Comparative histological and ultrastructural features of the tongue of the mallard domestic duck, Anas platyrhynchos f. domestica, Anatidae (Linnaeus, 1758) in different two age stages (post-hatching [P2] and adult female) captured from Egypt

The domestic duck is classified as a specialist filter-feeder bird living in the water. These birds also use grazing and pecking as terrestrial feeding methods. The tongues of domestic ducks, similar to those of other Anseriformes, exhibit numerous types and shapes of mechanical papillae that serve a number of purposes when collecting food. The current study attempts to describe the morphological characteristics of the tongue as well as the mechanical papillae's development. In addition, the study aims to determine whether the papillae observed post-hatching (P2) exhibit similar morphology to those found in adult female avian species, as well as to investigate the readiness of the tongue to fulfill its feeding function following hatching. The comprehensive examination of lingual mucosa is examined about the structural modifications necessary for this variety of feeding activities. In this study, the tongues of nine young (P2) and adult female were used. The tongue had three distinct parts: the apex, which had a lingual nail on its ventral surface; the body, which exhibits numerous small and large conical papillae on its lateral sides and a lingual prominence in the caudal region; and the root, which is covered with numerous conical papillae of varying sizes. Conical, filiform, and hair-like mechanical papillae, the three types of food filtration apparatus, are present in both stages. The intraoral transfer involves several structures, including the median groove, lingual combs, and the rostral border of the lingual prominence. The rostral border of the lingual prominence is characterized by distinct rows of conical papillae. The histological analysis demonstrated the presence of both keratinized and nonkeratinized epithelium on different tongue regions. The lingual salivary glands in the rostral and caudal lingual salivary glands exhibit a pronounced periodic acid-Schiff-positive reaction. Additionally, the yellow adipose tissue and sensory receptors, namely the Grandry and Herbst corpuscles, which collectively form the bill-tongue organ that monitors the movement of food. These results conclude the presence of microstructural species-specific alterations in specific tongue areas of domestic ducks' lingual mucosa. These modifications are formed by the filtering mechanism and terrestrial feeding mechanisms, such as grazing or pecking. Following hatching, the tongue of the domestic duck undergoes significant development, primarily in preparation for grazing activities. The anatomical and histological structure of the young (P2) tongue exhibited similarities to that of the adult female domestic duck while also displaying certain variations that could potentially be attributed to the bird's habitat and mode of feeding. RESEARCH HIGHLIGHTS: The results of this study concluded that the domestic duck exhibit a complex tongue structure characterized by the arrangement and morphology of its mechanical papillae, the presence of the lingual prominence with distinctive shape and the lingual comb. These features are believed to be adaptations that enable the duck to actively and efficiently filter food particles from water, serving as its primary feeding mechanism. Additionally, the tongue of domestic ducks is specifically adapted to facilitate various terrestrial activities, such as grazing and pecking. This adaptation is achieved through the presence of conical papillae and a lingual nail. These investigations facilitate our comprehension of both the anatomical and histological characteristics of the domestic duck tongue, as well as enhance our understanding of bird adaptations to various feeding mechanisms.

Brain mass explains prey size selection better than beak, gizzard and body size in a benthivorous duck species

Prey size selection in some bird species is determined by the size of the beak. However, we assumed for bird species swallowing whole prey that a cognitive process may be involved. As cognitive feature, brain mass was used. We hypothesized that the mass of the brain was more strongly positively correlated with prey size than morphological features such as beak volume, gizzard mass and body mass. We tested this hypothesis on eiders Somateria mollissima that swallow the prey whole, by using mean and maximum size of nine prey categories. Eiders were collected at the main wintering grounds in Denmark. As index of brain mass we used head volume, which is positively correlated with brain mass (r² = 0.73). Head volume of eiders was significantly, positive correlated with mean and maximum size of blue mussels Mytilus edulis, razor clams Ensis directus and all prey sizes combined and the maximum size of draft whelk Hinia reticulata and conch Buccinum undatum. Gizzard mass was also significantly positively correlated with maximum size of draft whelk and conch. Beak volume and body mass was not significantly correlated with the size of any of the nine food items. Analyses of effect size for organs showed that head volume was positively related to prey size, whereas beak volume, gizzard mass and body mass did not show a significant positive relationship. These results indicate that cognitive processes connected to brain mass may be involved in prey size selection by eiders.

Histomorphology and gene expression profiles during early ovarian folliculogenesis in duck and goose

In contrast to the later stages of follicle development, little is known about the characteristics and mechanisms associated with early folliculogenesis in avian species. The objectives of the present study were to examine and compare the histomorphological and molecular changes of primordial, primary, and secondary follicles from duck and goose ovaries during the first 6 post-hatching week. Morphological analysis showed that the length and width of both duck and goose ovaries increased steadily during weeks 1 to 5 but increased acutely at week 6, whereas a greater increment was observed in the ovarian length of ducks than that of geese during weeks 4 to 5. Furthermore, smaller diameters of the 3 categories of follicles were observed in ducks than those in geese at the first appearance, but they reached a similar size at week 6. More importantly, secondary follicles were found in the ovaries of ducks 1 wk earlier than in those of geese. These results indicated a more rapid growth rate for ovarian follicles in ducks than in geese during early post-hatching development. At the molecular level, it was found that the mRNAs encoding follicle stimulating hormone receptor (FSHR), anti-Müllerian hormone (AMH), B-cell leukemia/lymphoma 2, and cysteine-dependent aspartate specific protease 3 (CASPASE3) were ubiquitously expressed in all ovarian follicles of ducks and geese with different expression profiles in each follicular category during the first 6 post-hatching week. Notably, transcript levels of FSHR, AMH, and CASPASE3 changed differently between ducks and geese during weeks 5 to 6, which was postulated to be one of the mechanisms inducing more rapid growth of ovarian follicles in ducks rather than in geese. In conclusion, our results revealed, for the first time, differences in early folliculogenesis, including the rate of growth of each follicular category and the timing of transition of primary to secondary follicles, between ducks and geese, and these differences could result from different expression profiles of FSHR, AMH, and CASPASE3 during early post-hatching development.

Cranial joint histology in the mallard duck (Anas platyrhynchos): new insights on avian cranial kinesis

The evolution of avian cranial kinesis is a phenomenon in part responsible for the remarkable diversity of avian feeding adaptations observable today. Although osteological, developmental and behavioral features of the feeding system are frequently studied, comparatively little is known about cranial joint skeletal tissue composition and morphology from a microscopic perspective. These data are key to understanding the developmental, biomechanical and evolutionary underpinnings of kinesis. Therefore, here we investigated joint microstructure in juvenile and adult mallard ducks (Anas platyrhynchos; Anseriformes). Ducks belong to a diverse clade of galloanseriform birds, have derived adaptations for herbivory and kinesis, and are model organisms in developmental biology. Thus, new insights into their cranial functional morphology will refine our understanding of avian cranial evolution. A total of five specimens (two ducklings and three adults) were histologically sampled, and two additional specimens (a duckling and an adult) were subjected to micro-computed tomographic scanning. Five intracranial joints were sampled: the jaw joint (quadrate-articular); otic joint (quadrate-squamosal); palatobasal joint (parasphenoid-pterygoid); the mandibular symphysis (dentary-dentary); and the craniofacial hinge (a complex flexion zone involving four different pairs of skeletal elements). In both the ducklings and adults, the jaw, otic and palatobasal joints are all synovial, with a synovial cavity and articular cartilage on each surface (i.e. bichondral joints) ensheathed in a fibrous capsule. The craniofacial hinge begins as an ensemble of patent sutures in the duckling, but in the adult it becomes more complex: laterally it is synovial; whereas medially, it is synostosed by a bridge of chondroid bone. We hypothesize that it is chondroid bone that provides some of the flexible properties of this joint. The heavily innervated mandibular symphysis is already fused in the ducklings and remains as such in the adult. The results of this study will serve as reference for documenting avian cranial kinesis from a microanatomical perspective. The formation of: (i) secondary articular cartilage on the membrane bones of extant birds; and (ii) their unique ability to form movable synovial joints within two or more membrane bones (i.e. within their dermatocranium) might have played a role in the origin and evolution of modern avian cranial kinesis during dinosaur evolution.

