Micro and macroclimate effects on reproductive performance of Common Eiders

The physical environment has a strong influence on the lives or organisms by limiting the way energy is gained and expended determining the capacity of organisms to invest in activities like reproduction. The avian nest site and structure, through its effects on the thermal conditions of the proximal environment of the incubating parent can affect several aspects of an individual’s reproductive success. On a larger scale, characteristics of the oviposition site can impact the spatial distribution of a species and consequently several aspects of population dynamics. In this thesis I investigate the importance of the thermal environment and nesting habitat on the reproductive performance of a sea duck, the Common Eider (Somateria mollissima) breeding in a cold environment. First I described the spatial variation in nest distribution in relation to female’s and nest attributes. Females of similar quality formed aggregations of nests and clusters of high productivity were occupied earlier in the season and at higher densities. Eiders seemed to choose to nest sites based on biotic (conspecifics) rather than abiotic (microclimate) cues. By providing females with artificial shelters I tested some of the effects of microclimate on individual physiology and use of energy during incubation. Females experienced improved microclimatic conditions provided by well-sheltered nest-sites. Nest shelter conferred advantages both to incubating females by allowing energy savings and to their clutches by providing more stable incubation conditions. Shelter did not have an appreciable effect on the female’s stress response. However, in exposed areas, females with high levels of corticosterone hatched a lower proportion of eggs than females with low corticosterone. Behavioural and functional aspects nest construction were tested first, by removing down from nests on repeated occasions throughout incubation and then by testing the effects of different amounts of down on the microclimate of incubation. Females did not replace the removed down suggesting the existence of constrains on the allocation of down to the nest. Large amounts of down in the nest contributed to more stable incubation conditions but females were able to counterbalance poor nest insulation and keep incubation temperature constant but the costs of doing this are unclear. Finally, I assessed the influence of environmental variability on the onset of incubation and short-term fluctuations in population size for the study colony with data from 1977 to 2006. I found that after mild winters female Eiders lay earlier in the season perhaps because milder conditions allow them to attain the necessary body condition for reproduction sooner. Summer temperature had a lagged effect (2 yr) on colony size that could be related to the delayed maturity (age at first reproduction) presented by Common Eiders and the influence of climate on influence recruitment rate to the population. The evidence presented here shows that Common Eiders are strongly influenced by their thermal environment on reproduction but by choosing a good nest they can ameliorate those effects. However nest site selection seems to be strongly linked to female quality rather than to nest properties

Micro and macroclimate effects on reproductive performance of Common Eiders

The physical environment has a strong influence on the lives or organisms by limiting the way energy is gained and expended determining the capacity of organisms to invest in activities like reproduction. The avian nest site and structure, through its effects on the thermal conditions of the proximal environment of the incubating parent can affect several aspects of an individual’s reproductive success. On a larger scale, characteristics of the oviposition site can impact the spatial distribution of a species and consequently several aspects of population dynamics. In this thesis I investigate the importance of the thermal environment and nesting habitat on the reproductive performance of a sea duck, the Common Eider (Somateria mollissima) breeding in a cold environment. First I described the spatial variation in nest distribution in relation to female’s and nest attributes. Females of similar quality formed aggregations of nests and clusters of high productivity were occupied earlier in the season and at higher densities. Eiders seemed to choose to nest sites based on biotic (conspecifics) rather than abiotic (microclimate) cues. By providing females with artificial shelters I tested some of the effects of microclimate on individual physiology and use of energy during incubation. Females experienced improved microclimatic conditions provided by well-sheltered nest-sites. Nest shelter conferred advantages both to incubating females by allowing energy savings and to their clutches by providing more stable incubation conditions. Shelter did not have an appreciable effect on the female’s stress response. However, in exposed areas, females with high levels of corticosterone hatched a lower proportion of eggs than females with low corticosterone. Behavioural and functional aspects nest construction were tested first, by removing down from nests on repeated occasions throughout incubation and then by testing the effects of different amounts of down on the microclimate of incubation. Females did not replace the removed down suggesting the existence of constrains on the allocation of down to the nest. Large amounts of down in the nest contributed to more stable incubation conditions but females were able to counterbalance poor nest insulation and keep incubation temperature constant but the costs of doing this are unclear. Finally, I assessed the influence of environmental variability on the onset of incubation and short-term fluctuations in population size for the study colony with data from 1977 to 2006. I found that after mild winters female Eiders lay earlier in the season perhaps because milder conditions allow them to attain the necessary body condition for reproduction sooner. Summer temperature had a lagged effect (2 yr) on colony size that could be related to the delayed maturity (age at first reproduction) presented by Common Eiders and the influence of climate on influence recruitment rate to the population. The evidence presented here shows that Common Eiders are strongly influenced by their thermal environment on reproduction but by choosing a good nest they can ameliorate those effects. However nest site selection seems to be strongly linked to female quality rather than to nest properties.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Manakins can produce iridescent and bright feather colours without melanosomes

