Pollination systems cause coevolution, as in the close relationships between figs and fig wasps as well as yuccas and yucca moths. If nectar robbers have an effect (direct or indirect) on a plant or pollinator fitness, they are part of the coevolution process. Where nectar robbing is detrimental to the plant, a plant species might evolve to minimize the traits that attract the robbers or develop some type of protective mechanism to hinder them. Another option is to try to neutralize negative effects of nectar robbers. Nectar robbers are adapted for more efficient nectar robbing: for instance, hummingbirds and "Diglossa" flowerpiercers have serrated bills that are thought to aid them in incising flower tissue for nectar robbing.