The body size-dependent diet composition of north american sea ducks in winter

Daily food requirements scale with body mass and activity in animals. While small species of birds have higher mass-specific field metabolic rates than larger species, larger species have higher absolute energy costs. Under energy balance, we thus expect the small species to have a higher energy value diet. Also the weight and time constraints for flighted and diurnal foragers should set a maximum to the amount of prey items taken in one meal and to the daily number of meals, respectively. Further, avoidance of competition causes the species to reduce the amount of shared prey in their diet. Some diet segregation is therefore to be expected between species. We tested these hypotheses and investigated the role of body mass in the diet composition of 12 sea duck species (Somateria mollissima, Somateria spectabilis, Somateria fischeri, Polysticta stelleri, Bucephala clangula, Bucephala islandica, Bucephala albeola, Melanitta nigra, Melanitta perspicillata, Melanitta deglandi, Histrionicus histrionicus and Clangula hyemalis) wintering in North America. This study was based on a literature survey with special emphasis given to the diet data from the former US Bureau of Biological Survey. The data supported our hypothesis that the energy value of winter diet of sea ducks scales negatively with body mass. Diet diversity also scaled negatively with body mass. Our results suggest the existence of a minimum for the energy value of avian diets.

Differential effects of early- and late-life access to carotenoids on adult immune function and ornamentation in mallard ducks (Anas platyrhynchos)

Environmental conditions early in life can affect an organism’s phenotype at adulthood, which may be tuned to perform optimally in conditions that mimic those experienced during development (Environmental Matching hypothesis), or may be generally superior when conditions during development were of higher quality (Silver Spoon hypothesis). Here, we tested these hypotheses by examining how diet during development interacted with diet during adulthood to affect adult sexually selected ornamentation and immune function in male mallard ducks (Anas platyrhynchos). Mallards have yellow, carotenoid-pigmented beaks that are used in mate choice, and the degree of beak coloration has been linked to adult immune function. Using a 2×2 factorial experimental design, we reared mallards on diets containing either low or high levels of carotenoids (nutrients that cannot be synthesized de novo) throughout the period of growth, and then provided adults with one of these two diets while simultaneously quantifying beak coloration and response to a variety of immune challenges. We found that both developmental and adult carotenoid supplementation increased circulating carotenoid levels during dietary treatment, but that birds that received low-carotenoid diets during development maintained relatively higher circulating carotenoid levels during an adult immune challenge. Individuals that received low levels of carotenoids during development had larger phytohemagglutinin (PHA)-induced cutaneous immune responses at adulthood; however, dietary treatment during development and adulthood did not affect antibody response to a novel antigen, nitric oxide production, natural antibody levels, hemolytic capacity of the plasma, or beak coloration. However, beak coloration prior to immune challenges positively predicted PHA response, and strong PHA responses were correlated with losses in carotenoid-pigmented coloration. In sum, we did not find consistent support for either the Environmental Matching or Silver Spoon hypotheses. We then describe a new hypothesis that should be tested in future studies examining developmental plasticity.

Effect of restricted preen-gland access on maternal self maintenance and reproductive investment in mallards

Background

As egg production and offspring care are costly, females should invest resources adaptively into their eggs to optimize current offspring quality and their own lifetime reproductive success. Parasite infections can influence maternal investment decisions due to their multiple negative physiological effects. The act of preening – applying oils with anti-microbial properties to feathers – is thought to be a means by which birds combat pathogens and parasites, but little is known of how preening during the reproductive period (and its expected disease-protecting effects) influences maternal investment decisions at the level of the egg.

Methodology/Principal Findings

Here, we experimentally prevented female mallards (Anas platyrhynchos) from accessing their preen gland during breeding and monitored female immunoresponsiveness (e.g., plasma lysozyme concentration) as well as some egg traits linked to offspring quality (e.g., egg mass, yolk carotenoid content, and albumen lysozyme levels). Females with no access to their preen gland showed an increase in plasma lysozyme level compared to control, normally preening females. In addition, preen-gland-restricted females laid significantly lighter eggs and deposited higher carotenoid concentrations in the yolk compared to control females. Albumen lysozyme activity did not differ significantly between eggs laid by females with or without preen gland access.

Conclusion/Significance

Our results establish a new link between an important avian self-maintenance behaviour and aspects of maternal health and reproduction. We suggest that higher yolk carotenoid levels in eggs laid by preen-gland-restricted females may serve to boost health of offspring that would hatch in a comparatively microbe-rich environment.

Brain size, brain composition and intracranial fat bodies in a population of free-living crested ducks (‘Hochbrutflugenten’)

(1) Brain sizes and brain structure volumes of crested specimens from a population of 'Hochbrutflugenten' ducks (HBTcr), living under seminatural conditions, were compared with those of other duck breeds, among them the breed 'Landente' with the same morphological trait, the crest (LEcr). (2) Brains of both HBTcr and LEcr were larger than expected from an allometric comparison with uncrested breeds. (3) Fat bodies invading the skull were observed in both breeds. (4) In LEcr they could be voluminous; after subtraction of their volume from the brain volume, most brain structures measured were allometrically of the same size as in uncrested breeds. (5) In contrast, HBTcr had small fat bodies, and most of their brain structures were allometrically larger than those of the other breeds. (6) A small fat body in the skull does not appear to influence the survival of HBTcr under seminatural conditions.

Comparative study on histological structures of the vitelline membrane of hen and duck egg observed by cryo-scanning electron microscopy

The histological structures of the vitelline membranes (VM) of hen and duck eggs were observed by cryo-scanning electron microscopy (cryo-SEM), and the chemical characteristics were also compared. The outer layer surface (OLS) of duck egg VM showed networks constructed by fibrils and sheets (0.1-5.2 microm in width), and that of hen egg presented networks formed only by sheets (2-6 microm in width). Thicker fibrils (0.5-1.5 microm in width) with different arrangement were observed on the inner layer surface (ILS) of duck egg VM as compared to those (0.3-0.7 microm in width) of hen egg VM. Upon separation, the outer surface of the outer layer (OSOL) and the inner surface of the inner layer (ISIL) of hen and duck egg VMs were quite similar to fresh VM except that the OSOL of duck egg VM showed networks constructed only by sheets. Thin fibrils interlaced above a bumpy or flat structure were observed at the exposed surface of the outer layer (ESOL) of hen and duck egg VMs. The exposed surfaces of inner layers (ESIL) of hen and duck egg VMs showed similar structures of fibrils, which joined, branched, and ran in straight lines for long distances up to 30 microm; however, the widths of the fibrils shown in ESOL and ESIL of duck egg VM were 0.1 and 0.7-1.4 microm, respectively, and were greater than those (<0.1 and 0.5-0.8 microm) of hen egg VM. The continuous membranes of both hen and duck egg VMs were still attached to the outer layers when separated. The content of protein, the major component of VM, was higher in duck egg VM (88.6%) than in hen egg VM (81.6%). Four and six major SDS-soluble protein patterns with distinct localization were observed in hen and duck egg VMs, respectively. Overall, the different histological structures of hen and duck egg VMs were suggested to be majorly attributable to the diverse protein components.

Hydrophobic duck feathers and their simulation on textile substrates for water repellent treatment

Inspired by the non-wetting phenomena of duck feathers, the water repellent property of duck feathers was studied at the nanoscale. The microstructures of the duck feather were investigated by a scanning electron microscope (SEM) imaging method through a step-by-step magnifying procedure. The SEM results show that duck feathers have a multi-scale structure and that this multi-scale structure as well as the preening oil are responsible for their super hydrophobic behavior. The microstructures of the duck feather were simulated on textile substrates using the biopolymer chitosan as building blocks through a novel surface solution precipitation (SSP) method, and then the textile substrates were further modified with a silicone compound to achieve low surface energy. The resultant textiles exhibit super water repellent properties, thus providing a simple bionic way to create super hydrophobic surfaces on soft substrates using flexible material as building blocks.

