Evolutionary Interactions of Feather Molt in Birds

Abstract

The evolution of feathers was a key innovation for birds. The many functions that feathers provide have allowed birds to diversify into myriad habitats and styles of life. However, feathers are lightweight and break down, and must be replaced regularly in a process known as molt. The patterns and timing with which birds molt varies within and between species, and these different strategies are likely a product of the different ways birds use their feathers and the uneven distribution of resources available for molt in time and space. So far, no studies have attempted to place these strategies into an evolutionary framework. In my dissertation research, I used phylogenetic comparative analyses combined with molt, phenotype, ecology, and spatial data to investigate how and why birds have evolved such a diverse array of molt strategies. I studied how molt affects the evolution of flightlessness and seasonal dichromatism in birds, as well as latitudinal gradients in the pace of feather growth. I found that molt strategies have profound effects on the evolutionary trajectories of birds. My major findings are that simultaneous wing molt facilitates and perhaps accelerated the evolution of flightlessness in birds, and that a secondary molt that evolved to replace worn feathers can serve as a preadaptation for phenotype alteration. I also found feather growth rate increases with latitude within bird species. Overall, feathers are integrally important to the biology of birds, and it makes sense that the patterns and strategies that birds use to replace their feathers are guided by and influence their evolutionary histories. This dissertation research provides some of the first evidence into the details of how molt strategies interact with other aspects of avian evolution.