Alex Braeger

Plants, Soils, and Climate

Mentor: Dr. John Carman

Inducing Reversions Between Asexual and Sexual Reproductive Strategies in Daphnia

Apomictic parthenogenises is a form a asexual reproduction in animals and plants where the sex cells of the mother divide mitotically rather than meiotically, resulting in the production of a diploid, rather than haploid, egg cells. As a consequence of this process, the egg cells do not require fertilization and the resultant offspring are essentially clones of their mother. This process of asexual reproduction often exists in nature facultatively (can switch between modes of reproduction when needed) thereby enabling the organism to rapidly reproduce via apomictic parthenogeniesis during time of low stress, and to reproduce sexually in times of high stress for greater variation in offspring. The apomixis/sex polyphenism hypothesis, proposed by Dr. Carman of Utah State University, indicates that the similarities in reproduction between apomicitc plants and apomictic parthenogenic animals are due to apomixis having evolved with sex in primitive eukaryotes. More specifically, it proposes that the TOR (target of rapamycin) signaling pathway is primarily responsible for switching modes of reproduction. Past studies with plants using treatments that access the TOR pathway have yielded results supporting this hypothesis. Our current study is investigating the effects of activating and disabling the TOR pathway in Daphnia Magna, a model organism that naturally displays the ability to facultatively switch between sexes. In a natural setting, with positive environmental conditions, Daphnia reproduce asexually (only females). In an adverse environment they often switch to sexual reproduction (males and females). We are attempting to trigger a sexual reproduction response that is not specific to the environment that they exist with chemicals that are known to exist in the TOR signaling pathway.