Structural coloration in a fossil feather

Investigation of feathers from the famous Middle Eocene Messel Oil Shale near Darmstadt, Germany shows that they are preserved as arrays of fossilized melanosomes, the surrounding beta-keratin having degraded. The majority of feathers are preserved as aligned rod-shaped eumelanosomes. In some, however, the barbules of the open pennaceous, distal portion of the feather vane are preserved as a continuous external layer of closely packed melanosomes enclosing loosely aligned melanosomes. This arrangement is similar to the single thin-film nanostructure that generates an iridescent, structurally coloured sheen on the surface of black feathers in many lineages of living birds. This is, to our knowledge, the first evidence of preservation of a colour-producing nanostructure in a fossil feather and confirms the potential for determining colour differences in ancient birds and other dinosaurs.     

The original colours of fossil beetles

Structural colours, the most intense, reflective and pure colours in nature, are generated when light is scattered by complex nanostructures. Metallic structural colours are widespread among modern insects and can be preserved in their fossil counterparts, but it is unclear whether the colours have been altered during fossilization, and whether the absence of colours is always real. To resolve these issues, we investigated fossil beetles from five Cenozoic biotas. Metallic colours in these specimens are generated by an epicuticular multi-layer reflector; the fidelity of its preservation correlates with that of other key cuticular ultrastructures. Where these other ultrastructures are well preserved in non-metallic fossil specimens, we can infer that the original cuticle lacked a multi-layer reflector; its absence in the fossil is not a preservational artefact. Reconstructions of the original colours of the fossils based on the structure of the multi-layer reflector show that the preserved colours are offset systematically to longer wavelengths; this probably reflects alteration of the refractive index of the epicuticle during fossilization. These findings will allow the former presence, and original hue, of metallic structural colours to be identified in diverse fossil insects, thus providing critical evidence of the evolution of structural colour in this group.     

The early evolution of feathers: fossil evidence from Cretaceous amber of France

The developmental stages of feathers are of major importance in the evolution of body covering and the origin of avian flight. Until now, there were significant gaps in knowledge of early morphologies in theoretical stages of feathers as well as in palaeontological material. Here we report fossil evidence of an intermediate and critical stage in the incremental evolution of feathers which has been predicted by developmental theories but hitherto undocumented by evidence from both the recent and the fossil records. Seven feathers have been found in an Early Cretaceous (Late Albian, ca 100 Myr) amber of western France, which display a flattened shaft composed by the still distinct and incompletely fused bases of the barbs forming two irregular vanes. Considering their remarkably primitive features, and since recent discoveries have yielded feathers of modern type in some derived theropod dinosaurs, the Albian feathers from France might have been derived either from an early bird or from a non-avian dinosaur.     

Eocene fossil is earliest evidence of flower-visiting by birds

Birds are important pollinators, but the evolutionary history of ornithophily (bird pollination) is poorly known. Here, we report a skeleton of the avian taxon Pumiliornis from the middle Eocene of Messel in Germany with preserved stomach contents containing numerous pollen grains of an eudicotyledonous angiosperm. The skeletal morphology of Pumiliornis is in agreement with this bird having been a, presumably nectarivorous, flower-visitor. It represents the earliest and first direct fossil evidence of flower-visiting by birds and indicates a minimum age of 47 million years for the origin of bird–flower interactions. As Pumiliornis does not belong to any of the modern groups of flower-visiting birds, the origin of ornithophily in some angiosperm lineages may have predated that of their extant avian pollinators.     

Plumage colour mutations and melanins in the feathers of the Japanese quail: a first comparison

The absorbance of melanin content from dorsal feathers was compared between wild-type Japanese quail and nine other quail plumage colours determined by single mutations in one of seven genes: extended brown ( MC1R ), yellow ( ASIP ), silver ( MITF ), lavender ( MLPH ), roux ( TYRP1 ), imperfect albinism ( SLC45A2 ) and rusty . As compared with wild-type quail, all mutations but extended brown decreased total melanins. The largest decrease was observed in quail with one of the dilution mutations at TYRP1 , MLPH or SLCA45A2 . No difference in eumelanins was found between the 10 plumage colours. Despite visible colour differences, homozygous and heterozygous mutants at MITF , or the two imperfect albino (white) and cinnamon (pale yellow) alleles at SLC45A2, could not be differentiated on the basis of melanins. In contrast, the two white phenotypes caused by mutations at MITF and SLC45A2, or the two reddish plumage colours caused by the roux and rusty non-allelic mutations had different total melanin contents. The results showed that rusty was not likely to be a dilution mutation.     

