The diet of Emperor Penguins Aptenodytes forsteri in Adelie Land, Antarctica

This first quantitative study of the diet of Emperor penguins is based on 29 stomach contents collected with a water off-loading method in Adelie Land. The Emperor is largely ichthyophagous (65% by number and 95% by weight) and feeds extensively on small nototheniids (97% of the fish are 40–125 mm in overall length). These results and data on meal size and feeding frequency of the chick suggest that Emperors are off-shore foraging birds offering little competition for food with other sea-birds or mammals.     

SCHIZOPTERID BUGS (INSECTA: HETEROPTERA) IN MID-CRETACEOUS AMBERS FROM FRANCE and MYANMAR (BURMA)

Abstract:  Bugs of two new genera and species are described as Buzinia couillardi and Tanaia burmitica . They are preserved in mid-Cretaceous amber from south-west France and northern Myanmar (Burma), respectively ( c . 100 Ma). These are the first formally described fossils of the heteropteran family Schizopteridae. Both belong to the subfamily Hypselosomatinae and are very similar to the extant genus Hypselosoma Reuter, providing evidence for the antiquity and morphological stability of this small bug family and the infraorder Dipsocoromorpha. Given the putative ecology of the fossils, a discussion is provided on the French and Burmese amber forest ecosystems. The geological setting of La Buzinie, a new amber deposit in south-west France that yielded the two specimens of Buzinia couillardi , is outlined.     

A Quantitative Theory of Affinity-driven T Cell Repertoire Selection

Binding of the T cell antigen receptor (TCR) to peptides presented on molecules encoded by major histocompatibility complex (MHC) genes is the key event driving T cell development and activation. Selection of the T cell repertoire in the thymus involves two steps. First, positive selection promotes the survival of cells binding thymic self-MHC-peptide complexes with sufficient affinity. The resulting repertoire is self-MHC restricted: it recognizes foreign peptides presented on self, but not foreign MHC. Second, negative selection deletes cells which may be potentially harmful because their receptors interact with self-MHC-peptide complexes with too high an affinity. The mature repertoire is also highly alloreactive: a large fraction of T cells respond to tissues harboring foreign MHC. We derive mathematical expressions giving the frequency of alloreactivity, the level of self-MHC restriction, and the fraction of the repertoire activated by a foreign peptide, as a function of the parameters driving the generation and selection of the repertoire: self-MHC and self-peptide diversity, the stringencies of positive and negative selection, and the number of peptide and MHC polymorphic residues that contribute to T cell receptor binding. Although the model is based on a simplified digit string representation of receptors, all the parameters but one relate directly to experimentally determined quantities. The only parameter without a biological counterpart has no effect on the model's behavior besides a trivial and easily preventable discretization effect. We further analyse the role of the MHC and peptide contribution to TCR binding, and find that their relative, rather than absolute value, is important in shaping the mature repertoire. This result makes it possible to adopt different physical interpretations for the digit string formalism. We also find that the alloreactivity level can be inferred directly from data on the stringency of selection, and that, in agreement with recent experiments, it is not affected by thymic selection.