In search of the Woolly Opossum

YSU graduate student Joe Rupert at the Arenal Volcano in Costa Rica.

YSU graduate student Joseph Rupert spent this past summer, machete in hand, hacking his way through Costa Rica’s dense tropical rainforest in search of Caluromys derbianus, an arboreal species of opossum known as the Central American Woolly Opossum.

Rupert’s trip to Costa Rica is part of YSU assistant professor of Biomechanics Michael Butcher’s research studying the prehensile tail structure and function of opossums.

Butcher and Rupert spent nearly a year planning his research team’s expedition in July to find and trap the elusive didelphid marsupial. The team spent eight days at a biological reserve in the Northern Central rainforest performing muscle biopsies on the tail muscles of Caluromys.

“The first three days of trapping were unsuccessful, but on days four through seven, we caught five opossums,” said Rupert, who plans to graduate this spring with a master’s degree in Biological Sciences with a concentration in Muscle Biomechanics. Rupert graduated from YSU in 2010 with a degree in Biological Sciences.

Rupert, who plans to pursue a Ph.D. at either Duke or Cornell, said he and Butcher worked alongside a wildlife veterinarian who monitored the animals’ vital signs during sedation while the opossums underwent a brief biopsy to harvest muscle tissue from their tails.

This is one of the Caluromys derbianus opossums that Rupert and Assistant Professor Michael Butcher studied in Costa Rica.

The opossums were then observed for approximately six hours post-biopsy to ensure complete reversal of the sedative and to be sure that they were completely fit to return to their habitat. The team ultimately sampled tail muscle from six animals.

“All opossums possess a prehensile tail, as they are linked evolutionarily to a common arboreal ancestor,” said Butcher. “Opossums first appeared as canopy dwellers of the South American rainforests about 60 million years ago.”

Rupert is working on identifying the composition of myosin proteins expressed in their tail muscles and is trying to determine if there has been a change in muscle myosin between arboreal and terrestrial species. Myosin proteins determine how fast or slow muscles contract.

The team hypothesizes arboreal species will have a large amount of fast, Type II myosin muscle fibers required for high force to suspend in trees, while terrestrial species will have a greater abundance slow, Type I myosin fiber for endurance activities involved with nest building.

Rupert is currently performing the experimental work to test these hypotheses. Finding a difference will allow a better understanding of how opossums have adapted to survive in terrestrial habitats.