I've been long interested in the evolution of group living and sociality in nonhuman animals (animals), so a recent report of the advantages of group swimming by sperm caught my eye and provided a nice respite from writing about what I usually write about.
The benefits of cooperation by sperm is that they travel straighter, not faster
Harvard University evolutionary biologist Heidi Fisher and her colleagues studied group formation and the path that the swimming sperm of two closely related species of mice take when traveling alone and when traveling in groups. They reported their very interesting results in a research paper titled "The dynamics of sperm cooperation in a competitive environment." Their essay is only available to subscribers to the journal, and many different summaries can be found here.
The results of this research project are very interesting and were related to the type of mating system shown by the different species of mice they studied. To wit, Dr. Fisher and her research team discovered that when they squirted the sperm of two different species of mice onto a microscope slide and then videotaped what they did, the sperm of monogamous beach mice when compared to the sperm of promiscuous North American deer mice tended to swim alone, and that groups of sperm (up to around seven) of the deer mice traveled in straighter trajectories, but not faster, than solo sperm of the same species. So, although cooperation among sperm is rare, forming groups in the promiscuous species seems to be advantageous as an adaptation to potential competition among individual sperm so that they arrive at their destination faster than lone sperm.