SPERM COOPERATION IN DEER MICE.
Source: Hoekstra Lab
Sperm from highly promiscuous deer mice (genus Peromyscus) form alliances. These sperm groups swim faster than individual sperm and thus have an advantage in the race to fertilize the female ova. Using fluorescent labeling, it has been possible to show that sperm from two different males (one labeled red, and one green) preferentially cooperate with related sperm -- these mice can even discriminate against sperm from a full-sib littermate, which suggests a highly-refined (and yet undescribed) recognition mechanism at the level of sperm cells. This discriminatory behavior does not occur in a closely-related monogamous species, suggesting this complex behavior is driven by sexual selection.