COCCIDIOIDOMYCOSIS IN SAN FERNANDO VALLEY—Report of a Study Carried Out in 1951-1952

Four cases of benign pulmonary coccidioidomycosis occurred during May 1951 among some 35 teenage students at a boarding school and farm for boys that occupies 30 acres in the northwestern section of the San Fernando Valley within the City of Los Angeles.Epidemiological and serological study of the patients yielded evidence that exposure had occurred on the farm or nearby.Correlation of results of skin testing for sensitivity to coccidioidin among students over the subsequent months and of serologic studies in cases in which there was positive reaction to skin tests indicated exposure to coccidioides during the time the subjects were in residence at the school. In addition, two boys had conversion from negative to positive reaction to coccidioidin while they were in residence.     

Convergence of the age structure: Applications of the projective metric

This paper states necessary and sufficient conditions for the convergence of the age structure (in a discrete time, one-sex model of population growth); it also contains a new and simple proof of the weak ergodic theorem of stable population theory. The main tool used to attain these results is Hilbert's notion of the projective metric. This metric provides a way of defining the distance between positive vectors in $\text{R}$ⁿ which has two important features: First, the distance between any two positive vectors depends only on the rays on which the vectors lie; and, second, positive matrices act as contractions in this metric.     

Absence of direct sexual selection for parasitoid encapsulation in Drosophila melanogaster

Resistance against parasites may play a role in female mate choice, especially if males that have actually survived parasitism can be discriminated from males that have not been parasitised. Larvae of several Drosophila species are subject to attack by hymenopteran parasitoids, but have the ability to kill the parasitoid egg through the process of encapsulation. Because an encapsulated egg remains visible in the abdomen of the adult fly throughout its life, its presence in a male signals to a female that the male has the genes to survive parasitism. The hypothesis that females preferentially mate with males bearing an encapsulated egg in their abdomen was tested using D. melanogaster. No indication was found for this female preference. The absence of preference for males with “good genes” could result from sensory constraints in the female or a negative correlation between encapsulation ability and some other fitness component. Alternatively, it is hypothesised that the black abdominal ends of the males of many species in the melanogaster-group evolved to mimic encapsulated eggs, leading to the breakdown of capsule recognition by the female.