54193
The importance of hybridisation in producing new species of animals is unclear , although cases have been seen in many types of animals , with the gray tree frog being a particularly well-studied example .
 gray tree frog
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: media, plant, vehicle, astronomical object, time, disease, animal, location, person, organization, mythical figure, food, biology, geographical phenomenon, instrument, event 
Text: {0} 
Answer:
 gray tree frog