Biology subjects

Lascoux, M.

Publications and source records attributed to Lascoux, M..

29 records · Page 2Linked to original sources

bioRxiv2020

Phenotypic plasticity, population structure and adaptation in a young weed species with a worldwide distribution

The colonization success of a species depends on phenotypic plasticity, adaptive potential and population structure. Assessing their relative contributions during a colonization process is challenging, and a large-scale experiment had yet to be done. In this study, we attempted to tease apart their effects on the fitness of one of the most common plant on Earth, the shepherds purse (Capsella bursa-pastoris), a self-fertilizing and allopolyploid weed, with a worldwide distribution. The overarching goal is to eventually understand how the shepherds purse extensive distribution range was established so rapidly. To do so, we carried out three common gardens, located in Europe, Asia and North America, and measured several life-history traits on field-collected accessions belonging to three distinct genetic clusters (Middle East, Europe, and Asia). Our experiment showed that (i) the success of C. bursa-pastoris is mainly due to its high degree of phenotypic plasticity; and (ii), genetic cluster effect reflected a classic pattern observed in core vs marginal populations, with the Middle Eastern cluster (putative core population) outperforming the European and Asian clusters. This study therefore revealed, in a model species, different relative contributions of plasticity and adaptation to fitness, depending on the population and the time since colonization occurred.

evolutionary biology↗

bioRxiv2020

The selfing syndrome overshadows other differences when comparing fitness across Capsella species

Self-fertilization has recurrently evolved from outcrossing. Self-fertilization provides an advantage in the short-term as individuals do not require a mate to reproduce, but self-fertilization is also associated with both decreased genetic diversity and accumulation of weakly deleterious mutations, which could, however, be alleviated in polyploid selfers. If pollinators are not limited, individual fitness is thus expected to be higher in outcrossers than in selfers. We measured several life history traits in four Capsella species under two different treatments (disturbed and undisturbed) to assess the effects of mating system and ploidy level on reproductive, vegetative and phenological traits. The experiment was carried out outdoor in Northwest Greece, within the range of the obligate outcrossing species, C. grandiflora, so it could be naturally pollinated and its fitness directly compared to that of its self-fertilizing relatives. Disturbance of the environment did not affect the phenotype in any of the four species. However, for most traits the obligate outcrossing species performed better than all selfing ones. In contrast, polyploidy did not seem to confer an advantage in terms of survival or reproduction compared to diploidy. Finally, plants from Asia and northern Europe had lower performances than accessions from southern Europe and the Middle-East.

evolutionary biology↗

bioRxiv2020

An introgressed gene causes meiotic drive in Neurospora sitophila

Meiotic drive elements cause their own preferential transmission following meiosis. In fungi this phenomenon takes the shape of spore killing, and in the filamentous ascomycete Neurospora sitophila, the Sk-1 spore killer element is found in many natural populations. In this study, we identify the gene responsible for spore killing in Sk-1 by generating both long and short-read genomic data and by using these data to perform a genome wide association test. Through molecular dissection, we show that a single 405 nucleotide long open reading frame generates a product that both acts as a poison capable of killing sibling spores and as an antidote that rescues spores that produce it. By phylogenetic analysis, we demonstrate that the gene is likely to have been introgressed from the closely related species N. hispaniola, and we identify three subclades of N. sitophila, one where Sk-1 is fixed, another where Sk-1 is absent, and a third where both killer and sensitive strain are found. Finally, we show that spore killing can be suppressed through an RNA interference based genome defense pathway known as meiotic silencing by unpaired DNA. Spk-1 is not related to other known meiotic drive genes, and similar sequences are only found within Neurospora. These results shed new light on the diversity of genes capable of causing meiotic drive, their origin and evolution and their interaction with the host genome. Significance StatementIn order to survive, most organisms have to deal with parasites. Such parasites can be other organisms, or sometimes, selfish genes found within the host genome itself. While much is known about parasitic organisms, the interaction with their hosts and their ability to spread within and between species, much less is known about selfish genes. We here identify a novel selfish "spore killer" gene in the fungus Neurospora sitophila. The gene appears to have evolved within the genus, but has entered the species through hybridization and introgression. We also show that the host can counteract the gene through RNA interference. These results shed new light on the diversity of selfish genes in terms of origin, evolution and host interactions.

evolutionary biology↗

bioRxiv2019

From drift to draft: How much do beneficial mutations actually contribute to predictions of Ohta’s slightly deleterious model of molecular evolution?

