The Plumage Rainbow
- Guy Riddihough
The plumage of birds ranges from the sublime to the (what some might consider) gaudy. Certainly, birds seem to possess a stunning range of colors in their plumage, with the most striking ones often relating to mate choice and social signaling. These colors probably evolved in response to the capabilities of the avian visual system (avian “color space”).
Stoddard and Prum determined the range of colors (the color gamut) of 965 plumage samples from a wide range of bird species and showed that they occupied a mere 26 to 30% of the available avian color space. Pigment-based colors (often diet-derived) occupied 6.9% of color space (26.7% of the color gamut), whereas structure-based colors (for example, iridescent barbules) occupied 17.9% of color space (and almost 70% of the color gamut): It is in these latter colors that bird plumage diverges most from plant colors. Over evolutionary time, structural colors have dramatically extended the range of plumage coloration mechanisms available to birds. Still, plumage colors only occupy hue “continents” and “archipelagos” in color space between unoccupied regions, with, for example, few purple and fully saturated green colors. Indeed, bird plumages do not include many of the hues available to flowers, likely because certain colors may be either difficult to create or selectively undesirable.
Behav. Ecol. 22, 10.1093/beheco/arr088 (2011).
- Climate Science
- H. Jesse Smith
Stalagmites recovered from caves in southern and eastern Asia contain a remarkable chronicle of changes in rainfall over the course of the last glacial cycle, including millennial-scale warm intervals and more prolonged episodes of cooling called Heinrich events. The oxygen isotope record of those stalagmites has been interpreted as reflecting mostly the amount of East Asian summer monsoonal rainfall there. Things may not be quite what they seem, however, according to a report by Pausata et al., who use a climate model to assess the causes of the observed oxygen isotopic variations during a simulated Heinrich event. They found that Northern Hemispheric cooling during the event weakens the Indian monsoon and shifts water vapor enriched in 18O from India to China. Therefore, they conclude, Chinese stalagmite oxygen isotopes actually record changes in the Indian monsoon over thousand-year time scales.
Nat. Geosci. 4, 10.1038/NGEO1169 (2011).
- Cell Biology
Know Your Place
- Stella M. Hurtley
The Golgi apparatus occupies a central position close to the nucleus in mammalian cells. This localization is determined by the position of the centrosome, the microtubule-organizing center that defines the layout of the cell and is critical for orchestrating mitosis. The importance of Golgi positioning and integrity for a variety of cell polarity–related phenomena has been difficult to distinguish. Hurtado et al. dissected the role of a centrosomal protein involved in Golgi positioning, AKAP450. Expression of a fragment of the protein that contains the Golgi targeting domain dissociated endogenous AKAP450 from the Golgi. Under these circumstances, the Golgi fragmented but, instead of scattering throughout the cytoplasm, the fragments collapsed around the centrosome, possibly because of the failure of the Golgi fragments to nucleate microtubules. Another fragment of AKAP450 had a different effect on Golgi positioning: The Golgi became localized in the cell periphery but reassembled into a ribbon-like morphology reminiscent of its normal unperturbed structure. Although neither fragment significantly perturbed membrane traffic through the Golgi, both fragments inhibited the formation of the primary cilium. Major effects on directional cell migration were observed only when Golgi positioning was disrupted.
J. Cell Biol. 193, 917 (2011).
- Cell Signaling
Keeping Kinases on Target
- L. Bryan Ray
Modification of proteins by protein kinase—mediated covalent phosphorylation regulates almost every biological process in the cell and especially those related to cell division. But with more than 500 kinases in a human cell phosphorylating tens of thousands of proteins, some at multiple sites, how is order maintained? One explanation is that kinases show specificity toward particular sequences in their substrates. Alexander et al. and Kettenbach et al. explored such specificity of five kinases with key roles in controlling cell division. Their phosphoproteomic and peptide screening approaches helped to define the preferred sequences of substrates for these kinases and identified previously unrecognized substrates. Furthermore, Alexander et al. showed that there are also some sequence elements that selectively prevent phosphorylation of a particular substrate by certain kinases. Alexander et al. further proposed that subcellular localization also contributes to specificity, so that kinases that have overlapping preferred motifs are kept spatially separated.
Sci. Sig. 4, rs5; ra42 (2011).
Swimming in Threes
- Jake Yeston
Understanding a liquid at the molecular level is a rather daunting prospect—even small droplets contain a number of molecules too vast for most people to easily imagine, let alone analyze. It turns out, though, that you can get a decent sense of many important properties by thoroughly analyzing the interaction of just a pair of molecules, and then extrapolating that interaction across the whole sample. Pieniazek et al. point out one instance where, although this approach falls short, consideration of three molecules' mutual interaction affords a much better match to experimental data. Specifically, they simulate the structure of a water surface and its associated response to a highly surface-selective vibrational probing technique (sum frequency generation). Past experimental studies in this vein, using isotopically labeled HOD-in-D2O solutions to simplify spectral interpretation, have produced puzzling features attributed to distinct ice-like and bulk liquid–like local arrangements at the interface. The three-body simulations reproduce the experimental data reasonably well and suggest no need to invoke ice-like ordering.
J. Am. Chem. Soc. 133, 10.1021/ja2026695 (2011).
- Caroline Ash
Large life on Earth shows striking gradients of diversity: from the poles to the tropics and from low to high altitude. Whether such large-scale gradients also apply to microorganisms, however, has been controversial. Stomp et al. took advantage of a comprehensive data set collected by the U.S. Environmental Protection Agency in 1973–1975. A range of physicochemical data and phytoplankton was sampled from 540 lakes, three times each year. The data were put through regression analysis to identify the most important local environmental variables affecting species richness, as well as a structural equation model to test for links between biodiversity, environmental variables, and geographical location. Although lake area and depth strongly influenced phytoplankton diversity, there was an overall signal of decreasing diversity as latitude and altitude increased, which reflected the overall topography of the United States. This work, when considered alongside other species richness analyses of microorganisms, suggests that very small organisms are subject to similar constraints governing large-scale distribution as the very large.
Ecology 92, 10.1890/10-1023.1 (2011).
Iron et Al
- Nicholas S. Wigginton
Naturally occurring iron-(hydr)oxide particles have a strong influence over nutrient and contaminant transport in Earth's aqueous surface environments. Most phases have stoichiometrically balanced chemical formulas such as FeOOH and Fe2O3, but ferrihydrite—an abundant yet metastable, poorly crystalline precursor to more thermodynamically stable phases—is not defined by a simple ordering. Furthermore, all natural iron-(hydr)oxides undoubtedly contain numerous internal and adsorbed impurities that have varying effects on reactivity and stability. To understand how these impurities get incorporated into growing particles, Bazilevskaya et al. used a combined experimental and computational approach to track coprecipitation of ferrihydrite with varying amounts of Al3+. When Al3+ was present at low levels, it was incorporated into the ferrihydrite structure; at high Al3+ levels, in contrast, two distinct Al- and Fe-rich phases formed. Computations suggest that when Al-rich ferrihydrite transforms into Al-rich FeOOH over time, Al clusters within the new phase are energetically more favorable than isolated substitutions of Al3+ for Fe3+. In a complementary study, Hansel et al. documented the inhibitory effect of Al-substitution on ferrihydrite transformation. Ferrihydrite was more strongly inhibited from transforming into other, more thermodynamically stable phases when Al was adsorbed on the surface than when it was incorporated into the structure.
Geochim. Cosmochim. Acta 75, 10.1016/j.gca.2011.05.041; 10.1016/j.gca.2011.05.033 (2011).