Evolution Of Complex Signals Research Articles

On the evolution of complex signals and structures in media without dispersion

The paper investigates the nonlinear evolution of complex signals and structures having two significantly different scales at the input: a high-frequency noise carrier and a regular modulating function. Consideration of the statistical characteristics of the velocity field is based on the asymptotic solution of the Burgers equation for a vanishingly small viscosity. This solution coincides with the weak solution of the Riemann equation (Hopf equation) and is known as the Oleinik-Laks absolute minimum principle. In this case, the solution of the partial differential equation is reduced to the procedure for finding the absolute minimum of some functional of the initial perturbation, which depends on the coordinate of the observation point and time. The problem of analyzing the statistical characteristics of the velocity and density fields of a one-dimensional flow of inelastically sticking particles is also considered on the basis of the global principle (E-Rykov-Sinai principle). In the special case of a constant initial density, this solution coincides with the Oleinik-Laks absolute minimum principle. In media without dispersion, the multiple interaction of harmonics leads to a strong distortion of the wave profile and the formation of discontinuities, and at long times the field is transformed into a sequence of triangular pulses with the same slope. It is shown that only a relative decrease in modulation occurs for a noise carrier, in contrast to a quasi-monochromatic wave, where, due to nonlinear effects, amplitude modulation is completely suppressed at the stage of developed discontinuities. The statistical characteristics of the velocity and density fields at long times are found, and the process of generating the mean field from a modulated signal perturbation with zero mean at the input is studied. It is shown that if the correlation scale of the noise filling is much smaller than the duration of the localized modulating function, then a practically deterministic signal is formed at large times. On the basis of the global principle, the problems of the escape of particles from a localized bunch with a random input field into free space and the evolution of a flow of particles with random velocities and harmonic modulation of the initial density are analytically considered. It is shown that at long times in both cases the average density field has a universal character. The analytical consideration is compared with the results of numerical simulation, which was carried out on the basis of the Fast Legendre transform algorithm.

The functions and evolution of graded complex calls in a treefrog

ABSTRACT Variation in signal complexity is common among different species. Understanding why some species have evolved extensive call complexity can offer insight into the evolution of complex signals. In this study, we investigated the functions of different call types in a treefrog using call network analysis, male playback experiments, and correlation analysis between call properties and body size. Our results show that the male treefrogs can produce three kinds of notes that can be combined to produce single-note call types as well as composite calls. We also identified an intermediate note type between the advertisement call and suppress call, indicating that male suppress calls may have evolved from advertisement calls. The call network revealed functional correlation and distinction between different calls. Additionally, our study revealed that the dominant frequencies of the advertisement calls and suppress calls can signal the size of calling males. Male frogs can combine different notes in different sequences to form graded complex calls, which may perform different communication functions. Our results indicate that different communication needs may drive the evolution of signal complexity, which provides new evidence to the social complexity hypothesis and deeper insights into the function and complexity of animal acoustic communication.

A rapidly evolving cricket produces percussive vibrations: how, who, when, and why

AbstractSexual signals are often transmitted through multiple modalities (e.g., visual and chemical) and under selection from both intended and unintended receivers. Each component of a multimodal signal may be more or less conspicuous to receivers, and signals may evolve to take advantage of available private channels. We recently documented percussive substrate-borne vibrations in the Pacific field cricket (Teleogryllus oceanicus), a species that uses airborne acoustic and chemical signals to attract and secure mates. The airborne signals of Hawaiian T. oceanicus are currently undergoing rapid evolution; at least five novel male morphs have arisen in the past 20 years. Nothing is yet known about the newly discovered percussive substrate-borne vibrations, so we ask “how” they are produced, “who” produces them (e.g., population, morph), “when” they produce them (e.g., whether they are plastic), and “why” (e.g., do they play a role in mating). We show that the vibrations are produced exclusively by males during courtship via foreleg drumming. One novel morph, purring, produces quieter airborne songs and is more likely to drum than the ancestral morph. However, drumming behavior is also contextually plastic for some males; when we removed the ability of males to produce airborne song, ancestral males became more likely to drum, whereas two novel morphs were equally likely to drum regardless of their ability to produce song. Opposite our prediction, females were less likely to mate with males who drummed. We discuss why that might be and describe what we can learn about complex signal evolution from this newly discovered behavior.

