Domestic cat larynges can produce purring frequencies without neural input

Most mammals produce vocal sounds according to the myoelastic-aerodynamic (MEAD) principle, through self-sustaining oscillation of laryngeal tissues.1,2 In contrast, cats have long been believed to produce their low-frequency purr vocalizations through a radically different mechanism involving active muscle contractions (AMC), where neurally driven electromyographic burst patterns (typically at 20–30 Hz) cause the intrinsic laryngeal muscles to actively modulate the respiratory airflow. Direct empirical evidence for this AMC mechanism is sparse.3 Here, the fundamental frequency (fo) ranges of eight domestic cats (Felis silvestris catus) were investigated in an excised larynx setup, to test the prediction of the AMC hypothesis that vibration should be impossible without neuromuscular activity, and thus unattainable in excised larynx setups, which are based on MEAD principles. Surprisingly, all eight excised larynges produced self-sustained oscillations at typical cat purring rates. Histological analysis of cat larynges revealed the presence of connective tissue masses, up to 4 mm in diameter, embedded in the vocal fold.4 This vocal fold specialization appears to allow the unusually low fo values observed in purring. While our data do not fully reject the AMC hypothesis for purring, they show that cat larynges can easily produce sounds in the purr regime with fundamental frequencies of 25 to 30 Hz without neural input or muscular contraction. This strongly suggests that the physical and physiological basis of cat purring involves the same MEAD-based mechanisms as other cat vocalizations (e.g., meows) and most other vertebrate vocalizations but is potentially augmented by AMC

Visualizing sound emission of elephant vocalizations: evidence for two rumble production types

Recent comparative data reveal that formant frequencies are cues to body size in animals, due to a close relationship between formant frequency spacing, vocal tract length and overall body size. Accordingly, intriguing morphological adaptations to elongate the vocal tract in order to lower formants occur in several species, with the size exaggeration hypothesis being proposed to justify most of these observations. While the elephant trunk is strongly implicated to account for the low formants of elephant rumbles, it is unknown whether elephants emit these vocalizations exclusively through the trunk, or whether the mouth is also involved in rumble production. In this study we used a sound visualization method (an acoustic camera) to record rumbles of five captive African elephants during spatial separation and subsequent bonding situations. Our results showed that the female elephants in our analysis produced two distinct types of rumble vocalizations based on vocal path differences: a nasally- and an orally-emitted rumble. Interestingly, nasal rumbles predominated during contact calling, whereas oral rumbles were mainly produced in bonding situations. In addition, nasal and oral rumbles varied considerably in their acoustic structure. In particular, the values of the first two formants reflected the estimated lengths of the vocal paths, corresponding to a vocal tract length of around 2 meters for nasal, and around 0.7 meters for oral rumbles. These results suggest that African elephants may be switching vocal paths to actively vary vocal tract length (with considerable variation in formants) according to context, and call for further research investigating the function of formant modulation in elephant vocalizations. Furthermore, by confirming the use of the elephant trunk in long distance rumble production, our findings provide an explanation for the extremely low formants in these calls, and may also indicate that formant lowering functions to increase call propagation distances in this species'

The evolution of acoustic size exaggeration in terrestrial mammals

Recent studies have revealed that some mammals possess adaptations that enable them to produce vocal signals with much lower fundamental frequency (F0) and formant frequency spacing (ΔF) than expected for their size. Although these adaptations are assumed to reflect selection pressures for males to lower frequency components and exaggerate body size in reproductive contexts, this hypothesis has not been tested across a broad range of species. Here we show that male terrestrial mammals produce vocal signals with lower ΔF (but not F0) than expected for their size in mating systems with greater sexual size dimorphism. We also reveal that males produce calls with higher than expected F0 and ΔF in species with increased sperm competition. This investigation confirms that sexual selection favours the use of ΔF as an acoustic size exaggerator, and supports the notion of an evolutionary trade-off between pre-copulatory signalling displays and sperm production

The evolution of language: a comparative review

For many years the evolution of language has been seen as a disreputable topic, mired in fanciful "just so stories" about language origins. However, in the last decade a new synthesis of modern linguistics, cognitive neuroscience and neo-Darwinian evolutionary theory has begun to make important contributions to our understanding of the biology and evolution of language. I review some of this recent progress, focusing on the value of the comparative method, which uses data from animal species to draw inferences about language evolution. Discussing speech first, I show how data concerning a wide variety of species, from monkeys to birds, can increase our understanding of the anatomical and neural mechanisms underlying human spoken language, and how bird and whale song provide insights into the ultimate evolutionary function of language. I discuss the ‘‘descended larynx’ ’ of humans, a peculiar adaptation for speech that has received much attention in the past, which despite earlier claims is not uniquely human. Then I will turn to the neural mechanisms underlying spoken language, pointing out the difficulties animals apparently experience in perceiving hierarchical structure in sounds, and stressing the importance of vocal imitation in the evolution of a spoken language. Turning to ultimate function, I suggest that communication among kin (especially between parents and offspring) played a crucial but neglected role in driving language evolution. Finally, I briefly discuss phylogeny, discussing hypotheses that offer plausible routes to human language from a non-linguistic chimp-like ancestor. I conclude that comparative data from living animals will be key to developing a richer, more interdisciplinary understanding of our most distinctively human trait: language

The structure of the cushions in the feet of African elephants (Loxodonta africana)

The uniquely designed limbs of the African elephant, Loxodonta africana, support the weight of the largest terrestrial animal. Besides other morphological peculiarities, the feet are equipped with large subcutaneous cushions which play an important role in distributing forces during weight bearing and in storing or absorbing mechanical forces. Although the cushions have been discussed in the literature and captive elephants, in particular, are frequently affected by foot disorders, precise morphological data are sparse. The cushions in the feet of African elephants were examined by means of standard anatomical and histological techniques, computed tomography (CT) and magnetic resonance imaging (MRI). In both the forelimb and the hindlimb a 6th ray, the prepollex or prehallux, is present. These cartilaginous rods support the metacarpal or metatarsal compartment of the cushions. None of the rays touches the ground directly. The cushions consist of sheets or strands of fibrous connective tissue forming larger metacarpal/metatarsal and digital compartments and smaller chambers which were filled with adipose tissue. The compartments are situated between tarsal, metatarsal, metacarpal bones, proximal phalanges or other structures of the locomotor apparatus covering the bones palmarly/plantarly and the thick sole skin. Within the cushions, collagen, reticulin and elastic fibres are found. In the main parts, vascular supply is good and numerous nerves course within the entire cushion. Vater–Pacinian corpuscles are embedded within the collagenous tissue of the cushions and within the dermis. Meissner corpuscles are found in the dermal papillae of the foot skin. The micromorphology of elephant feet cushions resembles that of digital cushions in cattle or of the foot pads in humans but not that of digital cushions in horses. Besides their important mechanical properties, foot cushions in elephants seem to be very sensitive structures