Theoretical considerations in the adaptation of animal communication systems.
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Apart from echolocation and the pursuit of prey by bats, the function of ultrasound in animal communication is poorly understood. This is mainly because of the broad range of responses that it can evoke and the widely varied contexts in which it is used (for example, in rodents of the Muridae family it may indicate distress in infants or a sexual or predatory encounter in adults). Here we find that a purely ultrasonic signal is produced in the wild by a rodent of the Sciuridae family, Richardson's ground squirrel, and show that its function is to warn conspecifics of impending danger. To our knowledge, ultrasonic alarm calls have not previously been detected in any animal group, despite their twin advantages of being highly directional and inaudible to key predators.
The dog has a special relationship with humans, going beyond that of other domestic animals. Recent evidence suggests this comes from domestication rather than wolf behaviour, perhaps involving something as simple as a change in natural looking behaviour.
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Birds adjust their songs to make themselves heard in the presence of ambient noise. New research comparing songs of great tits across Europe shows how animals adapt their signals to the urban din.
The response of signal recipients depends on information found in the signal itself and on other information sources known collectively as context. Context is the set of events, conditions, and changeable recipient characteristics that modify the effect of a signal on recipients' behavior. Sources of contextual information include (a) the characteristics of the recipient and (b) sources external to the recipient (the signaler and the setting). Contextual information is most commonly used when the signal itself does not provide enough information for the recipient to behave adaptively. The signal's referent may be ambiguous or deceptive, or recipients may need additional information to fine-tune their responses. When animal signals were thought to be information poor, contextual information was seen as being critically informative. Animal signals are now known to be much more informative, but even information-rich systems, such as human language, depend heavily on contextual sources of information.
Male field crickets produce species-specific and stereotyped calling songs. Conspecific females are attracted to the call. Reciprocal F1 hybrid females prefer the calls of sibling hybrids to reciprocal hybrids. Discrimination is probably based on temporal pattern and not carrier frequency of the call. The results imply that production of song by males and its detection by females have a common genetic basis.
The newly hatched laughing gull chick (Larus atricilla) begs food by pecking at the parent's dark red bill. The spectral reflectance of the bill over a range of 300 to 1200 nanometers reflects increasingly more with wavelength beginning about 575 nanometers. Because the chick shows a bimodal, true color preference in pecking, with modes at about 625 and 450 nanometers; the latter, blue peak in the spectral response curve is apparently not adapted to the natural stimulus of the parent's bill. The blue peak might thus be the result of limitations in the neural coding of color information in the chick's visual system.
Conflicts of interest arise between signaller and receiver in most kinds of biological communication. Some authors have argued that this conflict is likely to give rise to deceit and exploitation, as receivers lag behind in the coevolutionary 'arms race' with signallers. Others have argued that such manipulation is likely to be short-lived and that receivers can avoid being deceived by paying attention to signals that are costly and hence 'unfakeable.' These two views have been hard to reconcile. Here, we present results from simulations of signal evolution using artificial neural networks, which demonstrate that honesty can coexist with a degree of exploitation. Signal cost ensures that receivers are able to obtain some honest information, but is unable to prevent exploitative signalling strategies from gaining short-term benefits. Although any one receiver bias that is open to exploitation will subsist for only a short period of time once signallers begin to take advantage of it, new preferences of this kind are constantly regenerated through selection and random drift. Hidden preferences and sensory exploitation are thus likely to have an enduring influence on the evolution of honest, costly signals. At the same time, honesty and cost are prerequisites for the evolution of exploitation. When signalling is cost-free, selection cannot act to maintain honesty, and receivers rapidly evolve to ignore signals. This leads to a reduction in the extent of hidden preference, and a consequent loss of potential for exploitation.
Animals' sound-producing organs often act as an integrated whole--particular vocal structure are not directly associated with the creation of discrete syllables. But here we show that the 'chuck' of the 'whine-chuck' mating call of the túngara frog, Physalaemus pustulosus, is caused by a fibrous mass attached to the vocal folds; the chuck is eliminated by removal of this structure, although the frog still tries to produce the sound. Sexual selection affects the acoustic complexity of the frog's call, so evolution may have shaped this unusual vocalization, which is akin to the two-voiced song of songbirds.
Animal communication is typically non-syntactic, which means that signals refer to whole situations. Human language is syntactic, and signals consist of discrete components that have their own meanings. Syntax is a prerequisite for taking advantage of combinatorics, that is, "making infinite use of finite means. The vast expressive power of human language would be impossible without syntax, and the transition from non-syntactic to syntactic communication was an essential step in the evolution of human language. We aim to understand the evolutionary dynamics of this transition and to analyse how natural selection can guide it. Here we present a model for the population dynamics of language evolution, define the basic reproductive ratio of words and calculate the maximum size of a lexicon. Syntax allows larger repertoires and the possibility to formulate messages that have not been learned beforehand. Nevertheless, according to our model natural selection can only favour the emergence of syntax if the number of required signals exceeds a threshold value. This result might explain why only humans evolved syntactic communication and hence complex language.
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A new study of contact calls in dolphins shows that individuals can recognize one another using information encoded in the frequency modulation pattern of these calls, in the absence of general voice characteristics.
Scientists from many distinct disciplines often use concepts such as habitat, environment, and niche to describe among other things the physical characteristics of the communicative worlds of animals. Often these descriptions center on the physical characteristics most salient to humans' perceptual systems. In this article, the authors advocate an approach to the description and analysis of the physical characteristics of animal communicative worlds based on J. von Uexküll's (1934/1957) concept of the Umwelt. Such an approach emphasizes the physical characteristics of the world as perceived by the organism in question, and its use has often led to novel and unexpected insights into animal communicative systems.
Much animal communication takes place via symbolic codes, where each symbol's meaning is fixed by convention only and not by intrinsic meaning. It is unclear how understanding can arise among individuals utilizing such arbitrary codes, and specifically, whether evolution unaided by individual learning is sufficient to produce such understanding. Using a genetic algorithm implemented on a computer, I demonstrate that a significant though imperfect level of understanding can be achieved by organisms through evolution alone. The population as a whole settles on one particular scheme of coding/decoding information (there are no separate dialects). Several features of such evolving systems are explored and it is shown that the system as a whole is stable against perturbation along many different kinds of ecological parameters.