Understanding Loggerhead Population Demographics: the “Why” behind Genetic Studies

Blog Post By: Ashlyn, Sea Turtle Intern

Setting the scene: On every beach spanning the Atlantic Coast from North Carolina to Florida, night patrollers would be walking the beach from dusk until dawn, attempting to encounter every nesting loggerhead that emerges from the ocean to nest along the dunes. Tags must be given to each turtle encountered with thorough documentation occurring throughout the night, and fingers must be crossed that no turtles evade the nightly patrol. A logistical catastrophe.
 
Tagging studies on nesting beaches, the historical common practice to estimate nesting frequencies among other population demographic parameters, cannot obtain the magnitude of samples required for confident determination of sea turtle population demographics. Therefore, Dr. Brain Shamblin and his team at University of Georgia, altered the precedent. Since 2010, the Edisto Beach State Park beach along with beaches all along the Southeastern Coastline have participated in Dr. Shamblin’s genetic study of loggerhead sea turtles, allowing for a deeper understanding of loggerhead nesting population demographics, furthering sea turtle conservation efforts.
 
Rather than a focus on directly on the mother turtle, focus shifts to the eggs to obtain information about the mother. From each nest discovered on the beach, a single egg is obtained from the clutch within 15 hours of oviposition. In its entirety, the egg contains both the mother’s and father’s genetic material; however, the shell of the egg contains genetic information solely from the mother. For this reason, the yolk contents of the egg are sacrificed, and the shell of the egg is preserved in a 70% ethanol solution to allow for the isolation of DNA from the eggshell of the mother loggerhead sea turtle. Genotypes are derived from a single-locus from the unincubated egg shell, with an accuracy rate of 97.6% to the genotype that would have been derived if taken directly from a skin sample of the mother loggerhead.
 
The development of this single locus genotype frequenting technique serves as a groundbreaking noninvasive method in furthering our understanding of sea turtle population demographics. This methodology additionally is applicable to other marine turtle populations in which direct interception of the nesting female is logistically not feasible when genetics studies are being conducted.
 
For more information regarding the nesting patterns of loggerheads on the EBSP beach, visit www.seaturtle.org for maps and data information. For more information regarding the genetic extraction process within the laboratory, visit the website of Dr. Brain Shamblin for links to his published works.