The study of speciation is key to understanding the origins of biodiversity. Model organisms, with a host of genetic and molecular tools, are crucial to dissecting the genetics of speciation. Crosses between the recently-discovered Caenorhabditis sp. 9 and the well-known C. briggsae produce fertile F1 hybrid females, opening the door to genetic studies of speciation for the first time within the genus. I crossed eight different isogenic strains of C. briggsae reciprocally with six inbred lines of C. sp. 9 to investigate: Haldane’s rule, systematic asymmetries in hybrid viability, and whether genetic variation for hybrid viability segregates within each species. Results of these crosses confirm Haldane’s rule and demonstrate strong asymmetric parent-of-origin effects. Furthermore, I observed genotype-dependent differences in the number of F1 hybrid progeny. This provides evidence for genetic variation for hybrid viability within both species, allowing insights into the genetic forces driving the evolution of incompatibility loci.

The study of speciation is key to understanding the origins of biodiversity. Model organisms, with a host of genetic and molecular tools, are crucial to dissecting the genetics of speciation. Crosses between the recently-discovered Caenorhabditis sp. 9 and the well-known C. briggsae produce fertile F1 hybrid females, opening the door to genetic studies of speciation for the first time within the genus. I crossed eight different isogenic strains of C. briggsae reciprocally with six inbred lines of C. sp. 9 to investigate: Haldane’s rule, systematic asymmetries in hybrid viability, and whether genetic variation for hybrid viability segregates within each species. Results of these crosses confirm Haldane’s rule and demonstrate strong asymmetric parent-of-origin effects. Furthermore, I observed genotype-dependent differences in the number of F1 hybrid progeny. This provides evidence for genetic variation for hybrid viability within both species, allowing insights into the genetic forces driving the evolution of incompatibility loci.