Abstract Calling activity in frogs is energetically demanding to males because they usually perform at or near their physiological capacities.（Bevier，1997）
The preexisting bias for males with swords in fishes of the genera Xiphophorus and Priapella might result from a more general preference for body size, a preference that is widespread among these types of fishes.
Bat predation was the selection force responsible for opening the ultrasonic world to moths; its relaxation has allowed this sensory channel to be used for communication.
Thus, female preferences and male traits coevolve through genetic correlation.
Two interesting possibilities relate to how stimulus organization and presentation influence the receiver’s attention, and how processes of stimulus generalization and categorization can lead to receiver biases.
Alternatively, Greenfield et al. (19) argued that a precedence effect results in males evolving a resettable oscillator that controls male calling as an evolutionarily stable strategy, and that striking patterns of collective signaling thus emerge as incidental consequences.
Dobzhansky (1937) suggested that they evolve as a mechanism to ensure species integrity, and that reinforcement or reproductive character displacement is an outcome of this process.