Acoustic signals mediate mate choice, resource defense, and species recognition in a broad range of taxa. It has been proposed, therefore, that divergence in acoustic signals plays a key role in speciation. Nonetheless, the processes driving divergence of acoustic traits and their consequences in terms of speciation are poorly understood. A review of empirical and comparative studies reveals strong support for a role of sexual selection in acoustic divergence, but the possible concomitant influences of ecological context are rarely examined. We summarize a conceptual framework for testing the relative significance of both adaptive and neutral mechanisms leading to acoustic divergence, predictions for cases where these processes lead to speciation, and how their relative importance plays out over evolutionary time.

Evolutionary divergence in acoustic signals: causes and consequences

Reconstructing the evolution of laughter in great apes and humans.

Neural overlap in processing music and speech, as measured by the co-activation of brain regions in neuroimaging studies, may suggest that parts of the neural circuitries established for language may have been recycled during evolution for musicality, or vice versa that musicality served as a springboard for language emergence. Such a perspective has important implications for several topics of general interest besides evolutionary origins. For instance, neural overlap is an important premise for the possibility of music training to influence language acquisition and literacy. However, neural overlap in processing music and speech does not entail sharing neural circuitries. Neural separability between music and speech may occur in overlapping brain regions. In this paper, we review the evidence and outline the issues faced in interpreting such neural data, and argue that converging evidence from several methodologies is needed before neural overlap is taken as evidence of sharing.

https://royalsocietypublishing.org/doi/pdf/10.1098/rstb.2014.0090

Neural overlap in processing music and speech.

Background 
Speciation begins when populations become genetically separated through a substantial reduction in gene flow, and it is at this point that a genetically cohesive set of populations attain the sole property of species: the independent evolution of a population-level lineage. The comprehensive delimitation of species within biodiversity hotspots, regardless of their level of divergence, is important for understanding the factors that drive the diversification of biota and for identifying them as targets for conservation. However, delimiting recently diverged species is challenging due to insufficient time for the differential evolution of characters—including morphological differences, reproductive isolation, and gene tree monophyly—that are typically used as evidence for separately evolving lineages.
Methodology 
In this study, we assembled multiple lines of evidence from the analysis of mtDNA and nDNA sequence data for the delimitation of a high diversity of cryptically diverged population-level mouse lemur lineages across the island of Madagascar. Our study uses a multi-faceted approach that applies phylogenetic, population genetic, and genealogical analysis for recognizing lineage diversity and presents the most thoroughly sampled species delimitation of mouse lemur ever performed.
Conclusions 
The resolution of a large number of geographically defined clades in the mtDNA gene tree provides strong initial evidence for recognizing a high diversity of population-level lineages in mouse lemurs. We find additional support for lineage recognition in the striking concordance between mtDNA clades and patterns of nuclear population structure. Lineages identified using these two sources of evidence also exhibit patterns of population divergence according to genealogical exclusivity estimates. Mouse lemur lineage diversity is reflected in both a geographically fine-scaled pattern of population divergence within established and geographically widespread taxa, as well as newly resolved patterns of micro-endemism revealed through expanded field sampling into previously poorly and well-sampled regions.

/pdf/delimiting-species-without-nuclear-monophyly-in-madagascar-s-3b4gn29a81.pdf

Delimiting Species without Nuclear Monophyly in Madagascar's Mouse Lemurs

Human beings have been credited with unparalleled capabilities for digital prehension grasping. However, grasping behaviour is widespread among tetrapods. The propensity to grasp, and the anatomical characteristics that underlie it, appear in all of the major groups of tetrapods with the possible exception of terrestrial turtles. Although some features are synapomorphic to the tetrapod clade, such as well-defined digits and digital musculature, other features, such as opposable digits and tendon configurations, appear to have evolved independently in many lineages. Here we examine the incidence, functional morphology, and evolution of grasping across four major tetrapod clades. Our review suggests that the ability to grasp with the manus and pes is considerably more widespread, and ecologically and evolutionarily important, than previously thought. The morphological bases and ecological factors that govern grasping abilities may differ among tetrapods, yet the selective forces shaping them are likely similar. We suggest that further investigation into grasping form and function within and among these clades may expose a greater role for grasping ability in the evolutionary success of many tetrapod lineages.

Getting a grip on tetrapod grasping: form, function, and evolution

PART A: INTRODUCTORY SECTION 1 The evolutionary origin of multimodal synchronisation and emotional expression 2 Primate precursors to human language: Beyond discontinuity 3 Brain networks for the encoding of emotions in communication sounds of human and nonhuman primates PART B: DIFFERENT MAMMALIAN TAXA 4 Sound communication in house mice: Emotions in their voices and ears? 5 Vocalizations as indicators of emotional states in rats and cats 6 Beyond echolocation: Emotional acoustic communication in bats 7 Emotional communication in African Elephants 8 Toward the evolutionary roots of affective prosody in human acoustic communication: A comparative approach to mammalian voices 9 Emotional communication in monkeys: Music to their ears? PART C: NON-SPEECH HUMAN VOCALIZATIONS 10 Infant crying and the synchrony of arousal 11 Understanding spontaneous human laughter: The role of voicing in inducing positive emotion 12 Vocal expression of emotions in laughter PART D: HUMAN PROSODY 13 An integrative model of brain processes for the decoding of emotional prosody 14 On the orbito-striatal interface in (acoustic) emotional processing 15 The role of dopamine in perception and expression of emotional communication in Parkinson's disease 16 Vocal affect expression: Problems and promises PART E: MUSIC 17 Towards a neurobiology of musical emotions 18 Acoustically mediated emotional contagion as an across-species homology underlying music processing 19 A contribution to the evolutionary basis of music: Lessons from the chill-response PART F: SUMMARY: WHERE TO GO? 20 A cross-taxa concept of emotion in acoustic communication: An ethological perspective