Study of the live body weight and body characteristics of the African Muscovy duck (Caraina moschata)

Three hundred and twenty 1-week old ducklings (160 males and 160 females) were used to evaluate the body weight, body parts and carcass characteristics of the African Muscovy duck. Sexual dimorphism was in favour of the male for all the parameters throughout the experimental period, however the difference was significant (P<0.05) only after week 2. The 12-week old male weighed 1832.0+/-180.4 g while the female reached only 68.2% of the male weight. Metatarsus diameter, thoracic perimeter, body length, length of bill, foot and wing in cm were respectively 1.3, 29.5, 57.5, 7.0, 27.1 and 27.8 for the male as compared with 1.2, 25.8, 51.0, 6.3, 23.3 and 26.9 for the female. Body measurements were highly (P<0.01) correlated with body weight for both sexes, however the highest correlation coefficients were obtained with wing length (0.990 and 0.995) and thoracic perimeter (0.993 and 0.973) for female and male respectively. Live body weight had a linear relationship with both wing length (R2=0.991 and 0.81) and thoracic perimeter (R2=0.948 and 0.986) for male and female respectively. The female duck yielded higher percent ready-to-cook carcass (66.3%), breast (13.6%), liver (2.8%), heart (1.5%) and gizzard (3.8%) as compared to the male (65.0%, 12.0%, 2.5%, 1.1% and 3.4% respectively) although the difference was not significant (P>0.05). The male small intestine (185.1+/-3.4 cm), colon (14.8+/-1.0 cm) and caecum (17.9+/-0.4 cm) were significantly (P<0.05) longer than that of the female (152.2+/-1.8, 10.8+/-0.7 and 14.85+/-0.6 cm respectively).

Acute and chronic effects of perfluorobutane sulfonate (PFBS) on the mallard and northern bobwhite quail

Perfluorobutane sulfonate (PFBS) can be a final degradation product of perfluorobutane sulfonyl fluoride (PBSF)-based chemicals. Surfactants based on this chemistry are potential replacements for perfluorooctane sulfonate (PFOS)-related products and have many potential applications in industrial and commercial processes and applications. To evaluate the potential hazard that PFBS may pose to avian species, acute dietary studies with juvenile mallards and northern bobwhite quail, as well as a quail dietary chronic study of reproduction were conducted. In the acute studies, 10-day-old mallards and quail were exposed to nominal dietary concentrations of 1,000, 1,780, 3,160, 5,620 or 10,000 mg PFBS/kg feed, wet weight (ww) for 5 days and the birds were then fed an untreated diet and observed for up to 17 days. No treatment-related mortalities were observed in the study up to 10,000 mg PFBS/kg, ww feed. Body weight gains of quail exposed to 5620 or 10,000 mg PFBS/kg feed were statistically less than that of unexposed controls. Weight gain of mallards exposed to 10,000 mg PFBS/kg feed was statistically less than that of controls. There were no statistically significant effects on feed consumption of either species. In the acute studies, no observed adverse effect concentration (NOAEC) for mallards and quail were 5620 and 3160 mg PFBS/kg, ww feed, respectively. In a reproduction study, adult quail were exposed to nominal dietary concentrations of 100, 300, or 900 mg PFBS/kg, ww feed for up to 21 weeks. There were no treatment-related mortalities or effects on body weight, weight gain, feed consumption, histopathology measures, or reproductive parameters evaluated in the study when compared to the control group. Concentrations of PFBS in blood serum, liver, and eggs were dose-dependent but were less than the administered dose, indicating biodiminution. Based on the results from the quail reproduction study, the dietary NOAEC was 900 mg PFBS/kg, ww feed (equivalent to an ADI of 87.8 mg PFBS/kg bw/d).

Motor incoordination, intracranial fat bodies, and breeding strategy in Crested ducks (Anas platyrhynchos f.d.)

Some Crested ducks (CR) are burdened with an intracranial fat body that, depending on the size and location, may lead to varying degrees of motor incoordination. A behavioral test is proposed that helps to identify those CR individuals bearing the problematical fat body. The test consists of putting the ducks on their backs and measuring the time required to right themselves. This was repeated 13 times per animal, and means were calculated. The minimum time required was 0.5 s, and the maximum was 62.6 s. Individuals that show motor incoordination need more time than ducks without such problems (14.3 s in contrast to 1.2 s) and exhibit a larger intracranial fat body. Ducks used for breeding should require no more than approximately 1 to 2 s to right themselves. In an allometric comparison with 3 other domestic duck breeds, CR show a significantly smaller brain; specifically, the cerebellum, tegmentum, apicale hyperpallium, and olfactory bulb are reduced. The relationship between fat body and these structures was discussed.

Detection of quantitative trait loci for body weights and conformation traits in Beijing ducks

Quantitative trait loci (QTL) for body weights and conformation traits were detected in Beijing ducks. Traits included body weights (BW) at hatching and at 1-7 weeks of age; lengths of the body (BL), keel bone (KBL), shank (SL) and neck (NL) at 7 weeks of age; width of breast (BTW) at 7 weeks; and girths of shank (SG) and breast (BG) at 7 weeks. Using a half-sib analysis with a multiple-QTL model, linkage between the phenotypic traits and 95 microsatellite markers was studied. Six genome-wide suggestive QTL for three body weights and two conformation traits were identified in CAU1, CAU2, CAU6 and CAU12. Chromosome-wide significant QTL influencing one body weight trait and one conformation trait were located in CAU4 and CAU10 respectively. Twelve chromosome-wide suggestive QTL for six body weight traits and four conformation traits were found in seven linkage groups (CAU1, CAU2, CAU3, CAU4, CAU6, CAU10 and CAU12). In addition, the QTL in CAU6 at 21 and 73 cM jointly affected SG and explained 10.6% of the phenotypic variation. This study provides the first evidence for QTL involved in body weights and conformation traits in ducks, and will stimulate further investigations into the genetic architecture of these traits in this species.

Postcranial skeletal pneumaticity: a case study in the use of quantitative microCT to assess vertebral structure in birds

Limb elements in birds have been characterized as exhibiting a reduction in trabecular bone, thinner cortices and decreased bending strength when pneumatized, yet it is unclear if these characteristics generalize to the axial skeleton. Thin section techniques, the traditional gold standard for bone structure studies, have most commonly been applied to the study of avian bone. This destructive technique, however, makes it subsequently impossible to use the same samples in experimental testing systems that allow researchers to correlate structure with the mechanical properties of the bone. Micro-computed tomography (microCT), a non-destructive X-ray imaging technique, can be used to assess the effect of pneumatization on vertebral cortical and trabecular bone through virtual extraction and structural quantification of each tissue type. We conducted a preliminary investigation of the application of microCT methods to the study of cortical and trabecular bone structure in a small sample of pneumatic and apneumatic thoracic vertebrae. The sample consisted of two similar-sized anatids, Aix sponsa (n = 7) and Oxyura jamaicensis (n = 5). Volumes of interest were created that contoured (outlined) the boundaries of the ventral cortical bone shell, the trabecular compartment and the whole centrum (cortical bone + trabecular bone), and allowed independent structural analysis of each volume of interest. Results indicated that bone volume fraction of the whole centrum was significantly higher in the apneumatic O. jamaicensis than in the pneumatized A. sponsa (A. sponsa = 36%, O. jamaicensis = 48%, P < 0.05). In contrast, trabecular bone volume fraction was similar between the two species. The ventral cortical bone shell was approximately 23% thinner (P < 0.05) in A. sponsa (0.133 mm) compared with apneumatic O. jamaicensis (0.172 mm). This case study demonstrates that microCT is a powerful non-destructive imaging technique that may be applied to the three-dimensional study of avian bone. The preliminary results suggest that pneumatic and apneumatic vertebrae of comparably sized avian species differ in relative bone volume, with the largest difference apparent at the level of the cortex, and not within trabecular bone. The presence of relatively thin cortices in pneumatic vertebrae is consistent with previous studies contrasting diaphyseal cortical bone between pneumatic and apneumatic long bones. Methodological issues related to this and any comparative microCT study of bone structure are discussed.

The Syrinx of the Male Mallard (Anas platyrhynchos): Special Anatomical Features

The aim of this study was to investigate the special anatomical and topographical features of the syrinx in male adult stock ducks (Anas platyrhynchos). The syrinx of the mallard is a tracheobronchial type, consisting of a tympanum, a pessulus, medial tympaniform membranes, interanular membranes, an interbronchial ligament (bronchidesmus), and bronchosyringeal cartilage semi-rings. Using a frozen sagittal section, it was possible to document the syringeal valve at the right lateral side of the tympanum. In the male stock duck the pessulus was massive and showed a longish oval, transparent area ventrally. The middle part of the pessulus had a nose-shaped process on its left side, on which the left medial tympaniform membrane originated. The left-sided, pear-shaped syringeal bulla was divided into a left major and right minor chamber by a double-walled, semilunar and opaque septum, approximately 5-6 mm in height. The first left and right C-shaped bronchosyringeal cartilage was more prominent than the other ones and showed partial ossification. In addition, the first left bronchosyringeal cartilage was obviously thicker than the right one. In conclusion, it can be stated that the syrinx in male adult mallards shows some notable specific anatomical features that might have an influence on vocalization. However, to understand the complex mechanism of vocalization in mallards, more investigations, especially obtained by sonography and endoscopy, will be needed.

