Direct and Correlated Responses to Selection for Body Size and Oxygen Consumption in Tribolium

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Abstract
Between family selection was applied to four lines of Tribolium castaneum originating from the same base population to evaluate direct and correlated responses in body size and metabolic activity. Each line consisted of 24 full-sib families, and selection was performed at an intensity of 25% for six generations. Selection criteria were: Line 1 - low oxygen consumption per unit body weight at 12 days of age (02/mg), Line 2 — high 12-day larva weight, Line 3 — high 18-day pupa weight, and Line 4 — randomly selected. Significant direct responses were observed in all three lines; realized heritabilities were .44 ± .07, .20 ± .04 and .36 ± .04 for 02/mg, larva weight and pupa weight, respectively. Significant correlated responses were observed between larva and pupa weight, and between pupa weight and 02/mg. Asymmetry in the realized genetic correlations, particularly for pupa weight and 02/mg, indicated that different genetic systems responded to selection when selection criteria were interchanged. The growth curve response of the lines at generation 6 indicated that the developmental time had increased in lines 1 and 3 as compared to line 4, whereas line 2 realized no major developmental change as a consequence of selection. The cessation of response for low 02/mg in the early generations of selection was attributed to a probable approach to a physiological limit in metabolic activity. Causes of asymmetry in correlated responses between pupa weight and 02/mg are discussed in terms of the biological efficiency of the organisms. Inferences are made concerning further applications of the present findings to selection studies of growth in warm blooded organisms in which the objective is to obtain larger but metabolically more efficient animals. Copyright © 1976. American Society of Animal Science . Copyright 1976 by American Society of Animal Science