Biology subjects

Noble, L.

Publications and source records attributed to Noble, L..

4 recordsLinked to original sources

bioRxiv2023

Genome-wide association and environmental suppression of the mortal germline phenotype of wild C. elegans

The animal germline lineage needs to be maintained along generations. However, some Caenorhabditis elegans wild isolates display a mortal germline phenotype, whereby the lineage becomes sterile after several generations at 25{degrees}C. We used a genome-wide association approach to study the genetic basis for this phenotype in C. elegans populations. We detected a significant peak on chromosome III around 5 Mb, which was confirmed using introgression lines. These results indicate that a seemingly deleterious genotype is maintained at intermediate frequency in the species. Environmental rescue is a likely explanation and we indeed find that naturally associated bacteria and microsporidia suppressed the phenotype. The tested bacteria also suppressed the temperature-sensitive mortal germline phenotype of mutants in small RNA inheritance (nrde-2) and histone modifications (set-2). Even Escherichia coli strains of the K-12 lineage suppressed the phenotype compared to B strains. By shifting a strain cultured on E. coli K-12 back to E. coli B, we found that C. elegans can keep over several generations the memory of the suppressing conditions. Thus, the mortal germline phenotype of wild C. elegans is lin part revealed by laboratory conditions and may represent variation in epigenetic inheritance and environmental interactions. This study also points to the importance of non-genetic memory in the face of environmental variation.

evolutionary biology↗

bioRxiv2022

Variation in mutational (co)variances

1Because of pleiotropy, mutations affect the expression and inheritance of multiple traits and are expected to determine the structure of standing genetic variation and phenotypic evolution. It is thus important to find if the M matrix, describing mutational (co)variances between traits, varies between genotypes. We here estimate the M matrix for six locomotion behavior traits in two genotypes of the nematode Caenorhabditis elegans. We find significant mutational variance along at least one phenotypic dimension of the M matrix, but its size and orientation was similar between genotypes. We then tested if the M matrices were similar to one G matrix describing the standing genetic (co)variances of a domesticated population derived by the hybridization of several genotypes and adapted to a lab defined environment for 140 generations. M and G are different in part because the genetic covariances caused by mutational pleiotropy in the two genotypes are smaller than those caused by standing linkage disequilibrium in the lab population. If generalized to other genotypes, these observations indicate that selection is unlikely to shape the evolution of the M matrix for locomotion behavior and suggests that the genetic restructuring due to the hybridization of C. elegans genotypes allows for selection in the lab on new phenotypic dimensions of locomotion behavior, phenotypic dimensions which are inaccessible to natural populations.

evolutionary biology↗

bioRxiv2022

Phenotypic stasis with genetic divergence

1Whether or not genetic divergence on the short-term of tens to hundreds of generations is compatible with phenotypic stasis remains a relatively unexplored problem. We evolved predominantly outcrossing, genetically diverse populations of the nematode Caenorhabditis elegans under a constant and homogeneous environment for 240 generations, and followed individual locomotion behavior. Although founders of lab populations show highly diverse locomotion behavior, during lab evolution the component traits of locomotion behavior - defined as the transition rates in activity and direction - did not show divergence from the ancestral population. In contrast, transition rates genetic (co)variance structure showed a marked divergence from the ancestral state and differentiation among replicate populations during the final 100 generations and after most adaptation had been achieved. We observe that genetic differentiation is a transient pattern during the loss of genetic variance along phenotypic dimensions under drift during the last 100 generations of lab evolution. These results suggest that short-term stasis of locomotion behavior is maintained because of stabilizing selection, while the genetic structuring of component traits is contingent upon drift history.

evolutionary biology↗

bioRxiv2019

Selection and drift determine phenotypic stasis despite genetic divergence

1Evolutionary theory suggests that phenotypic stasis is explained by natural selection and genetic drift, or by constraints imposed by mutation and recombination of standing genetic variation. We performed experimental evolution from standing genetic variation with the nematode Caenorhabditis elegans, measuring individual locomotion in outcrossing populations for 240 generations. We find that, in our constant environment, locomotion bias shows no directional divergence, due to both stabilizing and disruptive selection on specific combinations of component traits. Despite phenotypic stasis, the genetic variance-covariance structure between component traits shows clear divergence from the ancestral state and extensive differentiation among replicated populations facing the same environment. Analysis of mutation accumulation experiments and genome-sequenced recombinant inbred lines from the experimental populations indicates that the evolution of the genetic variance-covariance structure is independent of de novo mutation or major effect QTL; being instead explained by the joint action of selection and drift in generating subtle linkage disequilibrium differences between small effect QTL among replicate populations. These findings indicate that phenotypic evolution is repeatable because of selection, even if the genetic structuring of component traits within lineages is mostly contingent upon drift history.

evolutionary biology↗