Developmental perspective on the evolution of sexual ornaments

Sexual ornaments are favoured to be both less integrated with other organismal traits for greater expression, and yet more integrated with organismal development and functions to better indicate the physiological quality of an organism. Two conceptual approaches in morphological evolution - the consideration of internal and external processes and the evolution of integration and modularity - are useful in resolving this apparent paradox, yet these approaches are mostly overlooked in studies of the development of sexual displays. Moreover, whereas recent studies have recognized the evolutionary continuum of the mechanisms by which sexual selection operates, the consequences for the evolution of development of sexual displays are not well understood. Here I suggest that the concept of morphological integration may provide a useful framework for understanding the development and evolution of sexual ornamentation.