A genetic mechanism for sexual dichromatism in birds.

Sexual dichromatism, a difference in coloration between males and females, may be due to sexual selection for ornamentation and mate choice. Here, we show that carotenoid-based dichromatism in mosaic canaries, a hybrid phenotype that arises in offspring of the sexually dichromatic red siskin and monochromatic canaries, is controlled by the gene that encodes the carotenoid-cleaving enzyme ß-carotene oxygenase 2 (BCO2). Dichromatism in mosaic canaries is explained by differential carotenoid degradation in the integument, rather than sex-specific variation in physiological functions such as pigment uptake or transport. Transcriptome analyses suggest that carotenoid degradation in the integument might be a common mechanism contributing to sexual dichromatism across finches. These results suggest that differences in ornamental coloration between sexes can evolve through simple molecular mechanisms controlled by genes of major effect.

Hidden neural states underlie canary song syntax.

Coordinated skills such as speech or dance involve sequences of actions that follow syntactic rules in which transitions between elements depend on the identities and order of past actions. Canary songs consist of repeated syllables called phrases, and the ordering of these phrases follows long-range rules1 in which the choice of what to sing depends on the song structure many seconds prior. The neural substrates that support these long-range correlations are unknown. Here, using miniature head-mounted microscopes and cell-type-specific genetic tools, we observed neural activity in the premotor nucleus HVC2-4 as canaries explored various phrase sequences in their repertoire. We identified neurons that encode past transitions, extending over four phrases and spanning up to four seconds and forty syllables. These neurons preferentially encode past actions rather than future actions, can reflect more than one song history, and are active mostly during the rare phrases that involve history-dependent transitions in song. These findings demonstrate that the dynamics of HVC include 'hidden states' that are not reflected in ongoing behaviour but rather carry information about prior actions. These states provide a possible substrate for the control of syntax transitions governed by long-range rules.

Characteristics of song, brain-anatomy and blood androgen levels in spontaneously singing female canaries.

Females of many northern temperate songbird species sing sporadically. However, detailed descriptions of female song are rare. Here we report a detailed analysis of song in a small number of spontaneously-singing female domesticated canaries (Serinus canaria) under non-breeding, laboratory conditions in a large population of domesticated birds. In-depth analysis showed that these females sang rarely, and the spontaneous songs varied between and within birds over time. Furthermore, spontaneous female songs were distinct from songs of testosterone-induced singing female canaries and from songs of male canaries in both temporal and spectral features. Singing females had significantly elevated plasma androgen levels and a larger size of the major song controlling brain nuclei HVC (used as a proper name) and the robust nucleus of the arcopallium (RA) than non-singing females housed under similar conditions. The sporadically observed production of song and accompanying differences in brain anatomy in female canaries may thus depend on minute intraspecific differences in androgen levels.

Tongue and lingual salivary glands of the canary: scanning electron microscopy and histochemical study.

In this study, morphological characteristics of the canary tongue were examined macroscopically and histologically besides using scanning electron microscopy. Furthermore, histochemical features of the lingual salivary glands of the canary were also examined. The results suggest that the tongue of the canary has an equilateral quadrangle shape is sloped towards the apex on its dorsal surface; where its sides are bounded by tall epithelial extensions. Additionally, histological examination showed that salivary glands were only present on the body of the tongue and there were no taste buds. However, the tongue has mechanical sen-sory cell groups in its subepithelial connective tissue. Histochemical examination, demonstrated that the salivary gland epithelial cells contained carbohydrates which were composed of acidic sialo-mucins.

Involvement of the avian song system in reproductive behaviour.

