Difficulties when Assessing Birdsong Learning Programmes under Field Conditions: A Re-Evaluation of Song Repertoire Flexibility in the Great Tit

There is a remarkable diversity of song-learning strategies in songbirds. Establishing whether a species is closed- or open-ended is important to be able to interpret functional and evolutionary consequences of variation in repertoire size. Most of our knowledge regarding the timing of vocal learning is based on laboratory studies, despite the fact that these may not always replicate the complex ecological and social interactions experienced by birds in the wild. Given that field studies cannot provide the experimental control of laboratory studies, it may not be surprising that species such as the great tit that were initially assumed to be closed-ended learners have later been suggested to be open-ended learners. By using an established colour-ringed population, by following a standardized recording protocol, and by taking into account the species' song ecology (using only recordings obtained during peak of singing at dawn), we replicated two previous studies to assess song repertoire learning and flexibility in adult wild great tits elicited by social interactions. First, we performed a playback experiment to test repertoire plasticity elicited by novel versus own songs. Additionally, in a longitudinal study, we followed 30 males in two consecutive years and analysed whether new neighbours influenced any change in the repertoire. Contrary to the previous studies, song repertoire size and composition were found to be highly repeatable both between years and after confrontation with a novel song. Our results suggest that great tits are closed-ended learners and that their song repertoire probably does not change during adulthood. Methodological differences that may have led to an underestimation of the repertoires or population differences may explain the discrepancy in results with previous studies. We argue that a rigorous and standardized assessment of the repertoire is essential when studying age- or playback-induced changes in repertoire size and composition under field conditions

Rapid Effects of Hearing Song on Catecholaminergic Activity in the Songbird Auditory Pathway

Catecholaminergic (CA) neurons innervate sensory areas and affect the processing of sensory signals. For example, in birds, CA fibers innervate the auditory pathway at each level, including the midbrain, thalamus, and forebrain. We have shown previously that in female European starlings, CA activity in the auditory forebrain can be enhanced by exposure to attractive male song for one week. It is not known, however, whether hearing song can initiate that activity more rapidly. Here, we exposed estrogen-primed, female white-throated sparrows to conspecific male song and looked for evidence of rapid synthesis of catecholamines in auditory areas. In one hemisphere of the brain, we used immunohistochemistry to detect the phosphorylation of tyrosine hydroxylase (TH), a rate-limiting enzyme in the CA synthetic pathway. We found that immunoreactivity for TH phosphorylated at serine 40 increased dramatically in the auditory forebrain, but not the auditory thalamus and midbrain, after 15 min of song exposure. In the other hemisphere, we used high pressure liquid chromatography to measure catecholamines and their metabolites. We found that two dopamine metabolites, dihydroxyphenylacetic acid and homovanillic acid, increased in the auditory forebrain but not the auditory midbrain after 30 min of exposure to conspecific song. Our results are consistent with the hypothesis that exposure to a behaviorally relevant auditory stimulus rapidly induces CA activity, which may play a role in auditory responses

A regional analysis of estrogen binding to hypothalamic cell nuclei in relation to masculinization and defeminization.

Gonadal steroids masculinize and defeminize neuroendocrine development, including behavior. Defeminization makes males less sensitive than females to estrogen for showing female sexual behavior and cyclic gonadotropin secretion. Masculinization makes males more sensitive than females to estrogen for showing male sexual behavior. Thus masculinization and defeminization produce opposite effects on estrogen sensitivity. To study the relationship between estrogen sensitivity and estrogen binding, we studied sex differences in estrogen binding to hypothalamic cell nuclei on a regional and temporal basis. We measured the amount of estradiol (E2) bound to cell nuclei in the preoptic area (POA), mediobasal hypothalamus (MBH), corticomedial amygdala, and cortex of gonadectomized male and female rats 30 and 60 min after [3H]E2 was injected intravenously. In the MBH, males consistently bound less E2 than females did. In the POA, males bound less E2 than females after 60 min, but they bound more E2 than females after 30 min. Decreased estrogen binding in the MBH may underlie defeminized sexual behavior. Similarly, decreased estrogen binding in the POA at 60 min may be a correlate of defeminized gonadotropin secretion, whereas increased estrogen binding in the POA at 30 min may be a correlate of masculinized sexual behavior. To test the hypothesis that decreased estrogen binding in the MBH and POA are correlates of defeminization, we measured E2 binding at 60 min in female rats in which masculinization and defeminization were manipulated independently. Defeminization decreased E2 binding to cell nuclei in both the POA and MBH to the level seen in males at this time point. Masculinization had no effect at this time point. The data suggest that sex differences in E2 binding to hypothalamic cell nuclei correlate reliably with sex differences in estrogen sensitivity even though masculinization and defeminization produce opposing effects on these parameters

Neuronal growth, atrophy and death in a sexually dimorphic song nucleus in the zebra finch brain

The song control nuclei of the zebra finch brain contain more neurones of larger diameter in the male than in the female. This sexual dimorphism is thought to result from differential growth of neurones in the two sexes. Using neurohistological techniques and radioactive tracers, we have studied the development of several forebrain nuclei involved in the control of song and find that the dimorphism arises from neuronal atrophy and death in the female brain as well as from an increase in cell-body size and afferent terminals from other forebrain nuclei in the male. Although the timing of these events varies from nucleus to nucleus, the sequence is essentially similar in all of them except area X. Here we describe the events in one of these nuclei, the robust nucleus of archistriatum (RA), as an example

VoICE: A semi-automated pipeline for standardizing vocal analysis across models

The study of vocal communication in animal models provides key insight to the neurogenetic basis for speech and communication disorders. Current methods for vocal analysis suffer from a lack of standardization, creating ambiguity in cross-laboratory and cross-species comparisons. Here, we present VoICE (Vocal Inventory Clustering Engine), an approach to grouping vocal elements by creating a high dimensionality dataset through scoring spectral similarity between all vocalizations within a recording session. This dataset is then subjected to hierarchical clustering, generating a dendrogram that is pruned into meaningful vocalization “types” by an automated algorithm. When applied to birdsong, a key model for vocal learning, VoICE captures the known deterioration in acoustic properties that follows deafening, including altered sequencing. In a mammalian neurodevelopmental model, we uncover a reduced vocal repertoire of mice lacking the autism susceptibility gene, Cntnap2. VoICE will be useful to the scientific community as it can standardize vocalization analyses across species and laboratories