[
International Worm Meeting,
2017]
Understanding the cause of reproductive barriers that demarcate species (e.g. hybrid lethality and sterility) is essential for understanding the process of speciation. We have discovered a genetic incompatibility between two wild-isolates (JU1825 and NIC59) of Caenorhabditis nouraguensis that results in F2 embryonic and larval lethality. Inviability seems to be the result of a maternally inherited cytoplasmic factor from each strain being incompatible with recessive nuclear loci from the other. Furthermore, cytoplasmic-nuclear incompatibility commonly occurs between other wild isolates, indicating that this is a significant reproductive barrier within C. nouraguensis. We hypothesize that the maternally inherited factor is the mitochondrial genome and that mitochondrial dysfunction underlies hybrid death. Multi-generation backcross experiments suggest that JU1825 mtDNA is heteroplasmic for both JU1825-like and NIC59-like incompatibility loci. We have generated genome assemblies of NIC59, JU1825 and JU2079 (an inbred strain derived from JU1825), and have mapped the nuclear incompatibility loci to single chromosomes by bulk sequencing of viable F2 hybrids. The nuclear incompatibility loci map to different chromosomes in reciprocal crosses, indicating genetically distinct cytoplasmic-nuclear incompatibilities. We have more finely mapped one of the nuclear incompatibility loci by generating recombinant introgression lines, which we are currently sequencing.