John L. Fitzpatrick

Department of Biology

McMaster University

Promiscuity promotes the evolution of faster swimming sperm.

The statement 'all's fair in love and war' could have been written about the sex lives of fish. Male and female fishes use a variety of tactics and tricks to ensure that they are able to reproduce. Some males spend their time mimicking females in order to get close to a mating male and female, while others sneak in at the last second and quickly release sperm without having gone through the time consuming process of courting a female. Females get in on the act by 'shopping' for sperm from several males (mating with multiple males). Sneaky male behaviour and female promiscuity lead to competition between the sperm of rival males to fertilize a female's eggs. While sperm competition is acknowledged to be an important evolutionary force shaping sperm characteristics, a number of important questions concerning sperm evolution remain open and hotly debated. I will address these questions as well as a number of critical predictions from sperm competition theory using within and between species studies. I will then explore how sperm competition influences sperm number, size and swimming speed, and demonstrate that sperm competition leads to the evolution of more competitive ejaculates.