Thesis: Selection shaping the size of gametes in Chlamydomoas reinhardtii
Why do sexes exist? In principal, organisms can reproduce sexually without having sexes, and many microorganisms actually do so. They produce a pool of similar sex cells. Pairs of the sex cells merge and give raise to a new generation.
But in plants, animals and many other organisms there are two kinds of sex cells: big, female cells (in humans ova) and small, male cells (in humans sperm).
I am trying to help provide an answer to the question why two kinds of sex cells evolved.
Several hypotheses have been proposed. In general, many scientist believe, that if an organism produces more sex cells, it can have more offspring; but the more sex cells the organism produces, the smaller they are, and as a consequence the fewer resources they supply to the offspring. So the two sexes represent two strategies of reproduction: either producing a lot of small sex cells, or producing well-equipped large sex cells. However, these theories rely on many assumptions about sex cells of simple sexual organisms.
I use a unicellular alga, Chlamydomoas reinhardtii, to test those assumptions. This alga has sex but not sexes. However, its sex cells can be smaller or larger depending on environmental or genetic factors. I examine sex cells production in the alga, the differences between smaller and larger sex cells (longevity, motility, mating efficiency, quality of offspring), and inheritance of sex cell size. I also test how the mode of sexual reproduction of this alga can evolve in the laboratory.
Why my research is important
The research will fill a big gap in experimental studies. By examining important properties of sexual organisms, it will help us understand why some of them have sexes, while others do not.