Flexibility as a Strategy for Avoiding Call Overlap in Male Anhui Treefrogs

Male-male vocal competition is critical for mating success in anuran species; however, it remains unknown that how males regulate their competitive strategies dynamically during competition because calling is highly time-consuming, energetically demanding and likely to increase predation risks. Since different parts of calls will encode different information for vocal communication, we hypothesized that competitive strategies of male frogs may be modulated by the temporal and spectral features of different call notes. To test this hypothesis, the natural advertisement calls(OC), its modified versions with the first call note replaced by white noise(WN) or other notes and with the fifth call note replaced by WN, were played back to the Anhui tree frogs(Rhacophorus zhoukaiyae). Results showed that 1) males produced more competitive calls in response to acoustic stimuli compared to their baseline calling during silence; and 2) males emitted more non-overlapping calls compared to overlapping calls in response to the acoustic stimuli. These results are consistent with the idea that males are flexible to acoustic signals and their competition strategies are modulated dynamically by social contexts.     

Sound imaging of nocturnal animal calls in their natural habitat

We present a novel method for imaging acoustic communication between nocturnal animals. Investigating the spatio-temporal calling behavior of nocturnal animals, e.g., frogs and crickets, has been difficult because of the need to distinguish many animals’ calls in noisy environments without being able to see them. Our method visualizes the spatial and temporal dynamics using dozens of sound-to-light conversion devices (called “Firefly”) and an off-the-shelf video camera. The Firefly, which consists of a microphone and a light emitting diode, emits light when it captures nearby sound. Deploying dozens of Fireflies in a target area, we record calls of multiple individuals through the video camera. We conduct two experiments, one indoors and the other in the field, using Japanese tree frogs (Hyla japonica). The indoor experiment demonstrates that our method correctly visualizes Japanese tree frogs’ calling behavior. It has confirmed the known behavior; two frogs call synchronously or in anti-phase synchronization. The field experiment (in a rice paddy where Japanese tree frogs live) also visualizes the same calling behavior to confirm anti-phase synchronization in the field. Experimental results confirm that our method can visualize the calling behavior of nocturnal animals in their natural habitat.     

The effects of time,space and spectrum on auditory grouping in túngara frogs

Male túngara frogs (Physalaemus pustulosus) produce complex calls consisting of two components, a ~350 ms FM sweep called the “whine” followed by up to seven ~40 ms harmonic bursts called “chucks”. In order to choose and locate a calling male, females attending to choruses must group call components into auditory streams to correctly assign calls to their sources. Previously we showed that spatial cues play a limited role in grouping: calls with normal spectra and temporal structure are grouped over wide angular separations (≤135°). In this study we again use phonotaxis to first test whether an alternative cue, the sequence of call components, plays a role in auditory grouping and second, whether grouping is mediated by peripheral or central mechanisms. We found that while grouping is not limited to the natural call sequence, it does vary with the relative onset times of the two calls. To test whether overlapping stimulation in the periphery is required for grouping, the whine and chuck were filtered to restrict their spectra to the sensitivity ranges of the amphibian and basilar papillae, respectively. For these dichotic-like stimuli, grouping still occurred (albeit only to 45° separation), suggesting that stream formation is mediated by central mechanisms.     

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.     

Acoustic Niches of Siberut Primates

The loud calls nonhuman primates use in long-distance communication have supposedly been selected for efficient information transfer in the habitat. The differential effects of scattering and reverberation and the masking effects of background noise predict that loud calls produced in rain forest habitats should be low-pitched and whistle-like with low-frequency modulation. Callers may also use particular calling posts or times of day with reduced background noise to increase the efficacy of sound transmission. We studied the loud calls of the 4 sympatric primate species on Siberut Island. Only Kloss gibbons (Hylobates klossii) fulfilled the predictions regarding both the structure and use of calls. Though the other 3 species —Mentawai macaques (Macaca siberu), pig-tailed langurs (Simias concolor), and Mentawai leaf monkeys (Presbytis potenziani)— also concentrated their main energies in the spectral window with the lowest background noise, their calls were not adapted to long-range transmission. All 4 species produced loud calls exclusively no lower than 18 m above ground, but food abundance and shelter in the canopy may also be factors. Though all 4 species produced the majority of loud calls in the morning, it was not the only time of day with reduced background noise. We suggest that phylogenetic inheritance may better explain the structure of calls than adaptation to the habitat. In sum, the observed usage of spectral and temporal niches is not solely an adaptation to the sound profile of the habitat, though it clearly improves their transmission.     