Males of many species often use colourful and conspicuous ornaments to attract females. Among these, male manakins (family: Pipridae) provide classic examples of sexual selection favouring the evolution of bright and colourful plumage coloration. The highly iridescent feather colours of birds are most commonly produced by the periodic arrangement of melanin-containing organelles (melanosomes) within barbules. Melanin increases the saturation of iridescent colours seen from optimal viewing angles by absorbing back-scattered light; however, this may reduce the wide-angle brightness of these signals, contributing to a dark background appearance. We examined the nanostructure of four manakin species (Lepidothrix isidorei, L. iris, L. nattereri and L. coeruleocapilla) to identify how they produce their bright plumage colours. Feather barbs of all four species were characterized by dense and fibrous internal spongy matrices that likely increase scattering of light within the barb. The iridescent, yet pale or whitish colours of L. iris and L. nattereri feathers were produced not by periodically arranged melanosomes within barbules, but by periodic matrices of air and β-keratin within barbs. Lepidothrix iris crown feathers were able to produce a dazzling display of colours with small shifts in viewing geometry, likely because of a periodic nanostructure, a flattened barb morphology and disorder at a microstructural level. We hypothesize that iridescent plumage ornaments of male L. iris and L. nattereri are under selection to increase brightness or luminance across wide viewing angles, which may potentially increase their detectability by females during dynamic and fast-paced courtship displays in dim light environments

Manakins can produce iridescent and bright feather colours without melanosomes

Males of many species often use colourful and conspicuous ornaments to attract females. Among these, male manakins (family: Pipridae) provide classic examples of sexual selection favouring the evolution of bright and colourful plumage coloration. The highly iridescent feather colours of birds are most commonly produced by the periodic arrangement of melanin-containing organelles (melanosomes) within barbules. Melanin increases the saturation of iridescent colours seen from optimal viewing angles by absorbing back-scattered light; however, this may reduce the wide-angle brightness of these signals, contributing to a dark background appearance. We examined the nanostructure of four manakin species (Lepidothrix isidorei, L. iris, L. nattereri and L. coeruleocapilla) to identify how they produce their bright plumage colours. Feather barbs of all four species were characterized by dense and fibrous internal spongy matrices that likely increase scattering of light within the barb. The iridescent, yet pale or whitish colours of L. iris and L. nattereri feathers were produced not by periodically arranged melanosomes within barbules, but by periodic matrices of air and beta-keratin within barbs. Lepidothrix iris crown feathers were able to produce a dazzling display of colours with small shifts in viewing geometry, likely because of a periodic nanostructure, a flattened barb morphology and disorder at a microstructural level. We hypothesize that iridescent plumage ornaments of male L. iris and L. nattereri are under selection to increase brightness or luminance across wide viewing angles, which may potentially increase their detectability by females during dynamic and fast-paced courtship displays in dim light environments

Exposure to UV radiance predicts repeated evolution of concealed black skin in birds

