Endless Forms Most Beautiful by Sean Carroll: Chapter 9 Summary

Summary of Chapter 9 of Endless Forms Most Beautiful by Sean Caroll: Chapter 9 begins by describing the views of Roosevelt and a hunter. The theories by these two individuals illustrated that not all answers are black and white. It is obvious that coloration plays an important role in animal interaction and evolution. Chapter 9 focuses on the evolution of one color: black. This Chapter highlights the evolution of black coloration in jaguars, birds, pocket mice, fruit flies, and a handful of domestic species. Melanism refers to the condition whereby an individual displays broader areas or greater amounts of black or dark coloration in place of other colors. The occurrence of melanism is widespread throughout animal kingdoms, and it can play an important role in protection from UV damage, thermal regulation, concealment and camouflage, and mate choice. The peppered moth is a great example of melanism and natural selection, and the genes involved in melanism have been identified. Jaguars display melanism and the gene MC1R is responsible for pigment type. Specific mutations in this gene allow for all black jaguars. A change in the protein’s sequence, deleting 5 amino acids and changing one into MC1R protein, is responsible for this mutation rather than a genetic switch. Therefore, the ability of pigmentation to evolve without affecting other functions is due to the evolution of the MC1R regulation. MC1R mutations have been able to cause changes in cats and melanic plumage in birds. There are speculations to the selective advantages or disadvantages in some species, but in other species, the speculation is very clear. For example, the rock pocket mice have coloration based on their habitat in order to protect themselves from predators. Light-colored mice are typically found around light-colored rocks, and dark-colored mice are found on dark lava flows. Other examples of melanism include Kermode bears and redheads. What about animals with stripes or spots? Melanocytes color these stripes and melanoblasts, the precursors, stream out of the neural crest and migrate along tracks that are generally perpendicular to the spinal cord. Mutations that slow of reduce this migration leave the areas white, which is the basis for white paint on horses and white bellies on dogs. In zebras, it has not known whether the white stripes are regions that lack melanocytes or if these areas have melanocytes that are inhibited from producing pigment. There can also be variations in stripe number. Evolutionary changes in in the switch that control how D. biarmipes is expressed in fruit fly wing cells, which allows for spots on fruit fly wings. These mutations may either be a result in the power of selection or elimination of mutations that are disadvantageous. These mutations can increase fitness in a population.
Questions:
1. Will the true color of a zebra ever be discovered?
2. Can it be said that differences in melanism can be related to differences in butterfly wing patterns?
3. Can species with different forms of melanism, like the jaguars, reproduce?