Genetic Mapping and Biochemical Basis of Yellow Feather Pigmentation in Budgerigars.

Parrot feathers contain red, orange, and yellow polyene pigments called psittacofulvins. Budgerigars are parrots that have been extensively bred for plumage traits during the last century, but the underlying genes are unknown. Here we use genome-wide association mapping and gene-expression analysis to map the Mendelian blue locus, which abolishes yellow pigmentation in the budgerigar. We find that the blue trait maps to a single amino acid substitution (R644W) in an uncharacterized polyketide synthase (MuPKS). When we expressed MuPKS heterologously in yeast, yellow pigments accumulated. Mass spectrometry confirmed that these yellow pigments match those found in feathers. The R644W substitution abolished MuPKS activity. Furthermore, gene-expression data from feathers of different bird species suggest that parrots acquired their colors through regulatory changes that drive high expression of MuPKS in feather epithelia. Our data also help formulate biochemical models that may explain natural color variation in parrots. VIDEO ABSTRACT.

FoxP1 Protein Shows Differential Layer Expression in the Parahippocampal Domain among Bird Species.

Different bird orders show diversity in neural capabilities supported by variations in brain morphology. The parahippocampal domain in the medial pallium, together with the hippocampus proper, plays an important role in memory skills. In the present work, we analyze the expression pattern of the FoxP1 protein in the parahippocampal area of four different bird species: the nonvocal learner birds quail and chicken (Galliformes) and two vocal learner birds, i.e. the zebra finch (Passeriformes) and the budgerigar (Psittaciformes), at different developmental and adult stages. We also analyze the expression of the calbindin protein in quails and zebra finches. We observed differences in the FoxP1 parahippocampal layer among bird species. In quails, chickens, and budgerigar, FoxP1 cells were located in the outer layers of the lateral and caudolateral parahippocampal sectors. In contrast, FoxP1 immunoreactive cells appeared in the inner layer of the same sectors in the zebra finch parahippocampal domain. These differences suggest two possibilities: either the FoxP1-positive cells described in quails, chickens, and budgerigars are a different population than the one described in the zebra finch, or there are changes in the pattern of radial migration in the parahippocampal area among birds. In the present study, we show that FoxP1 expression is more similar between quails, chickens, and budgerigars than between budgerigars and zebra finches in the parahippocampal area. This result contrasts with previous data in other telencephalic structures, like the calbindin-positive projection neurons described in the striatum of budgerigars and zebra finches but not in quails and chickens. All of these data point to diversity in the evolution of different morphological characters and, therefore, a mosaic model for telencephalic evolution in birds.

Radiographic reference limits for cardiac width of budgerigars (Melopsittacus undulatus).

Primary and secondary cardiovascular diseases are not uncommon in birds. Although radiologic standards for heart width have been developed for mammals, they are still not available for many avian species. The purpose of this study was to establish normal reference values for cardiac size in budgerigar (Melopsittacus undulatus), one of the most popular pet bird species all over the world. After clinical and radiographic (lateral and ventrodorsal views) evaluations, 27 adult, clinically healthy budgerigars (10 females and 17 males) were included in this study. High-quality ventrodorsal and lateral radiographic projections were obtained. The cardiac and thoracic width, distance between third and fourth ribs, synsacrum width, coracoid width, and the distance between clavicle bones were measured on ventrodorsal radiographs. The ratio between cardiac width and other mentioned indices was calculated. Correlation of each anatomical index with the cardiac width was evaluated by linear regression model. Sex and weight were included in all models. Mean + SD of cardiac width was 10.8 +/- 0.6 mm, with lower and upper limits of 9.5 and 12.0 mm. The results showed a significant correlation between the cardiac width and the thoracic width (R2 = 0.28; P = 0.005). There were no significant associations between weight, sex, and the heart width. The values and ratios obtained in this study can be used as a reference of normal cardiac size of budgerigar in radiology for detection of cardiomegaly in this bird.

Relative contributions of pigments and biophotonic nanostructures to natural color production: a case study in budgerigar (Melopsittacus undulatus) feathers.

