What happened when Dr. John Endler transferred the less colorful, dull male guppies from a region with dangerous predators to a region with less dangerous predators?

You answer is, Endlers

Endlers or Endler’s livebearers are a diminutive and colorful fish species that are popular in the hobby and ideal for tropical tanks. Interestingly, Endlers bear a striking resemblance with the Common guppy and some enthusiasts argue that both are the same species, however, this is not true.

Sure hope this helps you

biology is the study of life. it is the study of living organism.