Abstract
Thermal tolerances are affected by the range of temperatures that species encounter in their habitat. Daniel Janzen hypothesized in his “Why mountain passes are higher in the tropics” that temperature gradients were effective barriers to animal movements where climatic uniformity was high. Sea turtles bury their eggs providing some thermal stability that varies with depth. We assessed the relationship between thermal uniformity and thermal tolerance in nests of three species of sea turtles. We considered that barriers were “high” when small thermal changes had comparatively large effects and “low” when the effects were small. Mean temperature was lower and fluctuated less in species that dig deeper nests. Thermal barriers were comparatively “higher” in leatherback turtle (Dermochelys coriacea) nests, which were the deepest, as embryo mortality increased at lower “high” temperatures than in olive ridley (Lepidochelys olivacea) and green turtle (Chelonia mydas) nests. Sea turtles have temperature-dependent sex determination (TSD) and embryo mortality increased as temperature approached the upper end of the transitional range of temperatures (TRT) that produces both sexes (temperature producing 100% female offspring) in leatherback and olive ridley turtles. As thermal barriers are “higher” in some species than in others, the effects of climate warming on embryo mortality is likely to vary among sea turtles. Population resilience to climate warming may also depend on the balance between temperatures that produce female offspring and those that reduce embryo survival.
Highlights
Understanding the mechanisms behind thermal tolerances is critical for assessing potential responses of animal populations to anthropogenic climate warming [1, 2]
We compared the conditions in the nest environment of three sea turtle species, leatherback turtles (Dermochelys coriacea), green turtles (Chelonia mydas) and olive ridley turtles (Lepidochelys olivacea) that nest in the same general area in Northwest Costa Rica and dig their nests at different depths due to differences in body size [13]
North Pacific Costa Rica is a tropical area highly influenced by El Niño Southern Oscillation (ENSO) where previous studies have shown that climatic conditions influence the nest environment of leatherback turtles [17, 27]
Summary
Understanding the mechanisms behind thermal tolerances is critical for assessing potential responses of animal populations to anthropogenic climate warming [1, 2]. Especially in ectotherms, are related to the temperatures experienced in the habitat and are broader in those areas of higher climatic variability [3, 4]. In his 1967 seminal article Janzen hypothesized that animal thermal tolerances were lower where climatic uniformity was high [5]. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript
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