4 research outputs found

    Acoustic ranging in poison frogs—it is not about signal amplitude alone

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    Acoustic ranging allows identifying the distance of a sound source and mediates inter-individual spacing and aggression in territorial species. Birds and mammals are known to use more complex cues than only sound pressure level (SPL), which can be influenced by the signaller and signal transmission in non-predictable ways and thus is not reliable by itself. For frogs, only SPL is currently known to mediate inter-individual distances, but we hypothesise that the strong territoriality of Dendrobatids could make the use of complex cues for ranging highly beneficial for this family. Therefore, we tested the ranging abilities of territorial males of Allobates femoralis (Dendrobatidae, Aromobatinae) in playback trials, using amplitude-normalized signals that were naturally degraded over distance, and synthetic signals that were masked with different levels of noise. Frogs responded significantly less to signals recorded from larger distances, regardless of SPL and signal-to-noise ratio (SNR), but showed no differential response to natural minimum and maximum SNRs across the typical communication range in wild populations. This indicates that frogs used signal amplitude and SNR only as ancillary cues when assessing the distance of sound sources and relied instead mainly on more complex cues, such as spectral degradation or reverberation. We suggest that this ability mediates territorial spacing and mate choice in A. femoralis. Good ranging abilities might also play a role in the remarkable orientation performance of this species, probably by enabling the establishment of a mental acoustic map of the habitat. Significance statement: Acoustic ranging allows the distance of vocalizing competitors and mates to be identified. While birds and mammals are known to use complex cues such as temporal degradation, frequency-dependent attenuation and reverberation for ranging, previous research indicated that frogs rely only on signal amplitude (sound pressure level) to assess the distance of other callers. The present study shows for the first time that also poison frogs can make use of more complex cues, an ability which is likely to be highly beneficial in their territorial social organization and probably can also be used for orientation.© The Author(s) 201

    Low reproductive skew despite high male-biased operational sex ratio in a glass frog with paternal care

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    Background: Reproductive skew, the uneven distribution of reproductive success among individuals, is a common feature of many animal populations. Several scenarios have been proposed to favour either high or low levels of reproductive skew. Particularly a male-biased operational sex ratio and the asynchronous arrival of females is expected to cause high variation in reproductive success among males. Recently it has been suggested that the type of benefits provided by males (fixed vs. dilutable) could also strongly impact individual mating patterns, and thereby affecting reproductive skew. We tested this hypothesis in Hyalinobatrachium valerioi, a Neotropical glass frog with prolonged breeding and paternal care. Results: We monitored and genetically sampled a natural population in southwestern Costa Rica during the breeding season in 2012 and performed parentage analysis of adult frogs and tadpoles to investigate individual mating frequencies, possible mating preferences, and estimate reproductive skew in males and females. We identified a polygamous mating system, where high proportions of males (69 %) and females (94 %) reproduced successfully. The variance in male mating success could largely be attributed to differences in time spent calling at the reproductive site, but not to body size or relatedness. Female H. valerioi were not choosy and mated indiscriminately with available males. Conclusions: Our findings support the hypothesis that dilutable male benefits - such as parental care - can favour female polyandry and maintain low levels of reproductive skew among males within a population, even in the presence of direct male-male competition and a highly male-biased operational sex ratio. We hypothesize that low male reproductive skew might be a general characteristic in prolonged breeders with paternal care

    Adopt, ignore, or kill? Male poison frogs adjust parental decisions according to their territorial status

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    Systematic infanticide of unrelated young has been reported in several animal taxa. Particular attention has been given to carnivores and primates, where infanticide is a sexually selected strategy of males to gain increased access to female mating partners. Cannibals must ensure avoiding their own offspring and targeting only unrelated young. Therefore, decision rules are needed to mediate parental and cannibalistic behaviour. Here we show experimentally that male poison frogs adjust their parental responses – care or infanticide – towards unrelated clutches according to their territorial status. Male frogs followed the simple rule ‘care for any clutch’ inside their territory, but immediately switched to cannibalism when establishing a new territory. This demonstrates that simple cognitive rules can mediate complex behaviours such as parental care, and that care and cannibalism are antagonistically linked. Non-parental infanticide is mediated by territorial cues and presumably serves to prevent misdirected care in this poison frog. Our results thus prompt a re-consideration of evolutionary and causal aspects of parental decision making, by suggesting that selective infanticide of unrelated young may generally become adaptive when the risks and costs of misdirected care are high.© The Author(s) 201

    Calls during agonistic interactions vary with arousal and raise audience attention in ravens

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    Background: Acoustic properties of vocalizations can vary with the internal state of the caller, and may serve as reliable indicators for a caller’s emotional state, for example to prevent conflicts. Thus, individuals may associate distinct characteristics in acoustic signals of conspecifics with specific social contexts, and adjust their behaviour accordingly to prevent escalation of conflicts. Common ravens (Corvus corax) crowd-forage with individuals of different age classes, sex, and rank, assemble at feeding sites, and engage in agonistic interactions of varying intensity. Attacked individuals frequently utter defensive calls in order to appease the aggressor. Here, we investigated if acoustic properties of defensive calls change with varying levels of aggression, and if bystanders respond to these changes. Results: Individuals were more likely to utter defensive calls when the attack involved contact aggression, and when the attacker was higher in rank than the victim. Defensive calls produced during intense conflicts were longer and uttered at higher rates, and showed higher fundamental frequency- and amplitude-related measures than calls uttered during low-intensity aggression, indicating arousal-based changes in defensive calls. Playback experiments showed that ravens were more likely to react in response to defensive calls with higher fundamental frequency by orientating towards the speakers as compared to original calls and calls manipulated in duration. Conclusions: Arousal-based changes are encoded in acoustic parameters of defensive calls in attacked ravens, and bystanders in the audience pay attention to the degree of arousal in attacked conspecifics. Our findings imply that common ravens can regulate conflicts with conspecifics by means of vocalizations, and are able to gather social knowledge from conspecific calls.© The Author(s). 201
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