Turtle watch assists with DNA research
Anna Maria Island Turtle Watch is partnering with a University of Georgia researcher to create a DNA analysis of the sea turtles that nest on the Island’s beaches.
The work, which involves collecting genetic material from loggerhead turtle nests, is part of a broader, long-range effort to identify genetic differences among sea turtle populations in the southeastern United States.
“This genetics project is pretty extensive thanks to the willingness of personnel of state, county and federal agencies, as well as volunteer groups,” said Brian Shamblin, a doctoral student with the Warnell School of Forestry and Natural Resources at the University of Georgia. “We have over 30 partners in Florida, Georgia, South Carolina and North Carolina who have contributed samples or have assisted in beach access so I could sample in person.”
“Determining the number of subpopulations [of loggerheads] and their boundaries is the main focus of the research,” Shamblin added.
AMITW, whose members collect data about turtle crawls, nests and hatches on the Island, has identified at least 24 nests from which DNA samples will be collected for Shamblin’s research.
During nesting season, from about May 1 through October, female sea turtles return to their home region to crawl from the water to the sand to lay their eggs - about 100 to a nest. As of Aug. 20, Turtle Watch had identified 142 nests on the Island, as well as one at an unusual location, the DeSoto National Memorial on the shore of the Manatee River in Bradenton.
Some two months after the eggs are laid, hatchlings emerge and crawl across the sandy beach to the water. As of Aug. 20, AMITW estimates 2,903 hatchlings had emerged from 33 nests.
On Aug. 15, AMITW executive director Suzi Fox and coordinator Deb Basilius excavated a nest near the 70th Street beach access in Holmes Beach. Examining the nests after hatchlings leave is part of AMITW’s data collection routine during the nesting season.
But during the excavation last week, Fox and Basilius added some extra steps. After counting the hatched eggs - 116 out of 121 - they placed a sample of an egg in a test tube containing ethanol. They also placed a sample of a dead hatchling in a tube. The tubes were labeled “Section 3, Nest 13, Anna Maria Island.”
“We’re trying to prove west coast [Florida] turtles are west coast turtles,” Fox told the crowd of beachcombers that formed to observe the work. “This is going to tell us what kind of girl we have.”
Mitochondrial DNA - genetic material from the mother - will be drawn from the samples.
“Mitochondrial DNA is passed down unbroken from mother to daughter like surnames have traditionally been passed down the paternal line in the west,” Shamblin said. “Looking for differences in mitochondrial DNA allows us to piece together colonization histories and determine roughly how closely related one group of turtles is to another.”
Previous research based on differences in mitochondrial DNA has indicated that there are at least four subpopulations of loggerhead sea turtles along the U.S. coast - Florida Panhandle, south Florida, north Florida and the Dry Tortugas.
“Each study increased precision by increasing sample sizes and adding additional beaches over previous studies,” said Shamblin. “Still, cumulative sample sizes were small for the two southern-Atlantic Florida beaches sampled, and the high-density nesting areas around Jupiter Island and northern Palm Beach County were not represented at all. The overall impression from earlier work is that while distant sampled beaches may be distinct, two nearby beaches are not different because changes occur gradually over long stretches of beach.”
In this stage of the research, which is in its final sampling summer, Shamblin said he hopes to sample from nests on as many beaches as possible to test that hypothesis.
“That’s where Anna Maria Island comes in,” he said. “Previously, only Casey Key and Keewaydin Island have represented southwest Florida. Our goal is to saturate as many beaches as possible, and we are covering well over half of all surveyed beaches in Florida thanks to support and interest of the sea turtle community in the state.
“Southwest Florida is particularly well represented, so we should be able to determine if all the beaches act as a cohesive subpopulation unit or if there are differences present that warrant further subdivison.”
In other words, the research may reveal whether “South Florida” is too broad a description for the sea turtles who nest on Anna Maria Island’s beaches.