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Abstract Traits that have lost function sometimes persist through evolutionary time. Persistence may occur if there is not enough standing genetic variation for the trait to allow a response to selection, if selection against the trait is weak relative to drift, or if the trait has a residual function. To determine the evolutionary processes shaping whether nonfunctional traits are retained or lost, we investigated short stamens in 16 populations of Arabidopsis thaliana along an elevational cline in northeast Spain. A. thaliana is highly self-pollinating and prior work suggests short stamens do not contribute to self-pollination. We found a cline in short stamen number from retention of short stamens in high-elevation populations to incomplete loss in low-elevation populations. We did not find evidence that limited genetic variation constrains short stamen loss at high elevations, nor evidence for divergent selection on short stamens between high and low elevations. Finally, we identified loci associated with short stamens in northeast Spain that are different from loci associated with variation in short stamens across latitudes from a previous study. Overall, we did not identify the evolutionary mechanisms contributing to an elevational cline in short stamen number so further research is clearly warranted. 

Abstract The spatiotemporal genetic variation at early plant life stages may substantially affect the natural recolonization of human-altered areas, which is crucial to understand plant and habitat conservation. In animal-dispersed plants, dispersers’ behavior may critically drive the distribution of genetic variation. Here, we examine how genetic rarity is spatially and temporally structured in seedlings of a keystone pioneer palm ( Chamaerops humilis ) and how the variation of genetic rarity could ultimately affect plant recruitment. We intensively monitored the seed rain mediated by two medium-sized carnivores during two consecutive seasons in a Mediterranean human-altered area. We genotyped 143 out of 309 detected seedlings using 12 microsatellite markers. We found that seedlings emerging from carnivore-dispersed seeds showed moderate to high levels of genetic diversity and no evidence of inbreeding. We found inflated kinship among seedlings that emerged from seeds within a single carnivore fecal sample, but a dilution of such FSGS at larger spatial scales (e.g. latrine). Seedlings showed a significant genetic sub-structure and the sibling relationships varied depending on the spatial scale. Rare genotypes arrived slightly later throughout the dispersal season and tended to be spatially isolated. However, genetic rarity was not a significant predictor by itself which indicates that, at least, its influence on seedling survival was smaller than other spatiotemporal factors. Our results suggest strong C. humilis resilience to genetic bottlenecks due to human disturbances. We highlight the study of plant-animal interactions from a genetic perspective since it provides crucial information for plant conservation and the recovery of genetic plant resilience. 

Abstract Evolutionary change begins at the population scale. Therefore, understanding adaptive variation requires the identification of the factors maintaining and shaping standing genetic variation at the within‐population level. Spatial and temporal environmental heterogeneity represent ecological drivers of within‐population genetic variation, determining the evolutionary trajectory of populations along with random processes. Here, we focused on the effects of spatiotemporal heterogeneity on quantitative and molecular variation in a natural population of the annual plant Arabidopsis thaliana . We sampled 1093 individuals from a Spanish A. thaliana population across an area of 7.4 ha for 10 years (2012–2021). Based on a sample of 279 maternal lines, we estimated spatiotemporal variation in life‐history traits and fitness from a common garden experiment. We genotyped 884 individuals with nuclear microsatellites to estimate spatiotemporal variation in genetic diversity. We assessed spatial patterns by estimating spatial autocorrelation of traits and fine‐scale genetic structure. We analysed the relationships between phenotypic variation, geographical location and genetic relatedness, as well as the effects of environmental suitability and genetic rarity on phenotypic variation. The common garden experiment indicated that there was more temporal than spatial variation in life‐history traits and fitness. Despite the differences among years, genetic distance in ecologically relevant traits (e.g. flowering time) tended to be positively correlated to genetic distance among maternal lines, while isolation by distance was less important. Genetic diversity exhibited significant spatial structure at short distances, which were consistent among years. Finally, genetic rarity, and not environmental suitability, accounted for genetic variation in life‐history traits. Synthesis . Our study highlighted the importance of repeated sampling to detect the large amount of genetic diversity at the quantitative and molecular levels that a single A. thaliana population can harbour. Overall, population genetic attributes estimated from our long‐term monitoring scheme (genetic relatedness and genetic rarity), rather than biological (dispersal) or ecological (vegetation types and environmental suitability) factors, emerged as the most important drivers of within‐population structure of phenotypic variation in A. thaliana . 

Abstract Population differentiation is a pervasive process in nature. At present, evolutionary studies on plant population differentiation address key questions by undertaking joint ecological and genetic approaches and employing a combination of molecular and experimental means. In this special issue, we gathered a collection of papers dealing with various ecological and genetic aspects of population differentiation in plants. In particular, this special issue encompasses eight research articles and two reviews covering a wide array of worldwide environments, plant functional types, genetic and genomic approaches, and common garden experiments to quantify molecular and/or quantitative trait differentiation in plant populations. Overall, this special issue stresses the validity of traditional evolutionary studies focused on plant populations, whilst emphasizing the integration of classical biological disciplines and state-of-the-art molecular techniques into a unique toolkit for evolutionary plant research. 

Abstract Background Disentangling the drivers of genetic differentiation is one of the cornerstones in evolution. This is because genetic diversity, and the way in which it is partitioned within and among populations across space, is an important asset for the ability of populations to adapt and persist in changing environments. We tested three major hypotheses accounting for genetic differentiation—isolation-by-distance (IBD), isolation-by-environment (IBE) and isolation-by-resistance (IBR)—in the annual plant Arabidopsis thaliana across the Iberian Peninsula, the region with the largest genomic diversity. To that end, we sampled, genotyped with genome-wide SNPs, and analyzed 1772 individuals from 278 populations distributed across the Iberian Peninsula. Results IBD, and to a lesser extent IBE, were the most important drivers of genetic differentiation in A. thaliana . In other words, dispersal limitation, genetic drift, and to a lesser extent local adaptation to environmental gradients, accounted for the within- and among-population distribution of genetic diversity. Analyses applied to the four Iberian genetic clusters, which represent the joint outcome of the long demographic and adaptive history of the species in the region, showed similar results except for one cluster, in which IBR (a function of landscape heterogeneity) was the most important driver of genetic differentiation. Using spatial hierarchical Bayesian models, we found that precipitation seasonality and topsoil pH chiefly accounted for the geographic distribution of genetic diversity in Iberian A. thaliana . Conclusions Overall, the interplay between the influence of precipitation seasonality on genetic diversity and the effect of restricted dispersal and genetic drift on genetic differentiation emerges as the major forces underlying the evolutionary trajectory of Iberian A. thaliana .