Plumage is among the most well-studied components of integumentary colouration. However, plumage conceals most skin in birds, and as a result the presence, evolution and function of skin colour remains unexplored. Here we show, using a database of 2259 species encompassing >99% of bird genera, that melanin-rich, black skin is found in a small but sizeable percentage (5%) of birds, and that it evolved over 100 times. The spatial distribution of black skin follows Gloger's rule, which states that pigmentation of endothermic animals increases towards the equator. Furthermore, most black-skinned birds inhabit high irradiation regions, and tend to be bald and/or have white feathers. Thus, taken together, our results suggest that melanin-rich, black skin helps to protect birds against ultraviolet irradiation. More generally, our results illustrate that feathered skin colour varies taxonomically, ontogenetically and temporally, providing an additional dimension for avian colour research

Substrate thermal properties influence ventral brightness evolution in ectotherms

The thermal environment can affect the evolution of morpho-behavioral adaptations of ectotherms. Heat is transferred from substrates to organisms by conduction and reflected radiation. Because brightness influences the degree of heat absorption, substrates could affect the evolution of integumentary optical properties. Here, we show that vipers (Squamata:Viperidae) inhabiting hot, highly radiative and superficially conductive substrates have evolved bright ventra for efficient heat transfer. We analyzed the brightness of 4161 publicly available images from 126 species, and we found that substrate type, alongside latitude and body mass, strongly influences ventral brightness. Substrate type also significantly affects dorsal brightness, but this is associated with different selective forces: activity-pattern and altitude. Ancestral estimation analysis suggests that the ancestral ventral condition was likely moderately bright and, following divergence events, some species convergently increased their brightness. Vipers diversified during the Miocene and the enhancement of ventral brightness may have facilitated the exploitation of arid grounds. We provide evidence that integument brightness can impact the behavioral ecology of ectotherms. Jonathan Goldenberg et al. use photographic data and ancestral state reconstruction of 126 viper species to show that substrate type influences the evolution of ventral brightness for efficient heat transfer. Their results suggest that these patterns may have been involved in the diversification of vipers during the Miocene, and highlight the importance of ventral body regions when considering behavioral ecology and evolution.</p

Contributions of feather microstructure to eider down insulation properties

Insulation is an essential component of nest structure that helps provide incubation requirements for birds. Many species of waterfowl breed in high latitudes where rapid heat loss can necessitate a high energetic input from parents and use down feathers to line their nests. Common eider Somateria mollissima nest down has exceptional insulating properties but the microstructural mechanisms behind the feather properties have not been thoroughly examined. Here, we hypothesized that insulating properties of nest down are correlated to down feather (plumule) microstructure. We tested the thermal efficiency (fill power) and cohesion of plumules from nests of two Icelandic colonies of wild common eiders and compared them to properties of plumules of wild greylag goose Anser anser. We then used electron microscopy to examine the morphological basis of feather insulating properties. We found that greylag goose down has higher fill power (i.e. traps more air) but much lower cohesion (i.e. less prone to stick together) compared to common eider down. These differences were related to interspecific variation in feather microstructure. Down cohesion increased with the number of barbule microstructures (prongs) that create strong points of contact among feathers. Eider down feathers also had longer barbules than greylag goose down feathers, likely increasing their air-trapping capacity. Feather properties of these two species might reflect the demands of their contrasting evolutionary history. In greylag goose, a temperate, terrestrial species, plumule microstructure may optimize heat trapping. In common eiders, a diving duck that nests in arctic and subarctic waters, plumule structure may have evolved to maximize cohesion over thermal insulation, which would both reduce buoyancy during their foraging dives and enable nest down to withstand strong arctic winds

A Natural Experiment on the Condition-Dependence of Achromatic Plumage Reflectance in Black-Capped Chickadees

