Fast wing moves are the performance of Ecuador’s club wing manakin (Machaeropterus deliciosus) and his family members.
Murray Cooper / Minden Pictures
By Elizabeth Pennisi
For a glimpse into the power of sexual selection, the dance of the golden collar manakin is hard to beat. In the rainforests of Panama, the sparrow-male birds gather every June to fluff their brilliant yellow throats, raise their wings and clap together in rapid fire, up to 60 times per second. When a female favors a male with her attention, he follows up with acrobatic jumps, more wing buttons and maybe a second, meandering back flip. “If manakins were human, they would be one of the greatest artists, athletes, and social people in our society,” said Ignacio Moore, an integrative organism biologist at the Virginia Polytechnic Institute and State University.
As biologists have understood since Charles Darwin, such exhibitionism develops when females choose to mate with males that have the most extravagant appearance and display – an advocate for fitness. And now, by studying the genomes of the golden collar manakin (Manacus vitellinus) and his family members, researchers are investigating the genes that drive these extensive behaviors and traits. Last month during the Virtual Society of Integrative and Comparative Biology virtual meeting, Moore and other researchers introduced four manaquine genomes, which added to two already published, and singled out genes at work in birds’ muscles and brains that can make the exhibitions possible.
The work provides a better understanding of why manakins do all the amazing things they do, ‘says Emily DuVal, a behavioral ecologist at Florida State University. Over the past decade, researchers have learned a great deal about how natural selection affects genomes. “By contrast, we know very little about the underlying basis of sexually selected traits,” says Christopher Balakrishnan, an evolutionary biologist at East Carolina University (ECU). By mapping traits and genes on the manakin’s pedigree, researchers begin to detect the step-by-step genetic changes that have led to the most extensive exhibits and determine whether sexual selection works differently from natural selection.
Other species – especially the birds of paradise and the bowerbirds – also hold impressive sexual displays. But manakins have a greater variety of such traits, and because they are more abundant and accessible, it is easier to study in depth. We can ‘assess the genomic basis for this behavior in a way that is impossible for many other complex behavioral traits in vertebrates’, says Morgan Wirthlin, an evolutionary neurobiologist at Carnegie Mellon University.
As Balakrishnan and his colleagues reported during the meeting, a sweet tooth – or bill – may have set the scene for sexual selection in manakins. It is known that their ancestors switched their diet from insects to fruits, and researchers suspected that the change to a more available and abundant food source gave men extra energy to acquire mates.
Balakrishnan, Maude Baldwin of the Max Planck Institute of Ornithology, and colleagues found evidence that fruit eating and extensive male exhibits have evolved in stages, by comparing genomes of family visits that continue to eat insects with those of fruit-eating mannequins. The researchers learned that the genes that encode a salty taste receptor began to change even before manakins became fruit eaters. By the time the tyrant-manakin with saffronNeopelma chrysocephalum) developed, Baldwin reported during the meeting, the receptor became sensitive to the sweetness of ripe fruit – a trait that is rare among birds. That species track with simple hops – halfway to the extensive exhibits of the fruit-eating species that later evolved.
Wirthlin and others examined the DNA that changed to make this behavior possible. In her analysis of five mannequin genomes, she focused on elements that were not coded, that were not coded, segments of DNA that remained almost exactly the same for animals, ranging from chickens to humans and are considered to play an important role. in the regulation of other genes. Given this preservation, she thought it would be a good place to look for possible fingerprints of sexual selection.
In the manakin genome, 57 elements showed slight differences from the corresponding sequences in other species; these changes can alter the activity of the genes that regulate them. Some of these elements are grouped around genes for muscle proteins and hormone receptors, and others are close to genes that are expressed in the brain, including two, TLE4 and MEIS2, active in a region required for fast visual processing. Both genes are less active in manakins than in zebrafish, Wirthlin reported – a change that can help male manakins cope with the visual demands of their frenetic dances.
Matthew Fuxjager, an integrated biologist at Brown University, is excited about Wirthlin’s finding that evolution may have improved the activity of genes for birds’ hormone receptors. The high-speed wing that strikes some species requires extra fast and powerful meat breast muscles – which are very sensitive to the male hormone androgen. “Androgens are what increase speed,” by altering the activity of muscle performance genes, Fuxjager says.
At the meeting, Balakrishnan reported that he could identify other genes that could also strain the important muscles. His genomic analysis suggested that the activity of genes involved in muscle metabolism and growth changed early in the evolution of mankind, yielding more powerful muscles. He did not look at women, but he and Fuxjager think that the demands of flight, not mating, may have driven the early changes. When sexual selection began to act on species that later evolved, changes in the androgen receptors and other signaling pathways enabled the fly muscles in males to perform the very rapid movements necessary for the performance of courtship. (Other research shows that female muscles are not as sensitive to androgens.)
Performing the manakins involves more than sound and movement – in some species it is also a social act, coordinated among as many as 20 men. In all vertebrates, a network of ‘brain’ nuclei – clusters of similar nerve cells – help control social behavior, and studies presented at the meeting show that the pattern of gene activity in those nuclei varies with testosterone levels. The work, by evolutionary biologist Peri Bolton of ECU and ecologists Brent Horton of Millersville University and Brent Ryder of Smithsonian National Zoological Park, suggests that changes in androgen receptors could help the birds’ social sophistication as well as their athletics. .
It’s blinding as the manakins’ performances are, and researchers are just as amazed at their intricate genetic underpinnings. “Our studies teach us that beauty is more than deep,” Moore says.