The difference of pupa weight measurements in Tribolium and its effects on selection responses

Possible causes of asymmetrical direct and indirect selection responses in Tribolium which were observed in a series of various experiments have been investigated. In some experiments the pupae were weighed just after pupation and in others they were weighed on the 20th day of incubation. Weight loss between pupation time and the 20th day of incubation as well as systematic differences in weight between individuals, pupating at successive ages are considered to be responsible for the asymmetry. The concept of unconscious secondary selection was introduced to interpret the asymmetrics of realized heritability and genetic correlation observed in two-way selection experiments.