Nathan Reetz

nreetzfcmail.fresnostate.edu

Caenorhabditis briggsae is an excellent model system for the study of genetics and speciation. They are simple organisms with relatively small, fully sequenced genomes and short generation times. Most importantly for the ease of genetic research, as a hermaphroditic species, they can be crossed or selfed to control what traits are present in subsequent generations. In the study of speciation, it is important to look at dysfunction caused by the cross of two organisms. Two C. briggsae strains are currently being used to explore speciation: HK104, a temperate (20°C) strain from Japan, and AF16, a tropical (25°C) strain from India. The F1 Hybrids of these strains show reduced fitness in many traits including brood size and lifespan. This F1 dysfunction might be produced by a genetic incompatibility between strains that represents the onset of speciation. One trait that could be studied further to identify the genetic basis of species formation is embryonic lethality: does the hybrid F1 generation show a decreased number of embryos that surviving to hatch? Related questions that haven't yet been explored are: are these strains genetically adapted to their native temperatures, and does temperature therefore affect embryonic lethality in hybrids? To answer these questions, I will count unhatched eggs at both 20°C and 25°C for each pure strain to provide baseline egg lethality at both temperatures. This will provide the control for the experiment. HK104/AF16 and AF16/HK104 F1 generation hybrid eggs will then be observed at 20°C and 25°C. These results will be compared with the baseline data using a T-test to determine if the hybrids are experiencing increased embryonic lethality. Identifying such hybrid dysfunction would enhance our ability to use C. briggsae to identify the genetic basis of species formation by genetically mapping loci involved in producing this trait.