To imagine the life of a freshwater mussel living in a southeastern U.S. river, picture a couch potato with a constant buffet line rolling past. But the permanently sedentary lifestyle presents certain obvious problems: It’s kind of hard to hook up with another mussel when you don’t move. When it comes to sex, mussels master long-distance relationships. In fact, no direct contact is required. Male mussels simply eject their semen into the river’s current. A short distance downriver, the female — filtering water, as mussels do — collects the floating semen and fertilizes her eggs. Mission accomplished. Still, they’re not exactly charismatic.