Unilateral vocal nerve resection alters neurogenesis in the avian song system in a region-specific manner

New neurons born in the adult brain undergo a critical period soon after migration to their site of incorporation. During this time, the behavior of the animal may influence the survival or culling of these cells. In the songbird song system, earlier work suggested that adult-born neurons may be retained in the song motor pathway nucleus HVC with respect to motor progression toward a target song during juvenile song learning, seasonal song restructuring, and experimentally manipulated song variability. However, it is not known whether the quality of song per se, without progressive improvement, may also influence new neuron survival. To test this idea, we experimentally altered song acoustic structure by unilateral denervation of the syrinx, causing a poor quality song. We found no effect of aberrant song on numbers of new neurons in HVC, suggesting that song quality does not influence new neuron culling in this region. However, aberrant song resulted in the loss of left-side dominance in new neurons in the auditory region caudomedial nidopallium (NCM), and a bilateral decrease in new neurons in the basal ganglia nucleus Area X. Thus new neuron culling may be influenced by behavioral feedback in accordance with the function of new neurons within that region. We propose that studying the effects of singing behaviors on new neurons across multiple brain regions that differentially subserve singing may give rise to general rules underlying the regulation of new neuron survival across taxa and brain regions more broadly.

Bill size, bill shape, and body size constrain bird song evolution on a macroevolutionary scale

Studying macroevolutionary patterns of phenotypic variation and their driving forces in large radiations can shed light on how biodiversity is generated across broad spatiotemporal scales. In this study, we integrated song and morphological variation across more than 300 species representing the largest family of songbirds, the tanagers (Thraupidae), to uncover how morphological variables of the vocal tract combine to shape vocal evolution on a macroevolutionary scale. We found that body size correlated with multiple frequency parameters, concurring with past studies that show how body size constrains vocal evolution. Furthermore, bill size predicted multiple frequency and temporal song characters while bill shape was strongly associated with trill rates, suggesting that bill size and shape both constrain distinct elements of avian song independently of body size covariation. Our results demonstrate that the relationship between morphology and song exhibits modular variation when expanded to a macroevolutionary scale. Furthermore, our study emphasizes the need to consider multiple components of the avian vocal tract when exploring the macroevolutionary interplay of morphological traits and acoustic signals.

Mechanisms of recognition in birds and social Hymenoptera: from detection to information processing

In this opinion piece, we briefly review our knowledge of the mechanisms underlying auditory individual recognition in birds and chemical nest-mate recognition in social Hymenoptera. We argue that even though detection and perception of recognition cues are well studied in social Hymenoptera, the neural mechanisms remain a black box. We compare our knowledge of these insect systems with that of the well-studied avian ‘song control system’. We suggest that future studies on recognition should focus on the hypothesis of a distributed template instead of trying to locate the seat of the template as recent results do not seem to point in that direction. This article is part of the theme issue ‘Signal detection theory in recognition systems: from evolving models to experimental tests’.

Unilateral vocal nerve resection alters neurogenesis in the avian song system in a region-specific manner

New neurons undergo a critical period soon after migration during which the behavior of the animal may result in the survival or culling of these cells. In the songbird song system, new neurons may be maintained in the song motor pathway with respect to motor progression toward a target song--during juvenile song learning, seasonal song restructuring, and experimentally manipulated song variability. However, it is not known whether the quality of song per se, without progressive improvement, may also influence new neuron survival. To test this idea, we experimentally altered song acoustic structure by unilateral denervation of the syrinx. We found no effect of aberrant song on numbers of new neurons in the HVC of the song motor pathway, a loss of left-side dominance in new neurons in the auditory region caudomedial nidopallium (NCM), and a bilateral decrease in new neurons in the basal ganglia nucleus Area X. We propose new neuron survival may be determined in response to behavioral feedback in accordance with the function of new neurons within a given brain region. Studying the effects of singing behaviors on new neurons across multiple brain regions that subserve singing may give rise to general rules underlying the regulation of new neuron survival across taxa and brain regions more broadly.

From Beak to Quill

This chapter explores Richard de Fournival's Bestiaire d'amour (ca. 1250). It shows that Richard de Fournival maintains his predecessors' association of troubadour lyric with the avian but decouples it from its association with songbirds. In the Bestiaire, the troubadours are quoted in the passage on the hoopoe—a bird not thought of as a songster in medieval typologies. This decoupling of the bond between troubadour and avian song is indicative of a broader delyricization of Occitan lyric in the Bestiaire. If, as the previous three chapters demonstrate, troubadour song was elsewhere hyperlyricized—treated as a sonic event rather than a semantic one—in the Bestiaire, the troubadours are instead inserted into a writerly genealogy, and their poetry transformed into prose.

A subcortical circuit linking the cerebellum to the basal ganglia engaged in vocal learning

Speech is a complex sensorimotor skill, and vocal learning involves both the basal ganglia and the cerebellum. These subcortical structures interact indirectly through their respective loops with thalamo-cortical and brainstem networks, and directly via subcortical pathways, but the role of their interaction during sensorimotor learning remains undetermined. While songbirds and their song-dedicated basal ganglia-thalamo-cortical circuitry offer a unique opportunity to study subcortical circuits involved in vocal learning, the cerebellar contribution to avian song learning remains unknown. We demonstrate that the cerebellum provides a strong input to the song-related basal ganglia nucleus in zebra finches. Cerebellar signals are transmitted to the basal ganglia via a disynaptic connection through the thalamus and then conveyed to their cortical target and to the premotor nucleus controlling song production. Finally, cerebellar lesions impair juvenile song learning, opening new opportunities to investigate how subcortical interactions between the cerebellum and basal ganglia contribute to sensorimotor learning.