Honest advertisement models posit that only individuals in good health can produce and/or maintain ornamental traits. Even though disease has profound effects on condition, few studies have experimentally tested its effects on trait expression and even fewer have identified a mechanistic basis for these effects. Recent evidence suggests that black and white, but not grey, plumage colors of black-capped chickadees (Poecile atricapillus) are sexually selected. We therefore hypothesized that birds afflicted with avian keratin disorder, a condition that affects the beak and other keratinized tissues, would show reduced expression of black and white, but not grey, color. UV-vis spectrometry of black-capped chickadees affected and unaffected by avian keratin disorder revealed spectral differences between them consistent with this hypothesis. To elucidate the mechanistic bases of these differences, we used scanning electron microscopy (SEM), electron-dispersive x-ray spectroscopy (EDX) and a feather cleaning experiment. SEM showed extreme feather soiling in affected birds, and EDX revealed that this was most likely from external sources. Experimentally cleaning the feathers increased color expression of ornamental feathers of affected, but not unaffected, birds. These data provide strong evidence that black and white color is an honest indicator in chickadees, and that variation in feather dirtiness, likely due to differences in preening behavior is a mechanism for this association

Contributions of feather microstructure to eider down insulation properties

Insulation is an essential component of nest structure that helps provide incubation requirements for birds. Many species of waterfowl breed in high latitudes where rapid heat loss can necessitate a high energetic input from parents and use down feathers to line their nests. Common eider Somateria mollissima nest down has exceptional insulating properties but the microstructural mechanisms behind the feather properties have not been thoroughly examined. Here, we hypothesized that insulating properties of nest down are correlated to down feather (plumule) microstructure. We tested the thermal efficiency (fill power) and cohesion of plumules from nests of two Icelandic colonies of wild common eiders and compared them to properties of plumules of wild greylag goose Anser anser. We then used electron microscopy to examine the morphological basis of feather insulating properties. We found that greylag goose down has higher fill power (i.e. traps more air) but much lower cohesion (i.e. less prone to stick together) compared to common eider down. These differences were related to interspecific variation in feather microstructure. Down cohesion increased with the number of barbule microstructures (prongs) that create strong points of contact among feathers. Eider down feathers also had longer barbules than greylag goose down feathers, likely increasing their air-trapping capacity. Feather properties of these two species might reflect the demands of their contrasting evolutionary history. In greylag goose, a temperate, terrestrial species, plumule microstructure may optimize heat trapping. In common eiders, a diving duck that nests in arctic and subarctic waters, plumule structure may have evolved to maximize cohesion over thermal insulation, which would both reduce buoyancy during their foraging dives and enable nest down to withstand strong arctic winds

Properties, genetics and innate immune function of the cuticle in egg-laying species

International audienceCleidoic eggs possess very efficient and orchestrated systems to protect the embryo from external microbes until hatch. The cuticle is a proteinaceous layer on the shell surface in many bird and some reptile species. An intact cuticle forms a pore plug to occlude respiratory pores and is an effective physical and chemical barrier against microbial penetration. The interior of the egg is assumed to be normally sterile, while the outer eggshell cuticle hosts microbes. The diversity of the eggshell microbiome is derived from both maternal microbiota and those of the nesting environment. The surface characteristics of the egg, outer moisture layer and the presence of antimicrobial molecules composing the cuticle dictate constituents of the microbial communities on the eggshell surface. The avian cuticle affects eggshell wettability, water vapor conductance and regulates ultraviolet reflectance in various ground-nesting species; moreover, its composition, thickness and degree of coverage are dependent on species, hen age, and physiological stressors. Studies in domestic avian species have demonstrated that changes in the cuticle affect the food safety of eggs with respect to the risk of contamination by bacterial pathogens such as Salmonella and Escherichia coli . Moreover, preventing contamination of internal egg components is crucial to optimize hatching success in bird species. In chickens there is moderate heritability (38%) of cuticle deposition with a potential for genetic improvement. However, much less is known about other bird or reptile cuticles. This review synthesizes current knowledge of eggshell cuticle and provides insight into its evolution in the clade reptilia. The origin, composition and regulation of the eggshell microbiome and the potential function of the cuticle as the first barrier of egg defense are discussed in detail. We evaluate how changes in the cuticle affect the food safety of table eggs and vertical transmission of pathogens in the production chain with respect to the risk of contamination. Thus, this review provides insight into the physiological and microbiological characteristics of eggshell cuticle in relation to its protective function (innate immunity) in egg-laying birds and reptiles