Abstract
Patterns of temperature fluctuations in nature affect numerous biological processes, yet, empirical studies often utilize constant temperature treatments. This can limit our understanding of how thermally sensitive species respond to ecologically relevant temperatures. Research on turtles with temperature-dependent sex determination (TSD) provides good examples of this, since nest temperatures from many populations rarely exceed those necessary to produce females under constant laboratory conditions. We hypothesized that exposure to brief periods of warm temperatures (i.e., heat waves) are integral to sex determination in species with TSD, which requires tests that move beyond constant temperatures. We exposed Trachemys scripta embryos from multiple populations and across the nesting season to heat waves of variable durations and quantified sex ratios. We found that embryos from all populations were highly sensitive to brief exposures to female producing temperatures; only 7.9 days of exposure produced a 50:50 sex ratio, but the response varied across the nesting season. From these findings, a model was developed to estimate sex ratios from field temperature traces, and this model outperformed traditional methods. Overall, these results enhance our understanding of TSD and emphasize the importance of using biologically relevant temperatures when studying thermally sensitive processes.
Highlights
Temperature affects a wide range of biological processes, from the biochemical action of enzymes to cueing the onset of mass migrations[1,2,3]
Turtles have emerged as model temperature-dependent sex determination (TSD) organisms, and in these species, embryos experience incubation temperatures that fluctuate concurrent to ambient temperatures[12]
Studies that focus on how natural incubation temperatures affect sex ratios often report that more females are produced than would be expected under laboratory conditions
Summary
Temperature affects a wide range of biological processes, from the biochemical action of enzymes to cueing the onset of mass migrations[1,2,3]. If only a relatively short amount of time is needed at female producing temperatures to trigger ovary development, females could be produced at conditions that otherwise have averages (or CTEs) well below the Tpiv We hypothesize that these “heat waves” (i.e. brief periods where temperatures exceed the Tpiv) are integral to the determination of sex in species with TSD. We predict that turtle embryos are highly sensitive to brief durations of exposure to temperatures above the Tpiv, and that ovary determination can be triggered after only a few days of exposure to warm temperatures Such a finding would substantially alter our understanding of how sex is determined in species with TSD, and would serve as a case study for emphasizing the importance of thermal realism
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