Evolution of communication signals and information during species radiation

A cross-species framework for classifying sound-movement couplings

Sound and movement are entangled in animal communication. This is obviously true in the case of sound-constituting vibratory movements of biological structures which generate acoustic waves. A little less obvious is that other moving structures produce the energy required to sustain these vibrations. In many species, the respiratory system moves to generate the expiratory flow which powers the sound-constituting movements (sound-powering movements). The sound may acquire additional structure via upper tract movements, such as articulatory movements or head raising (sound-filtering movements). Some movements are not necessary for sound production, but when produced, impinge on the sound-producing process due to weak biomechanical coupling with body parts (e.g., respiratory system) that are necessary for sound production (sound-impinging movements). Animals also produce sounds contingent with movement, requiring neuro-physiological control regimes allowing to flexibly couple movements to a produced sound, or coupling movements to a perceived external sound (sound-contingent movement). Here, we compare and classify the variety of ways sound and movements are coupled in animal communication; our proposed framework should help structure previous and future studies on this topic.

Cetaceans are the next frontier for vocal rhythm research

While rhythm can facilitate and enhance many aspects of behavior, its evolutionary trajectory in vocal communication systems remains enigmatic. We can trace evolutionary processes by investigating rhythmic abilities in different species, but research to date has largely focused on songbirds and primates. We present evidence that cetaceans-whales, dolphins, and porpoises-are a missing piece of the puzzle for understanding why rhythm evolved in vocal communication systems. Cetaceans not only produce rhythmic vocalizations but also exhibit behaviors known or thought to play a role in the evolution of different features of rhythm. These behaviors include vocal learning abilities, advanced breathing control, sexually selected vocal displays, prolonged mother-infant bonds, and behavioral synchronization. The untapped comparative potential of cetaceans is further enhanced by high interspecific diversity, which generates natural ranges of vocal and social complexity for investigating various evolutionary hypotheses. We show that rhythm (particularly isochronous rhythm, when sounds are equally spaced in time) is prevalent in cetacean vocalizations but is used in different contexts by baleen and toothed whales. We also highlight key questions and research areas that will enhance understanding of vocal rhythms across taxa. By coupling an infraorder-level taxonomic assessment of vocal rhythm production with comparisons to other species, we illustrate how broadly comparative research can contribute to a more nuanced understanding of the prevalence, evolution, and possible functions of rhythm in animal communication.

Evolutionary radiation strategy revealed in the Scarabaeidae with evidence of continuous spatiotemporal morphology and phylogenesis

Evolutionary biology faces the important challenge of determining how to interpret the relationship between selection pressures and evolutionary radiation. The lack of morphological evidence on cross-species research adds to difficulty of this challenge. We proposed a new paradigm for evaluating the evolution of branches through changes in characters on continuous spatiotemporal scales, for better interpreting the impact of biotic/abiotic drivers on the evolutionary radiation. It reveals a causal link between morphological changes and selective pressures: consistent deformation signals for all tested characters on timeline, which provided strong support for the evolutionary hypothesis of relationship between scarabs and biotic/abiotic drivers; the evolutionary strategies under niche differentiation, which were manifested in the responsiveness degree of functional morphological characters with different selection pressure. This morphological information-driven integrative approach sheds light on the mechanism of macroevolution under different selection pressures and is applicable to more biodiversity research.

A genomic basis of vocal rhythm in birds

Vocal rhythm plays a fundamental role in sexual selection and species recognition in birds, but little is known of its genetic basis due to the confounding effect of vocal learning in model systems. Uncovering its genetic basis could facilitate identifying genes potentially important in speciation. Here we investigate the genomic underpinnings of rhythm in vocal non-learning Pogoniulus tinkerbirds using 135 individual whole genomes distributed across a southern African hybrid zone. We find rhythm speed is associated with two genes that are also known to affect human speech, Neurexin-1 and Coenzyme Q8A. Models leveraging ancestry reveal these candidate loci also impact rhythmic stability, a trait linked with motor performance which is an indicator of quality. Character displacement in rhythmic stability suggests possible reinforcement against hybridization, supported by evidence of asymmetric assortative mating in the species producing faster, more stable rhythms. Because rhythm is omnipresent in animal communication, candidate genes identified here may shape vocal rhythm across birds and other vertebrates.