Predicting Resource Partitioning and Community Organization of Filter‐Feeding Dabbling Ducks from Functional Morphology

Resource partitioning due to interspecific differences in phenotype is a key component of ecological and evolutionary theory, but the relationship between morphology and resource use is poorly understood for most species. In addition, ecologists often assume that morphological differences cause distinct resource preferences between species. Using mechanistic models that combine bill morphology and kinetics, I show that filter-feeding dabbling ducks face a morphology-mediated trade-off between particle size selection and water filtration rate. When detritus is absent, mallards (Anas platyrhynchos) and northern shovelers (Anas clypeata) should maximize their intake rates and exhibit high overlap in prey size. When prey and detritus co-occur, species should separate prey from detritus by size, leading to reduced intake rates and size-based prey partitioning. Models for both species correctly predicted variation in water filtration rates, particle retention probabilities, and prey ingestion rates due to variation in prey size, the presence of detritus, and experimental modification of bill morphology. Because species have both shared and distinct resource preferences, duck communities should exhibit strong density-dependent niche shifts (i.e., centrifugal dynamics), a finding that contradicts previous studies that assumed that ducks have distinct resource preferences only. Centrifugal dynamics may be widespread among filter feeders because of the common cost of separating prey from detritus.

Downregulation of aquaporins 1 and 5 in nasal gland by osmotic stress in ducklings, Anas platyrhynchos: implications for the production of hypertonic fluid

Using primers against highly conserved regions of mammalian and bird aquaporins in RT-PCR experiments, we amplified products derived from duck (Anas platyrhynchos) nasal gland RNA that were identified as homologues of mammalian and chicken aquaporin 1 and aquaporin 5 cDNAs by sequencing. Using digoxigenin-labelled probes derived from these PCR products in northern blot analyses of mRNA isolated from nasal glands of untreated (naïve) or osmotically stressed ducklings (replacement of drinking water with a 1% NaCl solution), we observed a decrease in aquaporin 1 (AQP1) and aquaporin 5 (AQP5) mRNA abundance (by approximately 40%) during saline adaptation in the animals. Western blot analysis of AQP1 and AQP5 expression in the glands revealed that protein abundance decreased in a similar fashion. Immunohistochemical analysis of AQP1 distribution in cryosections of nasal gland indicated that AQP1 is mainly expressed in endothelial cells of the capillaries, but definitely not in the secretory or ductal cells of the gland. AQP5 distribution in the gland, however, seems to be different, since staining was exclusively observed in apical and basolateral plasma membranes of individual epithelial cells of the primary and central ducts, which collect fluid from the secretory tubules. The observations are consistent with the hypothesis that strongly hyperosmotic fluid is produced by the secretory cells at very low (unstimulated gland) or high (activated gland) rates. In the unstimulated gland, secretions may be diluted by aquaporin-mediated transcellular water flux while passing through the ductal system flushing the glandular ducts, thereby potentially preventing ascending infections. In the activated gland, however, downregulation of aquaporins in capillaries and duct cells may prevent dilution of the initially secreted fluid, enabling the animals to excrete large volumes of a highly concentrated salt solution.

Corticosterone selectively decreases humoral immunity in female eiders during incubation

Immunity is hypothesized to share limited resources with other physiological functions and this may partly account for the fitness costs of reproduction. Previous studies have shown that the acquired immunity of female common eider ducks (Somateria mollissima) is suppressed during their incubation, during which they entirely fast. Corticosterone was proposed to be an underlying physiological mechanism for such immunosuppression. Therefore,the current study aimed to assess the effects of exogenous corticosterone on acquired immunity in captive eiders. To this end, females were implanted with corticosterone pellets at different stages of their incubation fast. We measured total immunoglobulin levels, T-cell-mediated immune response, body mass and corticosterone levels in these females and compared them with those of control females prior to and after manipulation (i.e. corticosterone pellet implantation). To mimic corticosterone effects on body mass, we experimentally extended fasting duration in a group of females termed `late fasters'. Implanted females had corticosterone levels 6 times higher and lost 35% more mass than control females. Corticosterone levels in `late fasters' were similar to those in control females but body mass was 8% lower in the former. The decrease in the immunoglobulin levels of corticosterone implanted females was twice as high as in control females, while the T-cell-mediated immune response was not significantly affected by the treatment. We found a decrease in the T-cell-mediated immune response only in `late fasters' (by 60%), while the immunoglobulin level was not lower in this group than in corticosterone implanted or control females. Our study shows that in incubating eiders,exogenous corticosterone only decreased humoral immunity. We suggest that the immunosuppressive effect of corticosterone could be mediated through its effects on body reserves. Further experiments are required to determine the relationship between body condition and immune system in fasting birds.

Morphoregulation of avian beaks: comparative mapping of growth zone activities and morphological evolution

Avian beak diversity is a classic example of morphological evolution. Recently, we showed that localized cell proliferation mediated by bone morphogenetic protein 4 (BMP4) can explain the different shapes of chicken and duck beaks (Wu et al. [2004] Science 305:1465). Here, we compare further growth activities among chicken (conical and slightly curved), duck (straight and long), and cockatiel (highly curved) developing beak primordia. We found differential growth activities among different facial prominences and within one prominence. The duck has a wider frontal nasal mass (FNM), and more sustained fibroblast growth factor 8 activity. The cockatiel has a thicker FNM that grows more vertically and a relatively reduced mandibular prominence. In each prominence the number, size, and position of localized growth zones can vary: it is positioned more rostrally in the duck and more posteriorly in the cockatiel FNM, correlating with beak curvature. BMP4 is enriched in these localized growth zones. When BMP activity is experimentally altered in all prominences, beak size was enlarged or reduced proportionally. When only specific prominences were altered, the prototypic conical shaped chicken beaks were converted into an array of beak shapes mimicking those in nature. These results suggest that the size of beaks can be modulated by the overall activity of the BMP pathway, which mediates the growth. The shape of the beaks can be fine-tuned by localized BMP activity, which mediates the range, level, and duration of locally enhanced growth. Implications of topobiology vs. molecular blueprint concepts in the Evo-Devo of avian beak forms are discussed.

Histological Aspects of the Syrinx of the Male Mallard (Anas platyrhynchos)

The syrinx of the duck is characterized by a conspicious sexual dimorphism. In the male mallard, a large osseous bulla is present on the left syringeal side. The present work describes the structures of the male syrinx, which were studied by means of histochemistry, immunohistochemistry and electron microscope. In the right distal tympanum a caudally oriented, protruding structure was observed, which was identified as the valvula syringealis. The syringeal structures like valvula, tympanum, bulla, pessulus and the bronchi were in general covered by a respiratory epithelium, however, local modifications in cellular height and numbers of ciliated and goblet cells were observed. The presence of intrinsic musculature was confirmed by means of immunohistochemistry. Smooth muscle cells reaching from the lateral parts of the inter-bronchial ligament to the medial line and cranially to the inner tympaniform membranes were demonstrated. We suppose that these muscle cells play a role in syringeal sound generation by influencing the tension of the medial tympaniform membranes.

Hybridization between white-headed ducks and introduced ruddy ducks in Spain

The ruddy duck, Oxyura jamaicensis, was introduced to Great Britain in the mid-20th century and has recently spread to other Western European countries. In Spain, ruddy ducks hybridize with the globally endangered white-headed duck, Oxyura leucocephala. We assessed the effects of hybridization on the Spanish white-headed ducks, which constitute 25% of the global population of this species, using a panel of eight nuclear intron markers, 10 microsatellite loci, and mtDNA control region sequences. These data allowed parental individuals, F(1) hybrids, and the progeny of backcrossing to be reliably distinguished. We show that hybrids between the two species are fertile and produce viable offspring in backcrosses with both parental species. To date, however, we found no extensive introgression of ruddy duck genes into the Spanish white-headed duck population, probably due to the early implementation of an effective ruddy duck and hybrid control programme. We also show that genetic diversity in the expanding European ruddy duck population, which was founded by just seven individuals, exceeds that of the native Spanish white-headed duck population, which recently recovered from a severe bottleneck. Unless effective control of ruddy ducks is continued, genetic introgression will compromise the unique behavioural and ecological adaptations of white-headed ducks and consequently their survival as a genetically and evolutionary distinct species.

