Sarah Livett wrote this post as a final project for Stacy Krueger-Hadfield’s Introduction to Evolutionary Processes course at the University of Alabama at Birmingham. Sarah was a 5th year MS student at UAB in Dr. Thane Wibbel‘s lab. She worked on Kemp’s Ridley sea turtles and is pursuing a MS degree in conservation and sustainability.
Unlike genetic sex determination in mammals, turtle sex is determined by temperature. In sea turtles, for example, males develop at lower temperatures, whereas females develop at higher temperatures. These temperature ranges are very small. We’re talking less than 3⁰C (Woo 2014). This means that a rise in global temperatures of just 3°C could shift the sex ratios from all female (Wibbels 2003).
Not only do higher nest temperatures produce more females, they also increase mortality of turtle hatchlings (Laloë et al, 2017).
Could heat shock proteins combat temperature-linked hatchling mortality?
Bentley et al. (2017) subjected embryonic sea turtles to biologically realistic thermal stress. Using de novo transcriptomic profiling, they found up-regulated genes in the high temperature treatments were associated with Hsp families. Genes from these families play vital roles in thermal tolerance, and the authors argued should be targets for investigating whether these reptiles can adaptive respond to the effects of climate change.
This could be very important for species such as the the Kemp’s Ridley. Temperatures less than 29°C will produce all males and greater than 32°C will produce all females (Wibbels 2003). Sand temperatures continually rise throughout the summer and over the course of the turtle nesting season from April to October. A global temperature rise would be great for holidaymakers, but sand temperature could already be too high to produce any male hatchlings – even at the beginning of the season. Green sea turtles in the Great Barrier Reef have already been producing clutches of up to 99% female hatchlings over the last 2 decades (Jensen et al. 2018).
Researchers and conservationists have been unable to pinpoint the exact temperatures required to produce a male and a female in the various species of sea turtles. This is partly due to variations in temperature between populations and nest sites. Future work will ascertain whether turtles will be able to ‘fend for themselves’ as temperatures increase, or whether we may have to step in with even more intense conservation efforts.
Bentley B, Haas B, Tedeschi J and Berry O. (2017) Loggerhead sea turtle embryos (Caretta caretta) regulate expression of stress response and developmental genes when exposed to a biologically realistic heat stress. Molecular Ecology 26: 2978-2992.
Laloë J-O, Cozens J, Renom B, Taxonera A and Hays G. 2017. Climate change and temperature-linked hatchling mortality at a globally important sea turtle nesting site. Global Change Biology 23: 4922-4931.