Chemical species recognition in an adaptive radiation of Hawaiian Tetragnatha spiders (Araneae: Tetragnathidae)

Studies of adaptive radiations have played a central role in our understanding of reproductive isolation. Yet the focus has been on human-biased visual and auditory signals, leaving gaps in our knowledge of other modalities. To date, studies on chemical signals in adaptive radiations have focused on systems with multimodal signalling, making it difficult to isolate the role chemicals play in reproductive isolation. In this study we examine the use of chemical signals in the species recognition and adaptive radiation of Hawaiian Tetragnatha spiders by focusing on entire communities of co-occurring species, and conducting behavioural assays in conjunction with chemical analysis of their silks using gas chromatography-mass spectrometry. Male spiders significantly preferred the silk extracts of conspecific mates over those of sympatric heterospecifics. The compounds found in the silk extracts, long chain alkyl methyl ethers, were remarkably species-specific in the combination and quantity. The differences in the profile were greatest between co-occurring species and between closely related sibling species. Lastly, there were significant differences in the chemical profile between two populations of a particular species. These findings provide key insights into the role chemical signals play in the attainment and maintenance of reproductive barriers between closely related co-occurring species.

Chimpanzees show the capacity to communicate about concomitant daily life events

One universal feature of human language is its versatility in communicating about juxtapositions of everyday events. Versatile combinatorial systems of communication can be selected for if (a) several vocal units are flexibly combined into numerous and long vocal sequences and (b) vocal sequences relate to numerous daily life events. We propose (b) is more likely during simultaneous or serial (concomitant) events than single events. We analyzed 9,391 vocal utterances across the repertoire of wild chimpanzees and their events of production. Chimpanzees used vocal sequences across a range of daily life events and twice as often during concomitant than single events. Also, utterance diversity correlated positively with event diversity. Our results show the potential of chimpanzee vocal sequences to convey combined information about numerous daily life events, a step from which generalized combinatoriality could have evolved.

Sex differences in vocal learning ability in songbirds are linked with differences in flexible rhythm pattern perception

Humans readily recognize familiar rhythmic patterns, such as isochrony (equal timing between events) across a wide range of rates. This reflects a facility with perceiving the relative timing of events, not just absolute interval durations. Several lines of evidence suggest this ability is supported by precise temporal predictions arising from forebrain auditory-motor interactions. We have shown previously that male zebra finches, Taeniopygia guttata, which possess specialized auditory-motor networks and communicate with rhythmically patterned sequences, share our ability to flexibly recognize isochrony across rates. To test the hypothesis that flexible rhythm pattern perception is linked to vocal learning, we ask whether female zebra finches, which do not learn to sing, can also recognize global temporal patterns. We find that females can flexibly recognize isochrony across a wide range of rates but perform slightly worse than males on average. These findings are consistent with recent work showing that while females have reduced forebrain song regions, the overall network connectivity of vocal premotor regions is similar to males and may support predictions of upcoming events. Comparative studies of male and female songbirds thus offer an opportunity to study how individual differences in auditory-motor connectivity influence perception of relative timing, a hallmark of human music perception.

Improving the workflow to crack Small, Unbalanced, Noisy, but Genuine (SUNG) datasets in bioacoustics: The case of bonobo calls

Despite the accumulation of data and studies, deciphering animal vocal communication remains challenging. In most cases, researchers must deal with the sparse recordings composing Small, Unbalanced, Noisy, but Genuine (SUNG) datasets. SUNG datasets are characterized by a limited number of recordings, most often noisy, and unbalanced in number between the individuals or categories of vocalizations. SUNG datasets therefore offer a valuable but inevitably distorted vision of communication systems. Adopting the best practices in their analysis is essential to effectively extract the available information and draw reliable conclusions. Here we show that the most recent advances in machine learning applied to a SUNG dataset succeed in unraveling the complex vocal repertoire of the bonobo, and we propose a workflow that can be effective with other animal species. We implement acoustic parameterization in three feature spaces and run a Supervised Uniform Manifold Approximation and Projection (S-UMAP) to evaluate how call types and individual signatures cluster in the bonobo acoustic space. We then implement three classification algorithms (Support Vector Machine, xgboost, neural networks) and their combination to explore the structure and variability of bonobo calls, as well as the robustness of the individual signature they encode. We underscore how classification performance is affected by the feature set and identify the most informative features. In addition, we highlight the need to address data leakage in the evaluation of classification performance to avoid misleading interpretations. Our results lead to identifying several practical approaches that are generalizable to any other animal communication system. To improve the reliability and replicability of vocal communication studies with SUNG datasets, we thus recommend: i) comparing several acoustic parameterizations; ii) visualizing the dataset with supervised UMAP to examine the species acoustic space; iii) adopting Support Vector Machines as the baseline classification approach; iv) explicitly evaluating data leakage and possibly implementing a mitigation strategy.

