Sexually dimorphic neural phenotypes in golden-collared manakins (Manacus vitellinus)

Male golden-collared manakins (Manacus vitellinus) perform a high-speed acrobatic courtship display punctuated by loud 'snaps' produced by the wings. Females join males on display courts to select individuals for copulation; females follow displaying males but do not perform acrobatics or make wing snaps. Sexually dimorphic courtship displays such as those performed by manakins are the result of intense sexual selection and suggest that differences between sexes exist at neural levels as well. We examined sex differences in the volume of brain areas that might be involved in the male manakin courtship display and in the female assessment of this display. We found that males had a larger hippocampus (HP, spatial learning) and arcopallium (AP, motor and limbic areas) than females when adjusted for the size of the telencephalon (TELE) minus the target area. Females had a larger ventrolateral mesopallium (MVL) both when adjusting for the size of the remaining TELE and by direct comparison. The entopallium (E) was not sexually dimorphic. The E is part of the avian tectofugal pathway and the MVL is linked to this pathway by reciprocal connections. The MVL likely modulates visually guided behavior via descending brainstem pathways. We found no sex differences in the volume of the cerebellum or cerebellar nuclei. We speculate that the HP is important to males for cross-season site fidelity and for local spatial memory, the AP for sexually driven motor patterns that are complex in males, and that the MVL facilitates female visual processing in selecting male display traits. These results are consistent with the idea that sexual selection has acted to select sex-specific behaviors in manakins that have neural correlates in the brain.