Crossbred response from purebred selection, an experimental check on selection theory withTribolium

Two unrelated populations ofTribolium castaneum were subjected to full-sib family selection for purebred 13-day larval weight. Over 30 selection generations, replicate lines became differentiated with respect to the trend of phenotypic variance and the path of response. All lines were responding in the latter generations indicating no tendency toward plateau. Crossbreds between the two populations responded over the total selection period. In the first ten generations, observed crossbred responses were much greater than those predicted by selection theory; it is postulated that additive maternal effects were responsible. In the remaining generations, the agreement between observed and expected response was reasonably good.