Multiple regression equations to estimate the content of breast muscles, meat, and fat in Muscovy ducks

The aim of the present study was to derive multiple regression equations for in vivo estimation of the carcass lean and fat content in Muscovy ducks. The experimental materials consisted of 240 White Muscovy ducklings (120 male and 120 female). One hundred sixteen females aged 10 wk and 112 males aged 12 wk were slaughtered. Before slaughter the ducks were weighed, and the following body measurements were taken: humerus length, drumstick length, chest girth, breast-bone crest length, width between the humeral bones, chest depth, and breast muscle thickness. The coefficients of simple correlation between carcass tissue components and body measurements were calculated. It was found that live body weight was highly correlated with the weights of all tissue components (r = 0.701 to 0.857). In males a significant interrelation was found between breast muscle weight and all body measurements, whereas in females breast muscle weight was correlated with breast-bone crest length, chest girth, width between the humeral bones, chest depth, and breast muscle thickness only. In both males and females the carcass lean content was closely correlated with drumstick length, breast-bone crest length, chest girth, and width between the humeral bones. In drakes the carcass fat content was closely correlated with all body measurements, whereas in hens significant correlations were observed between the carcass fat content and chest girth, width between the humeral bones, and chest depth only. The coefficients of simple correlation between the percentages of carcass tissue components and body measurements were generally low and statistically nonsignificant. Twelve multiple regression equations formulated based on the body measurements of live ducks were verified with respect to the accuracy of estimation of the content of breast muscles, meat, and fat with skin in the carcass. These equations give small SE of the estimate (Sy = 23.3 to 83.8 g), high values of coefficients of multiple correlation between the dependent variable and the set of independent variables, and high values of determination coefficients.

Yolk sac, body dimensions and hatchling quality of ducklings, chicks and poults

1. One-day-old chicks of Pekin duck, turkey, layer fowl and broiler fowl were examined for bacteria in the yolk sac and yolk fluid. 2. Whole hatchling, yolk-free hatchling and yolk sac weights were recorded for all species along with crown-rump length and beak-tip to toe-tip length. 3. Bacteriology revealed positive results for the whole yolk sacs of 43 to 64% of the birds in the sample of ducklings, poults and layer chicks. Broiler chicks had a 6.6% incidence of bacteria isolated from the whole yolk sac. By contrast, there were very few positive results from swabs of yolk fluid for any of the bird types. 4. The presence of bacteria in the yolk sac of hatchlings suggests that there is colonisation, rather than infection, of the yolk sac membrane during the hatching period or the first few hours post-hatching. Isolation of bacteria from the yolk sacs of young chicks might no longer be considered as solely indicative of yolk sac infection but further research is required to confirm this result. 5. Contrary to what is being suggested in commercial practice relationships between linear dimensions and hatchling weight suggest that measurement of chick length is at best a very crude measure of chick quality.

[Intracranial fat bodies and their potential effect on brain composition and behaviour in domestic ducks with feather crests (3 case studies)]

Intracranial fat tissue was found in the brains of three crested ducks. The three ducks differed in the size of their crest and in the volume and the location of the fat body within their brains. The duck with the large crest showed a fat body which counts for 19 % of its brain volume. Due to this fat accumulation, brain structures, mainly the cerebellum, were moved laterally. This duck had serious problems in motor coordination. Fat body of the second duck with a middle sized crest was situated in neostriatum and constituted 0,6 % of total brain volume. Additionally this duck displayed an encephalocele. The last duck did show a small crest. Its fat body was found in the area of the tentorium cerebelli and made up 17 % of its brain volume. The later two ducks were not hampered behaviourally.

Attenuation of cell cycle regulator p27(Kip1) expression in vertebrate epithelial cells mediated by extracellular signals in vivo and in vitro

Cell cycle arrest in potentially dividing cells is often mediated by inhibitors of G1/S-phase cyclin-dependent kinases. The cyclin E/CDK2-inhibitor p27(Kip1) has been implicated in this context in epithelial cells. We cloned and sequenced p27(Kip1) of ducklings (Anas platyrhynchos) and used an in vitro assay system to study the mechanism of p27(Kip1) downregulation in the nasal gland which precedes an increase in proliferation rate upon initial exposure of the animals to osmotic stress. Western blot studies revealed that p27(Kip1) is downregulated during 24 h of osmotic stress in ducklings with the steepest decline in protein levels between 5 and 8 h. As indicated by the results of Northern blot and semi-quantitative PCR studies, protein downregulation is not accompanied by similar changes in mRNA levels indicating that Kip1 is regulated mainly at the translational (synthesis) or posttranslational level (degradation). Using recombinant duck Kip1 protein expressed in E. coli, we showed that Kip1 is subject to polyubiquitinylation by cytosolic enzymes from nasal gland cells indicating that loss of Kip1 may be regulated, at least in part, by acceleration of protein degradation. In cultured nasal gland tissue, attenuation of Kip1 expression could be induced by activation of the muscarinic acetylcholine receptor indicating that mAChR-receptor signalling may play a role in the re-entry of quiescent gland cells into the cell cycle.

A 3D digital reconstruction of the components of the gas exchange tissue of the lung of the muscovy duck, Cairina moschata

To elucidate the shape, size, and spatial arrangement and association of the terminal respiratory units of the avian lung, a three-dimensional (3D) computer-aided voxel reconstruction was generated from serial plastic sections of the lung of the adult muscovy duck, Cairina moschata. The air capillaries (ACs) are rather rotund structures that interconnect via short, narrow passageways, and the blood capillaries (BCs) comprise proliferative segments of rather uniform dimensions. The ACs and BCs anastomose profusely and closely intertwine with each other, forming a complex network. The two sets of respiratory units are, however, absolutely not mirror images of each other, as has been claimed by some investigators. Historically, the terms 'air capillaries' and 'blood capillaries' were derived from observations that the exchange tissue of the avian lung mainly consisted of a network of minuscule air- and vascular units. The entrenched notion that the ACs are straight (non-branching), blind-ending tubules that project outwards from the parabronchial lumen and that the BCs are direct tubules that run inwards parallel to and in contact with the ACs is overly simplistic, misleading and incorrect. The exact architectural properties of the respiratory units of the avian lung need to be documented and applied in formulating reliable physiological models. A few ostensibly isolated ACs were identified. The mechanism through which such units form and their functional significance, if any, are currently unclear.

Definitive fossil evidence for the extant avian radiation in the Cretaceous

Long-standing controversy surrounds the question of whether living bird lineages emerged after non-avian dinosaur extinction at the Cretaceous/Tertiary (K/T) boundary or whether these lineages coexisted with other dinosaurs and passed through this mass extinction event. Inferences from biogeography and molecular sequence data (but see ref. 10) project major avian lineages deep into the Cretaceous period, implying their 'mass survival' at the K/T boundary. By contrast, it has been argued that the fossil record refutes this hypothesis, placing a 'big bang' of avian radiation only after the end of the Cretaceous. However, other fossil data--fragmentary bones referred to extant bird lineages--have been considered inconclusive. These data have never been subjected to phylogenetic analysis. Here we identify a rare, partial skeleton from the Maastrichtian of Antarctica as the first Cretaceous fossil definitively placed within the extant bird radiation. Several phylogenetic analyses supported by independent histological data indicate that a new species, Vegavis iaai, is a part of Anseriformes (waterfowl) and is most closely related to Anatidae, which includes true ducks. A minimum of five divergences within Aves before the K/T boundary are inferred from the placement of Vegavis; at least duck, chicken and ratite bird relatives were coextant with non-avian dinosaurs.