Since its inception in 1973 the slightly deleterious model of molecular evolution, aka the Nearly Neutral Theory of molecular evolution, remains a central model to explain the main patterns of DNA polymorphism in natural populations. This is not to say that the quantitative fit to data is perfect. In a recent study CO_SCPLOWASTELLANOC_SCPLOW et al. (2018) used polymorphism data from D. melanogaster to test whether, as predicted by the Nearly Neutral Theory, the proportion of effectively neutral mutations depends on the effective population size (Ne). They showed that a nearly neutral model simply scaling with Ne variation across the genome could not explain alone the data but that consideration of linked positive selection improves the fit between observations and predictions. In the present article we extended their work in two main directions. First, we confirmed the observed pattern on a set of 59 species, including high quality genomic data from 11 animal and plant species with different mating systems and effective population sizes, hence a priori different levels of linked selection. Second, for the 11 species with high quality genomic data we also estimated the full Distribution of Fitness Effects (DFE) of mutations, and not solely the DFE of deleterious mutations. Both Ne and beneficial mutations contributed to the relationship between the proportion of effectively neutral mutations and local Ne across the genome. In conclusion, the predictions of the slightly deleterious model of molecular evolution hold well for species with small Ne. But for species with large Ne the fit is improved by incorporating linked positive selection to the model.

evolutionary biology↗

bioRxiv2019

Ecological strategy and genetic load in the shepherd's purse (Capsella bursa-pastoris) from the core and the limit of its natural range.

Species range expansion is a complex process whose outcome depends on the interplay of demographic, environmental and genetic factors. In plants, self-fertilizing species that do not require a mate to reproduce usually show higher invasive ability. However, this comes at a cost as both selfing and bottlenecks occurring during colonization lead to an increase in deleterious mutations accumulation (genetic load). Although they are theoretically clearly spelled out, the relationships between genomic and phenotypic characteristics of expanding populations have hitherto rarely been characterized. In the present study we analyzed how different accessions of the shepherds purse, C. bursa-pastoris, coming from the front of colonization or from the core of the natural range performed under increasing density of competitors. We first showed that, as expected, accessions from the front of colonization performed the worst for most life history traits compared with accessions from core populations. Second, competitor density had a negative impact on both vegetative growth and reproductive output in term of fruits production for all accessions. However, somewhat unexpectedly given their higher genetic load and their lower absolute performance, accessions from the front of colonization were less affected by competition than accessions from the core of the species range. This could be due to phenotypic tradeoffs and a shift in phenology that allow the accessions from the front of colonization to avoid competition. These results are discussed in terms of ecological strategies of expanding populations.

evolutionary biology↗

bioRxiv2018

Assessing the potential for assisted gene flow using past introduction of Norway spruce in Southern Sweden: Local adaptation and genetic basis of quantitative traits in trees.

Norway spruce (Picea abies) is a dominant conifer species of major economic importance in Northern Europe. Extensive breeding programs were established to improve phenotypic traits of interest. In southern Sweden seeds used to create progeny tests were collected on about 3000 trees of outstanding phenotype (\"plus\" trees) across the region. Some were of local origin but many were recent introductions from the rest of the natural range. The mixed origin of the trees together with partial sequencing of the exome of >1,500 of these trees and phenotypic data retrieved from the Swedish breeding program offered us a unique opportunity to dissect the genetic basis of local adaptation of three quantitative traits (height, diameter and budburst). Through a combination of multivariate analyses and genome-wide association studies, we showed that there was a very strong effect of geographical origin on growth (height and diameter) and phenology (budburst) with trees from southern origins outperforming local provenances. Association studies also indicated that growth traits were highly polygenic and budburst somewhat less. Hence, our results suggest that assisted gene flow and genomic selection approaches could help alleviating the effect of climate change on P. abies breeding programs in Sweden.

evolutionary biology↗

bioRxiv2018

Towards the new normal: Transcriptomic and genomic changes in the two subgenomes of a 100,000 years old allopolyploid, Capsella bursa-pastoris

Allopolyploidy has played a major role in plant evolution but its impact on genome diversity and expression patterns remains to be understood. Some studies found important genomic and transcriptomic changes in allopolyploids, whereas others detected a strong parental legacy and more subtle changes. The allotetraploid C. bursa-pastoris originated around 100,000 years ago and one could expect the genetic polymorphism of the two subgenomes to become more similar and their transcriptomes to start functioning together. To test this hypothesis, we sequenced the genomes and the transcriptomes (three tissues) of allote-traploid C. bursa-pastoris and its parental species, the outcrossing C. grandiflora and the self-fertilizing C. orientalis. Comparison of the divergence in expression between subgenomes, on the one hand, and divergence in expression between the parental species, on the other hand, indicated a strong parental legacy with a majority of genes exhibiting a conserved pattern and cis-regulation. However, a large proportion of the genes that were differentially expressed between the two subgenomes, were also under trans-regulation reflecting the establishment of a new regulatory pattern. Parental dominance varied among tissues: expression in flowers was closer to that of C. orientalis and expression in root and leaf to that of C. grandiflora. Since deleterious mutations accumulated preferentially on the C. orientalis subgenome, the bias in expression towards C. orientalis observed in flowers suggests that expression changes could be adaptive and related to the selfing syndrome, while biases in the roots and leaves towards the C. grandiflora subgenome may be reflective of the differential genetic load.

evolutionary biology↗

bioRxiv2018

Genomic data provides new insights on the demographic history and the extent of recent material transfers in Norway spruce

