Wing-assisted incline running and the evolution of flight. (57/576)

Flapping wings of galliform birds are routinely used to produce aerodynamic forces oriented toward the substrate to enhance hindlimb traction. Here, I document this behavior in natural and laboratory settings. Adult birds fully capable of aerial flight preferentially employ wing-assisted incline running (WAIR), rather than flying, to reach elevated refuges (such as cliffs, trees, and boulders). From the day of hatching and before attaining sustained aerial flight, developing ground birds use WAIR to enhance their locomotor performance through improved foot traction, ultimately permitting vertical running. WAIR provides insight from behaviors observable in living birds into the possible role of incipient wings in feathered theropod dinosaurs and offers a previously unstudied explanation for the evolution of avian flight.  (+info)

Shift of localized growth zones contributes to skin appendage morphogenesis: role of the Wnt/beta-catenin pathway. (58/576)

Skin appendage formation represents a process of regulated new growth. Bromodeoxyuridine labeling of developing chicken skin demonstrated the presence of localized growth zones, which first promote appendage formation and then move within each appendage to produce specific shapes. Initially, cells proliferate all over the presumptive skin. During the placode stage they are organized to form periodic rings. At the short feather bud stage, the localized growth zones shifted to the posterior and then the distal bud. During the long bud stage, the localized growth zones descended through the flank region toward the feather collar (equivalent to the hair matrix). During feather branch formation, the localized growth zones were positioned periodically in the basilar layer to enhance branching of barb ridges. Wnts were expressed in a dynamic fashion during feather morphogenesis that coincided with the shifting localized growth zones positions. The expression pattern of Wnt 6 was examined and compared with other members of the Wnt pathway. Early in feather development Wnt 6 expression overlapped with the location of the localized growth zones. Its function was tested through misexpression studies. Ectopic Wnt 6 expression produced abnormal localized outgrowths from the skin appendages at either the base, the shaft, or the tip of the developing feathers. Later in feather filament morphogenesis, several Wnt markers were expressed in regions undergoing rearrangements and differentiation of barb ridge keratinocytes. These data suggest that skin appendages are built to specific shapes by adding new cells from well-positioned and controlled localized growth zones and that Wnt activity is involved in regulating such localized growth zone activity.  (+info)

EGF signaling patterns the feather array by promoting the interbud fate. (59/576)

Feather buds form sequentially in a hexagonal array. Bone morphogenetic protein (BMP) signaling from the feather bud inhibits bud formation in the adjacent interbud tissue, but whether interbud fate and patterning is actively promoted by BMP or other factors is unclear. We show that epidermal growth factor (EGF) signaling acts positively to establish interbud identity. EGF and the active EGF receptor (EGFR) are expressed in the interbud regions. Exogenous EGF stimulates epidermal proliferation and expands interbud gene expression, with a concurrent loss of feather bud gene expression and morphology. Conversely, EGFR inhibitors result in the loss of interbud fate and increased acquisition of feather bud fate. EGF signaling acts directly on the epidermis and is independent of BMP signaling. The timing of competence to interpret interbud-promoting signals occurs at an earlier developmental stage than previously anticipated. These data demonstrate that EGFR signaling actively promotes interbud identity.  (+info)

A female melanin ornament signals offspring fluctuating asymmetry in the barn owl. (60/576)

Sexual selection theory predicts that males advertise quality by displaying extravagant ornaments. By contrast, whether phenotypic variation in females has a signalling function remains an open question. Here, to our knowledge, we provide the first evidence that a female plumage trait can signal fluctuating asymmetry in the offspring. We experimentally demonstrate in wild barn owls (Tyto alba) that the extent to which females display black spots on their plumage does not only signal offspring parasite resistance as shown in a previous study but also developmental homeostasis in the offspring. A greater number of spotted females produced offspring that had more symmetrical feathers during the period of growth. Males, that pair non-randomly with respect to female plumage spottiness therefore appear to gain substantial benefits by mating with heavily spotted females. Genetic variation in plumage spottiness is nevertheless maintained as the covariation between offspring body mass and mother plumage spottiness varies annually depending on environmental conditions.  (+info)

Sex chromosome evolution and speciation in Ficedula flycatchers. (61/576)

Speciation is the combination of evolutionary processes that leads to the reproductive isolation of different populations. We investigate the significance of sex-chromosome evolution on the development of post- and prezygotic isolation in two naturally hybridizing Ficedula flycatcher species. Applying a tag-array-based mini-sequencing assay to genotype single nucleotide polymorphisms (SNPs) and interspecific substitutions, we demonstrate rather extensive hybridization and backcrossing in sympatry. However, gene flow across the partial postzygotic barrier (introgression) is almost exclusively restricted to autosomal loci, suggesting strong selection against introgression of sex-linked genes. In addition to this partial postzygotic barrier, character displacement of male plumage characteristics has previously been shown to reinforce prezygotic isolation in these birds. We show that male plumage traits involved in reinforcing prezygotic isolation are sex linked. These results suggest a major role of sex-chromosome evolution in mediating post- and prezygotic barriers to gene flow and point to a causal link in the development of the two forms of reproductive isolation.  (+info)

Ultraviolet signals in birds are special. (62/576)

