Up to 93% of green turtle hatchlings could be female by 2100, as climate change causes “feminisation” of the species, new research suggests.
The sex of turtle hatchlings is determined by temperature, and at present about 52% of hatching green turtles – one of seven species of sea turtle – are female.
But a study by the University of Exeter and the Marine and Environmental Sciences Centre (Portugal) shows that in warmer temperatures predicted by Intergovernmental Panel on Climate Change (IPCC) scenarios, 76-93% of hatchlings would be female.
The figures are specific to the study site in Guinea-Bissau, West Africa, but researchers say they expect a similar picture globally.
They say the changing gender ratio would initially lead to more females nesting, increasing the population, before by a decline “as incubation temperatures approach lethal levels”.
They also predict rising sea levels will submerge 33-43% of current nesting areas used by green turtles on the beaches where the study was carried out.
“Green turtles are facing trouble in the future due to loss of habitats and increasing temperatures,” said Dr Rita Patricio, of the Centre for Ecology and Conservation on the University of Exeter’s Penryn Campus in Cornwall.
“Our results suggest the nesting population of green turtles the Bijagós Archipelago, Guinea-Bissau, will cope with the effects of climate change until 2100.
“Cooler temperatures, both at the end of the nesting season and in shaded areas, will guarantee some hatchlings are male.
“Although rising temperatures will lead to more female hatchlings – and 32-64% more nesting females by 2120 – mortality in eggs will also be higher in these warmer conditions.
“As temperatures continue to rise, it may become impossible for unhatched turtles to survive.”
The research team, which included the Institute of Biodiversity and Protected Areas of Guinea-Bissau, say nesting sites submerged by rising seas may not simply “move” inland.
“Beach retreat may be OK in some areas, but the turtles we studied were nesting on a small island (Poilão Island) so there is a limit to how far the beach can go,” Dr Patricio said.
“In other places there may be natural barriers or human constructions that stop beaches moving inland.”
The Bijagós Archipelago is the most important nesting place for green turtles in Africa, and the main breeding ground for the species in the South Atlantic.
The research was funded by the MAVA Foundation.
The paper, published in the journal Global Change Biology, is entitled: “Climate change resilience of a globally important sea turtle nesting population.”
RavingRationality on December 31st, 2018 at 15:53 UTC »
While this is concerning, it is being reported in a sensationalistic way. The estimates for the sex ratio of green sea turtles in the wild were already heavily skewed female, with multiple studies done between 1957 and 1981 suggesting natural ratios of between 59% and 92% female.
1957 - Carr and Giovannoli: 71% female
1962 - Caldwell: 68%-92% female
1970 - Hirth and Carr: 56% female
1981 - Mortimer: 59% female
The wide range is likely due to where they were tested. Those few Green Sea Turtles from colder regions tend to be mostly male, while the multitudes from warmer areas tend to be mostly female.
One would hope that as their habitat warms, more green sea turtles would migrate into more temperate zones that more closely matched their previous climate, like other animals do during periods of climate change.
travis-42 on December 31st, 2018 at 12:29 UTC »
Does the article discuss the optimal ratio for maximum birth rate? It’s rarely 1:1 male:female for the simple fact that only females give birth and one male can impregnate multiple females (at least in general, I don’t know about these turtles). Some species have even evolved to have unbalanced ratios, although it’s rare because of Fisher’s Principle.
93% strikes me as too high, but I wonder what the ideal ratio is and if there’s a chance the overall birth rate could increase as a result of this imbalance (at least as long as the temperature is not so high as to be lethal, which is predicted eventually). It seems to suggest this from the abstract.
mvea on December 31st, 2018 at 10:12 UTC »
The title of the post is a copy and paste from the subtitle of the linked academic press release here:
Journal Reference:
Ana R. Patrício, Miguel R. Varela, Castro Barbosa, Annette C. Broderick, Paulo Catry, Lucy A. Hawkes, Aissa Regalla, Brendan J. Godley.
Climate change resilience of a globally important sea turtle nesting population.
Global Change Biology, 2018;
DOI: 10.1111/gcb.14520
Link: https://onlinelibrary.wiley.com/doi/full/10.1111/gcb.14520
Abstract
Few studies have looked into climate change resilience of populations of wild animals. We use a model higher vertebrate, the green sea turtle, as its life history is fundamentally affected by climatic conditions, including temperature‐dependent sex determination and obligate use of beaches subject to sea level rise (SLR). We use empirical data from a globally important population in West Africa to assess resistance to climate change within a quantitative framework. We project 200 years of primary sex ratios (1900–2100) and create a digital elevation model of the nesting beach to estimate impacts of projected SLR. Primary sex ratio is currently almost balanced, with 52% of hatchlings produced being female. Under IPCC models, we predict: (a) an increase in the proportion of females by 2100 to 76%–93%, but cooler temperatures, both at the end of the nesting season and in shaded areas, will guarantee male hatchling production; (b) IPCC SLR scenarios will lead to 33.4%–43.0% loss of the current nesting area; (c) climate change will contribute to population growth through population feminization, with 32%–64% more nesting females expected by 2120; (d) as incubation temperatures approach lethal levels, however, the population will cease growing and start to decline. Taken together with other factors (degree of foraging plasticity, rookery size and trajectory, and prevailing threats), this nesting population should resist climate change until 2100, and the availability of spatial and temporal microrefugia indicates potential for resilience to predicted impacts, through the evolution of nest site selection or changes in nesting phenology. This represents the most comprehensive assessment to date of climate change resilience of a marine reptile using the most up‐to‐date IPCC models, appraising the impacts of temperature and SLR, integrated with additional ecological and demographic parameters. We suggest this as a framework for other populations, species and taxa.