Releaser
It is not necessary for both partners to benefit, nor to be of the same species. Some moths instantly fold their wings and drop to the ground if they encounter bat ultrasonic signals. This helps helps the moths, but obviously not the bats. In turn, some bats turn off the sound blips when they hear a moth, and glide in the last few feet. This also is an inherited behaviour. This example may be better described as a reflex action.