The evolution of behavioral cues and signaling in displaced communication

Displaced communication, whereby individuals communicate regarding a subject that is not immediately present (spatially or temporally), is one of the key features of human language. It also occurs in a few animal species, most notably the honeybee, where the waggle dance is used to communicate the location and quality of a patch of flowers. However, it is difficult to study how it emerged given the paucity of species displaying this capacity and the fact that it often occurs via complex multimodal signals. To address this issue, we developed a novel paradigm in which we conducted experimental evolution with foraging agents endowed with neural networks that regulate their movement and the production of signals. Displaced communication readily evolved but, surprisingly, agents did not use signal amplitude to convey information on food location. Instead, they used signal onset-delay and duration-based mode of communication, which depends on the motion of the agent within a communication area. When agents were experimentally prevented from using these modes of communication, they evolved to use signal amplitude instead. Interestingly, this mode of communication was more efficient and led to higher performance. Subsequent controlled experiments suggested that this more efficient mode of communication failed to evolve because it took more generations to emerge than communication grounded on the onset-delay and length of signaling. These results reveal that displaced communication is likely to initially evolve from non-communicative behavioral cues providing incidental information with evolution later leading to more efficient communication systems through a ritualization process.

Correlated evolution between colour conspicuousness and drum speed in woodpeckers

Sexual selection drives the evolution of many spectacular animal displays that we see in nature. Yet, how selection combines and elaborates different signal traits remains unclear. Here, we investigate this issue by testing for correlated evolution between head plumage colour and drumming behaviour in woodpeckers. These signals function in the context of mate choice and male-male competition, and they may appear to a receiver as a single multimodal display. We test for such correlations in males of 132 species using phylogenetic linear models, while considering the effect of habitat. We find that the plumage chromatic contrast is positively correlated with the speed of the drum, supporting the idea that species evolving more conspicuous plumage on their head also evolve faster drum displays. By contrast, we do not find evidence of correlated evolution between drum speed and head colour diversity, size of the head's red patch, or extent of the plumage achromatic contrast. Drum length was not correlated with any of the plumage coloration metrics. Lastly, we find no evidence that habitat acts as a strong selective force driving the evolution of head coloration or drumming elaboration. Coevolution between different signal modalities is therefore complex, and probably depends on the display components in question.

Using acoustics and artificial intelligence to monitor pollination by insects and tree use by woodpeckers

The collection and interpretation of field data is a prerequisite for informed conservation in protected environments. Although several techniques, including camera trapping and passive acoustic monitoring, have been developed to estimate the presence of animal species, very few attempts have been made to monitor ecological functions. Pollination by insects and wood use, including tree related foraging and intraspecific communication, by woodpeckers are key functions that need to be assessed in order to better understand and preserve forest ecosystems within the context of climate change. Here, we developed and applied for the first time an acoustic survey to monitor pollination by insects and wood use by woodpeckers in a protected Alpine forest in France. We deployed four autonomous recorders over a year, resulting in 2285 h of recordings. We trained a convolutional neural network (CNN) on spectrographic images to automatically detect the sounds of flying insects' buzzing and woodpeckers' drumming as they forage and call. We used the output of the CNN to estimate the seasonality, diel pattern, climatic breadth and distribution of both functions and their relationships with weather parameters. Our method showed that insects were flying (therefore potentially pollinating flowers) in bright, warm and dry conditions, after dawn and before dusk during spring and summer. Woodpeckers were mainly drumming around March at the time of pair formation in cool and wet conditions. Having considered the role of weather parameters, climate change might have contrasting effects on insect buzzing and woodpecker drumming, with an increase in temperature being favorable to pollination by insects but not to wood use by woodpeckers, and a concomitant increase in relative humidity being favorable to wood use but not to pollination. This study reveals that a systemic facet of biodiversity can be tracked using sound, and that acoustics provide valuable information for the environment description.

