Biology subjects

Mantel, S. J.

Publications and source records attributed to Mantel, S. J..

4 recordsLinked to original sources

bioRxiv2026

Environment-dependent and often antagonistic effects of dominance and epistasis on heterosis in crosses between natural populations

Genetic drift in natural populations reduces the efficacy of selection, promoting the fixation of deleterious recessive alleles with consequences for maladaptation and population persistence. Heterosis, or increased F1 fitness relative to the parental mean, has been proposed as a tool for investigating the role of drift on genetic variation in fitness, but its genetic basis and environmental dependence remain unclear in natural populations. We used heterozygous near-isogenic lines (NILs) derived from a cross between locally adapted Arabidopsis thaliana ecotypes to assess how specific genomic regions influence heterosis. Cumulative fitness, estimated as fruits per seedling, was evaluated in a greenhouse and two simulated native environments. There was strong overall heterosis in the greenhouse and one simulated environment. Non-additive effects in heterozygous NILs were highly environment- and background-dependent, varying in magnitude and sign, and no NIL had consistent effects across environments. The relative fitness of heterozygous NILs was not correlated with gene number or genomic load in the introgressed regions. Small heterozygous regions often had large effects, indicating that complementation of mildly deleterious alleles alone does not fully explain heterosis. Evidence of epistasis was also observed, including outbreeding depression in some NILs, likely due to negative additive-by-dominance interactions. Summed effects of individual heterozygous genomic regions often exceeded the fitness increase of the F1 suggesting dominance-by-dominance epistasis, but the direction of these epistatic effects depended on both genetic background and environment. Our results demonstrate that F1 fitness reflects both positive dominance and different epistatic interactions that are environment- and background-dependent.

evolutionary biology↗

bioRxiv2025

A panel of near-isogenic lines derived from locally adapted populations of a wild plant: A powerful tool for dissecting additive and non-additive effects on ecologically important traits

Identifying and estimating the effects of loci contributing to natural variation in ecologically important traits can be hampered by quantitative inheritance, dominance, epistasis, and environmentally dependent trait expression. Here we announce the availability of germplasm and sequence data for a reciprocal panel of near-isogenic lines (NILs) derived from locally adapted natural populations of Arabidopsis thaliana, for investigating the genetic basis of ecologically important traits. We created a panel of 54 NILs and performed whole genome sequencing to precisely locate introgression segments(s) in each NIL. Deep sequencing largely confirmed prior knowledge of NIL genotypes but also identified multiple novel small introgressions and regions of residual heterozygosity. To illustrate the utility of this panel, we identified genomic regions underlying ecotypic differences in flowering time in a laboratory common garden experiment. We detected strong additive effects on flowering time in multiple NILs with segments at the top of chromosome 5 implicating the floral regulator FLC, as expected based on previous quantitative trait locus studies. We also detected novel and complex contributions to ecotypic differences in flowering time, only visible in the NILs, suggesting the possibility of epistasis. Our results highlight the utility of this panel for dissecting the genetic architecture of ecologically important traits, including the future potential for fine mapping of additive effects and testing for epistasis and linkage using NILs derived from the panel. This panel can be used by any member of the research community to investigate any of a broad suite of traits for which the parents differ.

evolutionary biology↗

bioRxiv2023

Postzygotic barriers persist despite ongoing introgression in hybridizing Mimulus species

O_LIThe evolution of postzygotic isolation is thought to be a key step in maintaining species boundaries upon secondary contact, yet the dynamics and persistence of hybrid incompatibilities in sympatric species are not well understood. C_LIO_LIHere, we explore these issues using genetic mapping in three populations of recombinant inbred lines between naturally hybridizing monkeyflowers Mimulus guttatus and M. nasutus from the sympatric Catherine Creek population. C_LIO_LIThe three M. guttatus founders differ dramatically in admixture history. Comparative genetic mapping also reveals three putative inversions segregating among the M. guttatus founders, two due to admixture. We observe strong, genome-wide transmission ratio distortion, but patterns are highly variable among populations. Some distortion is explained by epistatic selection favoring parental genotypes, but tests of inter-chromosomal linkage disequilibrium also reveal multiple candidate Dobzhansky-Muller incompatibilities. We also map several genetic loci for hybrid fertility, including two interacting pairs coinciding with peaks of distortion. C_LIO_LIRemarkably, in this limited sample of M. guttatus, we discover abundant segregating variation for hybrid incompatibilities with M. nasutus, suggesting this population harbors diverse contributors to postzygotic isolation. Moreover, even with substantial admixture, hybrid incompatibilities between Mimulus species persist, suggesting postzygotic isolation might be a potent force in maintaining species barriers in this system. C_LI

genetics↗

bioRxiv2023

Genomic mechanisms and consequences of diverse postzygotic barriers between monkeyflower species

The evolution of genomic incompatibilities causing postzygotic barriers to hybridization is a key step in species divergence. Incompatibilities take two general forms - structural divergence between chromosomes leading to severe hybrid sterility in F1 hybrids and epistatic interactions between genes causing reduced fitness of hybrid gametes or zygotes (Dobzhansky-Muller incompatibilities). Despite substantial recent progress in understanding the molecular mechanisms and evolutionary origins of both types of incompatibility, how each behaves across multiple generations of hybridization remains relatively unexplored. Here, we use genetic mapping in F2 and RIL hybrid populations between the phenotypically divergent but naturally hybridizing monkeyflowers Mimulus cardinalis and M. parishii to characterize the genetic basis of hybrid incompatibility and examine its changing effects over multiple generations of experimental hybridization. In F2s, we found severe hybrid pollen inviability (< 50% reduction vs. parental genotypes) and pseudolinkage caused by a reciprocal translocation between Chromosomes 6 and 7 in the parental species. RILs retained excess heterozygosity around the translocation breakpoints, which caused substantial pollen inviability when interstitial crossovers had not created compatible heterokaryotypic configurations. Strong transmission ratio distortion and inter-chromosomal linkage disequilibrium in both F2s and RILs identified a novel two-locus genic incompatibility causing sex-independent gametophytic (haploid) lethality. The latter interaction eliminated three of the expected nine F2 genotypic classes via F1 gamete loss without detectable effects on the pollen number or viability of F2 double heterozygotes. Along with the mapping of numerous milder incompatibilities, these key findings illuminate the complex genetics of plant hybrid breakdown and are an important step toward understanding the genomic consequences of natural hybridization in this model system.

genetics↗