The Causes and Consequences of Color Vision

The ability to see colors is not universal in the animal kingdom. Those animals that can detect differences in the wavelengths of the electromagnetic spectrum glean valuable sensory information about their environment. They use color vision to forage, avoid predators, and find high-quality mates. In the past, the colors that humans could see clouded scientists’ study of animals’ color perception. Leaving that bias behind has led to new insights about how and why the color vision of animals evolved. This paper provides a brief introduction to color vision, the genetics of color vision in humans, what colors other animals see, and how scientists study color vision. We examine the consequences of having color vision, including speciation, loss of olfactory capabilities, and sexual selection.     

Collective unary decision-making by decentralized multiple-robot systems applied to the task-sequencing problem

When a complex mission must be undertaken, it often can be simplified by dividing it into a sequence of smaller subtasks, which are then completed in order. This strategy implicitly requires a system to recognize the completion of each subtask and make the decision to begin work on the next one. Decentralized multiple-robot systems can tackle many tasks, but their behavior is typified by continuous responses to stimuli. Task sequencing, however, demands a controlled, self-induced phase change in collective behavior—working on one task one moment and then on a different task the next—which is nontrivial for an emergent system. The main contribution of this study is a collective decision-making framework for decentralized multiple-robot systems that enables such a system to cooperatively decide that a current task has been completed and thus focus its attention on the next one in a sequence using only anonymous local communication. Central to the framework is the use of consensus, whereby task sequencing is delayed until a prespecified proportion of a system’s robots agree that the current task is complete, reducing the likelihood of premature decisions. Two low-cost consensus estimation strategies are presented, both of which are practical for the extremely simple robots that are expected to compose large decentralized systems. Experiments in simulation and with real robots demonstrate that the proposed decision-making framework performs as predicted. Although the specific application of collective decision-making in this work is the cooperative task-sequencing problem, the proposed decision-making framework potentially has many additional applications.     

Intensity contrast as a crucial cue for butterfly landing

Papilio butterflies use a tetrachromatic color vision to discriminate a rewarding flower, approach, land and take nectar from the flower. In the course of further analyzing their foraging behavior in a laboratory condition, we found that some butterflies could not land on the target flower even they discriminated and tried to land on it, especially when the target was dark. This phenomenon, which we call “landing suppression”, indicates that the cue for landing differs from the cue for visually locating a flower. We hypothesized that a possible cue for landing was intensity contrast between the target and background, and have initiated to test this hypothesis. We tested the butterflies’ landing behavior to targets of various colors and intensities presented on background of black or various densities of gray. As a result, the landing was most strongly suppressed when the intensity contrast was close to zero irrespective of the target colors, suggesting that the butterflies used the target-background intensity contrast when landing.     

Individual Variation in Advertisement Calls of Territorial Male Green Frogs, Rana clamitans: Implications for Individual Discrimination

Individuals of many territorial species discriminate between familiar territorial neighbors and unfamiliar strangers based on individual differences in acoustic signals. Many anuran amphibians are territorial and use primarily acoustic communication during social interactions, but evidence for acoustically mediated individual discrimination is available only for one species. As a first step in research designed to investigate individual discrimination in a second species of territorial frog, we examined patterns of within-male and among-male variability in 198 advertisement calls of 20 male green frogs, Rana clamitans . The aim was to determine which acoustic properties could be used by males to recognize their territorial neighbors and to estimate limits of reliability afforded by these properties for identifying different neighbors. All of the call properties that we examined exhibited significant inter-individual variation. Discriminant function analyses assigned between 52% and 100% of calls to the correct individual, depending on sample size and the call properties included in the model. This suggests that there is sufficient among-male variability to statistically identify individuals by their advertisement calls. The call properties of fundamental frequency and dominant frequency contributed the most towards discrimination among individuals. Based on their natural history and behavior and the results reported here, we suggest that male green frogs likely discriminate between strangers and adjacently territorial neighbors based on individual variation in advertisement calls.     

