• Sexual Selection and Plumage in the Polymorphic White-throated Sparrow

      Rathbun, Nathan (2010-07-20)
      Feather coloration has been known to be connected with sexual selection for many years. It also provides an opportunity to study evolution, focusing on sexual selection and natural selection. Plumage is affected by both of these forces and the equilibrium is where these forces balance. The white-throated sparrow gives us a unique opportunity to observe the effects of the different strengths of these forces within a species. First, I established that there were differences in plumage characteristics between the morphs and sexes. White males had the brightest white and darkest black feathers. White females and tan males were the next brightest, with tan females having the dullest white and lightest black head stripes. Using plumage characteristics I was able to predict the morph/sex class of the bird significantly more than by chance. With the exact differences between each morph/sex class now known, I looked at the relationship between fitness and plumage. White males with higher overall contrast (brighter white, darker black) were more successful than duller white males. This was attributed to the males displaying their quality to females. Duller tan males however, were more successful than brighter tan males. With duller plumage, they may reduce predation on their nest while they are feeding their offspring. The differences in reproductive strategy changed the relative strength of natural and sexual selection between the morphs. Observing this interaction in this system will let us judge the relative strength of these forces in other systems.