Genetic Trade-offs Research Articles

Evolutionary Demography of a Bruchid Beetle. IV. Genetic Trade-Off, Stabilizing Selection and a Model of Optimal Body Size

Body size is generally related to fecundity in arthropods, and in Callosobruchus maculatus (F.) fecundity and juvenile development rate are known to be genetically correlated, probably because both depend on body weight. Here we estimate the form of the genetic dependence on body weight from previously published breeding value plots, and we estimate physiological effects where necessary, to obtain a model of how natural selection affects body size in culture conditions. The genetic trade-off between fecundity and development rate leads to indirect stabilizing selection on female body weight at emergence. The model shows how optimal body weight increases with culture interval. Selection is shown to be weaker at longer culture intervals, so that genetic variation in body weight should there persist longer. Model predictions are shown to be robust by sensitivity analysis, and to fit the available data. Thus, predicted optimal body weights are intermediate, and observed body weights are close to those predicted on the basis of the culture history of the study population. Key-words: Callosobruchus maculatus, development rate, fecundity, life-history theory, optimal body size, stabilizing selection, trade-offs

The effect of new environment on adapted genetic architecture

Central to the study of life cycle evolution is the concept of genetic trade-offs. Genetic trade-offs between life cycle characters develop as a result of the accumulation of genes with antagonistic pleiotropic effects. In the present study a comparison was made between the genetic architecture that had evolved in the ancestral environment and the way that this genetic architecture was disrupted following transfer to a new environment. It was predicted that, in the ancestral environment, genetic trade-offs should have evolved between each life cycle character and, as a result of these genetic trade-offs, significant levels of additive genetic variation should remain despite many generations of selection.Following transfer to a new environment different genes might be expressed. Therefore, it was predicted that in the new environment the levels of additive genetic variation should increase and that the genetic trade-offs should break down. The predictions were well supported by the data.

Genetic Correlations among Life History Characters of Adult Females in the Azuki Bean Weevil, Callosobruchus chinensis (L.) (Coleoptera : Bruchidae)

Negative genetic correlation between reproductive effort and longevity has often been assumed when predicting the structure of the genetic equilibrium state of life history evolution. To examine the validity of this assumption, genetic correlations among life history characters of adult females of the azuki bean weevil, Callosobruchus chinensis (L.) were estimated by sib-analysis. Negative genetic correlations were obtained between fecundity and longevity characters. The most evident negative correlations were between total fecundity and longevity (-0.892). Genetic trade-off seems to exist between fecundity and lifespan characters, supporting the above assumption.

Family mean correlations among fitness components in wild radish: controlling for maternal effects on seed weight

Qualitative estimates of genetic associations among life-history and fitness components are reported for 30 sibships (or families) in a common garden population of Raphanus raphanistrum L. (Brassicaceae: wild radish). Genetic associations are detected in a qualitative way when correlation coefficients among family means are highly significant. In this study, correlation coefficients among family means are compared with phenotypic correlation coefficients and to each other to address three questions: (i) Do strong genetic trade-offs among fitness components exist in wild radish under experimental conditions? (ii) Do qualitative estimates of genetic associations differ from phenotypic correlations? and (iii) Since seed weight is strongly phenotypically correlated with many components of plant performance and since families differ in seed weight because of strong maternal environmental (nongenetic) effects, does controlling for seed weight affect the correlations among family means? Many heritable fitness components were positively correlated among families; however, strong positive phenotypic correlation coefficients were much more common than strong positive family-mean correlation coefficients. No strong negative genetic associations were detected. The tendency for phenotypic correlations to be more positive than family mean correlations is consistent with the expectation that environmental variation generates positive correlations among characters, masking genetically based trade-offs. Partitioning out the effect of seed weight had only a small effect on the magnitude of the among-family correlation coefficients.