The National Science Foundation this month announced that Lisa Komoroske, environmental conservation, will co-lead a four-year, $1.4 million, multi-institution grant to study how reproductive behaviors will influence the effects of climate change on green sea turtles (Chelonia mydas).
Her team will spend months in the field at turtle nesting beaches on Fernando de Noronha, a marine reserve and UNESCO World Heritage Site composed of an archipelago of 21 islands about 220 miles off the coast of Brazil. She and collaborators at Florida State and Oregon State universities will also work with the Brazil-based non-profit conservation organization PROJECTO TAMAR on the project.
Komoroske and her colleagues believe this work will be the first comprehensive examination of resilience to environmental change among these turtles and will provide insights relevant to other temperature sex-determined species.
Komoroske, an expert in the use of genomic tools to study wildlife populations, will use genetic samples from turtle mothers and hatchlings to estimate sex ratios in a breeding population. Understanding sex ratios is critical for predicting the impacts of environmental change, she points out, particularly for animals such as reptiles and fishes with temperature dependent sex determination. Whether they develop into males or females depends on temperatures they are exposed to early in life. In sea turtles, females are produced at higher incubation temperatures and males at lower temperatures.
She will team up with experts Mariana Fuentes in wildlife movement at Florida State and population modeling J. Wilson White at Oregon State to combine insights from new technologies – genomics, satellite telemetry, and unmanned aerial vehicles (drones) – to understand how the complex reproductive behaviors of sea turtles could provide a buffer against climate change.
She says that because of temperature dependent sex determination, these species are likely to be affected by environmental change and there is concern that extreme conditions will produce too many females, potentially destabilizing populations.
She adds, “We know that climate change is altering sex ratios in new generations of turtle hatchlings, but we don’t understand the broader consequences. These turtles have survived for millions of years through many climate shifts, but things are changing more rapidly now, at an unprecedented rate, and we don’t know what a healthy sex ratio looks like for species with complex life histories like sea turtles. We want to look at this problem from different angles and clarify the potential large-scale impacts.”
“Many conservation managers are discussing whether we can do anything to help the turtles such as shading or relocating nests to cooler beaches, but without this broader understanding, we don’t understand what the consequences of those actions would be. Anything we do now is based on incomplete information,” the ecologist notes.
In addition to temperature vulnerability, the turtles have a complex mating system that is little understood, Komoroske says. Males and females can mate with multiple partners, and females can store sperm and lay eggs with multiple fathers. Studies have shown more female vs. male turtles hatching at many nesting beaches, so some sex-skew may be natural, she says. But scientists do not know if there are limits to the number of females a male can mate with. Also, as female-bias increases with climate change, they hope to answer the critical question of how many males are enough.
To address such uncertainties, the team also plans to study female breeding behaviors and male migration. Researchers speculate that males may travel to mate at several breeding areas, mixing genetic material and perhaps offsetting female bias at warmer nesting beaches. Some limited evidence suggests that females migrate to nesting grounds only every two or three years because the long journey, followed by laying several hundred eggs is very energy intensive, while males may make the trip yearly, Komoroske says.
In the past, fixed-wing aerial surveys over breeding grounds were used to count male and female sea turtles. The numbers were then assessed separately in relation to other variables, Komoroske explains. This approach is expensive and makes it hard to answer many interrelated questions, including the sex ratio thresholds that will provide resilience for these species under climate change, she adds.
Her research team will use satellite telemetry for male migration and drones for aerial population surveys. Drones are cost effective, especially in remote areas; they have a small carbon footprint and are easier and less obtrusive in a national park. These and other datasets will be integrated into advanced mathematical population and evolutionary models to forecast sea turtle population viability under different climate scenarios.
“You need a more holistic picture, and that’s what we’re aiming to do with evaluating and integrating several aspects at once that up to now were studied in isolation. With better data, we hope to put the pieces of the puzzle together and have a stronger ability to make realistic projections on population viability,” Komoroske says.