Understanding the mechanistic bases of natural color diversity can provide insight into its evolution and inspiration for biomimetic optical structures. Metazoans can be colored by absorption of light from pigments or by scattering of light from biophotonic nanostructures, and these mechanisms have largely been treated as distinct. However, the interactions between them have rarely been examined. Captive breeding of budgerigars (Aves, Psittacidae, Melopsittacus undulatus) has produced a wide variety of color morphs spanning the majority of the spectrum visible to birds, including the ultraviolet, and thus they have been used as examples of hypothesized structure-pigment interactions. However, empirical data testing these interactions in this excellent model system are lacking. Here we used ultraviolet-visible spectrometry, light and electron microscopy, pigment extraction experiments and optical modeling to examine the physical bases of color production in seven budgerigar morphs, including grey and chromatic (purple to yellow) colors. Feathers from all morphs contained quasi-ordered air-keratin 'spongy layer' matrices, but these were highly reduced and irregular in grey and yellow feathers. Similarly, all feathers but yellow and grey had a layer of melanin-containing melanosomes basal to the spongy layer. The presence of melanosomes likely increases color saturation produced by spongy layers whereas their absence may allow increased expression of yellow colors. Finally, extraction of yellow pigments caused some degree of color change in all feathers except purple and grey, suggesting that their presence and contribution to color production is more widespread than previously thought. These data illustrate how interactions between structures and pigments can increase the range of colors attainable in birds and potentially in synthetic systems.

Morphological and morphometric study of the pecten oculi in the budgerigar (Melopsittacus undulatus).

The pecten oculi is a highly vascular and pigmented organ placed in the vitreous body of the avian eye. As no data are currently available on the morphological organization of the pecten in the Psittaciformes, the pecten oculi of the budgerigar (Melopsittacus undulatus) was studied. The eyes from adult male budgerigars were examined by light, transmission, and scanning electron microscopy and a morphometric study on both light and transmission electron microscopy specimens was also performed in the different parts of the organ. In the budgerigar, the type of the pecten oculi was pleated. Its basal part had a cranio-caudal and postero-anterior course; its body consisted of 10-12-folds joined apically by a densely pigmented bridge. The pecten showed many capillaries, whose wall was thick and formed by pericytes and endothelial cells. These latter had a large number of microfolds, rectilinear on their luminal surface and tortuous on their abluminal surface. Interstitial pigment cells were placed among the capillaries, filled with melanin granules and showed many cytoplasmic processes. The morphometric analysis demonstrated significant differences among the three parts of the organ relative to the length of the endothelial processes and to the number and size of the pigment granules. The morphological and morphometric analysis showed that the bridge of the budgerigar, different from the other birds, had a large number of capillaries, so that this part of the organ could also play a trophic role for the retina in addition to the choriocapillaris.

Lateralization of acoustic signals by dichotically listening budgerigars (Melopsittacus undulatus).

Sound localization allows humans and animals to determine the direction of objects to seek or avoid and indicates the appropriate position to direct visual attention. Interaural time differences (ITDs) and interaural level differences (ILDs) are two primary cues that humans use to localize or lateralize sound sources. There is limited information about behavioral cue sensitivity in animals, especially animals with poor sound localization acuity and small heads, like budgerigars. ITD and ILD thresholds were measured behaviorally in dichotically listening budgerigars equipped with headphones in an identification task. Budgerigars were less sensitive than humans and cats, and more similar to rabbits, barn owls, and monkeys, in their abilities to lateralize dichotic signals. Threshold ITDs were relatively constant for pure tones below 4 kHz, and were immeasurable at higher frequencies. Threshold ILDs were relatively constant over a wide range of frequencies, similar to humans. Thresholds in both experiments were best for broadband noise stimuli. These lateralization results are generally consistent with the free field localization abilities of these birds, and add support to the idea that budgerigars may be able to enhance their cues to directional hearing (e.g., via connected interaural pathways) beyond what would be expected based on head size.

Descripción anatómica del esqueleto de los tractos respiratorios superiores del periquito australiano (Melopsittacus undulatus) / Anatomical description of upper respiratory tracts skeleton of budgerigar (Melopsittacus undulatus)

Se describe detalladamente los elementos esqueléticos de los tractos respiratorios superiores de 10 periquitos australianos (Melopsittacus undulatus), dicha descripción permitió encontrar claras diferencias en su anatomía no referidas con anterioridad, debido posiblemente al interés por estudiar la siringe y no los tractos respiratorios completos, el objetivo principal fue describir la morfología y osificación de los tractos respiratorios superiores del periquito australiano, a través de la técnica de transparentación con doble tinción (rojo de alizarina "S" y azul de alciano), que permite observar la osificación de los tractos respiratorios; obteniendo como resultado dos diferencias óseas importantes: (1) la lengua exhibe dos pequeños huesos paraglosales asociados con la movilidad de la misma y (2) una importante osificación desde la lengua hasta los elementos "A" siringeales. En cuanto al patrón del esqueleto traqueal y siríngeo, no se observan grandes diferencias con respecto a otros psittaciformes. Se propone el estudio del esqueleto lingual para determinar su importancia en el establecimiento de relaciones de parentesco y su valor taxonómico, y de esta forma, abrir una puerta para nuevos estudios de morfología comparativa.

