We study the theoretical properties of the regular spacings found in the oscillation spectra of δ Scuti stars. A linear relation between the large separation and the mean density is predicted to be found in the low-frequency domain (i.e. radial orders spanning from 1 to 8, approximately) of the main-sequence δ Scuti stars' oscillation spectrum. This implies an independent direct measure of the average density of δ Scuti stars, analogous to that of the Sun, and places tight constraints on the mode identification and hence on the stellar internal structure and dynamics, and allows a determination the radii of planets orbiting around δ Scuti stars with unprecedented precision. This opens the way for studying the evolution of regular patterns in pulsating stars, and its relation to stellar structure and evolution.

Taking care of offspring suffering a long-term illness such as schizophrenia is one of the more stressful life experiences. Care conditions may act as a protective factor in the health of the caregiver. The present study assesses heart rate (HR), blood pressure (BP), and mood responses to psychosocial stress in 16 mothers receiving specialised support for the care of their offspring (CARE+) and in 11 mothers caring for their offspring without support (CARE−). The CARE− group take care of less functional and more symptomatic offspring; and display higher basal, but lower HR, responses after stress than the CARE+ group. No significant group effects were found for BP. For mood states, there were significant decreases in the anger subscale in the CARE− group that were not found in the CARE+ group. HR was related to active and passive coping styles, trait anxiety, and years spent providing care. In the total sample, other significant relationships between cardiovascular responses and life events and personality traits have been found. In sum, the data suggests that specialised support for patients may modulate cardiovascular responses to repeated stress in caregivers.

Experiments were designed to test in Drosophila melanogaster the effect of mating type at the Sod locus on fertility and viability. The experiments show that fertility is neither additive (or multiplicative) nor symmetric, i.e. that the fertility of a mating type cannot be predicted from the average fertility of the two genotypes involved in the mating. There is no significant male x female interaction with respect or progeny viability; but the interaction is significant for productivity, i.e. when fertility and viability are jointly taken into account. There is overdominance with respect to female fertility, but not with respect to male fertility or to viability. There also is alloprocoptic selection with respect to fertility and with respect to productivity, i.e. matings between like homozygotes are less fertile and productive than matings between dissimilar homozygotes. Selection at the Sod locus yields stable polymorphic equilibria, with the frequency of the F allele predicted at P = 0·641 or 0·695, respectively for low and high larval density.

RNA viruses consist of populations of extremely high genetic heterogeneity called quasispecies. Based on theoretical considerations, it has been suggested that the unit of selection in such complex genetic populations is not the single viral particle but a set of genetically related particles which form the quasispecies. In the present study we carried out a set of experiments with the vesicular stomatitis virus (VSV) dealing with the evolution of life-history characters under selection acting at two factors either in the same or in opposite directions. The two factors at which selective pressure is applied are the individual and the group. We show evidence that group selection modulates the virulence of VSV populations, in opposition to an unlimited increase in virulence by competitive optimization promoted by individual selection. The results are of relevance for understanding the evolution of parasite virulence.