Time: 2018-04-20 16:00
City: Wageningen & Ultuna
Location: Video brodcast to room Yggdrasil in VHC, Ultuna
Marjanović, J. (2018). Genetics of inherited variability. Increasing uniformity by reducing competition. Joint PhD thesis, Swedish University of Agricultural sciences, Uppsala, Sweden and Wageningen University, the Netherlands.
Social interactions are common for all living organisms. In animal breeding, these interactions are of interest as they are often source of indirect genetic effects (IGEs). An IGE is a heritable effect of one individual on the trait value of another individual. Both direct genetic effects of own genes and IGEs determine the potential of a trait to respond to selection. In aquaculture species and some plants, social interactions have an additional consequence – competition for the resources inflates variability of trait values among individuals. The phenotypic variability of a genotype has been studied as a quantitative trait in itself, and is often referred to as inherited variability. This thesis focusses on genetics of inherited variability with main interest in the relationship between competition (i.e., IGEs) and variability. In the thesis, we used Nile tilapia as a model species. Analyzing the real data, we found that variability of body weight and body size traits in Nile tilapia is heritable with substantial genetic component, which offers possibilities for improvement of uniformity by means of genetic selection. To study genetic relationship between social interactions and variability, we developed a quantitative genetic model that integrates both phenomena. In this model, competition between social partners leads to divergence of their phenotypes (e.g., body weight) over their life time. The effects of competition in the model are heritable and can evolve. These effects comprise direct genetic effect of the focal individual and IGE of its social partner. With simulation study we showed that model yields increased variability of body weight with increase of competition, similar to what is observed in real aquaculture populations. Selection for cooperation will therefore lead to decreased variability. These findings suggest that IGEs may be creating an entire level of genetic variation in variability, that has so far been overlooked. Using existing statistical models for inherited variability and trait values we show that direct genetic effect of competition on variability could be captured with direct model of inherited variability, and similarly, IGEs of competition could be captured with indirect model of inherited variability. According to kin selection theory individuals should show better social behavior, i.e., less competition towards relatives, which should be reflected on their body weight and variability of body weight. We tested this hypothesis by comparing two treatments in an experiment: rearing of fish in kin groups vs. rearing in non-kin groups. Results showed that individuals had significantly higher body weight in groups composed of kin, however, there was no difference in variability of body weight between the two treatments. Findings of this thesis demonstrate that variability of trait values is heritable and that genetic variation in variability may comprise not only direct genetic effects but also IGEs. Studies focusing on evolution of variability/uniformity, therefore, need to consider IGEs.
ISBN (print version): 978-91-7760-172-2
ISBN (electronic version): 978-91-7760-173-9