Increased signal complexity is associated with increased mating success.

The evolution of complex signals has often been explored by testing multiple functional hypotheses regarding how independent signal components provide selective benefits to offset the costs of their production. In the present study, we take a different approach by exploring the function of complexity per se. We test the hypothesis that increased vibratory signal complexity—based on both proportional and temporal patterning—provides selective benefits to courting male Schizocosa stridulans wolf spiders. In support of this hypothesis, all of our quantified metrics of vibratory signal complexity predicted the mating success of male S. stridulans. The rate of visual signalling, which is mechanistically tied to vibratory signal production, was also associated with mating success. We additionally found evidence that males can dynamically adjust the complexity of their vibratory signalling. Together, our results suggest that complexity per se may be a target of female choice.

Probing the myelin water compartment with a saturation-recovery, multi-echo gradient-recalled echo sequence.

To investigate the effect of varying levels of -weighting on the evolution of the complex signal from white matter in a multi-echo gradient-recalled echo (mGRE) saturation-recovery sequence. Analysis of the complex signal evolution in an mGRE sequence allows the contributions from short- and long- components to be separated, thus providing a measure of the relative strength of signals from the myelin water, and the external and intra-axonal compartments. Here we evaluated the effect of different levels of -weighting on these signals, expecting that the previously reported, short of the myelin water would lead to a relative enhancement of the myelin water signal in the presence of signal saturation. Complex, saturation-recovery mGRE data from the splenium of the corpus callosum from 5 healthy volunteers were preprocessed using a frequency difference mapping (FDM) approach and analyzed using the 3-pool model of complex signal evolution in white matter. An increase in the apparent as a function of echo time was demonstrated, but this increase was an order of magnitude smaller than that expected from previously reported myelin water -values. This suggests the presence of magnetization transfer and exchange effects which counteract the -weighting. Variation of the amplitude in a saturation-recovery mGRE sequence can be used to modulate the relative strength of signals from the different compartments in white matter, but the modulation is less than predicted from previously reported -values.

Study of development of bony labyrinth in dry fetal temporal bones

Signals used in communication are frequently complex, being composed of multiple signal components that in combination improve information transfer. A variety of morphological parts are typically used to transmit components of any given complex signal. Our understanding of why a given morphological part is used to transmit a given signal component is poor. We hypothesized that the function of a given signal component is improved by its association with its morphological part and that such parts interact functionally to transmit information. In a laboratory study we characterized the function of different floral signal components transmitted by associated floral parts and the interaction of those signal components. Using Solanum houstonii flowers, we focused on two major floral parts, corolla and anthers, involved in signalling bumblebee, Bombus impatiens, visitors. We further examined how experience affected the relationship between signal component and floral part. Floral visits involve a stepwise process in which bees approach, land and acquire pollen. We found that the corolla plays the dominant role in eliciting approaches by bees, whether naïve or experienced. Landing is elicited by corolla signals and, to a lesser but additive degree, anther signals. Following experience, anther signals nearly completely dominate corolla signals in eliciting landing. The anthers convey signals mediating pollen acquisition, regardless of the bee's experience level. Our findings suggest there is selection for specific relationships between signal components and morphological parts, which in turn might drive complex signal evolution.

Dynamic changes in display architecture and function across environments revealed by a systems approach to animal communication.

