Temperature-dependent Sex Determination: Evolutionary Significance and the Adaptive Potential of Sea Turtles to Climate Change

Research Report



Environmental sex determination (ESD) in sea turtles occurs as temperature-dependent sex determination (TSD), whereby the sex of an individual is determined by external thermal cues. All sea turtles exhibit TSD type Ia, which means that higher temperatures produce females and lower temperatures produce males (Heredero Saura et al. 2022). Sex is determined during the thermosensitive period, when temperature cues induce the production of sex hormones that determine the sex of the embryo (Heredero Saura et al. 2022). Pinpointing the evolutionary significance of TSD remains a challenge, despite the prevalence of TSD in sea turtles and other amniote vertebrates (Janzen & Phillips 2006). Sexing hatchlings requires sacrifice and histological examination of gonads (Lockley & Eizaguirre 2020); currently, however, six of the seven species of sea turtles are endangered, and three are critically endangered, which means that until alternative sexing methods are possible, our understanding of TSD in sea turtles—its evolutionary significance and the mechanisms for its maintenance—must remain restricted to laboratory incubation studies (Lockley & Eizaguirre 2006; Sea Turtle Conservation Bonaire, n.d.). In this paper, I will review the hypotheses that have been proposed so far for the evolutionary significance of TSD in sea turtles. I will then consider the plausibility of each of these hypotheses, particularly the Charnov-Bull model of differential fitness. I will also consider the risk that global warming poses for temperature-sensitive sea turtle populations around the globe and explore opportunities for future research. My studies at the University of Chicago trace the effects of climate change around the globe, from the water-stressed regions of Pakistan to the rapidly eroding nesting beaches along the coast of Australia. The topic of this paper is particularly relevant to conversations about how climate change will affect the critical ecosystems on which all life depends. Without sea turtles, 3 marine ecosystems around the globe risk collapsing entirely; sea turtles are considered keystone species, which means that they play a critical role in the productivity and biodiversity of these ecosystems (The Leatherback Trust, n.d.). The opportunities for future research considered in this paper might inform the policy choices and conservation efforts that could save sea turtles—and thus the ecosystems that sustain millions of communities, human and nonhuman, around the globe—from extinction

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