Expression of agouti-related protein (AgRP) in the hypothalamus and adrenal gland of the duck ( Anas platyrhynchos)

The presence and distribution of agouti-related protein (AgRP) immunoreactivity were investigated in the hypothalamus and adrenal gland of the duck using immunohistochemistry and Western blot analysis. Expression of AgRP mRNA was also studied using reverse transcriptase polymerase chain reaction (RT-PCR). A partial coding sequence (cds) of the duck AgRP gene was identified. Western blot analysis showed the presence of an AgRP-like peptide having a molecular weight consistent with the number of predicted amino acids of the avian AgRP. In the hypothalamus, AgRP immunoreactivity was found in neurons of the nucleus infundibularis and in fibers projecting to the median eminence. In the adrenals, AgRP immunoreactivity was observed in medullary cells. These findings suggest that in the duck, AgRP may play a role in regulating energy homeostasis and adrenal endocrine functions.

Trade‐Offs between Immune Investment and Sexual Signaling in Male Mallards

Allocation trade-offs between the immune system and sexual traits are central to current sexual selection hypotheses but remain contentious. Such trade-offs could be brought about by the dual action of testosterone that stimulates sexual signals but also suppresses immune functions and/or by competition for carotenoids that can be deposited in ornaments or used as antioxidants in support of immune functions. We investigated the trade-off between investment in immunity and maintenance of testosterone, carotenoids, and sexually selected, carotenoid-based bill color in male mallards. Following a nonpathogenic immune challenge, facultative immune investment resulted in a syndrome of changes in allocation. Plasma carotenoids disappeared from circulation proportional to antibody production. In addition, the reflectance spectrum of the bill was affected; greater antibody production was associated with an increase in relative UV reflectance. Although changes in bill reflectance and plasma carotenoids were related, the relationship appeared more complex than direct competition with immunity. Finally, maintenance of testosterone was affected by immune investment: testosterone levels declined substantially when males produced more antibodies. Because males with high testosterone are preferred by females, the decline in testosterone, in addition to carotenoid depletion and effects on bill reflectance, could constitute a significant cost of immune investment.

Comparative anatomy of nitrergic intrinsic choroidal neurons (ICN) in various avian species

Intrinsic choroidal neurons (ICN) represent a peculiar feature of eyes in higher primates and birds. They account for up to 2000 in human and duck eyes but are virtually absent or rare in all other mammalian species investigated so far. It has been suggested that ICN are involved in regulation of ocular blood supply, hence influencing intraocular pressure, and changes in choroidal thickness, thus influencing accommodation. The present study was undertaken in order to compare differences in various avian species with respect to ICN as well as to provide data on some avian species relevant for experimental ophthalmic research, i.e. chicken and quail. Choroids from 12 avian species were processed for NADPH-diaphorase histochemistry or, in some cases, neuronal nitric oxide synthase immunocytochemistry. ICN were quantified and normalized to mean choroidal area. Three choroids of each galliformes (i.e. chicken, quail, turkey) and anseriformes (i.e. Muscovy duck, Mallard duck, goose) were rastered in squares of 1 mm2 and x/y coordinates were transferred into a 3D-diagram with the amount of ICN represented in the z-axis. ICN were detected in all species investigated. They were predominantly small cells with soma diameters of 20-30 microm. In turkey, and to a lesser amount in chicken, a subpopulation of ICN with somal diameters of up to 70 microm was observed. Highest mean cell counts were found in goose (6195.4; turkey 3558.4; chicken 1681.4; Muscovy duck 785.4; Mallard duck 640.8; quail 440.2). Normalized to choroidal area, highest mean cell counts were (per mm2): 12.62 in goose, 4.42 in both chicken and turkey, 2.86 in quail, 2.66 in Mallard duck and 1.89 in Muscovy duck. In galliformes, ICN were found to be accumulated temporo-cranial, while in anseriformes they were arranged in a more belt-like fashion, passing from cranio-nasal to temporo-caudal. Our results show that besides Muscovy duck, other avian species appear as suitable models for further functional experiments on ICN. The temporo-cranial accumulation of ICN in galliformes and the belt-like arrangement in anseriformes may reflect special functional requirements in regions of high visual acuity.

Effects of L-carnitine administration on growth performance, carcass traits, blood serum parameters and abdominal fatty acid composition of ducks

Effects of L-carnitine administration via drinking water on growth performance, carcass traits, blood serum parameters and abdominal fatty acid composition of ducks was examined. One hundred day-old Turkish native duck chicks were divided into two groups, each with five replicates and given the same diets with 0 and 200 mg/l carnitine chlorhydrate via drinking water. The study lasted 8 weeks, with the first 4 weeks as a starter and the last 4 weeks as grower period. At the end of the study five ducks were randomly selected from each subgroup for slaughter. Growth performance parameters of ducks were not affected significantly by L-carnitine administration. Live weight, daily weight gain, cumulative feed consumption and average feed conversion efficiency were found to be 1490 and 1621 g, 26.0 and 28.1 g, 5386 and 5662 g, 3.75 and 3.54 kg/kg in the control and in the carnitine groups respectively. L-carnitine administration did not effect carcass traits and serum cholesterol, total lipid, triglyceride and glucose levels. Total saturated fatty acid content of abdominal fat significantly decreased, mono- and polyunsaturated fatty acid content were not affected by L-carnitine administration. In conclusion, L-carnitine administration by drinking water did not affect growth performance, carcass traits and blood parameters in ducks.

Topography and neurochemistry of the enteric ganglia in the proventriculus of the duck (Anas platyrhynchos)

The topographical distribution of the enteric ganglia has been investigated in the proventriculus of the duck using protein gene product 9.5 (PGP 9.5) immunohistochemistry. Myenteric ganglia were usually located between the outer longitudinal and the inner circular muscle layer. Submucous ganglia were sparsely distributed and seemed to be substituted by ganglia located in the tunica mucosa. The neurochemical profile of proventricular ganglion cells was also investigated using nicotinamide adenine dinucleotide phosphate reduced-diaphorase (NADPH-d)-histochemistry and pituitary adenylate cyclase activating peptide (PACAP)/galanin (Gal) double-labelling immunohistochemistry. The majority of mucosal ganglion cells were shown to contain the NADPH-d enzyme and both the investigated peptides. These findings provide evidence for the presence of a mucosal ganglionated plexus in the glandular stomach of birds. Moreover, the neurochemical characteristics of this plexus suggest that it plays an important role in regulating several mucosal functions and, in particular, the production and the composition of the gastric juice.

The cellular and molecular origins of beak morphology

Cellular and molecular mechanisms underlying differences in beak morphology likely involve interactions among multiple embryonic populations. We exchanged neural crest cells destined to participate in beak morphogenesis between two anatomically distinct species. Quail neural crest cells produced quail beaks in duck hosts and duck neural crest produced duck bills in quail hosts. These transformations involved morphological changes to non-neural crest host beak tissues. To achieve these changes, donor neural crest cells executed autonomous molecular programs and regulated gene expression in adjacent host tissues. Thus, neural crest cells are a source of molecular information that generates interspecific variation in beak morphology.

Rapid technique for imaging the blood vascular system using stereoangiography

Data on vascular anatomy traditionally have been derived from time-consuming gross dissection and histology, which has prevented the assembly of large sample sizes. Vascular injection of radiopaque medium (angiography) is a rapid technique, but, as typically performed, it has limitations (e.g., superimposition and poor subsequent dissectibility). We present a novel angiographic technique comprised of two elements: 1) a new, dissectible injection medium; and (2) stereoradiography. The injection medium consists of liquid barium (providing radiopacity) and latex (providing dissectibility). Domestic duck heads were the study system. The relative concentrations of barium and latex were varied, and the resulting radiographs were assayed for vessel radiopacity and the number of observable vessels. A wide range of barium percentages yielded excellent results, suggesting that preparation of the medium can be "eyeballed" for most applications, which enhances processing speed. The stereoradiographic element solved the superimposition problem, allowing stunning resolution of the spatial relationships of vessels to each other and to other tissues. Stereoangiography is a fast and easy technique that permits the acquisition of detailed anatomical data from many specimens, thereby enabling something rarely achieved: population-level anatomical studies.

