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Zoology

A seductive dance

The behavior of the blue-backed manakin determines its genetic variability

maria guimarãesBright colors are not enough: manakins must whirl to attract mating partnersmaria guimarães

From the tip of a branch, the tiny olive-green manakin observes the line of males getting ready for the mating ritual. The first male takes off, hovers in the air for a few seconds and shows the female the red feathers on the top of its head before going to the end of the line. A male quickly succeeds the other one in this flirty maneuver that looks like a dispute between rivals, but is actually an organized ballet. The coordinated dance continues until one of the males lets out a high-pitched tee-tee-tee-tee-tee sound.

This is the leader of the group – or the alpha male, as the biologists refer to it – announcing that the party is over. If the bird is successful, it will fly to the privacy of the forest in the company of the bride. On this stage, which experts refer to as lek, it is always the male who gives the orders. But it will be unable to attract the attention of a female unless there is a corps de ballet comprised of one to seven subordinate males. This is a difficult task: during the mating period, the male birds dance every day, all day long. During the non-mating and cold winter season, they limit their performance to one or two dances each morning. “The females evaluate the male’s ability to maintain an organized group,” explains biologist Mercival Francisco, from the Sorocaba campus at the Federal University of São Carlos (UFSCar).

But what do the supporting actors gain from this? This is one of the questions that has kept Mercival busy, as he is also trying to identify how the genetic composition of the blue-backed manakins (Chiroxiphia caudata), the bird that is the symbol of the seaside town of Ubatuba, varies in the course of its distribution. He studied these birds – that have a 13-centimeter- long blue body, black head and wings and a red cap that they show off so proudly – on the longest strip of the remaining Mata Atlântica rain forest, which used to line most of the Brazilian coast.

Most of this continuous strip is in the State of São Paulo. Mercival chose five areas in environmentally protected zones to collect samples of the genetic diversity of the blue-backed manakins: the Petar state park, on the border of the State of Paraná, the Carlos Botelho state park, close to the city of Sorocaba, and the Cubatão, Caraguatatuba and Picinguaba Centers of the Serra do Mar State Park – all of them under the management of the Forestry Institute. The lucky animals that live in the 415 kilometers that separate the Petar and the Picinguaba Center enjoy more than 17,300 square kilometers of forest. In the researcher’s opinion, this was a unique opportunity to study the behavior of dancing birds when they are not restricted to clumps of forests surrounded by sugarcane plantations or urban areas.

In the five chosen areas, Mercival drew blood samples from males that participated in the dancing groups and analyzed ten stretches of selected DNA to analyze the kinship. The idea was to see whether family ties, that explain a lot of the solidarity in animals, are behind this dance – helping siblings is seen by biologists as an indirect way of perpetuating genes, a strategy encouraged by evolution. However, the results show that this is not the case with manakins. Groups of dancers might include kin males, but this is not what brings them together. “They remain where they were born, and sometimes by chance end up in a lek where they have no next-of-kin,” says the biologist.

All in all
This discovery is not really a surprise. The same pattern was already observed in other manakins of the Chiroxiphia lanceolata species that inhabit the Amazon Region and Central America, and that resemble the manakins of the Mata Atlântica rain forest, but the blue is restricted to their backs, as if it were a cover. Studies conducted in Panama since 1999 by American biologist Emily DuVal, from Florida State University, showed that these birds dance in pairs, which are not formed through family ties. Observing the feathered pas de deux year after year, Emily unraveled a stronger stimulus than brotherly solidarity: the subordinate males have a better chance of moving up to the alpha position than any of the males that do not take part in the dancing.

Mercival believes that the rules of the game are the same in the case of his manakins. “The chance of reproducing is zero for males that are not part of the lek. For those that participate, the opportunities are rare, but they do exist.” The researcher intends to continue detailed research to understand the succession in the ballet corps of the blue backed manakins.

He is worried about the deforestation of the Mata Atlântica rainforest, which isolates plants and animals in clumps of forest. In an article published at the end of 2007 in the journal Molecular Ecology, together with Pedro Galetti Junior, from the São Carlos campus of UFSCar, and with the Lisle Gibbs, from the State University of Ohio, in the United States, Mercival compared the genetic diversity in the five areas he was studying and showed that the greater the geographic distance, the more different the populations from the genetic point of view – a sign that the manakins stay close to where they were born, rather than migrating over long distances to spread their genetic material. “We found unique alleles in all the places where we did the research,” says the biologist, referring to the different forms that each gene can take on. This means that every lost forest takes with itself part of the genetic diversity of the blue backed manakin. In regions where the genetic variability is no longer so significant, the loss of whatever diversity still exists can result in populations that are highly susceptible to deformities and diseases caused by defective genes – for the same reason that consanguineous marriages between human beings are avoided. As deforestation advances, the word “dance” runs the risk of taking on its figurative meaning in the case of the manakins.

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