The song system of songbirds consists of an interconnected set of forebrain nuclei that has traditionally been regarded as dedicated to the learning and production of song. Here, however, we suggest that the song system could also influence muscles used in reproductive behaviour, such as the cloacal sphincter muscle. We show that the same medullary nucleus, retroambigualis (RAm), that projects upon spinal motoneurons innervating expiratory muscles (which provide the pressure head for vocalization) and upon vocal motoneurons for respiratory-vocal coordination also projects upon cloacal motoneurons. Furthermore, RAm neurons projecting to sacral spinal levels were shown to receive direct projections from nucleus robustus arcopallialis (RA) of the forebrain song system. Thus, by indicating a possible disynaptic relationship between RA and motoneurons innervating the reproductive organ, in both males and females, these results potentially extend the role of the song system to include consummatory as well as appetitive aspects of reproductive behaviour.

Análise da condição corpórea, biometria externa e das vísceras do trato gastrointestinal de canários-da-terra, Sicalis flaveola braziliensis / Analysis of body condition and external and gastrointestinal biometry of saffron finch, Sicalis flaveola braziliensis

Analisaram-se em canários-da-terra, Sicalis flaveola brasiliensis, apreendidos pelo Cetas-IBAMA/PB e que morreram logo após sua chegada, as medidas biométricas externas, condições corpóreas e de plumagem, medidas biométricas das vísceras do trato gastrointestinal (TGI), assim como a topografia visceral, a fim de fornecer dados morfológicos e caracterizar as condições em esses pássaros chegaram a esse centro de triagem. A topografia visceral estava em consonância com a de periquitos e avestruz, a exceção que essa última espécie apresenta um ceco. Verificou-se que há relação entre as condições corpóreas desfavoráveis e a perda de plumagem. Conclui-se, que S. flaveola braziliensis possui medidas biométricas em consonância á de outros Passeriformes, contudo possui divergências para aves do mesmo gênero e poucas diferenças biométricas entre machos e fêmeas. Através do estudo, verifica-se que as condições corpóreas de animais traficados devem ser consideradas nos centros de triagem, a fim de se fazer um melhor manejo nutricional e/ou clínico, diminuindo a mortalidade.

Forty-one saffron finch, Sicalis flaveola brasiliensis, were studied regarding the external biometry, corporeal and plumage conditions, gastrointestinal tract (GIT) biometry, and the visceral topography, in order to provide morphological data and to characterize the condition in which these birds came to the wild animal screening Center. The visceral topography was similar to the found in parakeets and ostriches; however the last have a cecum. There was also relationship between the unfavorable body conditions and the loss of feathers. It was concluded that S. flaveola braziliensis has biometric measurements similar to other Passeriformes, however with differences to birds of the same gender, and few biometric differences among males and females. The results demonstrate that the corporal conditions of trafficked animals should be considered in wild animal screening in order to perform a better nutritional and clinical management, and to lower mortality.

A customizable 3-dimensional digital atlas of the canary brain in multiple modalities.

Songbirds are well known for their ability to learn their vocalizations by imitating conspecific adults. This uncommon skill has led to many studies examining the behavioral and neurobiological processes involved in vocal learning. Canaries display a variable, seasonally dependent, vocal behavior throughout their lives. This trait makes this bird species particularly valuable to study the functional relationship between the continued plasticity in the singing behavior and alterations in the anatomy and physiology of the brain. In order to optimally interpret these types of studies, a detailed understanding of the brain anatomy is essential. Because traditional 2-dimensional brain atlases are limited in the information they can provide about the anatomy of the brain, here we present a 3-dimensional MRI-based atlas of the canary brain. Using multiple imaging protocols we were able to maximize the number of detectable brain regions, including most of the areas involved in song perception, learning, and production. The brain atlas can readily be used to determine the stereotactic location of delineated brain areas at any desirable head angle. Alternatively the brain data can be used to determine the ideal orientation of the brain for stereotactic injections, electrophysiological recordings, and brain sectioning. The 3-dimensional canary brain atlas presented here is freely available and is easily adaptable to support many types of neurobiological studies, including anatomical, electrophysiological, histological, explant, and tracer studies.

Sex steroid-induced neuroplasticity and behavioral activation in birds.