Geographic Variation in Social Vocalizations of the Great Himalayan Leaf-Nosed Bat, Hipposideros armiger: Acoustic Overflow Across Population Boundaries

Bat populations employ rich vocal repertoires for social communication in addition to emitting sound pulses for echolocation. Acoustic parameters of echolocation pulses can vary with the context in which they are emitted, and also with the individual and across populations as a whole. The acoustic parameters of social vocalizations, or “calls”, also vary with the individual and context, but not much is known about their variation across populations at different geographic locations. Here, we leveraged the detailed acoustic classification of social vocalizations available for the Great Himalayan leaf-nosed bat, Hipposideros armiger, to examine geographic variation in five commonly emitted simple syllable types. We hypothesized that individuals within geographically dispersed populations communicate using spectrographically similar constructs or “syllable types”. We also examined whether call syllables vary discordantly with the correlation pattern observed for echolocation pulses across those same geographic regions. Furthermore, we postulated that the acoustic boundaries of a syllable type are not uniquely constrained to its variation within a particular population of the same subspecies. To test our hypotheses, we obtained recordings of social calls of H. a. armiger from nine locations within the oriental region. These locations were consolidated into five geographic regions based on previously established region-specific differences in the peak frequency of echolocation pulses. A multivariate cluster analysis established that unlike echolocation pulses, syllable types exhibit a relatively large variance. Analysis of this variance showed significant differences in Least Squares Means estimates, establishing significant population-level differences in the multiparametric means of individual syllable types across geographic regions. Multivariate discriminant analysis confirmed the presence of region-specific centroids for different syllable constructs, but also showed a large overlap of their multiparametric boundaries across geographic regions. We propose that despite differences in the population-specific core construct of a syllable type, bats maximize acoustic variation across individuals within a population irrespective of its overflow and overlap with other populations.

In Vitro Evaluation and Mitigation of Niclosamide’s Liabilities as a COVID-19 Treatment.. [PMID: 35860224 PMCID: PMC9298134 DOI: 10.1101/2022.06.24.497526] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

Niclosamide, an FDA-approved oral anthelmintic drug, has broad biological activity including anticancer, antibacterial, and antiviral properties. Niclosamide has also been identified as a potent inhibitor of SARS-CoV-2 infection in vitro, generating interest in its use for the treatment or prevention of COVID-19. Unfortunately, there are several potential issues with using niclosamide for COVID-19, including low bioavailability, significant polypharmacology, high cellular toxicity, and unknown efficacy against emerging SARS-CoV-2 variants of concern. In this study, we used high-content imaging-based immunofluorescence assays in two different cell models to assess these limitations and evaluate the potential for using niclosamide as a COVID-19 antiviral. We show that despite promising preliminary reports, the antiviral efficacy of niclosamide overlaps with its cytotoxicity giving it a poor in vitro selectivity index for anti-SARS-CoV-2 inhibition. We also show that niclosamide has significantly variable potency against the different SARS-CoV-2 variants of concern and is most potent against variants with enhanced cell-to-cell spread including B.1.1.7. Finally, we report the activity of 33 niclosamide analogs, several of which have reduced cytotoxicity and increased potency relative to niclosamide. A preliminary structure-activity relationship analysis reveals dependence on a protonophore for antiviral efficacy, which implicates nonspecific endolysosomal neutralization as a dominant mechanism of action. Further single-cell morphological profiling suggests niclosamide also inhibits viral entry and cell-to-cell spread by syncytia. Altogether, our results suggest that niclosamide is not an ideal candidate for the treatment of COVID-19, but that there is potential for developing improved analogs with higher clinical translational potential in the future.