Animal communication is often structurally complex and dynamic, with signaler and receiver behavior varying in response to multiple environmental factors. To date, studies assessing signal dynamics have mostly focused on the relationships between select signaling traits and receiver responses in a single environment. We use the wolf spider Schizocosa floridana to explore the relationships between courtship display form and function across two social contexts (female presence vs absence) and two light environments (light vs dark). We use traditional analytical methods to determine predictors of copulation success (i.e., signal function) and examine these predictors in a structural context by overlaying them on signal phenotype networks (Wilkins etal. 2015). This allows us to explore system design principles (degeneracy, redundancy, pluripotentiality), providing insight into hypotheses regarding complex signal evolution. We found that both social context and light environment affect courtship structure, although the predictors of mating success remain similar across light environments, suggesting system degeneracy. Contrastingly, the same display traits may serve different functions across social environments, suggesting pluripotentiality. Ultimately, our network approach uncovers a complexity in display structure and function that is missed by functional analyses alone, highlighting the importance of systems-based methodologies for understanding the dynamic nature of complex signals.

Linking components of complex signals to morphological part: the role of anther and corolla in the complex floral display

Signals used in communication are frequently complex, being composed of multiple signal components that in combination improve information transfer. A variety of morphological parts are typically used to transmit components of any given complex signal. Our understanding of why a given morphological part is used to transmit a given signal component is poor. We hypothesized that the function of a given signal component is improved by its association with its morphological part and that such parts interact functionally to transmit information. In a laboratory study we characterized the function of different floral signal components transmitted by associated floral parts and the interaction of those signal components. Using Solanum houstonii flowers, we focused on two major floral parts, corolla and anthers, involved in signalling bumblebee, Bombus impatiens , visitors. We further examined how experience affected the relationship between signal component and floral part. Floral visits involve a stepwise process in which bees approach, land and acquire pollen. We found that the corolla plays the dominant role in eliciting approaches by bees, whether naive or experienced. Landing is elicited by corolla signals and, to a lesser but additive degree, anther signals. Following experience, anther signals nearly completely dominate corolla signals in eliciting landing. The anthers convey signals mediating pollen acquisition, regardless of the bee's experience level. Our findings suggest there is selection for specific relationships between signal components and morphological parts, which in turn might drive complex signal evolution.

Flamboyant sexual signals: multiple messages for multiple receivers

Animals are often faced with the challenge of signalling to multiple receivers that might differ in their detection abilities and preferences. Such conditions are expected to favour the evolution of complex signals. The superb fan-throated lizard, Sarada superba, possesses one of the most complex sexual trait of any lizard: an enlarged dewlap with blue, black and orange patches that is flapped rapidly during both courtship and aggressive displays. We examined the use of the tricoloured dewlap in social signalling to determine whether (1) movement enhances signal detection, and whether (2) males and females differ in their preference for colours. Using robotic lizard stimuli, we measured receiver responses to movement and colour individually, and found that movement attracted both sexes, but the latency to respond was faster when dewlaps had all three colours compared to none (white). Furthermore, the sexes did not differ in the ability to detect colours, as more than 80% of lizards preferred coloured to white dewlaps. Most strikingly, however, the sexes showed strong preferences for different colours. Females preferentially responded to orange colour on dewlaps, and males responded to blue and black, indicating that different colours are targeted at different receivers. These results highlight that complex signals can evolve due to simultaneous inter- and intrasexual selection.

Exploring the hidden landscape of female preferences for complex signals

A major challenge in evolutionary biology is explaining the origins of complex phenotypic diversity. In animal communication, complex signals may evolve from simpler signals because novel signal elements exploit preexisting biases in receivers' sensory systems. Investigating the shape of female preference functions for novel signal characteristics is a powerful, but underutilized, method to describe the adaptive landscape potentially guiding complex signal evolution. We measured female preference functions for characteristics of acoustic appendages added to male calling songs in the grasshopper Chorthippus biguttulus, which naturally produces only simple songs. We discovered both hidden preferences for and biases against novel complex songs, and identified rules governing song attractiveness based on multiple characteristics of both the base song and appendage. The appendage's temporal position and duration were especially important: long appendages preceding the song often made songs less attractive, while following appendages were neutral or weakly attractive. Appendages had stronger effects on songs of shorter duration, but did not restore the attractiveness of very unattractive songs. We conclude that sensory biases favor, within predictable limits, the evolution of complex songs in grasshoppers. The function-valued approach is an important tool in determining the generality of these limits in other taxa and signaling modalities.