Decrease in Alarm Call Response Among Tufted Capuchins in Competitive Feeding Contexts: Possible Evidence for Counterdeception

Animal signals function to elicit behaviors in receivers that ultimately benefit the signaler, while receivers should respond in a way that maximizes their own fitness. However, the best response may be difficult for receivers to determine when unreliable signaling is common. “Deceptive” alarm calling is common among tufted capuchins (Cebus apella nigritus) in competitive feeding contexts, and responding to these calls is costly. Receivers should thus vary their responses based on whether a call is likely to be reliable. If capuchins are indeed able to assess reliability, I predicted that receivers will be less likely to respond to alarms that are given during competitive feeding contexts than in noncompetitive contexts, and, within feeding contexts, that individuals inside or adjacent to a food patch will be less likely to respond to alarms than those further from the resource. I tested these predictions in a group of wild capuchins by observing the reactions of focal animals to alarm calls in both noncompetitive contexts and experimental feeding contexts. Antipredator escape reactions, but not vigilance reactions, occurred significantly less often in competitive feeding contexts than in noncompetitive contexts and individuals adjacent to food patches were more likely to respond to alarm calls than were those inside or further from food patches. Although not all predictions were fully supported, the findings demonstrate that receivers vary their behavior in a way that minimizes the costs associated with “deceptive” alarms, but further research is needed to determine whether or not this can be attributed to counterdeception.     

Observational Learning in the White-Eared Hummingbird (Hylocharis leucotis): Experimental Evidence

The adoption of new food resources can be facilitated by the ability to learn through observation of other individuals who use them. This behavior, termed observational learning, applies to any problem solving in which a naive individual who has observed an experienced individual learns a behavior faster than another who has not. Hummingbirds consume nectar from flowers of a large number of plant species, which are very diverse in morphology and color. During their local or migratory movements, they can observe the use of floral resources by conspecifics and heterospecifics which may change their foraging preferences. Although there is evidence that hummingbirds can use observational learning to exploit new floral resources, it is necessary to generate additional information by studying different hummingbird species. In this work, the learning performance of White‐eared hummingbirds (Hylocharis leucotis) was studied in the presence or absence of a knowledgeable tutor. In a first experiment, naïve hummingbirds learned to feed on arrays of artificial flower of two colors: red (previously known resource) and yellow (novel resource), where only one color had nectar. Naive hummingbirds visited red flowers faster and more often than rewarded yellow flowers. Individuals with the best performance on each color were further trained to ensure that they only visited flowers of a specific color, and were then used as tutors in the next experiment, in which new naive hummingbirds, caged individually, were allowed to observe them foraging on the artificial arrays. These naïve individual were then exposed alone to the same array used by their tutor. Tutored hummingbirds learned to feed faster and more frequently from nectar‐containing flowers of the array than naive individuals. Likewise, all tutored individuals only visited flowers of the color that had been previously visited by their tutors. This study provides experimental evidence that hummingbirds taken directly from the field can use observational learning as an efficient strategy to access new floral resources.     

Consequences of intraspecific niche variation: phenotypic similarity increases competition among recently metamorphosed frogs

Phenotype is often correlated with resource use, which suggests that as phenotypic variation in a population increases, intraspecific competition will decrease. However, few studies have experimentally tested the prediction that increased intraspecific phenotypic variation leads to reduced competitive effects (e.g., on growth rate, survival or reproductive rate). We investigated this prediction with two experiments on wood frogs (Rana sylvatica). In the first experiment, we found that a frog’s size was positively correlated with the size of its preferred prey, indicating that the feeding niche of the frogs changed with size. In the second experiment, we used an experimental design in which we held the initial mass of “focal” frogs constant, but varied the initial mass of their competitors. We found a significant quadratic effect of the average mass of competitors: focal frog growth was lowest when raised with similar-sized competitors, and highest when raised with competitors that were larger or smaller. Our results demonstrate that growth rates increase (i.e., competitive intensity decreases) when individuals are less similar to other members of the population and exhibit less overlap in resource use. Thus, changes in the amount of phenotypic variation in a population may ultimately affect population-level processes, such as population growth rate and extinction risk.     

