sources. In many ways, this task is analogous to the human 'cocktail party problem', where a partygoer struggles to follow the speech of a single interlocutor among many noisy guests. In masking noise, many animals show increased response thresholds and poorer performance in sound discrimination tasks, which potentially result in increased exposure to predators, increased energy expenditure, and selection of low-quality mates. It is often suggested that these effects are due, in part, to impaired sound localization in noise. While studies of human subjects demonstrate clear effects of masking noise on sound localization abilities, we know much less about how noise affects source localization in non-human (specifically, non-mammalian) animal models. Here, we report results from a study of sound source localization in frogs. In contrast to mammalian ears, frog ears are coupled through wide and open Eustachian tubes, making them inherently directional pressure-difference receivers. Using behavioral phonotaxis tests, we investigated the effects of masking noise, as well as noise level and signal level, on the localization of male mating calls by females of Cope’s gray treefrog in both open-loop and closed-loop listening conditions. Open-loop conditions assessed the fundamental localization acuity of the frog's auditory system; closed-loop conditions examined the frog's ability to use behavioral tactics to home in on a sound source or to improve localization by integrating information over time. By studying constraints faced by frogs localizing sounds in a complex acoustic environment, as well as adaptations for overcoming these challenges, we hope to uncover biologically diverse solutions to common problems of acoustic communication in noisy environments. Acknowledgements We thank Nate Buerkle for help testing frogs. This work is supported by NIDCD R01 5R01DC009582. Keywords: acoustic communication, chorus, closed-loop, cocktail party problem, Frog, open-loop, Sound Localization Conference: Tenth International Congress of Neuroethology, College Park. Maryland USA, United States, 5 Aug - 10 Aug, 2012. Presentation Type: Poster Presentation (see alternatives below as well) Topic: Communication Citation: Caldwell MS and Bee MA (2012). Sound source localization in noise: Open-loop and closed-loop tests with Cope’s gray treefrog (Hyla chrysoscelis). Conference Abstract: Tenth International Congress of Neuroethology. doi: 10.3389/conf.fnbeh.2012.27.00181 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 28 Apr 2012; Published Online: 07 Jul 2012. * Correspondence: Dr. Mark A Bee, University of Minnesota, Department of Ecology, Evolution and Behavior, St. Paul, United States, mbee@umn.edu Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Michael S Caldwell Mark A Bee Google Michael S Caldwell Mark A Bee Google Scholar Michael S Caldwell Mark A Bee PubMed Michael S Caldwell Mark A Bee Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Effect of anomalous pulse timing on call discrimination by females of the gray treefrog (Hyla versicolor): behavioral correlates of neurobiology

Research has demonstrated that certain midbrain neurons of anurans 'count' interpulse intervals (IPIs). Some neurons fire after exposure to fewer intervals than do others. Counting can be reset to zero if an IPI falls outside the cell's tolerance range. We tested female gray treefrogs for behavioral correlates of these neural response patterns using phonotaxis tests in order to gain a better understanding of the mechanistic bases of female responses to calls. For example, previous work demonstrated females often prefer longer to shorter pulsed advertisement calls, even when the former occur at lower rates. Call attractiveness can also be reduced when pulse duration and timing have been manipulated experimentally or disrupted by acoustic interference. In this study, female responses were consistent with neural data, emphasizing the importance of IPIs. Females discriminated in favor of calls with normal interpulse timing relative to those in which a single IPI was too long or too short. Our data suggest that neural resetting of interval counting by inappropriate intervals may more strongly influence females than reduced firing in response to such intervals on an individual basis. Data also suggest a transition point between 125 ms and 175 ms at which an interval between pulse strings is treated as an interval between calls.

The challenge of finding a high-quality male: a treefrog solution based on female assessment of male calls

In the context of sexual selection through mate choice, it has recently been suggested that the effectiveness of intersexual communication is affected not only by the honesty of male sexual signals but also by the number of signal components simultaneously used to convey information. We investigated female use of acoustic components in the chorusing treefrog Hyla arborea using two-choice phonotaxis tests. Females showed a significant preference for higher call rates and calls of short duration, as well as for higher call amplitudes. They also favoured lower peak frequencies. Since this call characteristic was negatively correlated with body weight, such a preference should lead to their selecting larger males. Females also exhibited a marginal preference for longer call bouts. The reliability of the multiple call components involved in mate choice in H. arborea are discussed, as well as the validity of these results for mate choice in the natural context of a noisy anuran chorus.