Female preference for multi-modal courtship: multiple signals are important for male mating success in peacock spiders.

A long-standing goal for biologists has been to understand how female preferences operate in systems where males have evolved numerous sexually selected traits. Jumping spiders of the Maratus genus are exceptionally sexually dimorphic in appearance and signalling behaviour. Presumably, strong sexual selection by females has played an important role in the evolution of complex signals displayed by males of this group; however, this has not yet been demonstrated. In fact, despite apparent widespread examples of sexual selection in nature, empirical evidence is relatively sparse, especially for species employing multiple modalities for intersexual communication. In order to elucidate whether female preference can explain the evolution of multi-modal signalling traits, we ran a series of mating trials using Maratus volans. We used video recordings and laser vibrometry to characterize, quantify and examine which male courtship traits predict various metrics of mating success. We found evidence for strong sexual selection on males in this system, with success contingent upon a combination of visual and vibratory displays. Additionally, independently produced, yet correlated suites of multi-modal male signals are linked to other aspects of female peacock spider behaviour. Lastly, our data provide some support for both the redundant signal and multiple messages hypotheses for the evolution of multi-modal signalling.

Multimodal signalling in the North American barn swallow: a phenotype network approach.

Complex signals, involving multiple components within and across modalities, are common in animal communication. However, decomposing complex signals into traits and their interactions remains a fundamental challenge for studies of phenotype evolution. We apply a novel phenotype network approach for studying complex signal evolution in the North American barn swallow (Hirundo rustica erythrogaster). We integrate model testing with correlation-based phenotype networks to infer the contributions of female mate choice and male-male competition to the evolution of barn swallow communication. Overall, the best predictors of mate choice were distinct from those for competition, while moderate functional overlap suggests males and females use some of the same traits to assess potential mates and rivals. We interpret model results in the context of a network of traits, and suggest this approach allows researchers a more nuanced view of trait clustering patterns that informs new hypotheses about the evolution of communication systems.

Real-Time Identification of Incipient Surface Morphology Variations in Ultraprecision Machining Process

Real-time monitoring and control of surface morphology variations in their incipient stages are vital for assuring nanometric range finish in the ultraprecision machining (UPM) process. A real-time monitoring approach, based on predicting and updating the process states from sensor signals (using advanced neural networks (NNs) and Bayesian analysis) is reported for detecting the incipient surface variations in UPM. An ultraprecision diamond turning machine is instrumented with three miniature accelerometers, a three-axis piezoelectric dynamometer, and an acoustic emission (AE) sensor for process monitoring. The machine tool is used for face-turning aluminum 6061 discs to a surface finish (Ra) in the range of 15–25 nm. While the sensor signals (especially the vibration signal in the feed direction) are sensitive to surface variations, the extraneous noise from the environment, machine elements, and sensing system prevents direct use of raw signal patterns for early detection of surface variations. Also, nonlinear and time-varying nature of the process dynamics does not lend conventional statistical process monitoring techniques suitable for characterizing UPM-machined surfaces. Consequently, instead of just monitoring the raw sensor signal patterns, the nonlinear process dynamics wherefrom the signal evolves are more effectively captured using a recurrent predictor neural network (RPNN). The parameters of the RPNN (weights and biases) serve as the surrogates of the process states, which are updated in real-time, based on measured sensor signals using a Bayesian particle filter (PF) technique. We show that the PF-updated RPNN can effectively capture the complex signal evolution patterns. We use a mean-shift statistic, estimated from the PF-estimated surrogate states, to detect surface variation-induced changes in the process dynamics. Experimental investigations show that variations in surface characteristics can be detected within 15 ms of their inception using the present approach, as opposed to 30 ms or higher with the conventional statistical change detection methods tested.