Structure and use of distance calls in wild bonobos (Pan paniscus)

We report the physical structure and use of a distance call (high-hoot) by wild bonobos (Pan paniscus).Although spectrographic analyses reveal high structural variability, the total sample can be subdivided according to the composition of units—the presence or absence of an initial segment—and the range of the lowest harmonic. Analyses of samples from male—female pairs,vocalizing simultaneously and in close proximity, reveal that both animals utter calls in more or less precise temporal alternation but with different spectral ranges. Whether these differences are gender-specific or related to other factors, such as age or the social relations between particular individuals, is not clear. We suggest that (a) individuals of the same party may coordinate their vocal activity on both the temporal and the spectral level and (b) high hootings stimulate emission of equal vocalizations by members of other parties and may increase cohesion among community members. Comparison of a restricted number of spectrograms from known individuals indicates that bonobos may be able to adjust spectral parameters of one type of distance calls (high- hoot) according to corresponding calls of conspecifics.     

Patterns of orientation behavior in marsh frogs (Rana ridibunda Pall.) of southern populations

The behavior of frogs from southern areas with an arid climate released during the reproductive period between their “home” pond and a less distant river is shown to be independent of weather conditions. The experiments were performed on frogs living near the village of Dosang, Astrakhan oblast. The frogs were released 60 to 150 m from their “home” breeding waterbody and 60 to 80 m from an “alien” waterbody. Four experiments were performed on 27 individuals. The movements of the frogs were traced by the method of “tracking by a thread.” The results revealed no preference in the frogs to return to their own breeding ponds, rather than to the nearby river. This behavior is peculiar to frogs of southern populations.     

White storks Ciconia ciconia eavesdrop on mating calls of moor frogs Rana arvalis

Mating calls of animals are often detected by unintended receivers which use sexual signals to obtain information about the signaller. We investigated whether white storks Ciconia ciconia can eavesdrop mating calls of moor frogs Rana arvalis . White storks are dependent on moor frog abundance in early breeding season. Interspecific eavesdropping by predators is common and well documented in tropical anurans, whereas it is less known in temperate zone. We compared the frequency of approaches of white storks to loudspeakers when frog calls and the song thrush Turdus philomelos songs were simultaneously played back using the later as controls. The loudspeaker broadcasting the calls of male moor frogs clearly attracted white storks at 22 out of 84 nests. The bird songs attracted white storks in only one case. In 19 cases birds left the nest for unknown reasons which were considered as potential foraging movements. The results of this field experiment report a new case of eavesdropping on acoustic signals showing that advertisement calls of temperate moor frogs are an important stimulus for white storks.     

Cues used in host‐seeking behavior by frog‐biting midges (Corethrella spp. Coquillet)

We investigated the role of carbon dioxide and host temperature in host attraction in frog‐biting midges (Corethrella spp). In these midges, females are known to use frog calls to localize their host, but the role of other host‐emitted cues has yet not been investigated. We hypothesized that carbon dioxide acts as a supplemental cue to frog calls. To test this hypothesis, we determined the responses of the midges to carbon dioxide, frog calls, and both cues. A significantly lower number of midges are attracted to carbon dioxide and silent traps than to traps broadcasting frog calls. Adding carbon dioxide to the calls does not increase the attractiveness to the midges. Instead, carbon dioxide can have deterrent effects on frog‐biting midges. Temperature of calling frogs is not a cue potentially available to the midges. Contrary to our hypothesis, there was no supplemental effect of carbon dioxide when presented in conjunction to calls. Midge host‐seeking behavior strongly depends on the mating calls emitted by their anuran host. Overall, non‐acoustic cues such as host body temperature and carbon dioxide are not important in long‐distance host location by frog‐biting midges.     

Ultraviolet components offer minimal contrast enhancement to an aposematic signal

Aposematic and sexual signals are often characterized by bright, highly contrasting colors. Many species can see colors beyond the human visible spectrum, and ultraviolet (UV) reflection has been found to play an important role in communication and sexual selection. However, the role of UV in aposematic signals is poorly explored. Poison frogs frequently produce high‐contrast signals that have been linked to both aposematism and intraspecific communication. Yet despite considerable efforts studying interspecific and intraspecific diversity in color, poison frogs are not known to perceive UV, and UV reflection of the integument has not been described. We report UV‐reflective spots in a population of Oophaga sylvatica and quantify the effect of UV on visual contrast with models of avian vision. We found that the frogs are highly contrasting, but UV had a minimal effect on signal saliency. These data highlight the importance of considering UV reflectance within aposematic signals, but that UV should not necessarily be regarded as an independent signal.     