Primeval forests are today exceedingly rare in Europe and transfer of forest reproductive material for afforestation and improvement have been very common, especially over the last two centuries. This can be a serious impediment when inferring past population movements in response to past climate changes such as the last glacial maximum (LGM), some 18,000 years ago. In the present study, we genotyped 1,672 individuals from three Picea species (P. abies, P. obovata, and P. omorika) at 400K SNPs using exome capture to infer the past demographic history of Norway spruce and estimate the amount of recent introduction used to establish the Norway spruce breeding program in Southern Sweden. Most of these trees belong to P. abies and originate from the base population of the Swedish breeding program. Others originate from populations across the natural ranges of the three species. Of the 1,499 individuals stemming from the breeding program, a large proportion corresponds to recent introductions. The split of P. omorika occurred 23 million years ago (mya), while the divergence between P. obovata and P. abies began 17.6 mya. Demographic inferences retrieved the same main clusters within P. abies than previous studies, i.e. a vast northern domain ranging from Norway to central Russia, where the species is progressively replaced by Siberian spruce (P. obovata) and two smaller domains, an Alpine domain, and a Carpathian one, but also revealed further subdivision and gene flow among clusters. The three main domains divergence was ancient (15 mya) and all three went through a bottleneck corresponding to the LGM. Approximately 17% of P. abies Nordic domain migrated from P. obovata ~103K years ago, when both species had much larger effective population sizes. Our analysis of genome-wide polymorphism data thus revealed the complex demographic history of Picea genus in Western Europe and highlighted the importance of material transfer in Swedish breeding program.

evolutionary biology↗

bioRxiv2018

Local adaptation and maladaptation during the worldwide range expansion of a self-fertilizing plant

Species having experienced rapid range expansion represent unique opportunities to evaluate the dynamics of adaptation during colonization of new environments. We investigated the consequences of range expansion on local adaptation of a successful worldwide colonizer, the shepherds purse Capsella bursa-pastoris. This species is an annual weed that originated recently in Eurasia and has now broadly colonized both temperate and subtropical areas. We assessed the performance, genetic diversity, and phenology of field-collected accessions belonging to three distinct genetic clusters of decreasing age (Middle East, Europe and Asia) in three common gardens in Europe, Asia and North America. To understand the genetic basis of local adaptation in this species, we also tested for correlation between SNP allele frequencies and environmental factors in Europe and Asia. Overall, we showed that patterns of local adaptation depended on population history: some older populations were weakly adapted to local conditions while those closer to the front of the colonization wave, far from the origin of the species, were maladapted whatever the common gardens. Altogether, our results have important consequences for the understanding of the evolution and adaptation of self-fertilizing plant during range expansion.

evolutionary biology↗

bioRxiv2017

Parental legacy, demography, and introgression influenced the evolution of the two subgenomes of the tetraploid Capsella bursa-pastoris (Brassicaceae)

Allopolyploidy is generally perceived as a major source of evolutionary novelties and as an instantaneous way to create isolation barriers. However, we do not have a clear understanding of how two subgenomes evolve and interact once they have fused in an allopolyploid species and how isolated they are from their relatives. Here, we address these questions by analyzing genomic and transcriptomic data of allotetraploid Capsella bursa-pastoris in three differentiated populations, Asia, Europe and the Middle East. We phased the two subgenomes, one descended from the outcrossing and highly diverse Capsella grandiflora (Cg) and the other one from the selfing and genetically depauperate Capsella orientalis (Co). For each subgenome, we assessed its relationship with the diploid relatives, temporal change of effective population size Ne, signatures of positive and negative selection, and gene expression patterns. Introgression between C. bursa-pastoris and its diploid relatives was widespread and the two subgenomes were impacted differentially depending on geographic region. In all three regions, Ne of the two subgenomes decreased gradually and the Co subgenome accumulated more deleterious changes than Cg. Selective sweeps were more common on the Cg subgenome in Europe and the Middle East, and on the Co subgenome in Asia. In contrast, differences in expression were limited with the Cg subgenome slightly more expressed than Co in Europe and the Middle-East. In summary, after more than 100,000 generations of co-existence, the two subgenomes of C. bursa-pastoris still retained a strong signature of parental legacy and were differentially affected by introgression and selection.

evolutionary biology↗

bioRxiv2017

Competitive ability of a tetraploid selfing species (Capsella bursa-pastoris) across its expansion range and comparison with its sister species

Self-fertilization is often associated with ecological traits corresponding to the ruderal strategy in Grimes Competitive-Stress-tolerant-Ruderal (CSR) classification of ecological strategies. Consequently, selfers are expected to be less competitive than outcrossers, either because of a colonization/competition trade-off or because of the deleterious genetic effects of selfing. Range expansion could reduce further competitive ability while polyploidy could mitigate the effects of selfing. Although suggested by meta-analyses, these predictions have not been directly tested yet. We compared the competitive ability of four Capsella species differing by their mating system and ploidy level. We found that the two diploid selfing species (C. rubella and C. orientalis) were more sensitive to competition than the diploid outcrosser (C. grandiflora), and that the tetraploid selfer (C. bursa-pastoris) was intermediate. Within C. bursa-pastoris, we also found that sensitivity to competition increased in parallel to range expansion. These results highlight the possible roles of ecological context and ploidy in the evolutionary trajectories of selfing species.

evolutionary biology↗