An experimental test of optimum and desired-gains indexes in Tribolium

Abstract

Three generations of restricted selection index involving pupal weight at 21 days (X1) and adult weight at 31 days (X2) were carried out in each of three replicates of Tribolium castaneum. The efficiency of two restricted indexes-optimum (O) and desired gains (G)-was evaluated experimentally. The optimum index (-0.0260X1 + 0.1551X2) was designed to maximize adult weight while setting the response of pupal weight by a fixed amount The desired-gains index (4.71X1 - 6.26X2) was intended to achieve genetic gains in pupal weight and adult weight at a prechosen ratio of 31. Both methods of selection were considered examples of antagonistic selection, with the positive genetic correlation between pupal and adult weight being very large. The results confirmed theoretical expectations. The optimum index set the response of pupal weight by a fixed amount while increasing adult weight; observed responses in the O line were significant for pupal weight and adult weight. The results from the G line showed that responses approximated a ratio of 61 for pupal weight and adult weight. In this line, the response for pupal weight was very similar to the expected value, and it did not change adult weight significantly. © 1989 The American Genetic Association.