Movement-based signalling by four species of dragon lizard (family Agamidae) from the Kimberley region of Western Australia

Communication signals underpin the social lives of animals, from species recognition to mate selection and territory defense. Animal signals are diverse in structure between and within species, with the diversity reflecting interacting factors of shared evolutionary history, constraints imposed on senders and receivers and the ecological context in which signalling takes place. The dragon lizards of Australia (family Agamidae) are known for their movement-based visual displays and are useful models for how ecology influences behaviour. However, we know little about the communication strategies of many species. Our aim here was to provide new knowledge on some of these species, focusing on the north-west of Western Australia. We filmed within-species pairwise interactions of Diporiphora superba, D. bennetti, D. sobria and Ctenophorus isolepis isolepis. We describe and quantify for the first time push-up displays by D. superba and C. isolepis isolepis and tail waving displays of D. bennetti. Only D. sobria did not generate movement-based visual signals. We have confirmed that more species engage in such behaviour than previously reported, but further work is required to document the full repertoire of these species. The implications of our work are discussed in the context of signal structure, function and environmental context.

Social pressure drives "conversational rules" in great apes

In the last decade, two hypotheses, one on the evolution of animal vocal communication in general and the other on the origins of human language, have gained ground. The first hypothesis argues that the complexity of communication co-evolved with the complexity of sociality. Species forming larger groups with complex social networks have more elaborate vocal repertoires. The second hypothesis posits that the core of communication is represented not only by what can be expressed by an isolated caller, but also by the way that vocal interactions are structured, language being above all a social act. Primitive forms of conversational rules based on a vocal turn-taking principle are thought to exist in primates. To support and bring together these hypotheses, more comparative studies of socially diverse species at different levels of the primate phylogeny are needed. However, the majority of available studies focus on monkeys, primates that are distant from the human lineage. Great apes represent excellent candidates for such comparative studies because of their phylogenetic proximity to humans and their varied social lives. We propose that studying vocal turn-taking in apes could address several major gaps regarding the social relevance of vocal turn-taking and the evolutionary trajectory of this behaviour among anthropoids. Indeed, how the social structure of a species may influence the vocal interaction patterns observed among group members remains an open question. We gathered data from the literature as well as original unpublished data (where absent in the literature) on four great ape species: chimpanzees Pan troglodytes, bonobos Pan paniscus, western lowland gorillas Gorilla gorilla gorilla and Bornean orang-utans Pongo pygmaeus. We found no clear-cut relationship between classical social complexity metrics (e.g. number of group members, interaction rates) and vocal complexity parameters (e.g. repertoire size, call rates). Nevertheless, the nature of the society (i.e. group composition, diversity and valence of social bonds) and the type of vocal interaction patterns (isolated calling, call overlap, turn-taking-based vocal exchanges) do appear to be related. Isolated calling is the main vocal pattern found in the species with the smallest social networks (orang-utan), while the other species show vocal interactions that are structured according to temporal rules. A high proportion of overlapping vocalisations is found in the most competitive species (chimpanzee), while vocal turn-taking predominates in more tolerant bonobos and gorillas. Also, preferentially interacting individuals and call types used to interact are not randomly distributed. Vocal overlap ('chorusing') and vocal exchange ('conversing') appear as possible social strategies used to advertise/strengthen social bonds. Our analyses highlight that: (i) vocal turn-taking is also observed in non-human great apes, revealing universal rules for conversing that may be deeply rooted in the primate lineage; (ii) vocal interaction patterns match the species' social lifestyle; (iii) although limited to four species here, adopting a targeted comparative approach could help to identify the multiple and subtle factors underlying social and vocal complexity. We believe that vocal interaction patterns form the basis of a promising field of investigation that may ultimately improve our understanding of the socially driven evolution of communication.

Testosterone amplifies the negative valence of an agonistic gestural display by exploiting receiver perceptual bias

Many animals communicate by performing elaborate displays that are incredibly extravagant and wildly bizarre. So, how do these displays evolve? One idea is that innate sensory biases arbitrarily favour the emergence of certain display traits over others, leading to the design of an unusual display. Here, we study how physiological factors associated with signal production influence this process, a topic that has received almost no attention. We focus on a tropical frog, whose males compete for access to females by performing an elaborate waving display. Our results show that sex hormones like testosterone regulate specific display gestures that exploit a highly conserved perceptual system, evolved originally to detect 'dangerous' stimuli in the environment. Accordingly, testosterone makes certain gestures likely to appear more perilous to rivals during combat. This suggests that hormone action can interact with effects of sensory bias to create an evolutionary optimum that guides how display exaggeration unfolds.

