Biology subjects

Short, A. W.

Publications and source records attributed to Short, A. W..

4 recordsLinked to original sources

bioRxiv2024

The genomic outcomes of hybridization vary over time within a monkeyflower radiation

The accumulation of genetic differences through time can lead to reproductive isolation between populations and the origin of new species. However, hybridization between emerging species can occur at any point before isolation is complete. The evolutionary consequences of this hybridization may vary depending on when it occurred. If hybridization occurred later during the process, when ecological and genetic differences have accumulated between diverging lineages, low hybrid fitness can result in selection against gene flow. If hybridization occurred earlier, when barriers present were too weak to limit introgression, then hybridization can lead to genetic swamping. Alternatively, adaptive introgression can occur at any point during speciation. Thus, by understanding the history and genomic consequences of hybridization at different points along the speciation continuum, we can begin to understand how variation present within populations translates to divergence between species. Here, we identified the genomic signals of introgressive hybridization at different points during the divergence of two monkeyflower taxa endemic to the Channel Islands of California. We found that both ancient and recent introgression have shaped their genomes, but the impacts of selection on this foreign material varied. There was no signal of selection against ancient introgression, but we did find strong evidence for selection against recent introgression, potentially because there are more reproductive barriers in place now, reducing fitness in recent hybrids. Thus, this study reveals that hybridization can occur at multiple points throughout the divergence history of a radiation, but the processes shaping genome wide levels of introgression can change over time.

evolutionary biology↗

bioRxiv2024

Inheritance of somatic mutations can affect fitness in monkeyflowers

Plants possess the unique ability to transmit mutations to progeny that arise both through meiotic and mitotic (somatic) cell divisions. This is because the same meristem cells responsible for vegetative growth also generate gametes for sexual reproduction. Despite the potential for somatic mutations to be an additional source of genetic variation for adaptation, their role in plant evolution remains largely unexplored. We performed multiple experiments in the bush monkeyflower (Mimulus aurantiacus) to determine the fitness effects of somatic mutations inherited across generations. We tracked somatic mutations transmitted to progeny by generating self-pollinations within a flower (autogamy) or between stems of the same plant (geitonogamy). Autogamy and geitonogamy lead to different segregation patterns of somatic mutations among stems, making it possible to compare average fitness due to somatic variants. We found increased fecundity following autogamy, as well as significant impacts on drought tolerance, survival, and biomass. The variance in fitness was also greater following autogamy, consistent with the effects of somatic mutations impacting fitness. Effect sizes were small, but predictable, given that M. aurantiacus is a long-lived, drought-adapted shrub. These results reveal the importance of inherited somatic mutations as a source of genetic variation that can be relevant for plant adaptation.

evolutionary biology↗

bioRxiv2024

The genome of Lolium multiflorum reveals the genetic architecture of paraquat resistance

- Herbicide resistance in agricultural weeds has become one of the greatest challenges for sustainable crop production. The repeated evolution of herbicide resistance provides an excellent opportunity to study the genetic and physiological basis of the resistance phenotype and the evolutionary responses to human-mediated selection pressures. Lolium multiflorum is a ubiquitous weed that has evolved herbicide resistance repeatedly around the world in various cropping systems. - We assembled and annotated a chromosome-scale genome for L. multiflorum and elucidated the genetic architecture of paraquat resistance by performing quantitative trait loci analysis, genome-wide association studies, genetic divergence analysis, and transcriptome analyses from paraquat-resistant and -susceptible L. multiflorum populations. - Results suggested that two regions of chromosome 5 were associated with paraquat resistance. The regions contain candidate genes that encode cellular transport functions, including a novel multidrug and toxin extrusion (MATE) protein, and a cation transporter previously shown to interact with polyamines. - Our results reveal the genetic architecture of paraquat resistance and identified promising candidate genes for future functional studies. Given that L. multiflorum is a weed and a cultivated crop species, the genomic resources generated will prove valuable to a wide spectrum of the plant science community.

plant biology↗

bioRxiv2023

Ancient hybridization leads to the repeated evolution of red flowers across a monkeyflower radiation

The re-use of old genetic variation can promote rapid diversification in evolutionary radiations, but in most cases, the historical events underlying this divergence are not known. For example, ancient hybridization can generate new combinations of alleles that sort into descendant lineages, potentially providing the raw material to initiate divergence. In the Mimulus aurantiacus species complex, there is evidence for widespread gene flow among members of this radiation. In addition, allelic variation in the MaMyb2 gene is responsible for differences in flower color between the closely related ecotypes of subspecies puniceus, contributing to reproductive isolation by pollinators. Previous work suggested that MaMyb2 was introgressed into the red-flowered ecotype of puniceus. However, additional taxa within the radiation have independently evolved red flowers from their yellow-flowered ancestors, raising the possibility that this introgression had a more ancient origin. In this study, we used repeated tests of admixture from whole-genome sequence data across this diverse radiation to demonstrate that there has been both ancient and recurrent hybridization in this group. However, most of the signal of this ancient introgression has been removed due to selection, suggesting that widespread barriers to gene flow are in place between taxa. Yet, a roughly 30 kb region that contains the MaMyb2 gene is currently shared among the red-flowered taxa. Patterns of admixture, sequence divergence, and extended haplotype homozygosity across this region confirm a history of ancient hybridization, where functional variants have been preserved due to positive selection in red-flowered taxa but lost in their yellow-flowered counterparts. The results of this study reveal that selection against gene flow can reduce genomic signatures of ancient hybridization, but that historical introgression can provide essential genetic variation that facilitates the repeated origins of phenotypic traits between lineages.

evolutionary biology↗