Among‐year variation in selection during early life stages and the genetic basis of fitness in Arabidopsis thaliana

Abstract

Incomplete information regarding both selection regimes and the genetic basis of fitness limits our understanding of adaptive evolution. Among-year variation in the genetic basis of fitness is rarely quantified, and estimates of selection are typically based on single components of fitness, thus potentially missing conflicting selection acting during other life-history stages. Here, we examined among-year variation in selection on a key life-history trait and the genetic basis of fitness covering the whole life cycle in the annual plant Arabidopsis thaliana. We planted freshly matured seeds of >200 recombinant inbred lines (RILs) derived from a cross between two locally adapted populations (Italy and Sweden), and both parental genotypes at the native site of the Swedish population in three consecutive years. We quantified selection against the nonlocal Italian genotype, mapped quantitative trait loci (QTL) for fitness and its components, and quantified selection on timing of germination during different life stages. In all 3 years, the local Swedish genotype outperformed the nonlocal Italian genotype. However, both the contribution of early life stages to relative fitness, and the effects of fitness QTL varied among years. Timing of germination was under conflicting selection through seedling establishment vs. adult survival and fecundity, and both the direction and magnitude of net selection varied among years. Our results demonstrate that selection during early life stages and the genetic basis of fitness can vary markedly among years, emphasizing the need for multiyear studies considering the whole life cycle for a full understanding of natural selection and mechanisms maintaining local adaptation.

Root microbiota assembly and adaptive differentiation among European Arabidopsis populations

“…In their native habitats, the two populations are exposed to widely different climates and also to differences in seasonal changes of day length. Previous work has demonstrated that the relative survival of the Italian genotype in Sweden is negatively related to minimum soil temperature in winter 15 , and also that genetic differences in phenological traits such as timing of germination and flowering can explain a substantial portion of selection against the non-local genotype at the two sites 51, 52, 53 . Taken together, our data indicate that differences in climate have been more important than differences in soil and endogenous microbiota for the adaptive divergence between the two study populations.…”

Fitness of reciprocal F1hybrids betweenRhinanthus minorandRhinanthus majorunder controlled conditions and in the field

“…Although we obtained data for the full life cycle of the two parental species and their F1 hybrids, our field experiment only looked 447 at a single habitat type in a single year. This has given us valuable insight into the fitness of these 448 first-generation hybrids, suggesting that they can perform as well as the parent with the best 449 performance in this given situation, but more field transplants are needed to cover the full range of 450 habitat types and to account for variability among years (Postma & Ågren, 2018). Since the 451 formation and establishment of F1 hybrids are clearly not a bottleneck, we will focus our future 452 work on advanced hybrids, including F2 and backcrosses, but also hybrids in natural populations, 453 not only to determine fitness in transplant experiments, but also to identify introgressed loci 454 involved in local adaptation (Martin et al, 2006;Suarez-Gonzalez et al, 2018).…”

Fitness of reciprocal F1 hybrids between Rhinanthus minor and Rhinanthus major under controlled conditions and in the field

“…This gives the advantage of being able to replicate the same genotype in several environments, but the downside is that part of the life cycle, from seed to established young plant, is missing. This can be justified for long‐lived species, but for annual species, including the seed stage is crucial in understanding local adaptation (Postma & Ågren, ).…”

“…This can be justified for long-lived species, but for annual species, including the seed stage is crucial in understanding local adaptation (Postma & Ågren, 2018).…”