Caenorhabditis briggsae Recombinant Inbred Line Genotypes Reveal Inter-Strain Incompatibility and the Evolution of Recombination

Abstract

The nematode Caenorhabditis briggsae is an emerging model organism that allows evolutionary comparisons with C. elegans and exploration of its own unique biological attributes. To produce a high-resolution C. briggsae recombination map, recombinant inbred lines were generated from reciprocal crosses between two strains and genotyped at over 1,000 loci. A second set of recombinant inbred lines involving a third strain was also genotyped at lower resolution. The resulting recombination maps exhibit discrete domains of high and low recombination, as in C. elegans, indicating these are a general feature of Caenorhabditis species. The proportion of a chromosome's physical size occupied by the central, low-recombination domain is highly correlated between species. However, the C. briggsae intra-species comparison reveals striking variation in the distribution of recombination between domains. Hybrid lines made with the more divergent pair of strains also exhibit pervasive marker transmission ratio distortion, evidence of selection acting on hybrid genotypes. The strongest effect, on chromosome III, is explained by a developmental delay phenotype exhibited by some hybrid F2 animals. In addition, on chromosomes IV and V, cross direction-specific biases towards one parental genotype suggest the existence of cytonuclear epistatic interactions. These interactions are discussed in relation to surprising mitochondrial genome polymorphism in C. briggsae, evidence that the two strains diverged in allopatry, the potential for local adaptation, and the evolution of Dobzhansky-Muller incompatibilities. The genetic and genomic resources resulting from this work will support future efforts to understand inter-strain divergence as well as facilitate studies of gene function, natural variation, and the evolution of recombination in Caenorhabditis nematodes.

Causes and Consequences of Genetic Background Effects Illuminated by Integrative Genomic Analysis

“…These loci may have been influenced by unintended selection for alleles influencing viability, rather than for wing phenotypes. Indeed, such unanticipated genetic effects have been observed in other studies (e.g., Seidel et al 2008;Ross et al 2011;King et al 2012). Moreover, there was some inconsistency among introgression lines.…”

Sex-Biased Gene Expression and Evolution of the X Chromosome in Nematodes

“…When we compared our C. briggsae gene assignments to the current WormBase assignment [based on a high-density recombination map (Hillier et al 2007;Koboldt et al 2010;Ross et al 2011)] we found that we correctly assigned 236 of 236 contigs to autosomes and 27 of 28 contigs to the X chromosome ( Figure 1D). The inconsistent contig, cb25.…”

Temperature-dependent behaviours are genetically variable in the nematode Caenorhabditis briggsae

“…Caenorhabditis briggsae is morphologically very similar to C. elegans, sharing a common life cycle and similar androdioecious sexual system (Nigon and Dougherty, 1949;Baird, 2001), but C. briggsae exhibits greater molecular differentiation among wild strains that might, in turn, underlie higher phenotypic variation (Cutter et al, 2006). As more genetic tools become available in C. briggsae, it is quickly catching up to C. elegans as a model system in its own right (Koboldt et al, 2010;Ross et al, 2011).…”