Mobility of Membrane Lipids and Proteins at the Animal and Vegetal Pole of the Sea Urchin Egg

We have compared the mobility of a fluorescent lipid analogue and of fluorescently labeled membrane proteins at the animal and vegetal poles of the egg of the sea urchin Paracentrotus lividus. Translational diffusion coefficients have been measured by fluorescence microphotolysis ("photo-bleaching") on the egg which was rotated on its poles. Lipid and protein diffusion coefficients averaged 0.8 μm²/sec and 0.04 μm²/sec, respectively at both animal and vegetal pole of the egg. Substances which were known to animalize (Zn⁺⁺) or vegetalize (Li⁺) the sea urchin egg had no significant effect on protein diffusion coefficients.     

Münch,morphology, microfluidics – our structural problem with the phloem

The sieve tubes of the phloem are enigmatic structures. Their role as channels for the distribution of assimilates was established in the 19th century, but their sensitivity to disturbations has hampered the elucidation of their transport mechanisms and its regulation ever since. Ernst Münch's classical monograph of 1930 is generally regarded as the first coherent theory of phloem transport, but the ‘Münchian’ pressure flow mechanism had been discussed already before the turn of the century. Münch's impact rather rested on his simple physical models of the phloem that visualized pressure flow in an intuitive way, and we argue that the downscaling of such models to realistic, low‐Reynolds‐number sizes will boost our understanding of phloem transport in this century just as Münch's models did in the previous one. However, biologically meaningful physical models that could be used to test predictions of the many existing mathematical models would have to be designed in analogy with natural phloem structures. Unfortunately, the study of phloem anatomy seems in decline, and we still lack basic quantitative data required for evaluating the plausibility of our theoretical deductions. In this review, we provide a subjective overview of unresolved problems in angiosperm phloem structure research within a functional context.     

Long‐distance call evolution in the Felidae: effects of body weight,habitat, and phylogeny

Long‐distance calls used for mate attraction and territorial spacing are distinctive signals in the felid vocal repertoire. Their evolution is subject to natural and sexual selection, as well as various constraints. Body size is an important morphological constraint, with the scaling of the spectral characteristics of a species' vocalizations with its body size being established for several vertebrate groups. Alternatively, the structure of long‐distance calls may have been optimized for transmission in species' habitats (acoustic adaptation hypothesis). The present study assessed whether the mean dominant frequency of long‐distance calls in the Felidae (approximately 70% of all species incorporated) is influenced by the species' body size and/or conforms to the acoustic adaptation hypothesis. After controlling for phylogenetic relationships, we found a significant correlation between mean dominant frequency of a taxon's long‐distance calls and conditions for sound transmission in its habitat type (‘open/heterogeneous’ versus ‘dense’), although no significant influence of body size. Taxa living in more open habitat types have long‐distance calls with significantly lower mean dominant frequencies than those living in dense habitats. The result obtained in the present analysis is fairly robust against random removal of single or few taxa from the data, and also against the use of different branch‐length transformation models in phylogenetic regression. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 101 , 487–500.