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Shell Mass (shell + mass)
Selected AbstractsThe effects of low dietary calcium during egg-laying on eggshell formation and skeletal calcium reserves in the Zebra Finch Taeniopygia guttataIBIS, Issue 2 2001S. JAMES REYNOLDS Many small passerines forage intensively for calcium-rich foods during laying. Increased incidences of shell defects in eggs of small passerines have been reported, particularly in western Europe, and these have been explained in terms of declining calcium availability in soils, resulting from prolonged anthropogenic acid deposition. Studies in the field have provided laying birds, nesting in areas of low calcium availability, with calcium supplements. An alternative approach was adopted in this study by allowing captive Zebra Finches Taeniopygia guttata to lay first clutches on ad libitum calcium, switching them to a low calcium diet for 72 hours for the formation of all but the first egg of the second clutch and reinstating ad libitum calcium for the final clutch. Control females had access to ad libitumcalcium for all three clutches. Clutch sizes did not vary significantly between birds on low calcium and controls. The former took over three days longer to lay clutch 3 than did controls but the difference was not statistically significant. Birds on low calcium laid eggs that declined in shell ash mass with laying sequence, indicating that birds may have been calcium-limited. Although not statistically significant, eggshell thickness also declined with laying sequence in clutches laid by females on low calcium. The remaining egg measurements (shell mass, shell surface area and volume] of clutches laid by birds on low calcium did not differ significantly from those of controls. Furthermore, females on low calcium did not resort to skeletal reserves to provide sufficient calcium for egg formation. Dietary calcium appears to be of paramount importance in providing sufficient calcium for clutch formation. [source] Mechanism of a plastic phenotypic response: predator-induced shell thickening in the intertidal gastropod Littorina obtusataJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 3 2007J. I. BROOKES Abstract Phenotypic plasticity has been the object of considerable interest over the past several decades, but in few cases are mechanisms underlying plastic responses well understood. For example, it is unclear whether predator-induced changes in gastropod shell morphology represent an active physiological response or a by-product of reduced feeding. We address this question by manipulating feeding and growth of intertidal snails, Littorina obtusata, using two approaches: (i) exposure to predation cues from green crabs Carcinus maenas and (ii) reduced food availability, and quantifying growth in shell length, shell mass, and body mass, as well as production of faecal material and shell micro-structural characteristics (mineralogy and organic fraction) after 96 days. We demonstrate that L. obtusata actively increases calcification rate in response to predation threat, and that this response entails energetic and developmental costs. That this induced response is not strictly tied to the animal's behaviour should enhance its evolutionary potential. [source] Distant future of the Sun and Earth revisitedMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2008K.-P. Schröder ABSTRACT We revisit the distant future of the Sun and the Solar system, based on stellar models computed with a thoroughly tested evolution code. For the solar giant stages, mass loss by the cool (but not dust-driven) wind is considered in detail. Using the new and well-calibrated mass-loss formula of Schröder & Cuntz, we find that the mass lost by the Sun as a red giant branch (RGB) giant (0.332 M,, 7.59 Gyr from now) potentially gives planet Earth a significant orbital expansion, inversely proportional to the remaining solar mass. According to these solar evolution models, the closest encounter of planet Earth with the solar cool giant photosphere will occur during the tip-RGB phase. During this critical episode, for each time-step of the evolution model, we consider the loss of orbital angular momentum suffered by planet Earth from tidal interaction with the giant Sun, as well as dynamical drag in the lower chromosphere. As a result of this, we find that planet Earth will not be able to escape engulfment, despite the positive effect of solar mass loss. In order to survive the solar tip-RGB phase, any hypothetical planet would require a present-day minimum orbital radius of about 1.15 au. The latter result may help to estimate the chances of finding planets around white dwarfs. Furthermore, our solar evolution models with detailed mass-loss description predict that the resulting tip-AGB (asymptotic giant branch) giant will not reach its tip-RGB size. Compared to other solar evolution models, the main reason is the more significant amount of mass lost already in the RGB phase of the Sun. Hence, the tip-AGB luminosity will come short of driving a final, dust-driven superwind, and there will be no regular solar planetary nebula (PN). The tip-AGB is marked by a last thermal pulse, and the final mass loss of the giant may produce a circumstellar (CS) shell similar to, but rather smaller than, that of the peculiar PN IC 2149 with an estimated total CS shell mass of just a few hundredths of a solar mass. [source] Density gradients in Galactic planetary nebulaeMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2007J. P. Phillips ABSTRACT Certain hydrodynamic models of planetary nebulae (PNe) suggest that their shells possess appreciable radial density gradients. However, the observational evidence for such gradients is far from clear. On the one hand, Taylor et al. claim to find evidence for radio spectral indices 0.6 < , < 1.8, a trend which is taken to imply a variation ne,r,2 in most of their sample of PNe. On the other hand, Siódmiak & Tylenda find no evidence for any such variations in density; shell inhomogeneities, where they occur, are primarily attributable to ,blobs or condensations'. It will be suggested that both of these analyses are unreliable, and should be treated with a considerable degree of caution. A new analysis within the log(F(5 GHz)/F(1.4 GHz)),log(TB(5 GHz)) plane will be used to show that at least 10,20 per cent of PNe are associated with strong density gradients. We shall also show that the ratio F(5 GHz)/F(1.4 GHz) varies with nebular radius; an evolution that can be interpreted in terms of varying shell masses, and declining electron densities. [source] | ||||||||||