Morphological changes in the efferent ducts during the main phases of the reproductive cycle of birds

The changes that take place in the efferent ducts during the major phases of the reproductive cycle of birds were studied morphologically using standard histological, morphometric, and ultrastructural methods in prepuberal, sexually mature and sexually active, and sexually mature but sexually inactive domestic fowl (Gallus domesticus), drake (Anas platyrhynchos), and guinea fowl (Numida meleagris). Profound structural and dimensional changes occurred in both segments (proximal and distal) of the efferent ducts and, in particular, in the nonciliated (Type I) cell of the proximal duct of sexually mature but inactive birds. The subapical tubulovacuolar system was markedly atrophic in nonciliated (Types I and II) cells and the numerous round dense globules of Type I cells that normally occurred in sexually active birds were replaced by fewer and more pleomorphic bodies containing lipofuscin granules in sexually resting birds. Lipid droplets, few and extremely large in inactive drakes but numerous and smaller in size in guinea fowls and domestic fowls, occurred in the Type I cell at both infra- and supranuclear levels of resting but not in prepuberal or sexually active birds. Ciliated cells in both segments of the ducts exhibited fewer and less profound phase-dependent changes ultrastructurally. Generally, the Type I cells of the proximal efferent duct appeared to be more sensitive to androgen deprivation than the Type II cell of the distal efferent duct or ciliated cells in both ducts. These morphologically phase-dependent features of the efferent ducts of birds may be used, together with or independent of testicular changes, in the determination of the status of the testis and epididymis of a male bird with regard to the reproductive cycle, especially in seasonally breeding species.

Cyclical reproductive changes in the non-ciliated epithelia of the epididymis of birds

The epididymis of two species of domestic birds, the domestic fowl (Gallus domesticus), duck (Anas platyrhynchos), and of domestic and feral guinea-fowl (Numida meleagris) was studied during the three main phases of the reproductive cycle (prepuberal, sexually mature and active, and sexually mature but inactive or resting) with a view to identifying major histological and ultrastructural changes associated with and distinctive for each phase. Rete testis cells accumulated numerous variably sized lipid droplets in all birds, as well as large heterogeneous and lipofuscin-containing dense bodies in the guinea-fowl, during the resting but not in the other phases. The principal or Type III cells of the connecting and epididymal ducts exhibited profound structural changes, including, but not limited to, rarefied cytoplasm, inconspicuous and general loss of sparsely granular endoplasmic reticulum, loss of secretory vesicles in the drake, and an enhanced and conspicuous presence of lipid droplets in the guinea-fowl. The rete cells appeared to be less sensitive than the Type III cells to a reduced level or absence of lumenal androgens. These phase-dependent changes may help to prevent or minimize discrepancies in the interpretation of the normal structure of the epididymis in birds during the sexually active phase, as distinct from the other two phases and their intermediate phases.

Bone typology and growth rate: testing and quantifying 'Amprino's rule' in the mallard (Anas platyrhynchos)

Periosteal bone histology expresses its rate of deposition. This fundamental relationship between bone structure and growth dynamics, first assumed by Amprino many decades ago, was quantified in preliminary studies, but never statistically tested. Moreover, the precise typological characters of bone tissue linked to growth rate remained poorly known. Here, we present the first statistical analysis of 'Amprino's rule', measured on comprehensive growth series of the mallard, Anas platyrhynchos. Growth rates were assessed by fluorescent labelling. Bone typology was described according to Ricqlès' typological classification. Results show that the presence and proportion of primary osteons, two consequences of bone initial porosity at the time of its deposit, are strongly related to bone growth rate. However, no significant relationship between primary osteons orientation and bone growth rate could be detected, at least for osteonal orientations (longitudinal, laminar and reticular) and growth rates values observed in mallard long bones. These results suggest that Amprino's rule holds for some major typological characters of primary compact bone tissues (i.e. primary osteons presence and proportion). However, it is irrelevant to some other characters (i.e. osteonal orientation), the meaning of which remains to be discovered.

Ultrastructure and blood supply of the tegmentum vasculosum in the cochlea of the duckling

The tegmentum vasculosum of the duckling consists of a highly folded epithelium which extends over the dorsal and lateral walls of the cochlear duct, separating the scala media from the scala vestibuli. This epithelium consists of two distinct cell types, dark cells and light cells, and is well vascularized. The surface of the epithelium is formed by a mosaic of alternating dark and light cells. The goblet-shaped dark cells have an electron-dense, organelle-rich cytoplasm, and are expanded basally by extensive basolateral plasma membrane infoldings, within which are numerous mitochondria. Dark cells are isolated from each other and from the capillaries within the epithelium by intervening light cells. In contrast, columnar light cells exhibit an electron-lucent, organelle-poor cytoplasm and may extend from the underlying capillaries to the endolymphatic surface. Light cells contain abundant, coated endocytic vesicles on their apical surfaces and are bound, apically, to other light cells or to dark cells by tight junctions and desmosomes. Laterally, light cells are linked to each other either by complex, fluid-filled membrane interdigitations or by extensive gap junctions. Plasma membrane interdigitations and obvious, fluid-filled intercellular spaces characterize the lateral borders between light and dark cells. Vascular corrosion casting reveals the three-dimensional anatomy of the cochlear vasculature. A continuous arteriolar loop fed by anterior and posterior cochlear arterioles encircles the cochlear duct. The rich capillary beds of the tegmentum vasculosum are supplied by arching arterioles arising from this loop. These capillaries are the continuous type and are situated primarily within the core of the epithelium or along its border with the scala vestibuli. The structure and blood supply of the tegmentum vasculosum are characteristic of an epithelium involved in active transport.

Na+,K+-ATPase activity and ultrastructural localization in the tegmentum vasculosum in the cochlea of the duckling

The tegmentum vasculosum of the avian cochlear duct mimics the stria vascularis of the mammalian cochlear duct in both location and structure, and previous studies indicate that it may be its functional counterpart with regard to endolymph synthesis. In the present study, we report on the enzymatic activity and ultrastructural localization of the Na+,K+-ATPase in the tegmentum vasculosum of the duckling. Na+,K+-ATPase activity was determined by measuring K+-dependent, ouabain-sensitive p-nitrophenyl phosphatase (p-NPPase) activity in homogenates of dissected regions of the cochlear duct. The ultrastructural localization of the Na+,K+-ATPase was identified using K+-dependent, ouabain-sensitive, p-NPPase cytochemistry. Specific enzyme activity was localized primarily in homogenates of the tegmentum vasculosum (2.27 micromol p-nitrophenyl phosphate/mg protein/min) when compared to homogenates of the entire cochlear duct (0.69 micromol p-nitrophenyl phosphate/mg protein/min). Reaction product for p-NPPase was localized primarily along the basolateral plasma membrane folds of the dark cells. The cytochemical deposits appeared to be located exclusively on the cytoplasmic side of the plasma membrane. The light cells were devoid of reaction product. Biochemical and cytochemical localization of p-NPPase activity on the basolateral plasma membrane folds of the dark cells of the tegmentum vasculosum in conjunction with the ultrastructural morphology of these cells is compatible with a Na+,K+-ATPase-dependent ion transport function related to endolymph synthesis.

Growth curve analyses in selected duck lines

1. Growth patterns of male ducks from 4 lines (lines A, B, C and D) selected for market weight were analysed and compared to growth patterns of ducks in the respective line 7 generations earlier. Growth curves were analysed using procedures derived from the Weibull sigmoidal function and the linear-linear relative growth rate model and simple allometry. 2. The ducks were fed ad libitum under 24-h lighting throughout the experiment. At weekly intervals from the time of hatch through 70 d of age, 16 ducks from each line were killed to determine body, carcase, breast-muscle, leg and thigh-muscle, and abdominal fat weights. 3. Line A was the heaviest line, followed by line B, line C and line D. However, body weight, carcase weight and breast-muscle weight at 49 d of age were not significantly different between lines A and B. After 7 generations of selection, the breast-muscle yield was increased to >19% and the abdominal fat percent was reduced to <1.4% in all lines. 4. The Weibull growth curve analysis of body weight showed an increase in the asymptotes during selection, while the age of the inflection point remained constant in all lines (21.3 to 26.0 d). For breast-muscle growth, ducks reached the inflection point 12.8 to 14.3 d later than for body weight. Between line A and line B, asymptotes for body weight, asymptotes for breast-muscle weight and allometric growth coefficients of breast muscle and leg and thigh muscles from 14 to 49 d were not significantly different. 5. The relative growth rate model discriminated body and breast-muscle growth patterns of line A and line B. The initial decline in the relative body growth rate was less and the time to reach the transition was longer in line A than line B. On the other hand, the initial decline in the relative breast-muscle growth rate was greater in line A than line B.

Sexual selection. Are ducks impressed by drakes' display?

