Hybridization events can increase genetic variation through the introduction of new alleles that can cause transgressive segregation, a process that expands functional trait values that exceed the parental source, or generates new trait values. To test the effect of recombination events and the environment on the variance and traits interaction in hybrids’ phenotypes, we examined how often hybrids are able to exceed or create a novel phenotype from their parents under limiting growing conditions using constructed hybrids of Arabidopsis thaliana. We grew hybrids and their parental ecotypes under three conditions designed to simulate drought, high temperature, or over-wintering in the field. We estimated a phenotypic space of phenology, growth and fitness traits using a non-metric multidimensional scaling (NMDS) approach. We compared mean phenotypic values and estimated heterosis and/or outbreeding depression of 13 F2 hybrid families created from selfed-F1 hybrids of A. thaliana ecotypes that differ in their genetic distance between parents.
Results/Conclusions
We found that some F2 hybrids had a higher mean and variance in bolting speed, height and number of fruits produced than their parental progenitors and that this shift was strongly affected by the environment. The differences in variance were found under control conditions and not under limiting environment conditions such as drought or high temperature. Similarly, F2 hybrids showed evidence of transgressive segregation in phenology, growth and fitness traits across the experimental conditions in which drought promoted transgressive phenotypes. Using a non-metric multidimensional approach, we found that one recombination event is sufficient to generate a new phenotypic space in almost half of the cases. 48% of F2 hybrids shifted their phenotype away from their parental ecotypes across multiple traits. We did not find a strong effect of the environment on the phenotype shift of the hybrids. In this study, we found support for hybridization increases genetic variation and generate novel trait combinations which accelerate evolutionary responsiveness to novel sources of selection, especially when populations are locally adaptive. This study documents how recombination events can increase variation of offspring genotypes, shifting the phenotypes away from their parental ecotypes and in some cases, generating transgressive segregation, heterosis and/or outbreeding depression. We also provide empirical evidence of the effect of different limiting growth conditions on admixed genotypes and their parental ecotypes.