Carotenoids, colour and conservation in an endangered passerine, the hihi or stitchbird (Notiomystis cincta)

Carotenoids are essential dietary components utilized not only in pigmentation but also as immuno-stimulants and antioxidants. Reduced availability can have consequences on individual health and survival, thus making carotenoids a good indicator of environmental stress. We compared carotenoid profiles and plumage colour characteristics of an endangered passerine species in New Zealand, between its remnant island source population and two reintroduced island populations. Circulating carotenoids were predominantly lutein (mean of 82.2%) and zeaxanthin (mean of 14.8%), and these were the major carotenoids present as yellow pigments in the males' plumage. There were clear differences in total carotenoid concentrations and plumage colour among the three populations. Circulating carotenoid concentration was significantly higher in one of the reintroduced populations, and the yellow plumage of males was significantly higher in both reintroduced populations in comparison with the remnant population (reflected as a significant increase in hue). Understanding how these differences arise may be of importance to this species given the health benefits carotenoids impart and our ability to select plant species containing these compounds or artificially supplement them.     

Cell organization of barb ridges in regenerating feathers of the quail: implications of the elongation of barb ridges for the evolution and diversification of feathers

This ultrastructural study on the regenerating feathers of quail describes the cellular organization of the barb ridges responsible for the ramification of adult feathers. Bilateral symmetry of the barb ridges determines the organization of feather cells into feather branching. The length of the barb ridges, derived from the number of cells associated to form the barbule plates, determines the length of the barbule branching. Long chains of barb cells form long barbs that branch from the rachis with an increase of feather size. Supportive cells function as spacers between the barbule cells. New cells derive from stem cells localized in the collar region of the feather follicle, as indicated from the re‐organization of collar cells into barb ridges (a morphogenetic process inherited from that of embryonic feathers), production of an embryonic type of keratin (feather keratin), permanence of periderm granules (typical embryonic organelles) in barb vane ridge cells. Variations in the process of barb ridge morphogenesis allow the fusion of ridges into a rachis. The differentiation of hooklets contributes to the origin of planar feathers. Separation between rachis and merging barb ridges is by supportive cells, derived from the marginal plates of the barb ridges. Speculations on the evolution and diversification of feathers are presented.     

Resonating feathers produce courtship song

Male Club-winged Manakins, Machaeropterus deliciosus (Aves: Pipridae), produce a sustained tonal sound with specialized wing feathers. The fundamental frequency of the sound produced in nature is approximately 1500 Hz and is hypothesized to result from excitation of resonance in the feathers'' hypertrophied shafts. We used laser Doppler vibrometry to determine the resonant properties of male Club-winged Manakin''s wing feathers, as well as those of two unspecialized manakin species. The modified wing feathers exhibit a response peak near 1500 Hz, and unusually high Q-values (a measure of resonant tuning) for biological objects (Q up to 27). The unmodified wing feathers of the Club-winged Manakin do not exhibit strong resonant properties when measured in isolation. However, when measured still attached to the modified feathers (nine feathers held adjacent by an intact ligament), they resonate together as a unit near 1500 Hz, and the wing produces a second harmonic of similar or greater amplitude than the fundamental. The feathers of the control species also exhibit resonant peaks around 1500 Hz, but these are significantly weaker, the wing does not resonate as a unit and no harmonics are produced. These results lend critical support to the resonant stridulation hypothesis of sound production in M. deliciosus.     

Comparative evidence for costs of secondary sexual characters: adaptive vane emargination of ornamented feathers in birds

We used a comparative approach, by comparing bird species with tail ornamentation with sister taxa without ornamentation, to deduce the aerodynamic function of extravagant feather ornaments and the costs of such ornaments in birds. First, the aerodynamic function of tail feather ornaments in birds can be deduced from asymmetry in the width of tail feather vanes, since flightless birds have symmetrical vanes while flying birds without feather exaggeration by sexual selection have asymmetrical vanes. Distal inner vanes at the tip of tail feathers were more narrow in ornamented as compared to nonornamented birds, and vane asymmetry at the tip of the feather was therefore reduced in ornamented species, suggesting marginal aerodynamic function of the distal part of extravagant feather ornaments. Second, the cost of feather ornaments due to parasite drag is proportional to the area of feathers extending beyond the maximum continuous width of the tail, and aerodynamic costs of long tails could therefore be diminished by a reduction in feather width. Consistent with this prediction, the outermost tip of feather ornaments was narrower than the homologous character in nonornamented sister taxa, while the base of the feather had similar width in the two groups of birds. These results suggest that the costs of extravagant ornamentation have been diminished by a reduction in feather width, leading to a reduction in drag. Costs of feather ornaments, as demonstrated by their fine morphology, thus appear to have been extensive during the evolution of these characters.     

