Students study sloths in Costa Rica

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Ever wondered how sloths hang upside down in trees for such long periods of time? Or how it is that sloths can climb so high, and yet move so slow? Dr. Michael Butcher, of the Department of Biological Sciences, has pondered these questions and is attempting to answer them by researching the specialized anatomy of the brown-throated three-toed sloth (Bradypus variegatus). These animals are somewhat rare in the wild, and having the opportunity to study their muscles is a once-in-a-lifetime experience for Butcher and his students.

Dr. Butcher traveled to The Sloth Sanctuary in Penshurst-Limon, Costa Rica, on May 26 accompanied by his graduate student, Dylan Thomas, his undergraduate research assistant, Zachary Glenn, and former graduate student, Rachel Olson (YSU 2013). The team collaborated with Rebecca Cliffe, a British zoologist who has dedicated her life to studying these primitive mammals and has been featured on Discovery Channel’s “Meet the Sloths”.

“It was a once in a lifetime trip to work with the sloths and venture into the jungle with some of the most diverse wildlife on the planet,” Dylan said. “It was such a culture shock going from living in the city and waking up with an alarm clock to living in the jungle and waking up to Howler Monkeys securing their territory at sunrise around 4:30 [or] 5 a.m.”

The trip proved to be highly productive, and together they performed several experiments evaluating the strength of sloths, including detailed dissections of their limb anatomy to allow for quantifications of muscle force and power and bone stress.

“Sloths are very unique in their movement and behavior because of their very slow movement through the trees. Sloths are thought to be weak because of this and their small muscles, but this couldn’t be farther from the truth,” Dylan said. “Sloths are able to suspend their entire body weight hanging from one limb for long periods of time and have unbelievable grip strength. Sloths can produce an incredible amount of force for how ‘wimpy’ their muscles are, in fact if you were to arm-wrestle a sloth, the sloth would win every time!”

Dr. Butcher and his team also harvested muscle tissue to determine the distributions of slow-twitch and fast-twitch muscles in their limbs, and how these collective muscle properties relate to their ability to ‘walk’ while hanging beneath tree branches. These tissue-type analyses will be conducted in his laboratory at YSU.

“Each day was an early start to get a jump on the dissections because each limb took approximately 10 to 12 hours to gather measurements and collect muscle samples,” Dylan said.

In addition, Butcher was able to biopsy fresh tissue from their heart, liver, and kidneys for a future project that will map out their genome. The outcomes of all of these studies will provide answers to numerous questions about the unusual biology of sloths. Perhaps most importantly, assembling a set of anatomical and genomic characteristics from three-toed sloths will allow Dr. Butcher to further test hypotheses surrounding the evolution of mammals.

Sloths are members of an assemblage of ancient placental mammals known as Xenarthrans, and knowledge of their emergence is important to understanding how and when other placental mammals like humans evolved.

“I took a lot from this trip, not only from the collected data but also from the personal experience. I realized all of the opportunities that research could bring and how much of the jungle is unknown,” Dylan said. “In the future, I would like to travel back down to Central American and do more research because it’s an area with infinite knowledge, not only for studying muscle anatomy and physiology but also possible treatments for clinical disease.”