European eels (Anguilla anguilla) have a life cycle in which both larvae and adults travel incredible distances. The eggs hatch in the Sargasso Sea near North America and the larvae swim all the way to Europe.
Having a choice for a mating partner is extremely important for females, so they can be critical in choosing which male to mate with.
Often in animal research, animals with a certain genetic alteration are compared to a “wild-type”. One might assume that there is no differences between wild-types, but many different strains of wild-type animals are used.