Surprisingly few birds have penises, but among those that do, the Argentine lake duck (Oxyura vittata) tops the bill - the penis of this small stifftail duck from South America is shaped like a corkscrew and, at almost half a metre long, is the largest of any bird measured so far. Factors responsible for the evolution of this remarkable organ could include runaway selection, whereby drakes with longer penises gain dominance and copulate with more females, or preference by females for drakes with longer and more decorated penises.

Brain alterations in crested versus non-crested breeds of domestic ducks (Anas platyrhynchos f.d.)

A comparison of brain size and brain composition was made between two uncrested duck breeds and Crested Ducks (CR) and between CR individuals that do possess crests and those that do not have the crest. Domestic ducks of the breed CR have allometrically larger brains than uncrested duck breeds. The crest inserts on a cushion of fat and connective tissue that is partly nourished by brain vessels via small holes in the skull. Through these holes, fat tissue may invade the brain cavity. Because the fat accumulations are sometimes hidden deep between the telencephalon, tectum, and cerebellum, they may be invisible macroscopically and, thus, give the impression of a large brain. The size of the crest, however, is not strictly correlated with fat accumulations in the brain, because 2 among 10 specimens of CR showed no fat body at all, and the investigation of 10 uncrested CR (ducks from the same genetic stock, but without the crests) also revealed fat accumulations in 6 specimens. After subtraction of the volume of the fat body, the brain volume of CR (crested and uncrested) was of equal size to that of "Hochbrutflugenten" and Pommeranian ducks, as was the volumes of most brain structures measured. Significantly smaller in CR were the olfactory bulbs, the prepiriform area, and the cerebellum, which was always situated in close proximity to the fat body in CR.

Seasonal patterns of LH, testosterone and semen quality in the Northern pintail duck (Anas acuta)

This study characterized seasonal changes in circulating LH and testosterone and in semen production and quality in the Northern pintail duck. Plasma LH and testosterone were measured in blood samples collected weekly throughout the year from eight males exposed to natural fluctuations in day length and temperature. Semen quality was evaluated weekly in these same males from April-June, the months when spermatozoa were produced. Semen quality (based on sperm concentration and normal morphology) peaked 0-2 weeks after sperm production onset and decreased sharply before sperm production cessation in late June. Nadir LH concentrations were measured in July and August with peak LH observed in May and November. There were clear seasonal patterns in circulating testosterone with July-September values being less (P<0.05) than October-December which, in turn, were less (P<0.05) than January-March. Maximal circulating testosterone (P<0.05) occurred during April-June, coincident with semen production. Weekly circulating LH during the breeding season was directly related to testosterone concentrations (P<0.01), but was not correlated to any specific semen or sperm trait (P>0.05). Testosterone concentrations throughout the breeding season were correlated (P<0.05) to total numbers of spermatozoa produced (volume x cell concentration) and percent normal sperm morphology. In summary, the Northern pintail experiences seasonal hormone fluctuations, with maximum circulating testosterone coinciding with peak ejaculate quality reflected by the production of high numbers of morphologically normal spermatozoa.

Dynamics of mallard (Anas platyrynchos) gastrocnemius function during swimming versus terrestrial locomotion

This study investigates how the contractile function of a muscle may be modulated to accommodate changes in locomotor mode and differences in the physical environment. In vivo recordings of lateral gastrocnemius (LG) activation, force development (measured using tendon buckle transducers) and length change (measured using sonomicrometry) were obtained from mallard ducks (Anas platyrhynchos) as they swam at steady speeds in a water tank and walked or ran on land. LG force recordings were compared with combined lateral and medial gastrocnemius (MG) muscle-tendon force recordings obtained from the contralateral limb, allowing force development by the MG to be estimated relative to that of the LG. Although similar stresses were calculated to act in the LG and MG muscles during terrestrial locomotion (126 and 115 kPa, respectively), stresses were considerably greater in the LG compared with the MG during swimming (62 versus 34 kPa, respectively). During both steady swimming and terrestrial locomotion, the LG developed force while shortening over a considerable range of its length (swimming 23.6 % versus terrestrial 37.4 %). Activation of the muscle occurred near the end of passive lengthening during the recovery stroke, just prior to muscle shortening. As a result, the muscle generated broad positive work loops during both locomotor modes. LG work during swimming (4.8 J kg(−)(1)) averaged 37 % of the work performed during terrestrial locomotion (13.1 J kg(−)(1)), consistent with the twofold greater force and 58 % greater strain of the muscle during walking and running. Because limb cycle frequency was similar for the two locomotor modes (swimming 2.65 versus terrestrial 2.61 Hz), differences in power output (swimming 12.6 W kg(−)(1)versus terrestrial 32.4 W kg(−)(1)) largely reflected difference in work per cycle. Tendon elastic energy savings was a small fraction (&lt;5 %) of the work performed by the muscle, consistent with a fiber-tendon design of these two muscles that favors muscle work to produce limb movement with little tendon strain. These results are consistent with a higher cost of terrestrial locomotion in ducks compared with other, more cursorial birds that may operate their muscles more economically and achieve greater tendon elastic savings.

Intrinsic choroidal neurons in the duck eye receive sympathetic input: anatomical evidence for adrenergic modulation of nitrergic functions in the choroid

Intrinsic choroidal neurons (ICN) in the duck eye form an intramural ganglionic plexus that may subserve complex integrative functions. A key feature of such ganglia is an innervation by sympathetic postganglionic neurons. The present study was thus aimed at determining the sympathetic postganglionic innervation of ICN. Choroids were processed for double immunofluorescence labelling with the following markers: tyrosine-hydroxylase (TH)/nitric oxide synthase (nNOS), TH/galanin (GAL), dopamine-beta-hydroxylase (DBH)/vasoactive intestinal polypeptide (VIP), TH/DBH and DBH/alpha-smooth-muscle actin (alphaSMA), and for triple immunofluorescence labelling with VIP/DBH/TH. Epifluorescence and confocal laser scanning microscopy were used for evaluation. Immunoperoxidase staining for TH or DBH in combination with NADPH-diaphorase histochemistry was applied for electron microscopy. ICN spread over the entire choroid but were concentrated in an equatorial zone passing obliquely from naso-cranial to temporocaudal. More than 80% of nNOS-positive ICN showed close appositions of TH/DBH-immunoreactive varicose nerve fibres at the light-microscopic level, as could be confirmed by confocal laser scanning microscopy. Ultrastructurally, these appositions could be defined as both synapses or close contacts without synaptic specialisation. Vascular and non-vascular smooth muscle fibres also received TH/DBH-immunopositive innervation. Our findings suggest that most ICN receive a sympathetic input that might modulate their nitrergic effects upon vascular and non-vascular smooth muscle fibres in the choroid and that they may have more complex functions than merely being a simple parasympathetic relay.

Influence of hydration on the mechanical performance of duck down feathers

1. We report the first measurements to be made on the effects of hydration on the mechanical properties of commercially-prepared duck down feathers. Tensile tests were performed, to failure, on isolated barbs of down feathers at 50% RH and with fully-hydrated (wet) feathers. 2. The Young's modulus (stiffness) and ultimate stress (strength) of the feathers was higher at 50% RH than when wet. Wet feathers, however, failed at greater extension than dry feathers. The implications for down feather performance and for the use of feathers as a structural material are discussed.

Spinal cord monoaminergic system response to age and cold-acclimatization in muscovy duckling

The effect of age and cold acclimatization on the regional distribution of monoamines in duckling spinal cord was studied. In thermoneutral controls (TN), the high dopamine (DA) to norepinephrine (NE) ratios (0.25 at 4 weeks of age and 0.15 at 6 weeks of age) suggest the presence of specific (non precursor) dopaminergic pools in cervical spinal cord. DA levels and the ratio of DA to NE were lowered by age and cold exposure in the cervical cord. In TN ducklings, serotonin (5-HT) and its metabolite 5-hydroxyindoleacetic acid (5-HIAA) showed a decline with age in the spinal cord, indicating that this system is affected with development, whereas cold exposure prevents this decrease. The contents of 5-HT (+58%), 5-HIAA (+93%) and the ratio of 5-HIAA to 5-HT (+50%) are higher in the cervical spinal cord of cold acclimated than in TN ducklings. These results indicate that central monoaminergic systems are markedly affected by age and cold exposure.