Behavioral measures of signal recognition thresholds in frogs in the presence and absence of chorus-shaped noise

Anuran amphibians are superb animal models for investigating the mechanisms underlying acoustic signal perception amid high levels of background noise generated by large social aggregations of vocalizing individuals. Yet there are not well-established methods for quantifying a number of key measures of auditory perception in frogs, in part, because frogs are notoriously difficult subjects for traditional psychoacoustic experiments based on classical or operant conditioning. A common experimental approach for studying frog hearing and acoustic communication involves behavioral phonotaxis experiments, in which patterns of movement directed toward sound sources indicate the subjects' perceptual experiences. In this study, three different phonotaxis experiments were conducted using the same target signals and noise maskers to compare different experimental methods and analytical tools for deriving estimates of signal recognition thresholds in the presence or absence of "chorus-shaped noise" (i.e., artificial noise with a spectrum similar to that of real breeding choruses). Estimates of recognition thresholds based on measures of angular orientation, response probabilities, and response latencies were quite similar in both two-choice and no-choice phonotaxis tests. These results establish important baselines for comparing different methods of estimating signal recognition thresholds in frogs tested in various masking noise conditions.

Processing of clustered sensory signals in gray treefrogs (Hyla versicolor): Behavioral responses in the laboratory and field.

Anuran mating choruses may consist of hundreds of sympatric and conspecific males calling in addition to other biotic and abiotic noise, representing a complex auditory scene whose characteristics change with distance. Detecting and localizing individual males in the chorus poses a challenge to the female, especially at long ranges. We carried out a series of recordings and behavioral experiments that are aimed at determining the distance at which female treefrogs (Hyla versicolor) use the chorus as an acoustic cue for their orienting responses. We analyzed natural choruses recorded at distances of 1–100 m and used these to create stimuli for phonotaxis experiments evaluating how the chorus attracts and provides cues for localization by females. In addition, we performed phonotaxis tests in the field near natural choruses to compare the frog’s behavior under laboratory and field conditions. We found that females utilize acoustic cues for orientation toward choruses at a distance up to 50 m, but additional cues may be used to ensure orientation in the field at distances &amp;gt;50 m. Additional experiments revealed that temporal coherence of the male call, as opposed to a general reduction in stimulus intensity, was the most important factor in female phonotactic behavior.

Estradiol induces sexual behavior in female túngara frogs

Steroid hormones play an important role in regulating vertebrate sexual behavior. In frogs and toads, injections of exogenous gonadotropins, which stimulate steroid hormone production, are often used to induce reproductive behavior, but steroid hormones alone are not always sufficient. To determine which hormonal conditions promote sexual behavior in female túngara frogs, we assessed the effect of hormone manipulation on the probability of phonotaxis behavior toward conspecific calls in post-reproductive females. We injected females with human chorionic gonadotropin (HCG), estradiol, estradiol plus progesterone, saline, or HCG plus fadrozole (an aromatase blocker) and tested their responses to mating calls. We found that injections of HCG, estradiol, and estradiol plus progesterone all increased phonotaxis behavior, whereas injections of saline or HCG plus fadrozole did not. Since injections of estradiol alone were effective at increasing phonotaxis behavior, we concluded that estradiol is sufficient for the expression of phonotaxis behavior. Next, to determine if estradiol-injected females display the same behavioral preferences as naturally breeding females, we compared mating call preferences of naturally breeding females to those of post-reproductive females injected with estradiol. We found that, when injected with estradiol, females show similar call preferences as naturally breeding females, although they were less likely to respond across multiple phonotaxis tests. Overall, our results suggest that estradiol is sufficient for the expression of sexual responses to mating calls in túngara frogs. To our knowledge, ours is the only study to find that estradiol alone is capable of promoting phonotaxis behavior in a frog.

Preferred songs predict preferred males: consistency and repeatability of zebra finch females across three test contexts

Male mating signals are often multidimensional, potentially providing multiple messages to females. However, the relative importance of different signal dimensions and their context dependency are poorly understood. Even in a well-studied species such as the zebra finch, Taeniopygia guttata , an important avian model for the study of mate choice, there is little consensus on the relative weighting of visual versus acoustic signals in mate choice. We therefore tested the consistency and repeatability of female mating preferences across different test contexts, presenting male song only or full courtship displays. We concurrently conducted a detailed analysis of male song characteristics and morphological traits. Females' individual preferences were consistent across three commonly used binary test paradigms (operant and phonotaxis tests with songs and association tests with live males). Preference direction was thus independent of test contexts. Preference strength was repeatable only between the operant and live male tests, possibly because these two tests allowed active interaction with songs or males whereas exposure to songs in the phonotaxis test was passive. The song structure parameters that predicted female preferences best were context independent and also predicted male morphology. We conclude from the combined results that song structure (in addition to song rate or absolute output as previously suggested) does contain sufficient information on the singer for female mate choice. We suggest that the earlier focus on song rate rather than song content might partly account for the differences between studies in the importance attributed to acoustic versus visual signals.