Noble, Luke et al. (2017) International Worm Meeting "The C. elegans multiparent experimental evolution mapping panel."

Dayarian, Adel, Cavalho, Sara, Guzella, Thiago, Riccardi, David, Ammerman, Patrick, Teotonio, Henrique, Pino-Querido, Ania, Rockman, Matthew, Shraiman, Boris, Crist, Anna, Afonso, Bruno, Noble, Luke, Chelo, Ivo

[International Worm Meeting, 2017]

We report a recombinant inbred line (RIL) quantitative trait locus (QTL) mapping panel for the hermaphroditic nematode Caenorhabditis elegans, the C. elegans multiparental experimental evolution (CeMEE) panel. The CeMEE panel, comprising 507 RILs, was created by hybridization of 16 wild isolates, experimental evolution at moderate population sizes for 140-190 discrete generations, and inbreeding by selfing for 13-16 generations. The panel contains around 22% of single nucleotide polymorphisms known to segregate in natural populations, and complements existing mapping resources for C. elegans by providing high nucleotide diversity across >95% of the genome, and fine-scale mapping resolution.

Noble, Luke et al. (2017) International Worm Meeting "Polygenicity and epistasis underlie fitness-proximal traits in the Caenorhabditis elegans multiparental experimental evolution (CeMEE) panel."

Guzella, Thiago, Noble, Luke, Riccardi, David, Dayarian, Adel, Afonso, Bruno, Shraiman, Boris, Teotonio, Henrique, Rockman, Matthew, Pino-Querido, Ania, Crist, Anna, Chelo, Ivo, Ammerman, Patrick, Cavalho, Sara

[International Worm Meeting, 2017]

Understanding the genetic basis of complex traits remains a major challenge in biology. Polygenicity, phenotypic plasticity and epistasis contribute to phenotypic variance in ways that are rarely clear. This uncertainty is problematic for estimating heritability, for predicting individual phenotypes from genomic data, and for parameterizing models of phenotypic evolution. Here we report a recombinant inbred line (RIL) quantitative trait locus (QTL) mapping panel for the hermaphroditic nematode Caenorhabditis elegans, the C. elegans multiparental experimental evolution (CeMEE) panel. The CeMEE panel, comprising 507 RILs, was created by hybridization of 16 wild isolates, experimental evolution at moderate population sizes for 140-190 discrete generations, and inbreeding by selfing for 13-16 generations. The panel contains around 22% of single nucleotide polymorphisms known to segregate in natural populations, and complements existing mapping resources for C. elegans by providing high nucleotide diversity across >95% of the genome, and fine-scale mapping resolution. We apply it to study the genetic basis of two fitness components, fertility and adult hermaphrodite body size, with high broad sense heritability in the CeMEE. While simulations show we should detect common alleles with additive effects as small as 5%, at gene-level resolution, the genetic architectures of these traits does not feature such alleles. We instead find that a significant fraction of trait variance, particularly for fertility, can be explained by sign epistasis with weak main effects. Multiple interactions involving egl-18 (and potentially the functionally related flanking genes egl-4 and elt-6 as well) are highly influential for fertility, consistent with selection for embryo retention during experimental evolution. Phenotype prediction, while generally poor (r2<10%), requires modeling epistasis for optimal accuracy, with most variance attributed to the highly recombinant, rapidly evolving chromosome arms.

ZHANG, Gaotian et al. (2019) International Worm Meeting "A genetically divergent C. elegans wild isolate exhibits extremely high male frequency."

Andersen, Erik, Crombie, Tim, Zhang, Gaotian, Zdraljevic, Stefan

[International Worm Meeting, 2019]

Caenorhabditis elegans is an androdioecious nematode with hermaphrodites and males. A self-fertilizing hermaphrodite rarely produces males, with frequencies of approximately 0.1% in the laboratory strain N2. By contrast, a hermaphrodites fertilized by males have 50% male progeny. Many studies have suggested that self-fertilization is the primary reproduction mode of C. elegans in nature, and the transition from obligately outcrossing might be recent (Cutter et al., 2008). Natural variation of male frequencies were also observed in C. elegans, ranging from 0.1% to 35% (Teotonio et al., 2006; Anderson et al., 2010). In a recent sampling of Caenorhabditis in Hawaii (see abstract by Crombie et al.), we isolated a C. elegans strain, named ECA701, which exhibited extremely high male frequencies of 34% - 57% and low brood sizes of 80 - 170 by selfing of hermaphrodites. Mating of ECA701 between hermaphrodites and males showed male frequencies of 47% - 70% and brood sizes of 150 - 290. We further found that ECA701 produced embryos with high levels of embryonic lethality (30% in young adults), which is exacerbated in older adults (60% in two-days old adults). Investigations on meiotic prophase I demonstrated that ECA701 is defective in the meiotic processes (see abstract by Adler et al.). Notably, using whole genome sequencing and phylogenetic analysis, we also found that ECA701 is one of the most divergent C. elegans strains that have yet been described. Taken together, ECA701 provides a great opportunity to improve our understanding on the possible ancestral state and the evolution of reproduction mode in C. elegans.