In this work describes in detail skeletical elements of upper respiratory tracts of 10 budgerigars (Melopsittacus undulatus), the description obtains evident differences in its anatomy doesn't relate before, this should to be possible at interest to study syrinx and not full respiratory tracts the objective was to describer morphology and ossification of full upper respiratory tracts of budgerigar, this obtained utilizing clearing technique's with stain double (alizarin red "S" and alcian blue) it allows to observe ossification of respiratory tracts, it obtained like result two principal evident differences: (1) the lingual shows two small paragloss bones associates with its mobility and (2) a important ossification from the lingual to "A" syrinx elements. Respectful at patron tracheal and syrinx skeletical doesn't show evident differences in comparation with other psittacidae. It proposes a study of lingual skeletical to determination of importance for to establish relationship and its taxonomic value and this form meets a door for new studies of comparative morphology.

Osteological examinations on the budgerigar (Melopsittacus undulatus Shaw 1805) with special reference to skeletal alterations conditioned by breeding.

The aims of this study were to examine the skeleton of domesticated budgerigars of phenotypically different breeding types, to describe the expression of skeletal changes and to discuss the results with special reference to the causes and effects of breed-conditioned alterations. Complete skeletons of 39 adult budgerigars of both sexes were the object of our research. The examinations demonstrated that almost all metrically sized skeleton dimensions of budgerigars of the exhibition type were increased significantly, compared with those of the non-exhibition type. Only for the scapula significant length differences between the budgerigars of both breeding types could not be verified. It can be stated that the measuring parameters 'occipital width', 'maxilla length', 'skull length' and 'prefrontal width' are suitable for the characterization of exhibition budgerigars. However, sexual dimorphisms could be verified in only three parameters (width of the pars symphysialis mandibulae, height of the skull, width of the skull within the range of the occiput). It has to be clarified in future studies to what extent the changes in the skeleton of budgerigars of the exhibition type have already had consequences for their flying ability, metabolism, health and well-being.

Vocal area-related expression of the androgen receptor in the budgerigar (Melopsittacus undulatus) brain.

The androgen receptor is a steroid hormone receptor widely expressed in the vocal control nuclei in songbirds. Here, we analysed androgen receptor expression in the brains of juvenile and adult budgerigars. With a species-specific probe for budgerigar androgen receptor mRNA, we found that the androgen receptor was expressed in the vocal areas, such as the central nucleus of the lateral nidopallium, the anterior arcopallium, the oval nucleus of the mesopallium, the oval nucleus of the anterior nidopallium and the tracheosyringeal hypoglossal nucleus. With the present data, together with previous reports, it turned out that the androgen receptor expression in telencephalic vocal control areas is similar amongst three groups of vocal learners--songbirds, hummingbirds and parrots, suggesting the possibility that the androgen receptor might play a role in vocal development and that the molecular mechanism regulating the androgen receptor expression in the vocal areas might be important in the evolution of vocal learning.

Cannabinoid system in the budgerigar brain.

Cannabinoid receptor density and cannabinoid receptor-mediated G protein stimulation were studied by autoradiographic techniques throughout the budgerigar (Melopsittacus undulatus) brain. The maximal CB(1) receptor density value (using [(3)H]CP55,940 as radioligand) was found in the molecular layer of the cerebellum (Mol), and high binding values were observed in the nucleus taeniae amygdalae (TnA), nucleus preopticus medialis, and nucleus pretectalis. The highest net-stimulated [(35)S]GTPgammaS binding values induced by the selective CB(1) receptor agonist WIN55,212-2 were observed in the nucleus paramedianus internus thalami, and high values of [(35)S]GTPgammaS binding were observed in the TnA, Mol, arcopallium dorsale and arcopallium intermedium. The distribution data suggest that in the budgerigar, as previously indicated in mammals, cannabinoid receptors may be related to the control of several brain functions in the motor system, memory, visual system, and reproductive behavior. The discrepancies between the cannabinoid receptor densities and the cannabinoid receptor-mediated stimulation found in several budgerigar brain nuclei support the hypothesis, previously described for mammals, of the existence of different G(i/o) protein populations able to associate with the cannabinoid receptors, depending on the brain structure, and could reflect the relative importance that cannabinoid transmission could exerts in each cerebral area.