Amazoniac
Member
Members that never dropped out of an etiquette course for finding the content of the classes too basic;
Jennifer, PakPik, Sheila;
Pretty interesting hypothesis on eggshell pigmentation:
http://qcpages.qc.edu/Biology/Lahti/Publications/LahtiAuk08.pdf
"An alternative hypothesis is that solar radiation has an influence on egg color that is detectable in the absence of functions for crypsis [fancy for camouflage] or egg recognition in this species. In particular, bird eggs may be subject to embryonic damage from solar radiation, and pigment may be photoprotective (McAldowie 1886, Romanoff and Romanoff 1949). Theoretically, solar damage to bird embryos can take two forms: conducted heat from light absorbed by the shell surface, and light transmitted through the eggshell. Pigment increases absorbance and so is unlikely to ameliorate conductance from the shell surface. Pigment decreases transmittance, however, and in so doing would decrease any adverse effects of light passing through the shell."
"One possible detriment from transmitted light is embryonic heating. The optimal incubation temperature for bird eggs, usually 37–38°C, is close to the upper lethal limit for embryos (Webb 1987). Although bird eggs can sustain cold temperatures with little loss of viability, even a brief exposure to temperatures 2–3° higher than optimal results in a sharp decline in survival of embryos (Bartholomew and Dawson 1979, Bennett et al. 1981). Moreover, even moderate increases in embryonic temperature during the laying period (when eggs are maximally exposed) can initiate development and result in hatching asynchrony. Eggshells appear to be adapted to intercept solar heat via high infrared reflectance (Bakken et al. 1978). Eggshell color may modulate this effect, given that pigment blocks light from entering the eggshell (Romanoff and Romanoff 1949, Shafey et al. 2002), but whether the effect is great enough to be biologically significant is still uncertain (Kilner 2006, Westmoreland et al. 2007). There is likely a firm upper limit to how much pigment is beneficial in a given light environment, however, if the eggshell absorbs too much solar radiation for the resulting heat to be dissipated, heat will build up in the shell and be conducted into the egg, ultimately killing the embryo."
"A poultry study (Shafey et al. 2002) showed that eggshells are particularly efficient at blocking UV light by absorbing it and that the brown eggs of at least one breed are more effective than white eggs in this regard. Biliverdin, the dominant pigment in blue-green eggs, has a high absorbance peak in the UV (Kennedy and Vevers 1973, Inomata et al. 2005). Consequently, biliverdin, including that occurring in eggs, has been hypothesized to function in photoprotection in invertebrates (McDonagh 2001), fish (Yamaguchi et al. 1976), and lizards (Austin and Jessing 1994)."
"In particular, because Village Weavers tend to nest in isolated trees and denude the vegetation around their nests (probably for predator-avoidance and mate-attraction functions; Collias and Collias 1959, 1969, 1970), their globular nests are commonly exposed to direct light throughout the day. The females generally lay eggs when the nests are still green (Jacobs et al. 1978); given the translucence of the nesting materials, the light environment of the nest’s interior is blue-green, similar to a forest shade as described by Endler (1993). Blue-green eggs in such an environment would reflect light across the visible spectrum in proportion to the incident light intensity and would block UV transmittance as well."
Also relevant to the story is that when the eggshells are blue, their entire body is blue; not just a thin pigmented outer layer (like those deep brown eggshells). I recently added a quote by Albert Szent-Györgyi about chlorophyll being a green pigment to allow leaves to absorb red light better - in the case of eggshells, as the author stated, there must be a balance: if the pigment starts to become too dark, it starts absorbing more than reflecting and overheating the interior; the green-blue light coloration not only (theoretically) reflects well but also filters the desired spectrum. If this adaptation was just for the purpose of camouflaging the eggs, a thin outer layer would suffice.
Jennifer, PakPik, Sheila;
Pretty interesting hypothesis on eggshell pigmentation:
http://qcpages.qc.edu/Biology/Lahti/Publications/LahtiAuk08.pdf
"An alternative hypothesis is that solar radiation has an influence on egg color that is detectable in the absence of functions for crypsis [fancy for camouflage] or egg recognition in this species. In particular, bird eggs may be subject to embryonic damage from solar radiation, and pigment may be photoprotective (McAldowie 1886, Romanoff and Romanoff 1949). Theoretically, solar damage to bird embryos can take two forms: conducted heat from light absorbed by the shell surface, and light transmitted through the eggshell. Pigment increases absorbance and so is unlikely to ameliorate conductance from the shell surface. Pigment decreases transmittance, however, and in so doing would decrease any adverse effects of light passing through the shell."
"One possible detriment from transmitted light is embryonic heating. The optimal incubation temperature for bird eggs, usually 37–38°C, is close to the upper lethal limit for embryos (Webb 1987). Although bird eggs can sustain cold temperatures with little loss of viability, even a brief exposure to temperatures 2–3° higher than optimal results in a sharp decline in survival of embryos (Bartholomew and Dawson 1979, Bennett et al. 1981). Moreover, even moderate increases in embryonic temperature during the laying period (when eggs are maximally exposed) can initiate development and result in hatching asynchrony. Eggshells appear to be adapted to intercept solar heat via high infrared reflectance (Bakken et al. 1978). Eggshell color may modulate this effect, given that pigment blocks light from entering the eggshell (Romanoff and Romanoff 1949, Shafey et al. 2002), but whether the effect is great enough to be biologically significant is still uncertain (Kilner 2006, Westmoreland et al. 2007). There is likely a firm upper limit to how much pigment is beneficial in a given light environment, however, if the eggshell absorbs too much solar radiation for the resulting heat to be dissipated, heat will build up in the shell and be conducted into the egg, ultimately killing the embryo."
"A poultry study (Shafey et al. 2002) showed that eggshells are particularly efficient at blocking UV light by absorbing it and that the brown eggs of at least one breed are more effective than white eggs in this regard. Biliverdin, the dominant pigment in blue-green eggs, has a high absorbance peak in the UV (Kennedy and Vevers 1973, Inomata et al. 2005). Consequently, biliverdin, including that occurring in eggs, has been hypothesized to function in photoprotection in invertebrates (McDonagh 2001), fish (Yamaguchi et al. 1976), and lizards (Austin and Jessing 1994)."
"In particular, because Village Weavers tend to nest in isolated trees and denude the vegetation around their nests (probably for predator-avoidance and mate-attraction functions; Collias and Collias 1959, 1969, 1970), their globular nests are commonly exposed to direct light throughout the day. The females generally lay eggs when the nests are still green (Jacobs et al. 1978); given the translucence of the nesting materials, the light environment of the nest’s interior is blue-green, similar to a forest shade as described by Endler (1993). Blue-green eggs in such an environment would reflect light across the visible spectrum in proportion to the incident light intensity and would block UV transmittance as well."
Also relevant to the story is that when the eggshells are blue, their entire body is blue; not just a thin pigmented outer layer (like those deep brown eggshells). I recently added a quote by Albert Szent-Györgyi about chlorophyll being a green pigment to allow leaves to absorb red light better - in the case of eggshells, as the author stated, there must be a balance: if the pigment starts to become too dark, it starts absorbing more than reflecting and overheating the interior; the green-blue light coloration not only (theoretically) reflects well but also filters the desired spectrum. If this adaptation was just for the purpose of camouflaging the eggs, a thin outer layer would suffice.
