Marine Biology Doctoral Student’s Research Leads to Discovery of Hybrid Sharks

By Richard Guerrero | Published: April 25, 2019

Marine Biology Doctoral Student’s Research Leads to Discovery of Hybrid Sharks

CORPUS CHRISTI, Texas – As a Marine Biology doctoral student whose research focuses on the genetics of scalloped hammerhead and Carolina hammerhead sharks to provide information for conservation and management, Amanda Barker clearly remembers the hot summer day in 2017 when she finally got to meet her study subject in the flesh.

A graduate research assistant in the Marine Genomics Laboratory run by Dr. David Portnoy, Texas A&M University-Corpus Christi Assistant Professor of Life Sciences, Barker spends her summers assisting with the management of a bottom longline survey used to determine which shark species use Corpus Christi Bay as nursery grounds for their young. The lab provides the survey data it obtains to the Texas Parks and Wildlife Department to assist in conservation efforts. 

“A lot of sharks will come into bays and give live birth. Basically, they drop off their pups and head out. We suspected that scalloped hammerheads were among the species to do this locally but had been unable to catch any in the previous two years,” Barker said. “It was really exciting to not only confirm that young scalloped hammerheads can be found in our bays but to also see my study species in person.”

Barker’s work on her dissertation, “Population Genomics and Molecular Ecology of the Scalloped Hammerhead and Carolina Hammerhead,” has led to an article in the London-based scientific journal Biology Letters, which was published in April. Barker plans to graduate from Texas A&M-Corpus Christi in the fall. Barker’s research was funded by a U.S. Fish and Wildlife Service Competitive State Wildlife grant and a National Oceanic and Atmospheric Administration/National Marine Fisheries Service Competitive Researched Program grant.

Dr. Portnoy said previous researchers had discovered that while scalloped and Carolina hammerheads were virtually morphologically indistinguishable, there was a difference in the number of vertebra. Genetic analysis confirmed that scalloped hammerheads and Carolina hammerheads are distinct, but little else was known.

“The federal government is interested in learning where the two species are distributed—particularly where the Carolina hammerheads are—along with the relative abundance of each species,” Portnoy said.   

In her article, Barker detailed previously unknown hybridization between scalloped hammerheads and Carolina hammerheads, which share an overlapping habitat, in the western North Atlantic Ocean. Barker analyzed DNA samples taken from fin clips of 600 individuals between 2010 and 2017 to arrive at her findings.   

“I was trying to find genetic markers that distinguish the two species. When I started to identify all of these individuals, I discovered that there were a handful of them that could not be identified,” she said. “When I took a closer look, I realized that the unidentified individuals were 50% one species and 50% the other.”

Portnoy said Barker publishing an article in a prestigious research journal like Biology Letters is an impressive accomplishment for a graduate student.

“To be a graduate student still working on her doctorate, publishing an article in a journal with a wide international readership is a real feather in her cap,” Portnoy said.

A native of San Diego, California, Barker is a first-generation college student whose academic career started at a community college before she transferred to the University of California San Diego to complete her Bachelor of Science degree in Ecology, Behavior and Evolution in 2012. She remained at UC-San Diego to earn her Master of Science degree in Biology two years later.

“I grew up going to the beach and as a kid, I always wanted to be a marine biologist,” she said.

While at UC-San Diego, Barker began volunteering at the Scripps Institution of Oceanography and eventually became a graduate research assistant assigned to investigate the population structure of leopard sharks using microsatellites and mitochondrial DNA for two years. She also conducted lab work on invasive quagga mussels.  

Barker said she chose to pursue a doctoral degree at A&M University-Corpus Christi based on the Island University’s facilities, research opportunities and academic faculty.

“Dr. Portnoy, my graduate advisor, had just received a grant to study scalloped and Carolina hammerhead sharks, which was perfectly suited to my research interests,” she said. “In addition, the campus’ proximity to the beach made it an easy decision for me.”

As an Islander, Barker was a founding member of the American Fisheries Society TAMU-CC Student Subunit, which is involved in various community outreach events to build awareness of fisheries science and research conducted at A&M-Corpus Christi. The organization also holds cleanup events at University Beach several times a year. 

Looking ahead, Barker plans to pursue a career as a conservation biologist at a state or federal agency.

“I really enjoy generating data that can then be used by managers to make decisions about how to preserve these populations of concern,” she said. “I want to conduct robust research that can become the foundation for well-founded, science-based management policies.”