The transmission of advertisement calls in Central American frogs

Acoustic communication signals change over distance due to lossof amplitude and fidelity, and it is assumed that signal degradationinfluences the receiver's ability to detect and decode signals.The degree of degradation depends on the signal's structureand the environment through which it transmits. We broadcastthe advertisement calls of 22 species of Central American frogsat two heights within forested and open environments in Panama. Werecorded these calls at five distances from the source and estimatedsignal degradation with a cross-correlation analysis, a measurethat combines the effects of decrement in signal amplitude andfidelity. Calls degraded less when broadcast higher above theground compared to on the ground, and less in open habitat comparedto forested habitat; there was an additional interaction betweenheight and environment. Furthermore, calls with low dominant frequenciesexperienced less degradation than calls with high dominant frequencies.There was no evidence, however, that the calls of these frogs haveevolved to maximize habitat-specific transmission.     

A micro-geography of fear: learning to eavesdrop on alarm calls of neighbouring heterospecifics

Many vertebrates eavesdrop on alarm calls of other species, which is a remarkable ability, given geographical variation in community composition and call diversity within and among species. We used micro-geographical variation in community composition to test whether individuals recognize heterospecific alarm calls by: (i) responding to acoustic features shared among alarm calls; (ii) having innate responses to particular heterospecific calls; or (iii) learning specific alarm calls. We found that superb fairy-wrens (Malurus cyaneus) fled to cover to playback of noisy miner (Manorina melanocephala) aerial predator alarm calls only in locations where miners were present, suggesting that learning rather than acoustic structure determines response. Sites with and without miners were well within the dispersal distance of fairy-wrens, and philopatric males and dispersing females showed the same pattern, so that local genetic adaptation is extremely unlikely. Furthermore, where miners were present, fairy-wrens responded appropriately to different miner calls, implying eavesdropping on their signalling system rather than fleeing from miners themselves. Learned eavesdropping on alarm calls enables individuals to harvest ecologically relevant information from heterospecifics on an astonishingly fine spatial scale. Such phenotypic plasticity is valuable in a changing world, where individuals can be exposed to new species.     

Trade-off in short- and long-distance communication in tungara (Physalaemus pustulosus) and cricket (Acris crepitans) frogs

Female phonotaxis in túngara(Physalaemus pustulosus)and cricket (Acris crepitans) frogsis biased toward male advertisementcalls or call components of lowerfrequency. This behavioralbias might result in part from a mismatch betweenthe spectralcharacteristics of the advertisement call and the most sensitivefrequencyof the peripheral end organ implicated in reception of thesesounds.In both species, females are tuned to frequencies lowerthan average for thecalls in their population. This mismatch,however, represents the situationduring short-distance communication.Female frogs can also use the call todetect choruses at longdistances, and the spectral distribution of callenergy canvary with transmission distance. We used computer simulationstotest the hypothesis that there is a better match betweentuning and callspectral energy at long distances from the callingmale than at shortdistances by comparing the performance (soundenergy received) of the naturaltuning curve relative to anoptimal tuning curve (i.e., one centered at thecall's dominantfrequency). The relative performance of the natural tuningcurveincreased with distance in túngarafrogs. For the twosubspecies of cricket frogs, however, the relativeperformancedecreased at longer distances. The performance did not equaltheoptimal tuning curve at the distances tested. The resultsindicate that therelationship between calls and auditory tuningcannot be optimal for both longand short distance reception.The relationship between female tuning and calldominant frequencymay represent a compromise between short and long distancecommunication,and the bias toward short or long distances may vary amongspecies.     

Mate choice copying as public information

We outline a framework that views mate choice copying as public information. In this framework, all individuals assess the quality of potential mates. Individuals can benefit by copying when they cannot discriminate differences in potential mates, as copying can result in better discrimination. This framework predicts that the discrimination ability of individuals will strongly determine the frequency of copying behaviour observed: individuals with poor discrimination ability should often copy, whereas individuals with superior discrimination ability should rarely copy. Copying behaviour may occur in a wide variety of taxa but only be observed when individuals are presented with difficult discrimination tasks.     

