Natural selection for covariation in growth components in Tribolium castaneum

Abstract

The relationships between various components of growth were studied, both at the intra- and inter-populational levels, in twelve laboratory populations of Tribolium castaneum with widely different geographic backgrounds. The components of growth related to body weight — at the 13th day of larval life, Lw, at the first day of pupal life, Pw, at the first day of adult life, Aw, — and to developmental time — at pupation, Pt, at emergence of the adults, At. The relationships between those traits, presumably brought about by natural selection, were compared with similar relationships as disclosed in a study using lines artificially selected for some growth components. The correlations between Pw and Aw and between Pt and At are positive in both naturally and artificially selected populations. This is due to the fact that the rate of decrease in weight between Pw and Aw depends on Pw and to the fact that the developmental time between Pt and At is constant. The consistent significant correlation between growth rate, Lw, and both Pt and At contrasts with the absence of association between Lw and either Pw or Aw. This indicates that the rate of growth relates to developmental time and not to the final body weight. This is confirmed by the lack of consistent correlations, both at the intra- and inter-populational level, between weight, Pw and Aw, and developmental time, Pt and At. The balance achieved between those components of growth are discussed in terms of natural versus artificial selection and their bearing on various triats related to fitness are analyzed.