Researchers have found that the larvae of all North American firefly species glow as a warning sign to ward off predators. However, the presence and use of lighting organs in adult fireflies vary greatly. Some species use glowing or light flashes as mating signals, while other species produce pheromones as mating signals and do not glow at all. Discuss how the physical characteristics and mating behavior of North American fireflies support the theory of speciation. In your discussion, provide a hypothesis to explain the driving force behind the differences in mating signals among the species.