Artificial selection on larval growth curves in Tribolium: correlated responses and constraints

Abstract

Body size is often constrained from evolving. Although artificial selection on body size in insects frequently results in a sizable response, these responses usually bear fitness costs. Further, these experiments tend to select only on size at one landmark age, rather than selecting for patterns of growth over the whole larval life stage. To address whether constraints may be caused by larval growth patterns rather than final size, we implemented a functionvalued (FV) trait method of selection, in which entire larval growth curves from Tribolium were artificially selected. The selection gradient function used was previously predicted to give the maximal response and was implemented using a novel selection index in the FV framework. Results indicated a significant response after one generation of selection, but no response in subsequent generations. Correlated responses included increased mortality, increased critical weight, and decreased development time (DT). The lack of response in size and development time after the first generation was likely caused by increased mortality suffered in selected lines; we demonstrated that the selection criterion caused both increased body size and increased mortality. We conclude that artificial selection on continuous traits using FV methods is very efficient and that the constraint of body size evolution is likely caused by a suite of trade-offs with other traits.

Functional Registration and Local Variations: Identifiability, Rank, and Tuning

“…Their analysis of Tribolium growth suggests that these beetles' growth patterns differ from those of other animals with determinate growth (that is, growth that is contained in certain life stages). Usually, the longer the growth period, the larger the maximal mass attained (see Irwin and Carter (2014), and references therein). In Tribolium, however, it seems that beetles that tend to grow faster, and thus have a shorter growth period, also tend to attain larger size (e.g.…”

Variation and Evolution of Function-Valued Traits

“…Ignoring and accounting for individuals in functional data set. Both panels, as well as those in Figure 2, show the same growth trajectory data, described in Supplemental Appendix 1, which consists of mass measurements collected from eight full siblings who were included in a study population of the flour beetle Tribolium castaneum (for details, see Irwin & Carter 2014). Supplemental Appendix 1 also details the analyses step by step and includes the R code used to generate the plots displayed in this figure and in Figures 2 and 3.…”

Tribolium beetles as a model system in evolution and ecology

“…Lines selected for low dispersal propensity have greater longevity, poorer flight ability, are better competitors, develop more quickly and have longer generation times than dispersers (e.g., Zirkle et al 1988 ). Some of these associations between traits can limit the response to selection (Irwin and Carter 2014 ), and attempts to break the correlations of pairs of traits through artificial selection have failed (Bell and Burris 1973 ; Tigreros and Lewis 2011 ).…”