The brain of adult homeothermic vertebrates exhibits a higher degree of morphological neuroplasticity than previously thought, and this plasticity is especially prominent in birds. In particular, incorporation of new neurons is widespread throughout the adult avian forebrain, and the volumes of specific nuclei vary seasonally in a prominent manner. We review here work on steroid-dependent plasticity in birds, based on two cases: the medial preoptic nucleus (POM) of Japanese quail in relation to male sexual behavior, and nucleus HVC in canaries, which regulates song behavior. In male quail, POM volume changes seasonally, and in castrated subjects testosterone almost doubles POM volume within 2 weeks. Significant volume increases are, however, already observable after 1 day. Steroid receptor coactivator-1 is part of the mechanism mediating these effects. Increases in POM volume reflect changes in cell size or spacing and dendritic branching, but are not associated with an increase in neuron number. In contrast, seasonal changes in HVC volume reflect incorporation of newborn neurons in addition to changes in cell size and spacing. These are induced by treatments with exogenous testosterone or its metabolites. Expression of doublecortin, a microtubule-associated protein, is increased by testosterone in the HVC but not in the adjacent nidopallium, suggesting that neuron production in the subventricular zone, the birthplace of newborn neurons, is not affected. Together, these data illustrate the high degree of plasticity that extends into adulthood and is characteristic of avian brain structures. Many questions still remain concerning the regulation and specific function of this plasticity.

Area-specific migration and recruitment of new neurons in the adult songbird brain.

Neuron recruitment has been implicated in morphological and functional plasticity in the adult brain. Whereas mammals restrict neuron recruitment specifically to two regions of known plasticity, the hippocampus and olfactory bulb, newborn neurons are found throughout the forebrain of adult songbirds. In order to study the area-specificity of the widespread proliferation and recruitment in the songbird brain, six adult male canaries received repetitive intraperitoneal injections of the mitotic marker BrdU (5-bromo-2-deoxyuridine) and were sacrificed after 24 hours to study proliferation or after 38 days to study recruitment. Migration and incorporation of new neurons was apparent throughout many but not all parts of the canary forebrain and was quantitatively related to mitotic levels in the most closely associated proliferative zones. Surprisingly, some areas of the vocal control system sensitive to plastic changes, such as nucleus higher vocal center (HVC) and area X, recruited similar numbers of new neurons as their surrounding brain tissues, employing no specific directional mechanisms. The distribution pattern in and around HVC could best be described by a random displacement model, where cells originating from the overlying lateral ventricle can move independently in any direction. Other plastic song control areas, such as the medial magnocellular nucleus of anterior nidopallium and the robust nucleus of arcopallium, were specifically avoided by migrating neurons, while migration toward the olfactory bulb showed high specificity, similar to the mammalian rostral migratory stream. Thus, different mechanisms appear to organize area-specific neuron recruitment in different recipients of the adult songbird brain, unrelated to global plasticity of brain regions.

Expression of reelin, its receptors and its intracellular signaling protein, Disabled1 in the canary brain: relationships with the song control system.

Songbirds produce learned vocalizations that are controlled by a specialized network of neural structures, the song control system. Several nuclei in this song control system demonstrate a marked degree of adult seasonal plasticity. Nucleus volume varies seasonally based on changes in cell size or spacing, and in the case of nucleus HVC and area X on the incorporation of new neurons. Reelin, a large glycoprotein defective in reeler mice, is assumed to determine the final location of migrating neurons in the developing brain. In mammals, reelin is also expressed in the adult brain but its functions are less well characterized. We investigated the relationships between the expression of reelin and/or its receptors and the dramatic seasonal plasticity in the canary (Serinus canaria) brain. We detected a broad distribution of the reelin protein, its mRNA and the mRNAs encoding for the reelin receptors (VLDLR and ApoER2) as well as for its intracellular signaling protein, Disabled1. These different mRNAs and proteins did not display the same neuroanatomical distribution and were not clearly associated, in an exclusive manner, with telencephalic brain areas that incorporate new neurons in adulthood. Song control nuclei were associated with a particular specialized expression of reelin and its mRNA, with the reelin signal being either denser or lighter in the song nucleus than in the surrounding tissue. The density of reelin-immunoreactive structures did not seem to be affected by 4 weeks of treatment with exogenous testosterone. These observations do not provide conclusive evidence that reelin plays a prominent role in the positioning of new neurons in the adult canary brain but call for additional work on this protein analyzing its expression comparatively during development and in adulthood with a better temporal resolution at critical points in the reproductive cycle when brain plasticity is known to occur.