Contingency and determinism in the evolution of bird song sound frequency

Sexual signals are archetypes of contingent evolution: hyper-diverse across species, often evolving fast and in unpredictable directions. It is unclear to which extent their evolutionary unpredictability weakens deterministic evolution, or takes place bounded by deterministic patterns of trait evolution. We compared the evolution of sound frequency in sexual signals (advertisement songs) and non-sexual social signals (calls) across > 500 genera of the crown songbird families. Contrary to the acoustic adaptation hypothesis, we found no evidence that forest species used lower sound frequencies in songs or calls. Consistent with contingent evolution in song, we found lower phylogenetic signal for the sound frequency of songs than calls, which suggests faster and less predictable evolution, and found unpredictable direction of evolution in lineages with longer songs, which presumably experience stronger sexual selection on song. Nonetheless, the most important deterministic pattern of sound frequency evolution—its negative association with body size—was stronger in songs than calls. This can be explained by songs being longer-range signals than most calls, and thus using sound frequencies that animals of a given size produce best at high amplitude. Results indicate that sexual selection can increase aspects of evolutionary contingency while strengthening, rather than weakening, deterministic patterns of evolution.

Cost-reducing traits for agonistic head collisions: a case for neurophysiology

Many animal species have evolved extreme behaviors requiring them to engage in repeated high-impact collisions. These behaviors include mating displays like headbutting in sheep and drumming in woodpeckers. To our knowledge, these taxa do not experience any notable acute head trauma, even though the deceleration forces would cause traumatic brain injury in most animals. Previous research has focused on skeletomuscular morphology, biomechanics, and material properties in an attempt to explain how animals moderate these high-impact forces. However, many of these behaviors are understudied, and most morphological or computational studies make assumptions about the behavior without accounting for the physiology of an organism. Studying neurophysiological and immune adaptations that co-vary with these behaviors can highlight unique or synergistic solutions to seemingly deleterious behavioral displays. Here, we argue that selection for repeated, high-impact head collisions may rely on a suite of coadaptations in intracranial physiology as a cost-reducing mechanism. We propose that there are three physiological systems that could mitigate the effects of repeated head trauma: (i) the innate neuroimmune response, (ii) the glymphatic system, and (iii) the choroid plexus. These systems are interconnected yet can evolve in an independent manner. We then briefly describe the function of these systems, their role in head trauma, and research that has examined how these systems may evolve to help reduce the cost of repeated, forceful head impacts. Ultimately, we note that little is known about cost-reducing intracranial mechanisms making it a novel field of comparative study that is ripe for exploration.

Sister species diverge in modality-specific courtship signal form and function

Understanding the relative importance of different sources of selection (e.g., the environment, social/sexual selection) on the divergence or convergence of reproductive communication can shed light on the origin, maintenance, or even disappearance of species boundaries. Using a multistep approach, we tested the hypothesis that two presumed sister species of wolf spider with overlapping ranges and microhabitat use, yet differing degrees of sexual dimorphism, have diverged in their reliance on modality-specific courtship signaling. We predicted that male Schizocosa crassipalpata (no ornamentation) rely predominantly on diet-dependent vibratory signaling for mating success. In contrast, we predicted that male S. bilineata (black foreleg brushes) rely on diet-dependent visual signaling. We first tested and corroborated the sister-species relationship between S. crassipalpata and S. bilineata using phylogenomic scale data. Next, we tested for species-specific, diet-dependent vibratory and visual signaling by manipulating subadult diet and subsequently quantifying adult morphology and mature male courtship signals. As predicted, vibratory signal form was diet-dependent in S. crassipalpata, while visual ornamentation (brush area) was diet-dependent in S. bilineata. We then compared the species-specific reliance on vibratory and visual signaling by recording mating across artificially manipulated signaling environments (presence/absence of each modality in a 2 × 2 full factorial design). In accordance with our diet dependence results for S. crassipalpata, the presence of vibratory signaling was important for mating success. In contrast, the light and vibratory environment interacted to influence mating success in S. bilineata, with vibratory signaling being important only in the absence of light. We found no differences in overall activity patterns. Given that these species overlap in much of their range and microhabitat use, we suggest that competition for signaling space may have led to the divergence and differential use of sensory modalities between these sister species.