Recent behavioural experiments have shown that birds use ultraviolet (UV)-reflective and fluorescent plumage as cues in mate choice. It remains controversial, however, whether such UV signals play a special role in sexual communication, or whether they are part of general plumage coloration. We use a comparative approach to test for a general association between sexual signalling and either UV-reflective or fluorescent plumage. Among the species surveyed, 72% have UV colours and there is a significant positive association between UV reflectance and courtship displays. Among parrots (Psittaciformes), 68% of surveyed species have fluorescent plumage, and again there is a strong positive association between courtship displays and fluorescence. These associations are not artefacts of the plumage used in courtship displays, being generally more 'colourful' because there is no association between display and colours lacking UV reflectance or fluorescence. Equally, these associations are not phylogenetic artefacts because all results remain unchanged when families or genera, rather than species, are used as independent data points. We also find that, in parrots, fluorescent plumage is usually found adjacent to UV-reflective plumage. Using a simple visual model to examine one parrot, the budgerigar Melopsittacus undulatus, we show that the juxtaposition of UV-reflective and fluorescent plumage leads to a 25-fold increase in chromatic contrast to the budgerigar's visual system. Taken together, these results suggest that signals based on UV contrast are of special importance in the context of active sexual displays. We review briefly six hypotheses on why this may be the case: suitability for short-range signalling; high contrast with backgrounds; invisibility to predators; exploitation of pre-existing sensory biases; advertisement of feather structure; and amplification of behavioural signals.  (+info)

Effect of feather meal on live animal performance and carcass quality and composition of growing-finishing swine. (63/576)

A total of 252 crossbred pigs were used in two experiments to determine the effect of feeding hydrolyzed feather meal (FM) during the growing-finishing period on animal performance, carcass composition, and pork quality. All pigs were blocked by weight, and dietary treatments were assigned randomly to pens within blocks. In Exp. 1, 24 pens were randomly assigned to one of three dietary treatments: 1) control corn-soybean meal starter, grower, and finisher diets devoid of FM; 2) control diets formulated with 3% FM; and 3) control diets formulated with 6% FM. During the starter phase, there was a quadratic decrease in average daily gain (P < 0.06) and gain:feed (P < 0.01) with increasing FM, and during the grower-II phase, gain:feed increased linearly (P < 0.07) with increasing FM inclusion level. However, dietary FM had no effects (P > 0.10) on performance during the grower-I phase, finisher phase, or in the overall trial. Moreover, carcasses from pigs fed 3% FM had greater (P < 0.05) average backfat depth than carcasses of pigs fed 0 and 6% FM, but FM did not affect (P > 0.10) ham or carcass lean composition. In Exp. 2, 24 pens were randomly allotted to one of four dietary treatments: 1) positive control corn-soybean meal-based starter, grower, and finisher diets; 2) negative control corn-soybean meal- and wheat middlings-based starter, grower, and finisher diets; 3) negative control diets formulated with 3% FM; and 4) negative control diets formulated with 6% FM. Dietary FM had no effect (P > 0.10) on average daily gain, average daily feed intake, or gain:feed during any phase of the experiment. Ham weight decreased linearly (P < 0.04), whereas ham lean weight increased linearly (P < 0.09), with increasing levels of FM in the diet. Pork from pigs fed 3% FM tended (quadratic effect, P < 0.10) to receive higher Japanese color scores than pork from pigs fed either negative control or 6% FM diets. Moreover, pork color became lighter (P c 0.08), less red (P < 0.001), and less yellow (P < 0.003) as FM level was increased in swine diets. Results from these two experiments indicate that as much as 6% FM can be incorporated into isolysinic diets of growing-finishing pigs without adversely impacting animal performance, carcass composition, or pork quality.  (+info)

Association of feather colour with constitutively active melanocortin 1 receptors in chicken. (64/576)

Seven alleles of the chicken melanocortin (MC) 1 receptor were cloned into expression vectors, expressed in mammalian cells and pharmacologically characterized. Four of the clones e(+R), e(+B&D), e(wh)/e(y), E(Rfayoumi) gave receptors to which melanocortin stimulating hormone (alpha-MSH) and NDP-MSH bound with similar IC50 values and responded to alpha-MSH by increasing intracellular cAMP levels in a dose-dependent manner. Three of the cMC1 receptors; e(b), E and E(R), did not show any specific binding to the radioligand, but were found to be constitutively active in the cAMP assay. The E and E(R) alleles are associated with black feather colour in chicken while the eb allele gives rise to brownish pigmentation. The three constitutively active receptors share a mutation of Glu to Lys in position 92. This mutation was previously found in darkly pigmented sombre mice, but constitutively active MC receptors have not previously been shown in any nonmammalian species. We also inserted the Glu to Lys mutation in the human MC1 and MC4 receptors. In contrast with the chicken clones, the hMC1-E94K receptor bound to the ligand, but was still constitutively active independently of ligand concentration. The hMC4-E100K receptor did not bind to the MSH ligand and was not constitutively active. The results indicate that the structural requirements that allow the receptor to adapt an active conformation without binding to a ligand, as a consequence of this E/K mutation, are not conserved within the MC receptors. The results are discussed in relationship to feather colour in chicken, molecular receptor structures and evolution. We suggest that properties for the 'E92K switch' mechanism may have evolved in an ancestor common to chicken and mammals and were maintained over long time periods through evolutionary pressure, probably on closely linked structural features.  (+info)