The importance of the fixation of colour,pattern and form in tropical Pseudocerotidae (Platyhelminthes,Polycladida)

At last a fixation method that ensures tropical pseudocerotid polyclads are fixed flat, preserved for histological preparation and which also retains their colour pattern has been developed. FCA-PGPP (Formaldehyde Calcium Acetate-Propylene Glycol, Propylene Phenoxetol) fixative is frozen and worms are coaxed onto filter paper which is then laid on the frozen fixative. As a consequence, over 230 species have been documented from the southern Great Barrier Reef and eastern Papua New Guinea (Newman & Cannon, 1994; in press). It was determined that species diagnoses need to be based on colour pattern, general morphology of living animals and serial reconstructions of the male anatomy.Christensen Research Institute Contribution No. 82     

An improved model of heat transfer through penguin feathers and down

Penguins, mostly live in the extremely cold Antarctic, are known to have feathers and down, which are light weight, compact and extremely efficient in preventing heat loss. Nevertheless, the mechanisms of heat transfer through the penguin feathers and down, and how the unique characteristics of penguin feathers and down make them such good thermal insulators are not fully understood. In this paper, an integrated model of heat transfer through the penguin feathers and down is developed and computed using finite volume method, with the geometrical structure of the barbules being considered. Monte-Carlo method is adopted to determine the radiative absorption and emission constant in the integrated model. The effective thermal conductance of penguin feathers and down computed from our model compared well with the experimentally measured value reported in the literature. Three models (penguin model, random fibre model (fibre radius=3microm) and random fibre model (fibre radius=10microm)) are further simulated and compared. Results showed that the relative small radius of the barbules of penguin feather and their geometrical structure are responsible for the reduction of heat loss in cold environment.     

The colour of flowers in spectrally variable illumination and insect pollinator vision

The spectral reflectance of differently coloured Australian native plant flowers and foliage was measured and plotted in a colour triangle to represent the colour space of the honeybee. Spectral variations in illumination are shown to significantly change plant colours for bee vision without colour constancy. A model of chromatic adaptation based upon the von Kries coefficient law shows a reduction in plant colour shift, with the degree of correction depending upon position in colour space. A set of artificial reflectances is used to map relative colour shift caused by spectrally variable illumination for the entire colour space of the honeybee. The rarity of some flower colours in nature shows a correlation to a larger colour shift for these colours when illuminated by spectrally variable radiation. The model of chromatic adaptation is applied to illuminations used in a behavioural study on honeybee colour constancy by Neumeyer 1981. Surface colours used by Neumeyer are plotted in colour space for the various illuminations. The results show that an illumination-dependent colour shift correlates to a decrease in the frequency of bees correctly choosing a colour to which it was trained. Accepted: 23 February 1998     

Shell colour polymorphism associated with substrate colour in the intertidal snail Littorina saxatilis Olivi (Prosobranchia: Littorinidae)

Littorina saxatilis Olivi (1792), the rough winkle, is highly polymorphic in shell colour. Shell colour frequencies were studied at six locations in south-western Wales, U.K., each at a geological contact between red sandstone and grey limestone or volcanic rock. At each site shell colour frequencies were determined in samples from the contact zone and on red or grey rock on either side. Highly significant associations were found between shell colour frequencies and substrate colour. Grey shells were always more common on grey rock than on red rock, and brown shells were usually more common on red than on grey rock, suggesting selection for cryptic colouration. Shell colour frequency differences were also found between replicate samples taken only 5 m apart from the same kind of rock, and between samples from the same kind of rock at the six study sites. These latter differences suggest that selection for camouflage is not the only factor involved in maintaining shell colour polymorphism in this species.     

Unidirectionality of floral colour changes

Many angiosperms have arranged their flowers in inflorescences forming a distinct signalling unit to flower visitors. In some species, the flowers of inflorescences undergo a temporal colour change corresponding exactly to a change in the reward status. Based on information obtained from the spectral reflection curves of pre-change and postchage colours of flower corollas and/or floral guides, it was possible to demonstrate that the colour phase associated with reward closely corresponds to the visual stimuli which trigger behavioural responses of inexperienced flower visitors, and that the colour phase associated with less reward corresponds to visual stimuli less attractive to naïve flower visitors. Reciprocal colour changes were not observed. It is to be assumed that the unidirectionality of floral colour changes is an adaptation of angiosperms aimed at the guidance of first-time flower visitors. Signalling reward to inexperienced flower visitors is an additional function of floral colour changes. The main function of floral colour changes, however, is to provide cues with which the flower visitors can learn to associate one colour phase with reward.