Comparing Aerodynamic Efficiency in Birds and Bats Suggests Better Flight Performance in Birds

Flight is one of the energetically most costly activities in the animal kingdom, suggesting that natural selection should work to optimize flight performance. The similar size and flight speed of birds and bats may therefore suggest convergent aerodynamic performance; alternatively, flight performance could be restricted by phylogenetic constraints. We test which of these scenarios fit to two measures of aerodynamic flight efficiency in two passerine bird species and two New World leaf-nosed bat species. Using time-resolved particle image velocimetry measurements of the wake of the animals flying in a wind tunnel, we derived the span efficiency, a metric for the efficiency of generating lift, and the lift-to-drag ratio, a metric for mechanical energetic flight efficiency. We show that the birds significantly outperform the bats in both metrics, which we ascribe to variation in aerodynamic function of body and wing upstroke: Bird bodies generated relatively more lift than bat bodies, resulting in a more uniform spanwise lift distribution and higher span efficiency. A likely explanation would be that the bat ears and nose leaf, associated with echolocation, disturb the flow over the body. During the upstroke, the birds retract their wings to make them aerodynamically inactive, while the membranous bat wings generate thrust and negative lift. Despite the differences in performance, the wake morphology of both birds and bats resemble the optimal wake for their respective lift-to-drag ratio regimes. This suggests that evolution has optimized performance relative to the respective conditions of birds and bats, but that maximum performance is possibly limited by phylogenetic constraints. Although ecological differences between birds and bats are subjected to many conspiring variables, the different aerodynamic flight efficiency for the bird and bat species studied here may help explain why birds typically fly faster, migrate more frequently and migrate longer distances than bats

Dark Matter in the Milky Way's Dwarf Spheroidal Satellites

The Milky Way's dwarf spheroidal satellites include the nearest, smallest and least luminous galaxies known. They also exhibit the largest discrepancies between dynamical and luminous masses. This article reviews the development of empirical constraints on the structure and kinematics of dSph stellar populations and discusses how this phenomenology translates into constraints on the amount and distribution of dark matter within dSphs. Some implications for cosmology and the particle nature of dark matter are discussed, and some topics/questions for future study are identified.Comment: A version with full-resolution figures is available at http://www.cfa.harvard.edu/~mwalker/mwdsph_review.pdf; 70 pages, 22 figures; invited review article to be published in Vol. 5 of the book "Planets, Stars, and Stellar Systems", published by Springe

Mass Spectrometric Strategies to Improve the Identification of Pt(II)-Modification Sites on Peptides and Proteins

To further explore the binding chemistry of cisplatin (cis-Pt(NH3)2Cl2) to peptides and also establish mass spectrometry (MS) strategies to quickly assign the platinum-binding sites, a series of peptides with potential cisplatin binding sites (Met(S), His(N), Cys(S), disulfide, carboxyl groups of Asp and Glu, and amine groups of Arg and Lys, were reacted with cisplatin, then analyzed by electron capture dissociation (ECD) in a Fourier transform ion cyclotron resonance mass spectrometer (FT-ICR MS). Radical-mediated side-chain losses from the charge-reduced Pt-binding species (such as CH3S(•) or CH3SH from Met, SH(•) from Cys, CO2 from Glu or Asp, and NH2(•) from amine groups) were found to be characteristic indicators for rapid and unambiguous localization of the Pt-binding sites to certain amino acid residues. The method was then successfully applied to interpret the top-down ECD spectrum of an inter-chain Pt-crosslinked insulin dimer, insulin + Pt(NH3)2 + insulin (>10 kDa). In addition, ion mobility MS shows that Pt binds to multiple sites in Substance P, generating multiple conformers, which can be partially localized by collisionally activated dissociation (CAD). Platinum(II) (Pt(II)) was found to coordinate to amine groups of Arg and Lys, but not to disulfide bonds under the conditions used. The coordination of Pt to Arg or Lys appears to arise from the migration of Pt(II) from Met(S) as shown by monitoring the reaction products at different pH values by ECD. No direct binding of cisplatin to amine groups was observed at pH 3 ~ 10 unless Met residues were present in the sequence, but noncovalent interactions between cisplatin hydrolysis and amination [Pt(NH3)4](2+) products and these peptides were found regardless of pH