A new research paper published on strawberry poison dart frogs in Bocas del Torro found that one of the reasons we have polymorphism or so many different color forms within one species of frog. Female tadpoles prefer to mate with males that have the same color as their parents (sexual imprinting), and males defend their territories more vigorously from other males that are the same color as their parents (rival imprinting). The researchers demonstrated this experimentally by using foster parents of different color forms to raise offspring, and then tested mate or rival preference of the adult offspring.
This process of sexual selection can lead to sexual isolation even in populations that live in the same places. From an evolutionary perspective this would be a rare example of sympatric speciation, or the evolution through natural selection without geographical isolation.
Read the paper here Yang, Y., Servedio, M.R., Richards-Zawacki, C.L., 2019. Imprinting sets the stage for speciation. Nature 574, 99–102.