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1.
The principles which govern gas exchange by diffusion acrossthe pores of the avian eggshell are reviewed and compared withconvective gas exchange. The concept of conductance is definedfor both diffusive and convective gas exchange through pores,and methods of calculating pore size are described. Estimatesof conductances of the elements in the gas transfer path fromatmosphere to chorioallantoic capillary blood are discussed,and recent studies on the role of ternary diffusion and a convectivecomponent to gas fluxes are presented.  相似文献   

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Synchrotron microfocus small angle X-ray scattering was used to investigate the nanostructure and microscopic variation of eggshells. It uses a microbeam allowing the ability to probe interactions between the organic and inorganic components at nanometer level and is ideal for mapping over small areas to obtain a detailed analysis of structural variations. Thin sections of eggshells were scanned from the shell membrane (inner) to the cuticle (outer) surface. The data collected was used to produce two-dimensional maps showing microscopic changes within the different layers of the eggshell. The structural alterations ap- parently could have implications at the macroscopic level of the resulting eggshell. As the organic matrix is embedded within the eggshell this may contribute to the variations observed in calcite crystal form and texture, Structural information obtained about a biomaterial at different length scales is important in relating the structure to its functional properties. This knowledge and the principles behind the formation of biomaterials could be used in the attempt of bioengineering new systems.  相似文献   

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Background

The exceptional diversity of coloration found in avian eggshells has long fascinated biologists and inspired a broad range of adaptive hypotheses to explain its evolution. Three main impediments to understanding the variability of eggshell appearance are: (1) the reliable quantification of the variation in eggshell colours; (2) its perception by birds themselves, and (3) its relation to avian phylogeny. Here we use an extensive museum collection to address these problems directly, and to test how diversity in eggshell coloration is distributed among different phylogenetic levels of the class Aves.

Methodology and Results

Spectrophotometric data on eggshell coloration were collected from a taxonomically representative sample of 251 bird species to determine the change in reflectance across different wavelengths and the taxonomic level where the variation resides. As many hypotheses for the evolution of eggshell coloration assume that egg colours provide a communication signal for an avian receiver, we also modelled reflectance spectra of shell coloration for the avian visual system. We found that a majority of species have eggs with similar background colour (long wavelengths) but that striking differences are just as likely to occur between congeners as between members of different families. The region of greatest variability in eggshell colour among closely related species coincided with the medium-wavelength sensitive region around 500 nm.

Conclusions

The majority of bird species share similar background eggshell colours, while the greatest variability among species aligns with differences along a red-brown to blue axis that most likely corresponds with variation in the presence and concentration of two tetrapyrrole pigments responsible for eggshell coloration. Additionally, our results confirm previous findings of temporal changes in museum collections, and this will be of particular concern for studies testing intraspecific hypotheses relating temporal patterns to adaptation of eggshell colour. We suggest that future studies investigating the phylogenetic association between the composition and concentration of eggshell pigments, and between the evolutionary drivers and functional impacts of eggshell colour variability will be most rewarding.  相似文献   

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Abstract

Howard Gardner The Disciplined Mind: What All Students Should Understand New York: Simon &; Schuster, 1999. 287 pp. $25.00 hardback.  相似文献   

7.
Chick embryos have been water stressed during the last week of incubation by either withdrawing 6 cm3 of allantoic fluid or by increasing shell porosity three to four fold. Despite the large increase in water loss from these eggs they were successfully incubated to produce hatchlings of apparently normal water content. The chicks produced by water deprivation were significantly smaller than controls and it appears that the growth of embryos is therefore modulated according to the metabolites available. If this interpretation is correct it suggests that the critical role of eggshell porosity in avian development has been over-emphasized.  相似文献   

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Eggshell strength in cuckoos and cowbirds   总被引:6,自引:0,他引:6  
M. G. BROOKER  L. C. BROOKER† 《Ibis》1991,133(4):406-413
Parasitic cuckoos of the genus Clamator and parasitic cowbirds Molothrus spp. lay eggs that appear to be stronger than those of their hosts. Similar differences in eggshell strength between the eggs of the Cuculus/Cacomantis/Chrysococcyx cuckoos and their hosts are not apparent. We suggest that the advantage of a strong eggshell in the Clamator and Molothrus species is to protect the parasite's egg from damage if the nest is multiply parasitized. This suggestion relies on the observation that Clamator and Molothrus species commonly lay more than one egg per nest and often remove or damage eggs in the process.  相似文献   

