Different types of response to selection for sex ratio in the flour beetle Tribolium castaneum

Abstract

In an attempt to investigate the genetic basis of sex ratio, three wild populations and a synthetic population assembled from beetles collected all over Israel, were employed in a two way selection program for high and for low sex ratio. Different types of response to selection have been demonstrated by the four populations, revealing different modes of inheritance. In the synthetic population the selection was successful. Of the three wild popu-lations, the first did not respond to selection, the second responded in one replica but exhibited consistent negative response in the other replica and in the third population, both positive and negative responses were observed in the various lines. In the lines where selection for high proportion of females was successful (especially in the synthetic popu-lation) a small decrease in the number of offspring was observed, indicating the existence of deleterious genes. High proportion of females may be a consequence of X-linked dele-terious genes. Therefore, the evidence for the existence of additive genetic variation for sex ratio does not come from the lines successfully selected for high proportion of females, but from the fact that of the successfully selected lines, about half were successful in achieving a high proportion of males.