Species differences in auditory processing dynamics in songbird auditory telencephalon.

The caudomedial nidopallium (NCM) of songbirds is a telencephalic area involved in the auditory processing and memorization of complex vocal communication signals. We used pure tone stimuli and multiunit electrophysiological recordings in awake birds to investigate whether the basic properties of song-responding circuits in NCM differ between canaries and zebra finches, two species whose songs are markedly different in their spectral and temporal organization. We found that the responses in zebra finch NCM are characterized by broad tuning and sustained responses that may facilitate the integration of zebra finch song syllables and call notes that are of long duration and have a broad harmonic structure. In contrast, we found that the responses in canary NCM show narrower tuning and less sustained responses over the time periods analyzed. These characteristics may contribute to enhanced processing of the narrow-band whistles, rapid trills, and steep frequency modulations that are prominent features of canary song. These species differences are much less pronounced in field L2, the direct thalamorecipient region that represents a preceding station in the central avian auditory pathway. NCM responses did not differ across sexes of either species, but field L2 did show wider tuning in zebra finch females relative to males. In sum, species differences in the response properties of NCM likely reflect selectivity for the acoustic elements of each species' vocal repertoire.

Song and brain development in canaries raised under different conditions of acoustic and social isolation over two years.

Early isolation experiments indicate that male songbirds learn their songs during an early sensitive period, although later work has shown that some open-ended learners modify songs in later years. Recent isolation experiments suggest that in some species song has a stronger genetic basis than previously thought. This study raised domestic canaries under different combinations of acoustic and social isolation and followed song development into the second year. Males raised alone in acoustic isolation developed songs with normal syllables, but larger repertoires and also produced syllables with lower repetition rates when compared to controls. The smallest repertoire occurred in males raised in a peer group. Isolate males had a smaller song control nucleus HVC than controls, but there was no effect on nucleus RA or on brain weight in general. In the second year, after introduction into a large normal colony, isolate and peer group males adjusted their syllable repertoire to normal size. In particular, the isolates reduced their repertoire even though the size of HVC showed a significant increase in volume. However, songs of isolate and peer group males still differ in repetition rate and number of single syllables in the common aviary. In contrast, control males showed low syllable turnover and no significant change in repertoire size. Nor did they show any significant change in the volumes of song control nuclei. It seems that complete isolation affects only some aspects of song and brain development, and later socialization corrects some but not all of these in the second year.

Local differentiation in the presence of gene flow in the citril finch Serinus citrinella.

It is well known theoretically that gene flow can impede genetic differentiation between populations. In this study, we show that in a highly mobile bird species, where dispersal is well documented, there is a strong genetic and morphological differentiation over a very short geographical scale (less than 5 km). Allocation tests revealed that birds caught in one area were assigned genetically to the same area with a very high probability, in spite of current gene flow. Populations were also morphologically differentiated. The results suggest that the relationship between gene flow and differentiation can be rather complicated and non-intuitive.

Signs of normal proliferation in the telencephalon of adult male songbirds (serinus serinus), as shown by PCNA-positivity.

