The gray tree frog is closely related to the green tree frog genetically, but they have different mating calls. this suggests that speciation occurred because of

The gray tree frog is closely related to the green tree frog genetically, but they have different mating calls. This suggests that speciation occurred because of reproductive isolation.

Explanation:

It is a speciation that occurs due to a type of reproductive isolation.  The song of each of these frogs has specific patterns only recognizable by members of the same species, so they are called a mechanism of reproductive isolation.

Different courtship rituals in animal species create extremely potent reproductive barriers, which keep the two frog species isolated despite They are  genetically close

since there are no options posted i'll give you a few examples.

a dolphin's flipper, bird's wing, cat's leg.