Genetic basis of local adaptation and flowering time variation in Arabidopsis lyrata

Abstract

Understanding how genetic variation at individual loci contributes to adaptation of populations to different local environments is an important topic in modern evolutionary biology. To date, most evidence has pointed to conditionally neutral quantitative trait loci (QTL) showing fitness effects only in some environments, while there has been less evidence for single-locus fitness trade-offs. At QTL underlying local adaptation, alleles from the local population are expected to show a fitness advantage. Cytoplasmic genomes also can have a role in local adaptation, but the role of cytonuclear interactions in adaptive differentiation has remained largely unknown. We mapped genomic regions underlying adaptive differentiation in multiple fitness components and flowering time in diverged populations of a perennial plant Arabidopsis lyrata. Experimental hybrids for this purpose were grown in natural field conditions of the parental populations in Norway and North Carolina (NC), USA, and in the greenhouse. We found QTL where high fitness and early flowering were associated with local alleles, indicating a role of different selection pressures in phenotypic differentiation. At two QTL regions, a fitness component showing local adaptation between the parental populations also showed signs of putative fitness trade-offs. Beneficial dominance effects of conditionally neutral QTL for different fitness components resulted in hybrid vigour at the Norwegian site in the F(2) hybrids. We also found that cytoplasmic genomes contributed to local adaptation and hybrid vigour by interacting with nuclear QTL, but these interactions did not show evidence for cytonuclear coadaptation (high fitness of local alleles combined with the local cytoplasm).

Complex Genetic Effects on Early Vegetative Development Shape Resource Allocation Differences BetweenArabidopsis lyrataPopulations

“…QTL for flowering time in Norway were detected on LG1 and LG3, with the former coinciding with the LG1 resource allocation QTL detected in North Carolina ( Figure 8C; Leinonen et al 2013). In both cases, Norway alleles contributed additively to earlier flowering, consistent with the population differences detected in Norway (Leinonen et al 2013).Two QTL regions, on LG1 and LG8, explained much of the cumulative survival variation in each year following the first reproductive season ( Figure 8D; Leinonen et al 2013). These regions corresponded to the LG1 and LG8 resource allocation QTL regions in North Carolina.…”

Early life stages contribute strongly to local adaptation in Arabidopsis thaliana

“…In conclusion, early life stages are known to be under strong selection (15)(16)(17)(18)(19) and to have cascading effects across the whole life cycle (16,20,21), but they are seldom included in studies on the genetic basis of local adaptation (12)(13)(14)(22)(23)(24)(25)(26)(27)(28). By conducting a reciprocal transplant experiment including the whole life cycle and maternal effects, we have shown that selection during early life stages contributes strongly to both the magnitude and the genetic basis of adaptive differentiation among natural populations of A. thaliana.…”

“…The remaining seedling was monitored until fruit maturation. At fruit maturation (April [26][27][28]2013 in Italy, June 24-26, 2013 in Sweden), we recorded the survival (from the moment of thinning of established seedlings until fruit maturation) and fecundity (number of fruits containing viable seeds) of surviving plants. We calculated total fitness as the number of fruits produced per planted viable seed (establishment × survival × fecundity), using the focal plant as a proxy for the survival and fecundity of removed seedlings.…”

“…For instance, field experiments with plants are usually based on the transplantation of seedlings (12)(13)(14)(22)(23)(24)(25)(26)(27)(28) and therefore do not assess the importance of possible adaptive differentiation and genetic tradeoffs expressed at the seed and germination stage. Indirect evidence suggests that the seed stage may contribute considerably to local adaptation.…”

The evolution of quantitative traits in complex environments

“…To appreciate the effects of environmental heterogeneity on the evolution of quantitative traits, we must link classical quantitative genetics to ecology using manipulative experiments in realistic natural settings. Field studies can uncover novel functions of previously characterized genes (Brock et al, 2009), examine how divergent selection contributes to local adaptation at the organismal level (Hall and Willis, 2006), address the genetic basis of adaptive population differentiation (Leinonen et al, 2013), expose genetic correlations among traits that could constrain adaptation (Brock et al, 2009) and reveal whether genetic variation is sufficient to enable evolutionary responses to selection imposed by anthropogenic disturbance (Etterson and Shaw, 2001).…”