A biomechanical perspective on the use of forelimb length as a measure of sexual selection in frogs

Differences in forelimb length between male and female frogs and between amplexing and non-amplexing males have been interpreted to be the results of sexual selection on forelimb length. The causal feature of the forelimb that has been posited to cause such selection is the observation that non-amplexing males attempt to disrupt breeding by prying amplexing males from females. A biomechanical model of forelimb function suggests that total length per se may not be the most appropriate measure to use. There are more functionally significant aspects of forelimb morphology, such as lever arm lengths, that should influence amplexing ability and may make measures of overall forelimb length misleading. This example highlights the relevance of functional analysis to current questions in evolutionary biology that rely on postulated roles for morphological structures under selection.     

Foraging nine-spined sticklebacks prefer to rely on public information over simpler social cues

Social animals can observe others' behavior and in the processacquire information of varying quality about a given resource.Theoretical models predict that blind copying of others' behavioris more likely when individuals are only able to observe thedecisions (here "social cues") of others rather than the cues(here "public information") on which such decisions are based.We investigated information use by nine-spined sticklebacks(Pungitius pungitius) in a two-patch foraging context. Socialcues were provided by the number of demonstrator fish presentat each patch (two versus six), which either conflicted withthe demonstrators' observed feeding rate at each patch (publicinformation) or was the only information available. Consistentwith predictions, observers preferred the patch previously associatedwith six demonstrators when social cues were the only availablesource of information but preferred the patch previously associatedwith two demonstrators ("rich" patch) when also provided withpublic information. On the bases of these experiments, we arguethat it is because these fish preferentially base decisionson public information rather than social cues that they canpotentially avoid engaging in erroneous informational cascades.Thus, the availability of public information can help socialanimals make adaptive decisions.     

The use and misuse of public information by foraging red crossbills

Group foragers may assess patch quality more efficiently bypaying attention to the sampling behavior of group members foragingin the same patch (i.e., using "public information"). To determinewhether red crossbills (Loxia curvirostra) use public informationto aid their patch departure decisions, we conducted experimentsthat compared the sampling behavior of crossbills foraging ona two-patch system (one patch was always empty, one patch containingseeds) when alone, in pairs, and in flocks of three. When foragingalone, crossbills departed from empty patches in a way thatwas qualitatively consistent with energy maximization. We foundevidence for the use of public information when crossbills werepaired with two flock mates, but not when paired with one flockmate. When foraging with two flock mates, crossbills sampledapproximately half the number of cones on the empty patch beforedeparting as compared to when solitary. Furthermore, as expected ifpublic information is used, the variance in both the numberof cones and time spent on the empty patch decreased when crossbillsforaged with two flock mates as compared to when alone. Althoughhigh frequencies of scrounging reduce the availability of publicinformation, scrounging is usually uncommon in crossbills, apparentlybecause they exploit divisible patches. Consequently, publicinformation is likely to be important to crossbills in the wild.We also show that feeding performance is greatly diminishedwhen the feeding performances of flock mates differ. This providesa mechanism that will favor assortative grouping by phenotypewhen phenotypes affect feeding performance, which may in turnpromote speciation in some groups of animals.     

Bidirectional communication system in katydids: the effect on chorus structure

Unlike most acoustic systems evolved for pair formation whereonly males signal, the katydidPhaneroptera nana has a bidirectional communication system where both males and females sing. Despiteextensive study on male chorusing behavior in different communicationsystems, this behavior has rarely been explored in duettingspecies. I examined how this bidirectional communication systemaffects the collective pattern of male signaling.P. nana malesalternate their songs, and in response to synthetic stimulidelay their calls, according to the phase of stimulation. Pairsof synthetic calls (simulating alternating males) presentedto females elicited equal female response, as long as the intercallinterval was 200 ms. Thus, male alternation is imposed by thefemale's responsiveness and may be interpreted as a "jammingavoidance reaction." Further evidence suggests that chorusstructure is not merely constrained by the female sensory temporalresolution, but rather is adaptively related to female choicein this species.     