Restoration of call attractiveness by novel acoustic appendages in grey treefrogs

Ethologists have often reported preferences for novel signals, especially if they are more extravagant than normal signals. Such preferences presumably reflect sensory biases that may promote the evolution of both novel and complex signals. We tested behavioural responses of female grey treefrogs, Hyla versicolor, to novel complex calls in relation to the response properties of previously described temporally selective neurons in the auditory midbrain. As predicted by the selectivity of interval-counting neurons, females discriminated against synthetic advertisement calls containing a gap, a missed pulse or a pulse of abnormally short duration. The addition of a novel tonal appendage to such defective calls often resulted in partial restoration of the attractiveness of the signal. The restorative effect occurred only when an appendage with a higher amplitude followed (rather than led) the defective call. Our results show how the consideration of proximate mechanisms can provide insights about the evolution of complex signals; the behavioural results, in turn, suggest new ways of assessing the response properties of the auditory system.

Orchestrating the score: complex multimodal courtship in the Habronattus coecatus group of Habronattus jumping spiders (Araneae: Salticidae)

Jumping spiders in the genus Habronattus use complex multimodal signals during courtship displays. In the present study, we describe multimodal displays from the Habronattus coecatus clade, comprising a diverse group of 23 described species. Habronattus coecatus group displays are made up of sex-specific ornamentation and temporally coordinated combinations of motion displays and vibratory songs. Vibratory songs are complex, consisting of up to 20 elements organized in functional groupings (motifs) that change as courtship progresses. This temporal structuring of displays is analogous to a musical composition. Vibratory elements are associated with movement displays involving coloured and patterned ornaments on the male body. We describe general patterns of multimodal displays for 11 species including one, Habronattus borealis, which appears to have lost complex display behaviour. Habronattus coecatus group courtship is one of the most complex communication systems yet described in arthropods and this group may reveal important factors driving the evolution of complex signals. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 105, 522–547.

Inter-signal interaction and uncertain information in anuran multimodal signals

Abstract Disentangling the influence of multiple signal components on receivers and elucidating general processes influencing complex signal evolution are difficult tasks. In this study we test mate preferences of female squirrel treefrogs Hyla squirella and female túngara frogs Physalaemus pustulosus for similar combinations of acoustic and visual components of their multimodal courtship signals. In a two-choice playback experiment with squirrel treefrogs, the visual stimulus of a male model significantly increased the attractivness of a relatively unattractive slow call rate. A previous study demonstrated that faster call rates are more attractive to female squirrel treefrogs, and all else being equal, models of male frogs with large body stripes are more attractive. In a similar experiment with female túngara frogs, the visual stimulus of a robotic frog failed to increase the attractiveness of a relatively unattractive call. Females also showed no preference for the distinct stripe on the robot that males commonly bear on their throat. Thus, features of conspicuous signal components such as body stripes are not universally important and signal function is likely to differ even among species with similar ecologies and communication systems. Finally, we discuss the putative information content of anuran signals and suggest that the categorization of redundant versus multiple messages may not be sufficient as a general explanation for the evolution of multimodal signaling. Instead of relying on untested assumptions concerning the information content of signals, we discuss the value of initially collecting comparative empirical data sets related to receiver responses.

