A large part of sexual selection research is understanding what makes boys different from girls, and why those differences exist in the first place. I recently wrote a post about how female golden-collared manakins prefer acrobatic males. A new research article from members of the same group was published this month in the journal Brain, Behavior, and Evolution. They have identified regions of the brain that differ between the sexes in this bird species.
Males and females are different in a lot of ways, and the brain is no exception. In humans, scientists have mapped many of the brain differences between men and women (see related articles below), including a higher stimulation in men of brain areas involved in sexual arousal when viewing erotic material.
In birds, species in which only males sing have larger areas in the brain for singing in males but not in females. Other sex-specific activities in birds are also linked to brain differences, but so far no one has shown a link between sex differences in the brain and sex differences in courtship displays.
Golden-collared manakins have a crazy courtship display that is under intense sexual selection (see previous post). Presumably, there would be intense selection on male brains to perform these displays.
The study found a number of differences between male and female golden-collared manakin brains. First, females have larger telencephalons (all of the brain except brain stem and cerebellum), after controlling for whole brain size. They also have a larger ventrolateral mesopallium. This brain area isn’t entirely understood, but may have an important role in visual processing. Female manakins have to be able to see tiny differences between male performances that are very, very fast.
Males, on the other hand, have a larger hippocampus, which is involved in spatial learning, and a larger arcopallium which is important for motor function. The hippocampus is the brain’s storage space for maps, among other things. Male manakins always use the same mating arena, year after year, but they don’t hang out there during the off-season. So, they may need a larger hippocampus to find their way back each year and recognize their spot, even though it may have changed somewhat. These arenas are tiny compared to the whole forest: only about 75cm in diameter. Females don’t need to remember specific areas. They can always find them again by following the sounds males make during their displays.
The arcopallium is a region of the brain that controls motor function and is associated with song learning in songbirds. Manakin males had a larger arcopallium, and the researchers think that this helps them perform their courtship displays, but which parts of the arcopallium are specifically involved (and whether their similar to the song regions of the brain in other birds) is still not known.
These results show that selection for males to perform high-speed acrobatics has resulted in differences between male and female brains. As males became better at performing their displays, females had to be able to tell males apart by how fast they perform–down to differences of a fraction of a second.
So, male brains become better at controlling high-speed flips and snaps, and female brains become better at judging male performance.
- 10 Big Differences between Men’s and Women’s Brains (mastersofhealthcare.com)
- Girl Brain, Boy Brain? (scientificamerican.com)
- Sexually dimorphic neural phenotypes in golden-collared manakins (Pubmed abstract).
- Athletic Courtship in Birds [Life Lines] (scienceblogs.com)
- Sex or nice weather – the agonizing choice some birds face (news.bioscholar.com)
- Bird Brain (pbs.org)