Mechanisms for frequency-dependent mating success

We consider ways in which non-frequency-dependent processes could generate negatively frequency-dependent male mating success (the rare male effect). Various forms of male competition and female preference could produce the phenomenon, and further experiments are needed to examine their occurrence. We conclude that the rare male effect is likely to be of limited evolutionary relevance.     

The Rat Populations of NIMH: Density, Reproduction, and the Neocortex

Investigations of the effects of crowding on social behaviorhas long been a major focus of the research on rodent populationsconducted in the laboratory of John B. Calhoun, at the NationalInstitute of Mental Health. In these studies, rats living undercrowded conditions exhibited many behavioral abnormalities,including poor parental behavior, and excessive aggression.These behavior patterns are similar to those displayed by ratswith neocortex damage except that the latter were tested undercontrolled, uncrowded conditions. An experiment was designedto examine the concomitant effects of forebrain lesions andpopulation density upon a rat's capacity to cope with socialcomplexity. The behaviors of rats with less than 50 percentof the normal neocortex, resulting from prenatal chemical treatment,were compared at two population densities to similar groupsof normal rats. The micrencephalic rats were initially and generallyless capable parents and were more aggressive than normals.In both types of rats, females in populations of eight bisexualpairs reared proportionally fewer of their offspring to weaningage than females in populations of four pairs. The overall reproductivesuccess of normal rats at the higher population density wasas poor as that of the micrencephalic rats at the lower populationdensity. These results have been interpreted as showing thatrats are sensitive to differences in population density evenat relatively low absolute population sizes, and that increasedpopulation density interferes with the capacity of the neocortexto cope with environment complexity.     

The structure of the female reproductiiye system in the Agaonidae (Chalcidoidea,Hymenoptera)

An account is given of the gaster, ovipositor mechanism and reproductive system in female Agaonidae. The structure and possible functions are compared with that of other chalcid families and the phylogenetic relationships of the group are discussed.