Functional Relationship between Skull Form and Feeding Mechanics in Sphenodon, and Implications for Diapsid Skull Development

The vertebrate skull evolved to protect the brain and sense organs, but with the appearance of jaws and associated forces there was a remarkable structural diversification. This suggests that the evolution of skull form may be linked to these forces, but an important area of debate is whether bone in the skull is minimised with respect to these forces, or whether skulls are mechanically “over-designed” and constrained by phylogeny and development. Mechanical analysis of diapsid reptile skulls could shed light on this longstanding debate. Compared to those of mammals, the skulls of many extant and extinct diapsids comprise an open framework of fenestrae (window-like openings) separated by bony struts (e.g., lizards, tuatara, dinosaurs and crocodiles), a cranial form thought to be strongly linked to feeding forces. We investigated this link by utilising the powerful engineering approach of multibody dynamics analysis to predict the physiological forces acting on the skull of the diapsid reptile Sphenodon. We then ran a series of structural finite element analyses to assess the correlation between bone strain and skull form. With comprehensive loading we found that the distribution of peak von Mises strains was particularly uniform throughout the skull, although specific regions were dominated by tensile strains while others were dominated by compressive strains. Our analyses suggest that the frame-like skulls of diapsid reptiles are probably optimally formed (mechanically ideal: sufficient strength with the minimal amount of bone) with respect to functional forces; they are efficient in terms of having minimal bone volume, minimal weight, and also minimal energy demands in maintenance

Coherent Imaging of Biological Samples with Femtosecond Pulses at the Free Electron Laser FLASH

Coherent x-ray imaging represents a new window to imaging noncrystalline, biological specimens at unprecedented resolutions. The advent offree-electron lasers (FEL) allows extremely high flux densities to be delivered to a specimen resulting in stronger scattered signal from these samples to be measured. In the best case scenario, the diffraction pattern is measured before the sample is destroyed by these intense pulses, as the processes involved in radiation damage may be substantially slower than the pulse duration. In this case, the scattered signal can be interpreted and reconstructed to yield a faithful image of the sample at a resolution beyond the conventional radiation damage limit. We employ coherent x-ray diffraction imaging (CXDI) using the free-electron LASer in Hamburg (FLASH) in a non-destructive regime to compare images ofa biological sample reconstructed using different, single, femtosecond pulses of FEL radiation. Furthermore, for the first time, we demonstrate CXDI, in-line holography and Fourier transform holography (FTH) of the same unicellular marine organism using an FEL and present diffraction data collected using the third harmonic of FLASH, reaching into the water window. We provide quantitative results for the resolution of the CXDI images as a function of pulse intensity, and compare this with the resolutions achieved with in-line holography and FTH

Coherent Imaging of Biological Samples with Femtosecond Pulses at the Free Electron Laser FLASH

Coherent x-ray imaging represents a new window to imaging noncrystalline, biological specimens at unprecedented resolutions. The advent offree-electron lasers (FEL) allows extremely high flux densities to be delivered to a specimen resulting in stronger scattered signal from these samples to be measured. In the best case scenario, the diffraction pattern is measured before the sample is destroyed by these intense pulses, as the processes involved in radiation damage may be substantially slower than the pulse duration. In this case, the scattered signal can be interpreted and reconstructed to yield a faithful image of the sample at a resolution beyond the conventional radiation damage limit. We employ coherent x-ray diffraction imaging (CXDI) using the free-electron LASer in Hamburg (FLASH) in a non-destructive regime to compare images ofa biological sample reconstructed using different, single, femtosecond pulses of FEL radiation. Furthermore, for the first time, we demonstrate CXDI, in-line holography and Fourier transform holography (FTH) of the same unicellular marine organism using an FEL and present diffraction data collected using the third harmonic of FLASH, reaching into the water window. We provide quantitative results for the resolution of the CXDI images as a function of pulse intensity, and compare this with the resolutions achieved with in-line holography and FTH

Physical Constraints on the Evolution of Cooperation

The evolution of psychological adaptations for cooperation is still puzzling due to a tendency to frame social interaction in mathematical and game-theoretical terms, without systematically examining its causal structure and underlying mechanisms. Complementarily, empirical approaches to cooperation tend to focus on isolated components of mechanisms without sufficiently indicating how different components are combined into a single mechanism and different mechanisms fit into a single organism. An alternative approach to the evolution of cooperation is proposed, starting from a description of basic physical properties of individuals and their environment, and the limited physical or mechanistic possibilities to generate adaptive responses to those properties. This approach reveals that some forms of symmetrical cooperation do not require mechanisms “specifically designed for” benefiting others, whereas effective helping requires a specific mechanism that relatively unconditionally and persistently responds to the vulnerability of other individuals. Unraveling the causal structure of different types of other-benefiting shows that a mechanism for asymmetrical helping may considerably improve symmetrical cooperation through properties such as tolerance, patience, and the human capacity to experience a wide variety of moral emotions. The proposed mechanistic approach to cooperation provides the mathematical/game-theoretical approach with realistic assumptions about psychological adaptations, and helps to integrate the scattered facts about mechanisms gathered by the empirical approach. It also helps to build bridges between the two approaches by providing a common language for thinking about psychological mechanisms