Invasion of the acoustic niche: variable responses by native species to invasive American bullfrog calls

Biological invasions are a major threat to biodiversity. Invasive species that use acoustic communication can affect native species through interference in the acoustic niche. The American Bullfrog Lithobates catesbeianus is a highly invasive anuran that is widely distributed in the Brazilian Atlantic Rainforest. Adult male bullfrogs emit loud advertisement calls at frequencies that overlap with the calls of several native species of frogs. Given that spectral overlap is a major factor in acoustic masking, the purpose of this study was to test the effects of the acoustic invasion of L. catesbeianus on native frogs that have calls with and without spectral overlap with the invader. In field experiments, we exposed calling males of two overlapping species and two non-overlapping species to recorded bullfrog vocalizations, white noise, and the vocalization of another native frog species. To identify effects, we compared calls recorded before, during, and after exposure. Our results showed that native species altered their calls in response to the bullfrog calls. However, we also observed similar responses to white noise and heterospecific native calls. Both the invasive and heterospecific calls were emitted at low frequencies, which suggests that the observed responses might be specific to low-frequency calls. Our results provide evidence that the introduction of new sounds can cause native species to modify their calls, and that responses to exogenous sounds are species- and stimulus-specific.     

Frogs Have Rules: Selective Attention Algorithms Regulate Chorusing in Physalaemus pustulosus (Leptodactylidae)

In various acoustic insects and frogs, females preferentially orient towards the leading of two or more males' advertisement signals that occur closely in time. Such preferences in receivers have apparently selected for timing mechanisms whereby male signallers actively refrain from calling immediately following the onset of a neighbour's call and thereby increase their production of leading calls. However, indiscriminate application of this inhibitory mechanism to all neighbours might severely reduce a male's calling rate, particularly in high density. Consequently, mechanisms of selective attention to only a subset of signalling neighbours are expected.
Female Túngara frogs ( Physalaemus pustulosus ) exhibit strong preferences for leading male calls, and males refrain from calling immediately following a neighbour. Four-loudspeaker playback experiments demonstrated that males do selectively apply this inhibitory mechanism to only a subset of close signalling neighbours. Selective attention is regulated by a combination of sliding threshold and fixed number rules: (i) Attend to the loudest (nearest) conspecific neighbour and those additional ones whose calls are within 6–8 dB of the loudest one; (ii) attend to only two neighbours in total when the calls are weak or the second one is much farther than the first; (iii) attend to three neighbours when the calls are loud or all neighbours are approximately equidistant. The means by which such plasticity may be achieved and its potential adaptiveness are discussed.     

Vocal response of male European water frogs (Rana Esculenta complex) to mating and territorial calls

The responses of male European water frogs (the two species Rana lessonae and Rana ridibunda and their hybrid, Rana esculenta) to playback of their mating and territorial calls were studied during the mating season.In order to select biologically relevant intensities for the presentation of the recorded calls, the sound pressure of the calls produced by the frogs themselves was established prior to the experiment. At a distance of 1 m the most intense calls were those of R. ridibunda, with a sound pressure of 110 dB (peak SPL). The smaller males of R. esculenta gave calls about 5 dB lower in intensity. The calls of R. lessonae, the smallest phenotype, were still less intense, 10 dB lower than those of R. ridibunda.The territorial calls of all three phenotypes elicited territorial calls in all of the males tested, as a rule accompanied by approach to the sound source. The sound pressure required to elicit a vocal response was nearly the same for each of the three different territorial calls. Sometimes encounter calls and warning calls were given in addition to territorial calls.When the mating calls were presented at low intensity, in some cases the males responded with their own mating calls. Mating calls at higher intensity elicited the same behavior that appeared following presentation of territorial calls, but significantly higher sound pressures were required to elicit such a response to mating calls than to territorial calls. The males of R. lessonae and R. esculenta did not respond to the mating calls of R. ridibunda, and each of them had significantly lower thresholds to the mating call of its own phenotype than to that of the other. The males of R. ridibunda responded only to conspecific mating calls.The vocal-response thresholds are compared with those of the electrodermal response reacting to the same stimuli. The significance of the different calls of the European water frogs is discussed.