Inhibitory interactions between multimodal behavioural responses may influence the evolution of complex signals

Most animal displays make use of multiple sensory modalities (visual, acoustic and chemical signals) to convey similar information. Although multimodal displays may allow producers to use displays in a wider variety of social and physical contexts, it is difficult to explain their evolution because of the likely increased costs to senders and receivers. In this study, playback experiments in two contexts were used to study the behavioural responses to visual (headbob displays) and chemical (femoral pore secretions) signals in sagebrush lizards, Sceloporus graciosus. Lizards in the field tended to headbob in response to headbob displays and to engage in chemical exploratory behaviour when presented with chemical secretions. Territorial residents produced fewer headbob displays and head-turns in response to a combined signal produced by a robotic lizard than they did to either signal presented alone. This inhibition was confirmed in the laboratory, where presentation of a visual stimulus alone decreased chemical exploratory behaviour and presentation of a chemical stimulus alone decreased the number of headbob displays produced. The absolute cost of this interaction between sensory modalities may be low because the two behavioural responses are redundant, both allowing the receiver to acquire additional information, either by engaging a second lizard in a bout of interactive visual displays or by absorbing more of their scent. Thus, in sagebrush lizards, multiple signals may be evolutionarily maintained because behavioural responses to different sensory modalities are redundant and, hence, the cost of negative interactions between those responses is low.

Female preference for complex/novel signals in a spider

Identifying the various factors that influence complex signal evolution is a difficult task, yet it is fundamental to understanding the evolution of animal communication. Here we explore the evolution of complex courtship signaling by taking advantage of a system in which sexual selection on male courtship traits has driven the diversification of geographically isolated populations of the jumping spider Habronattus pugillis Griswold. Using 2 populations (Santa Rita [SR] and Atascosa [AT]) in which SR females show xenophilic mating preferences for foreign (AT) over local males (SR), we examine the mechanisms driving this preference. Both AT and SR males produce multimodal signals (visual + seismic), and while SR and AT signals share certain seismic components, AT seismic signals are more complex and contain novel components. We conducted mate choice trials where SR females were presented with AT or SR males that were either muted or nonmuted. SR females preferred to mate and mated more quickly with foreign AT males over local SR males only if AT males could produce seismic signals (nonmuted treatment). In addition, we found that SR females spent a higher proportion of time attentive to foreign AT males only if they could produce seismic signals. This evidence suggests that SR females have a bias for complex and/or novel forms of seismic signals.

Location, location, location: stripe position effects on female sword preference

The evolution of complex signals via sexual selection is becoming a primary focus in mate choice studies. Male swordtail fish, Xiphophorus helleri, have a secondary sexual trait, the sword, which is a composite trait consisting of four components favoured by sexual selection via female mate choice. The components include three coloured stripes and size. Although a complete sword is most attractive to female green swordtails, females prefer partial swords containing complete black stripes to incomplete swords lacking black coloration. Female swordtails also prefer longer swords. We addressed how subcomponents of the sword affect female mate choice. Digitally altered videos were used to investigate whether females respond differently to swords with proximal black stripes than to swords with distal black stripes. Although females preferred complete swords to both of the stimuli with partial stripes, they preferred males with distally striped swords to males with proximally striped swords. These results are discussed in light of hypotheses concerning the evolution of mating preferences for multicomponent traits. This study contributes to the growing body of information regarding the response of females to multicomponent visual traits.

Complex signal function: developing a framework of testable hypotheses

The basic building blocks of communication are signals, assembled in various sequences and combinations, and used in virtually all inter- and intra-specific interactions. While signal evolution has long been a focus of study, there has been a recent resurgence of interest and research in the complexity of animal displays. Much past research on signal evolution has focused on sensory specialists, or on single signals in isolation, but many animal displays involve complex signaling, or the combination of more than one signal or related component, often serially and overlapping, frequently across multiple sensory modalities. Here, we build a framework of functional hypotheses of complex signal evolution based on content-driven (ultimate) and efficacy-driven (proximate) selection pressures (sensu Guilford and Dawkins 1991). We point out key predictions for various hypotheses and discuss different approaches to uncovering complex signal function. We also differentiate a category of hypotheses based on inter-signal interactions. Throughout our review, we hope to make three points: (1) a complex signal is a functional unit upon which selection can act, (2) both content and efficacy-driven selection pressures must be considered when studying the evolution of complex signaling, and (3) individual signals or components do not necessarily contribute to complex signal function independently, but may interact in a functional way.