Why so Many Seminal Fluid Proteins?
Surely 133 proteins to transfer along with sperm is an embarrassment of riches? To date, seminal fluid proteins are unevenly divided between just 12 functional classes, but with the majority being in the protease, protease inhibitor, immunity, and lipid metabolism categories. It is an intriguing and unanswered question of seminal fluid biology as to why there are multiple representatives of each type. It will be interesting to test whether each seminal fluid protein produces a distinct phenotype (Table 1). One explanation for the apparent abundant degeneracy is that the male reproductive system carries the baggage of previous evolutionary contests between males or between males and females. Hence one member of each functional class is the current “favourite”, but declines in importance when sexual competition becomes too intense, or when one side becomes insensitive to the actions of the current player (Table 1). A contrasting situation is apparently found for one of the best functiona