Sexual selection in a moth: effect of symmetry on male mating success in the wild

Sexual selection is generally caused by female choice and male–malecompetition. In female choice process, female preference isfavored indirectly and/or directly by sexual selection. In indirectselection, females expressing the preference might gain indirectgenetic benefits. In direct selection, females expressing thepreference might gain direct benefits or avoid male-imposedcosts. The white-tailed zygaenid moth Elcysma westwoodii ismonandrous, and males often gather around a female to mate withher, suggesting a high opportunity for sexual selection on maletraits. We quantified phenotypic selection on male morphologyin this species in the field. The morphological characters analyzedincluded body weight, antenna length, forewing length, hindwing length, hind wing tail length, genital clasper length,and the fluctuating asymmetry (FA) of these bilateral traits.In E. westwoodii, selection favored males with more symmetricgenital claspers, as well as longer and more symmetrical hindwings and antennae. Negative correlations between FA and sizewere also detected in the clasper and the antenna. Our resultssuggest that FAs of male traits, in particular the genital clasper,may have indirect and direct influences on mating success. Duringa copulatory attempt, an E. westwoodii male will try to graspthe female's abdominal tip with his claspers but often failto do so because of the female's reluctance to mate. The femaleabdominal tips are smooth and strongly sclerotized and couldthus be difficult for males to grasp. We hypothesize that moresymmetrical male claspers are more efficient in overcoming femalereluctance.     

Vigilance against predators induced by eavesdropping on heterospecific alarm calls in a non-vocal lizard Oplurus cuvieri cuvieri (Reptilia: Iguania)

Prey animals can reduce their risk of predation by detecting potential predators before encounters occur. Some animals gain information about nearby predators by eavesdropping on heterospecific alarm calls. Despite having well-developed ears, most lizards do not use vocal information for intraspecific communication, and few studies have shown practical use of the ears in wild lizards. Here, we show that the Madagascan spiny-tailed iguana (Oplurus cuvieri cuvieri) obtains auditory signals for predator detection. The Madagascan spiny-tailed iguana and the Madagascar paradise flycatcher (Terpsiphone mutata) are syntopic inhabitants of the Ampijoroa dry deciduous forest of Madagascar. The iguana and the flycatcher have neither a predator–prey relationship nor resource competition, but they have shared predators such as raptors and snakes. Using playback experiments, we demonstrated that the iguana discriminates mobbing alarm calls of the flycatcher from its songs and then enhances its vigilance behaviour. Our results demonstrate the occurrence of an asymmetrical ecological relationship between the Madagascan spiny-tailed iguana and the paradise flycatcher through eavesdropping on information about the presence of predators. This implies that indirect interspecific interactions through information recognition may be more common than generally thought in an animal community.     

Effects of territorial intrusions on eavesdropping neighbors: communication networks in nightingales

Animal communication often occurs in communication networksin which multiple signalers and receivers are within signalingrange of each other. In such networks, individuals can obtaininformation on the quality and motivation of territorial neighborsby eavesdropping on their signaling interactions. In songbirds,extracting information from interactions involving neighborsis thought to be an important factor in the evolution of strategiesof territory defense. In a playback experiment with radio-taggednightingales Luscinia megarhynchos we here demonstrate thatterritorial males use their familiar neighbors' performancein a vocal interaction with an unfamiliar intruder as a standardfor their own response. Males were attracted by a vocal interactionbetween their neighbor and a simulated stranger and intrudedinto the neighbor's territory. The more intensely the neighborhad interacted with playback, the earlier the intrusions weremade, indicating that males eavesdropped on the vocal contestinvolving a neighbor. However, males never intruded when wehad simulated by a second playback that the intruder had retreatedand sang outside the neighbor's territory. These results suggestthat territorial males use their neighbors' singing behavioras an early warning system when territorial integrity is threatened.Simultaneous responses by neighboring males towards unfamiliarrivals are likely to be beneficial to the individuals in maintainingterritorial integrity.