Small sex differences in song control dendrites are associated with minimal differences in song capacity

Previous work on canaries and zebra finches has shown that large differences between the sexes exist in the structure of dendrites in n. robustus archistriatalis (RA), one of the principal nuclei involved in the control of song. This sex difference is associated with a general or complete absence of song in females. If dendritic morphology in RA is causally related to capacity for song, large sex differences in structure should not occur in avian species in which both sexes sing. We now report this prediction confirmed for buff-breasted wrens (Thryothorus leucotis), a species in which the members of a breeding pair sing duets with each other. Total dendritic length and number of dendritic branches in RA do not differ in this species. Dendrites from males project about 8 micron further from the cell body than dendrites from females, apparently because of longer dendritic segments near the cell body. We argue that this suggests that differential influences on the structure of RA occurred early in the lives of the wrens.