Maternal effort mediates the prevalence of trypanosomes in the offspring of a passerine bird.

The relationships between parental effort, offspring growth, and offspring blood parasitemias are poorly known. We examined the effect of parental effort on offspring size and prevalence of trypanosomes in peripheral blood of nestling Pied Flycatchers Ficedula hypoleuca aged 13 days. Trypanosome infections were likely to be shared by siblings, indicating the role of a common environment and/or shared genes in the susceptibility to infection. Broods infected by trypanosomes had reduced growth, but this was due to decreased parental, especially maternal, energy expenditure in broods with nestlings infected by trypanosomes. There was no association between parental infection with trypanosomes and both their energy expenditure and the infection of their broods. Under stressful conditions caused by low maternal energy expenditure, the immune response of nestlings during growth was probably impaired, in a way analogous to the relapses of blood parasitemias with reproductive effort in breeding animals.

On a common circle: Natural scenes and Gestalt rules

To understand how the human visual system analyzes images, it is essential to know the structure of the visual environment. In particular, natural images display consistent statistical properties that distinguish them from random luminance distributions. We have studied the geometric regularities of oriented elements (edges or line segments) present in an ensemble of visual scenes, asking how much information the presence of a segment in a particular location of the visual scene carries about the presence of a second segment at different relative positions and orientations. We observed strong long-range correlations in the distribution of oriented segments that extend over the whole visual field. We further show that a very simple geometric rule, cocircularity, predicts the arrangement of segments in natural scenes, and that different geometrical arrangements show relevant differences in their scaling properties. Our results show similarities to geometric features of previous physiological and psychophysical studies. We discuss the implications of these findings for theories of early vision.