University of Central Florida researchers have discovered an abundance of new gene variants in the immune system of sea turtles, which could be key to one day saving the ancient marine animals from a major disease — fibropapillomatosis.

The discovery, which is detailed in a recent study in the journal Royal Society Open Science, sheds light on the role the gene variants, known as MHC class I  alleles, play in potentially protecting sea turtles from the disease.

This is the first time researchers have studied variation in MHC genes in green sea turtles. MHC proteins act as a gatekeeper of an adaptive immune system. If they recognize a pathogen threat, then the immune system responds specifically to it.

Fibropapillomatosis, or FP, causes sea turtles to develop tumors on their bodies, which can limit their mobility and also their health by interfering with their ability to catch and eat prey.

Researchers are still working to uncover the causes of FP, which could include environmental contamination. They are also trying to figure out why some sea turtles, such as loggerheads, are rarely observed with FP, while others, such as green sea turtles are often afflicted.

About half of the green sea turtles observed in the Indian River Lagoon have FP, researchers say.

Central Florida’s Atlantic coastline hosts about one-third of all green turtle nests in the state, and sea turtle health is important because the animals contribute to healthy oceans and coastlines by grazing and maintaining sea grass beds.

All sea turtles are categorized as threatened or endangered because of threats from pollution, coastal development and fishing, in addition to infectious diseases.

Better understanding the role genes play in protecting sea turtles can inform intervention strategies, such as captive breeding using turtles who have genetic defense against FP, says study co-author Anna Savage, an associate professor with UCF’s Department of Biology and a member of UCF’s Genomics and Bioinformatics research cluster.

“Just the baseline knowledge of how much variation is out there and is it relating to any certain phenotypes is really valuable, just for looking at how things change into the future,” Savage says. “But then also, if and when we do find really strong relationships between particular genetic variants and disease susceptibility, that’s a possible management tool if you need to intervene for the population to have a chance, if you know which of these MHC alleles are really important for surviving disease threats.”

The study’s lead author, Katherine Martin, a doctoral student in UCF’s Department of Biology, spearheaded the research in which MHC class I genes were sequenced from 268 green sea turtles and 88 loggerhead sea turtles.

researcher loads a next generation sequencer
Katherine Martin, a doctoral student in UCF’s Department of Biology, loads the next-generation sequencer that enabled the study.

The samples came from UCF’s Marine Turtle Research Group’s database of more than 30,000 Indian River Lagoon sea turtle records dating back to the early 1980s.

The researchers found 116 new-to-science alleles, some of which seemed to be associated either with the development of FP but also potentially the regression of tumors.

However, the researchers say even with all the new alleles discovered, they are still going to need more sampling to get a full picture of what role MHC alleles play in protecting sea turtles.

“We kind of have limited time to figure out what’s under the hood of their immune system,” Martin says. “And so I think studies like this show that there’s still a lot to learn about these organisms.”

The researchers’ next steps include expansion of sampling of green sea turtles and loggerheads as well as sampling and analyzing genetic information from other sea turtle species.

The work was funded by the Florida Sea Turtle License Plate Program and builds on previous studies, including research that looked at leeches as a possible vector that transmits FP to sea turtles.

The study also included co-author Kate Mansfield, director of UCF’s Marine Turtle Research Group. Mansfield is an associate professor in UCF’s Department of Biology and a member of UCF’s Sustainable Coastal Systems research cluster.