![]() Embryos are placed in incubators, hatched under a specified incubation regime and then released into the wild ( Páez et al., 2015). natural nests or gravid females that died on a road) or egg production after captive breeding. Artificial incubation typically follows the removal of eggs from the wild (e.g. Growth of wild populations may then be enhanced by protecting eggs and embryos, which reduces embryonic and hatchling mortality, and/or rearing individuals to larger body sizes before release ( