Sexually Dimorphic Neural Phenotypes in Golden-Collared Manakins <i>(Manacus vitellinus)</i>

Abstract

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.

Acrobatic Courtship Display Coevolves with Brain Size in Manakins (Pipridae)

“…1 ) [Bostwick and Prum, 2003;Prum, 1990Prum, , 1994Prum, , 1998]. Such behavioural complexity likely requires a range of motor, sensorimotor, perceptual, and cognitive skills [Barske et al, 2011;Bostwick and Prum, 2003;Coccon et al, 2012;Day et al, 2011;Prum, 1986;Rosselli et al, 2002;Schlinger et al, 2008Schlinger et al, , 2013Théry, 1990;Trainer et al, 2002].…”

“…In golden-collared manakins (Manacus vitellinus), females choose mates based on millisecond differences in the performance of postural display sequences [Barske et al, 2011], and males vary in terms of the timing of these display elements [Fusani et al, 2007b]. The discovery of specializations of both male motor control circuitry and female visual processing centres [Day et al, 2011] supports the idea that the manakin brain has been shaped by evolution to support both male performance and female assessment of courtship display [Day et al, 2011]. Enhanced spatial cognition may also be necessary for both choreographed use of the spatial structure within a display arena [Coccon et al, 2012;Fusani et al, 2007b] and spatial navigation between alternate arenas [Prum, 1986;Rosselli et al, 2002;Théry, 1990].…”

Seasonal Variation in Forebrain Region Sizes in Male Ruffed Grouse <b><i>(Bonasa umbellus)</i></b>

“…As a result of its multifunctional nature, the mesopallium is unlikely to be directly tied to drumming behaviour, which is why we did not expect to find a seasonal difference in mesopallial volume. That said, we did not measure sub-regions within the mesopallium, which could vary by sex [Day et al, 2011] and potentially with season.…”

“…For example, their wing muscles, and the spinal motor neurons that mediate their control, express relatively high levels of androgen receptors [Feng et al, 2010;Fuxjager et al, 2012]. Within the motor pathway of the brain, male manakins have high levels of androgen receptors in the arcopallium [Fusani et al, 2014b] and males have relatively larger arcopallial volumes than females [Day et al, 2011]. The arcopallium is a major source of premotor output from the telencephalon (TELE) [Reiner et al, 2005;Shanahan et al, 2013] and likely plays a key role in performing the complicated wing movements involved in the manakin's display.…”

“…Although nothing is known about the neural control of this display, we chose to focus primarily upon motor control regions: the arcopallium, cerebellum (Cb) and striatopallidal complex (SPC). The arcopallium is of particular interest because it is a premotor area implicated in the production of most motor behaviour [Rei ner et al, 2005;Feenders et al, 2008;Shanahan et al, 2013] and, as mentioned above, courtship behaviour in manakins [Day et al, 2011;Schlinger et al, 2013;Fusani et al, 2014b]. In addition, the RA nucleus within the oscine song system is nested within the arcopallium and undergoes seasonal changes in anatomy in relation to song production during the breeding season [DeVoogd et al, 1985;.…”