If you're a rattlesnake, you want to bring the right weapon to a squirrel fight. And that venomous weapon varies from place to place, evolutionarily calibrated to overpower the local squirrels' defenses, according to new research.
Link: https://www.sciencedaily.com/releases/2016/05/160519120940.htm
Link: https://www.sciencedaily.com/releases/2016/05/160519120940.htm