10.
Eggshell formation in polyclads (Turbellaria)   总被引:1,自引:1,他引:0  
Eggshell formation in polyclads was studied by means of transmission electron microscopy and histochemistry. Shell-forming granules (SFG) in the egg, as well as secretions of shell glands (SGS), play roles in eggshell formation. As the oocytes pass through the portion of the female tract where the shell glands open, they are surronded by a two-layered envelope of SGS. This envelope prevents the dispersion of SFGs discharged after oviposition, and its inner layer participates in eggshell formation with the SFGs. In Pseudostylochus sp., most SFGs consist of five parts. Similarities in staining between the parts of the SFGs and the parts of the eggshell indicate that discrete parts of the shell are derived from specific SFG components. Hardening of the eggshell and egg-plate matrix takes place through primary tanning of a sclerotin-like protein.  相似文献   

11.
Scanning electron microscopy (SEM) was used to examine the process of shell formation in tuatara. Tuatara carry eggs in the oviducts for ∼ 7–8 mo before nesting, a period of gravidity more than three times as long as in any other oviparous reptile. Our aim was to determine whether shell formation occurred rapidly after ovulation, or whether it occurred gradually throughout gravidity. Eggs were obtained from females in early gravidity (May, ∼ 1 mo after ovulation), midgravidity (August and September, 4–5 mo after ovulation), and late gravidity, immediately prior to nesting (December, 8 mo after ovulation). The shell membrane (fibrous layer) was well formed by May, but calcification of the outer surface had only just begun. Vertical columns of calcium carbonate were embedded in the shell membrane and appeared to erupt through the outer surface between early and midgravidity. Changes in the appearance of the outer calcareous layer were evident as gravidity progressed. In all shells, calcium carbonate was present as calcite. The appearance of the inner boundary (innermost layer of eggshell) was variable; some shells had a smooth and amorphous inner boundary as previously reported for tuatara and other reptiles, whereas other shells had an inner boundary composed of small spherical granules on the inner surface of which small calcareous spicules were scattered. A previously published model of the process of shell formation in tuatara eggshells is refined in light of our observations. We interpret the ability of female tuatara to shell their eggs gradually during winter as further evidence of their unusual physiological tolerance of cold conditions. © 1996 Wiley-Liss, Inc.  相似文献   

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Avian sleep     
《Current biology : CB》2014,24(1):R12-R14
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Avian influenza     
J Hoey 《CMAJ》1998,158(3):369
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Avian spurs   总被引:1,自引:0,他引:1  
Spur size and number in the various species of Galliformes are considered in relation to body size and social system. Spur length is absolutely and relatively greater among large tropical species. Multiple-spurred species are intermediate in size between spurless and single-spurred species, but have longer legs. Possession of spurs is common, and presumably originated among monogamous species, but is still commoner among polygamous ones. Different spur shapes possibly reflect wounding versus stunning strategies of fighting. Wing spurs in other birds are briefly compared.  相似文献   

19.
Avian Olfaction     
The literature and status of knowledge concerning olfactionin birds is reviewed, and the general anatomical plan of theavian olfactory chamber is discussed. Birds that show olfactoryability through the possession and utilization of well-developedolfactory equipment, or are suspect of olfactory perceptionbecause of behavioral patterns or olfactory equipment are discussed.These are: (1) the kiwi (Apteryx) of New Zealand, (2) procellariiformbirds, such as albatrosses, shearwaters, and petrels, (3) thecathartine vultures, particularly the turkey vulture (Cathartesaura), (4) the oilbird (Steatornis caripensis) of the islandof Trinidad, and northern South America, and (5) the honey guidesof the family Indicatoridae. Some new data suggesting a well-developedsense of smell in the honey guides (Indicatoridae) are alsopresented.  相似文献   

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