The immunocytochemical expression of Proliferating Cell Nuclear Antigen (PCNA) (a cycline that coadjuvates DNA polymerase delta) becomes appreciable in the cell cycle when DNA synthesis occurs; hence cells in the S phase can be revealed by means of monoclonal antibodies. Therefore, PCNA can be considered a marker of proliferation, and numerous literature reports have demonstrated the reliability of the PCNA test. Since normal neurogenic events can still occur in the brain tissue of adult homeothermic vertebrates (especially songbirds), we evaluated if the persistence of spontaneous proliferation could be revealed in adult male songbirds (Serinus serinus) using the PCNA marker, the same test we used previously to study the persistence of natural proliferation in the encephalon of adult heterothermic vertebrates. The patterns of PCNA positivity showed normal proliferation in the telencephalon of the adult male Serinus serinus. This activity was shown by cells interposed among the epithelial cells lining the lateral side of each ventricular cavity, both in correspondence to the apical tracts and declivities of the ependyma and arranged, here and there, either in groups or slightly separated. As in our previous studies on PCNA expression and persistence of spontaneous encephalic proliferation in adult poikilothermal vertebrates (in the telencephalon of Podarcis, Triturus and Rana, and in the telencephalon, mesencephalon and cerebellum of Carassius), the results of the present research largely agree with the findings of previous Authors, usually obtained with different methods. This agreement confirms the reliability of the PCNA test used for this type of investigation.

Coordinated and dissociated effects of testosterone on singing behavior and song control nuclei in canaries (Serinus canaria).

Temperate zone songbirds that breed seasonally exhibit pronounced differences in reproductive behaviors including song inside and outside the breeding season. Springlike long daylengths are associated with increases in plasma testosterone (T) concentrations, as well as with increases in singing and in the volume of several brain nuclei known to control this behavior. The mechanisms whereby T can induce changes in behavior and brain, and whether or not these effects are differentially regulated, have recently begun to be examined, as has the question of the relative contributions of T and its androgenic and estrogenic metabolites to the regulation of this seasonal behavioral and neural plasticity. In this experiment, we examined the effects of T, 5alpha-dihydrotestosterone, or 17beta-estradiol treatment on castrated male canaries housed on short days and compared neural and behavioral effects in these males to similarly-housed males given only blank implants. We observed that only T treatment was effective in eliciting significant increases in singing behavior after 11 days of hormone exposure. In addition, T alone was effective in increasing the volume of a key song production nucleus, HVC. However, at this time, none of the steroids had any effects on the volumes of two other song control nuclei, Area X of the medial striatum and the robust nucleus of the arcopallium (RA), that are efferent targets of HVC, known to be regulated by androgen in canaries and also to play a role in the control of adult song. T can thus enhance singing well before concomitant androgen-induced changes in the song control system are complete.

Syllable repertoire and the size of the song control system in captive canaries (Serinus canaria).

In songbirds, there is considerable interest in relationships between song structure and the size of the song control system in the forebrain. In male canaries, earlier studies have reported that repertoire size increased with age, and positive correlations were obtained between repertoire size and the volume of song control nuclei such as high vocal center (HVC). Here we investigate whether age has an effect upon both the song structure and the morphology of two song control nuclei [HVC and robustus archistriatalis (RA)] that are important in song production. We recorded songs from an aviary population of 1- and 2-year-old male domesticated canaries. We found that repertoire size, number of sexually attractive (sexy) syllables, and size of song nuclei did not differ between 1- and 2-year-old males. Neither did we find significant correlations between syllable repertoire size and the size of the song control nuclei. However, HVC size was positively correlated with the proportion of sexy syllables in the repertoires of 2-year-old males. Some older males may enhance vocal performance by modifying the control of syllables rather than by increasing repertoire size or neural space.

In vivo dynamic ME-MRI reveals differential functional responses of RA- and area X-projecting neurons in the HVC of canaries exposed to conspecific song.

