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Self/non-self-discrimination by vertebrate immune systems is based on the recognition of the presence of peptides in proteins of a parasite that are not contained in the proteins of a host. Therefore, a reduction of the number of ‘words’ in its own peptide vocabulary could be an efficient evolutionary strategy of parasites for escaping recognition. Here, we compared peptide vocabularies of 30 endoparasitic and 17 free-living unicellular organisms and also eight multicellular parasitic and 16 multicellular free-living organisms. We found that both unicellular and multicellular parasites used a significantly lower number of different pentapeptides than free-living controls. Impoverished pentapeptide vocabularies in parasites were observed across all five clades that contain both the parasitic and free-living species. The effect of parasitism on a number of peptides used in an organism's proteins is larger than effects of all other studied factors, including the size of a proteome, the number of encoded proteins, etc. This decrease of pentapeptide diversity was partly compensated for by an increased number of hexapeptides. Our results support the hypothesis of parasitism-associated reduction of peptide vocabulary and suggest that T-cell receptors mostly recognize the five amino acids-long part of peptides that are presented in the groove of major histocompatibility complex molecules. [ABSTRACT FROM AUTHOR]

Sex of the fetus is genetically determined such that an equal number of sons and daughters are born in large populations. However, the ratio of female to male births across human populations varies significantly. Many factors have been implicated in this. The theory that natural selection should favour female offspring under suboptimal environmental conditions implies that pathogens may affect secondary sex ratio (ratio of male to female births). Using regression models containing 13 potential confounding factors, we have found that variation of the secondary sex ratio can be predicted by seroprevalence of Toxoplasma across 94 populations distributed across African, American, Asian and European continents. Toxoplasma seroprevalence was the third strongest predictor of secondary sex ratio, β = -0.097, P < 0.01, after son preference, β = 0.261, P < 0.05, and fertility, β = -0.145, P < 0.001. Our preliminary results suggest that Toxoplasma gondii infection could be one of the most important environmental factors influencing the global variation of offspring sex ratio in humans. The effect of latent toxoplasmosis on public health could be much more serious than it is usually supposed to be. [ABSTRACT FROM AUTHOR]

Body odour may provide significant cues about a potential sexual partner's genetic quality, reproductive status and health. In animals, a key trait in a female's choice of sexual partner is male dominance but, to date, this has not been examined in humans. Here, we show that women in the fertile phase of their cycle prefer body odour of males who score high on a questionnaire-based dominance scale (international personality items pool). In accordance with the theory of mixed mating strategies, this preference varies with relationship status, being much stronger in fertile women in stable relationships than in fertile single women.

The size stability of natural populations indicates that natality and mortality rates are on average equal. Fine tuning of the two independent processes suggests the existence of a regulating mechanism. Two types of such mechanisms exist. A decrease in the number of organisms can either speed up the natality rate or slow down the mortality rate. The former mechanisms (chemostat-like) acts wherever the population growth is limited by the concentration of a resource. The latter (turbidostat-like) could be suspected whenever the population growth is limited by predators or parasites. Simulation experiments showed that under chemostat-like and turbidostat-like conditions, organisms are selected toward efficiency (grams of biomass produced/grams of resource consumed) and natality rate (grams of biomass/time), respectively. The existence of two types of selection and the nature of parameters that are selected to recall the old idea of r-K strategies. The main difference is that while the old model predicts the existence of r-K continuum, this model shows that the two strategies are exclusive.

A rapid and simple method for the isolation and purification of dsRNA is presented. The crucial step of this method is the extraction of proteins and DNA with acid phenol. After the extraction, only RNA is left in the aquaeous phase. ssRNA contamination of the RNA preparation can be greatly reduced when ammonium sulfate is present during the extraction.

Abstract: An indispensable step of any comparative study is testing the concordance between the distribution of phenetic traits and the evolutionary history of the taxa under study. Here we present a computer program TREEPT which can perform these tasks on the basis of a permutation test. The use of the program was demonstrated on trichomonad drug sensitivity data. The program can also perform permutation tests analogous to the t-test, analysis of variance (ANOVA) and correlation analysis and is available at http://www.natur.cuni.cz/∼ flegr/PROGRAMS/TREEPT.ZIP and http://www.karlin. mff.cuni.cz/-zaboj/treept.