In today’s Academic Minute, Dr. Stefan Lüpold of Syracuse University explain how females of certain species can pick the father of their offspring after mating with multiple males.
Stefan Lüpold is a research assistant professor in the Department of Biology at Syracuse University. His research is focused on behavioral ecology and sexual selection in birds and insects, with a specific focus on male and female adaptations to postcopulatory sexual selection. He earned his Ph.D. at the University of Sheffield in the United Kingdom.
Dr. Stefan Lüpold – Female Control of Sexual Selection
One of my main current interests is to understand what happens inside of a female when it mates with more than one male, causing sperm to compete for fertilization. Female promiscuity is extremely widespread throughout the animal kingdom and plays a critical role in the evolution of reproductive traits.
We use genetically engineered fruit flies whose sperm glow either green or red under a fluorescent microscope. These fluorescent markers allow us to visualize sperm within the female reproductive tract and to distinguish between the sperm from different males.
Using these flies, we have documented a significant fertilization advantage for males that transfer longer but―somewhat surprisingly―slower sperm than their competitors. When entering the female sperm-storage organs, long and slow sperm are better at displacing their counterparts than are short but fast sperm. Gaining such a numerical advantage is critical for males as the relative numbers of sperm in storage ultimately determine paternity.
More recently, we have also found that females don’t just provide a static arena in which sperm compete. They themselves can influence the paternity of their offspring by various means. Most importantly, females vary in the timing of interrupting the process of sperm displacement by ejecting sperm from their tract. The longer a female waits to eject sperm, the more time sperm of the second male have to enter storage and displace their rivals. Thus, females can influence the amount of sperm from each male competing for fertilization.
Together, these findings have major implications for the study of sexual selection and the coevolution of male and female reproductive traits.