Sperm Competition

The male's reproductive success isn't just based on the ability to mate with a female. It goes from direct male to male competition to sperm competition. If a female mates with two or more males, the male whose sperm reaches the eggs first or reaches the most eggs will have a higher reproductive success. Various species have developed adaptations or traits that could give them an advantage over another male. One trait that can be seen in the Mediterranean fruit fly is the production of large ejaculates. The more sperm the fly produces the greater probability that some of its sperm reaches the female's eggs. The larger the ejaculates the greater probability the fly has of reproductive success. Some males take a more direct route to insure their reproductive success. He will guard his mate to insure that no other male will mate with his female. Some spiders deposit a copulatory plug into the female. This plug insures that the female cannot mate with any other mate. Other adaptations include prolong copulation, applying pheromones, or barbed horns on the penis. The barbed horn adaptation is seen in damselflies. Scientists have studied these adaptations and they have shown to be very successful. They are sharp needle-like spikes coming off of the male’s penis. Their job is to scoop the sperm out of the female from her previous mates. This insures that his sperm is only competing against few or no other mates. Often though multiple males can impregnate the female. This produces offspring with different fathers at the same time. An animal’s main goal is to produce viable offspring. Many species have gained adaptations to help them better accomplish this goal. Some of these adaptations can be seen when comparing sperm competition among males. These adaptations enable males to insure that they have a high reproductive success.

For more information:

http://faculty.vassar.edu/suter/1websites/bejohns/mateselection/files/sperm_comp.htm

http://www.life.umd.edu/faculty/wilkinson/honr278c/PDF/Wigby04.pdf