Social dynamics and physiology: a Ph.D. student studies the biology and behavior of the male wire-tailed manakin

 

Ben Vernasco knew he wanted to pursue a Ph.D. in conservation biology while studying tropical birds in Peru. After his trip, he got in touch with his mentor, Brandt Ryder, a research ecologist at the Smithsonian Migratory Bird Center at the Smithsonian National Zoological Park in Washington, D.C.

Ryder and his Virginia Tech colleague Ignacio Moore, an associate professor of biological sciences in the College of Science, had just received a National Science Foundation grant with a spot for a graduate student. Vernasco was in luck.

Now, Vernasco is a doctoral student in biological sciences at Virginia Tech, and studies the wire-tailed manakin, or Pipra filicauda – a tropical bird named for the wired filaments on its tail and known by researchers for its unique social display: the males perform to attract the females.

To some researchers, this display looks like a dance – these birds perform with quick, smooth moves, back and forth on a branch, while flicking their wings to make sound. Some people have likened the movements of the red-capped manakin to Michael Jackson’s moonwalk: a seamless backward slide. And another species, the club-winged manakin, rubs its wings together over its back to make a buzzing noise, a movement so fast it is invisible to the naked eye.

As part of their display, manakins perform on the same designated perches within their territories. They even alter the habitat around their perch by tearing down leaves to make it a better arena to dance in, said Vernasco.

But dancing to attract females is not the only thing unique about these displays – males also display with other males. Within a particular territory, males will display together in order to form the basis of what Vernasco explained are social coalitions. Within these coalitions, the same males display together for years in order to develop social hierarchies.

During these male-to-male displays, one male will assume the position of the female, and the other will display to its comrade as if it were displaying to a female. Then, when a female comes by, the territory-holding male will take over and perform in order to mate, whereas the non-territory holders, or ‘floater’ males, will step aside until he makes his way up the social ladder.

“The more social bonds these floaters have,” said Vernasco, “the more likely they are to eventually gain a territory themselves and sire offspring.”

With Ryder and Moore’s guidance, Vernasco investigates this elaborate social behavior and its underlying physiology to get a better sense of the birds’ reproductive success and overall health. This includes measuring testosterone levels, which have been shown to increase when the males gain territory.

Male songbirds living in temperate climates with high testosterone levels tend to be more aggressive and defend larger territories, but little is known about the relationship between high testosterone levels and the behavior of male wire-tailed manakins living in the tropics. Understanding how testosterone levels influence behavior will offer Vernasco a deeper sense of how the wire-tailed species forms these sophisticated social relationships.

Vernasco also investigates the physiological costs of performing such an elaborate display by measuring how fast a bird’s telomeres degrade. Telomeres are like the capped ends of shoelaces; they protect and maintain chromosomes from breaking down like plastic tips protect shoelaces from fraying. The speed at which these caps break down can be used to measure a bird’s condition and therefore reproductive quality. The faster telomeres break down, the more likely a bird’s lifespan and physical health will decrease, making it more susceptible to disease.

Using radio telemetry, or radio transmitters, Vernasco and his mentors are able to track the manakin’s social movements at their field site, the Tiputini Biodiversity Station in Ecuador. These tags are like little lightweight backpacks – weighing only about three percent of the bird’s weight – that fit over each leg, with the main receiver resting on the bird’s back.

The researchers tag both the floaters and the territory holders, so they can see which birds come in and out of the territories and then measure the strength of these interactions. Mapping these social dynamics will provide further insight about this species and how physiology and behavior correlate.

“Few studies have looked at how the social environment influences telomeres, so that’s an important aspect of this research,” said Vernasco. “Broadening our understanding of hormones using these tropical birds that express unique behaviors will give us a better sense of how evolution works and acts on these behavioral and hormonal interactions.”

“This work is really exciting because we are scaling up from hormones in the brain and blood to an individual’s behavior and, ultimately, to their social organization,” said Moore.

Vernasco, who is also a fellow in the Interfaces of Global Change Interdisciplinary Graduate Education Program, hopes that this research will draw attention to sensitive ecosystems in the tropics, which are globally important for their species diversity and for showing the environmental impacts of people.

“In countries that are still developing, like many in the tropics, there’s a lack of regulation on things like deforestation and environmental contamination,” said Vernasco. “By drawing awareness of these birds and where they live, more people will be exposed to the Amazon and other habitats within the tropics.” 

From a Fralin Spotlight, written by Cassandra Hockman, communications coordinator at Fralin.

Posted April 17, 2015