HVC (nidopallial area, formerly known as hyperstriatum ventrale pars caudalis), a key centre for song control in oscines, responds in a selective manner to conspecific songs as indicated by electrophysiology. However, immediate-early gene induction cannot be detected in this nucleus following song stimulation. HVC contains neurons projecting either towards the nucleus robustus archistriatalis (RA; motor pathway) or area X (anterior forebrain pathway). Both RA- and area X-projecting cells show auditory responses. The present study analysed these responses separately in the two types of HVC projection neurons of canaries by a new in vivo approach using manganese as a calcium analogue which can be transported anterogradely and used as a paramagnetic contrast agent for magnetic resonance imaging (MRI). Manganese was stereotaxically injected into HVC and taken up by HVC neurons. The anterograde axonal transport of manganese from HVC to RA and area X was then followed by MRI during approximately 8 h and changes in signal intensity in these targets were fitted to sigmoid functions. Data comparing birds exposed or not to conspecific songs revealed that song stimulation specifically affected the activity of the two types of HVC projection neurons (increase in the sigmoid slope in RA and in its maximum signal intensity in area X). Dynamic manganese-enhanced MRI thus allows assessment of the functional state of specific neuronal populations in the song system of living canaries in a manner reminiscent of functional MRI (but with higher resolution) or of 2-deoxyglucose autoradiography (but in living subjects).

Nucleus magnocellularis and nucleus laminaris in Belgian Waterslager and normal strain canaries.

Belgian Waterslager (BWS) canaries are characterized by a mean 30% loss of hair cells in the basilar papilla compared to other canaries, and a corresponding increase in behavioral auditory thresholds. In spite of the large number of missing and damaged sensory cells, there is on average only a 12% reduction in the number of fibers in the VIIIth nerve. In this study, we examined cell number and size, and volume of auditory nuclei, specifically in nucleus magnocellularis and nucleus laminaris in Belgian Waterslager canaries. While the overall anatomical structure and organization of these nuclei and the total number of cells in the non-BWS and BWS canaries were comparable, BWS canaries showed a significant decrease in the volume of the auditory nuclei that was attributed to a reduction in cell size. These results provide further evidence in favor of a role of the sensory epithelium in the maintenance of central auditory structures.

Cuerno cutáneo asociado a un carcinoma en canario (Serinus canaria) / Cutaneous horn associated with a carcinoma in a canary (Serinus canaria)

Se describe histopatológicamente un caso de un gran cuerno cutáneo verdadero de origen tumoral en un canario, localizado en la porción lateral izquierda de la región abdominal. La base del cuerno está constituida por cordones irregulares y de diferentes grosores de epitelio estratificado plano queratinizado, soportado por tejido conectivo laxo y algunas laminillas óseas y cartilaginosas. Una delgada banda de tejido conectivo e infiltrados linfoides nodulares y difusos delimitan la base del cuerno. La porción libre del cuerno es queratina a semejanza de túbulos córneos y sustancia intertubular. El cuerno cutáneo era parte de la manifestación externa de un carcinoma. (AU)

Differences in auditory and physiological properties of HVc neurons between reproductively active male and female canaries (Serinus canaria).

Based on neuronal recordings in the HVc, this study investigated differences between reproductively active male and sexually receptive female canaries. It is the first study to describe auditory responses and cell characteristics of HVc neurons in female songbirds and to compare them with the responses and characteristics obtained in males. Extracellular single unit recordings showed that in males HVc cells exhibited two types of auditory responses to conspecific and heterospecific song playbacks: tonic and phasic responses. The major finding of the present study is the absence of tonic responses in females. Neurons in the HVc of females only responded phasically to song playbacks. In both sexes, neurons exhibiting auditory responses had thinner action potentials than the others. As all the tonic cells recorded in males were thin spike cells (action potential < or = 0.6 ms) [corrected] and had high firing rates (6 Hz in average), they are potentially interneurons. In both sexes, two categories of nonresponsive cells were found: neurons that did not fire at song onset and had the lowest spontaneous firing rate; and neurons that did not exhibit changes in activity in response to song playbacks. Analyses of physiological characteristics of HVc neurons revealed that the rate of spontaneous activity was higher in males than in females. This study is a first step towards identifying [corrected] the cellular bases of the sexual dimorphism in HVc function and highlights the pivotal role of interneurons in HVc auditory processing.