Evolution Of Emotional Communication From Sounds In Nonhuman Mammals To Speech And Music In Man

A central question in evolutionary biology is how cryptic species maintain species cohesiveness in an area of sympatry. The coexistence of sympatrically living cryptic species requires the evolution of species-specific signalling and recognition systems. In nocturnal, dispersed living species, specific vocalisations have been suggested to act as an ideal premating isolation mechanism. We studied the structure and perception of male advertisement calls of three nocturnal, dispersed living mouse lemur species, the grey mouse lemur (Microcebus murinus), the golden brown mouse lemur (M. ravelobensis) and the Goodman's mouse lemur (M. lehilahytsara). The first two species occur sympatrically, the latter lives allopatrically to them. A multi-parameter sound analysis revealed prominent differences in the frequency contour and in the duration of advertisement calls. To test whether mouse lemurs respond specifically to calls of the different species, we conducted a playback experiment with M. murinus from the field using advertisement calls and alarm whistle calls of all three species. Individuals responded significantly stronger to conspecific than to heterospecific advertisement calls but there were no differences in response behaviour towards statistically similar whistle calls of the three species. Furthermore, sympatric calls evoked weaker interest than allopatric advertisement calls. Our results provide the first evidence for a specific relevance of social calls for speciation in cryptic primates. They furthermore support that specific differences in signalling and recognition systems represent an efficient premating isolation mechanism contributing to species cohesiveness in sympatrically living species.

/pdf/acoustic-divergence-in-the-communication-of-cryptic-species-4pumszj79d.pdf

Acoustic divergence in the communication of cryptic species of nocturnal primates (Microcebus ssp.).

The sensory basis of prey detection in captive-born grey mouse lemurs, Microcebus murinus

Different cognitive processes underlying voice identity perception in humans may have precursors in mammals. A perception of vocal signatures may govern individualised interactions in bats, which comprise species living in complex social structures and are nocturnal, fast-moving mammals. This paper investigates to what extent bats recognise, and discriminate between, individual voices and discusses acoustic features relevant for accomplishing these tasks. In spontaneous presentation and habituation-dishabituation experiments, we investigated how Megaderma lyra perceives and evaluates stimuli consisting of contact call series with individual-specific signatures from either social partners or unknown individuals. Spontaneous presentations of contact call stimuli from social partners or unknown individuals elicited strong, but comparable reactions. In the habituation-dishabituation experiments, bats dishabituated significantly to any new stimulus. However, reactions were less pronounced to a novel stimulus from the bat used for habituation than to stimuli from other bats, irrespective of familiarity, which provides evidence for identity discrimination. A model separately assessing the dissimilarity of stimuli in syllable frequencies, syllable durations and inter-call intervals relative to learned memory templates accounted for the behaviour of the bats. With respect to identity recognition, the spontaneous presentation experiments were not conclusive. However, the habituation-dishabituation experiments suggested that the bats recognised voices of social partners as the reaction to a re-habituation stimulus differed after a dishabituation stimulus from a social partner and an unknown bat.

Perception of individuality in bat vocal communication: discrimination between, or recognition of, interaction partners?

Acoustic phenotypic variation is of major importance for speciation and the evolution of species diversity. Whereas selective and stochastic forces shaping the acoustic divergence of signaling systems are well studied in insects, frogs, and birds, knowledge on the processes driving acoustic phenotypic evolution in mammals is limited. We quantified the acoustic variation of a call type exchanged during agonistic encounters across eight distinct species of the smallest-bodied nocturnal primate radiation, the Malagasy mouse lemurs. The species live in two different habitats (dry forest vs. humid forest), differ in geographic distance to each other, and belong to four distinct phylogenetic clades within the genus. Genetically defined species were discriminated reliably on the phenotypic level based on their acoustic distinctiveness in a discriminant function analysis. Acoustic variation was explained by genetic distance, whereas differences in morphology, forest type, or geographic distance had no effect. The strong impact of genetics was supported by a correlation between acoustic and genetic distance and the high agreement in branching pattern between the acoustic and molecular phylogenetic trees. In sum, stochastic factors such as genetic drift best explained acoustic diversification in a social communication call of mouse lemurs.

/pdf/evolutionary-significance-of-the-variation-in-acoustic-3k56kdrgxu.pdf

Sabine Schmidt

Papers

Evolution Of Emotional Communication From Sounds In Nonhuman Mammals To Speech And Music In Man

Acoustic divergence in the communication of cryptic species of nocturnal primates (Microcebus ssp.).

The sensory basis of prey detection in captive-born grey mouse lemurs, Microcebus murinus

Perception of individuality in bat vocal communication: discrimination between, or recognition of, interaction partners?

Evolutionary significance of the variation in acoustic communication of a cryptic nocturnal primate radiation (Microcebus spp.).