Not all adaptions of species is related to physical change. Some organisms exhibit behavioral changes which separate themselves from other species or provide an advantage.
One example off adaptations in mating rituals is found among non-social orchid bees in Central and South America. The male bees collect various chemicals and odors from flowers & plants. They store these odors in pouches on their hind legs and release the chemicals during their mating rituals. Different species will collect different fragrances and chemicals from different plants or in different amounts based on their geography and biological needs. The females of each species only react to particular combinations of fragrances (Pokorny, et. al., 2013). This prevents female bees form trying to mate with bees of other species which will not produce viable offspring.
Koel are brood parasites, laying their eggs in the nests of other birds and letting the host bird hatch the eggs. The Jungle crow, an oft-parasitized species, has developed a highly aggressive behavioral pattern to prevent the koel from setting their eggs in the crow's nest. However, the koel has coevolved its own behavioral modification. The male will lure the aggressive crow out to chase it while the female koel sets the cuckoo eggs in the crow's nest (Rothstein, 1990).
Knoll, Fátima R. N., & Santos, Leandro M.. (2012). Orchid bee baits attracting bees of the genus Megalopta (Hymenoptera, Halictidae) in Bauru region, São Paulo, Brazil: abundance, seasonality, and the importance of odors for dim-light bees. Revista Brasileira de Entomologia, 56(4), 481-488. Rothstein, S. L. (1990). A MODEL SYSTEM FOR COEVOLUTION: AVIAN BROOD PARASITISM. Annual Review Of Ecology & Systematics, 21481-508.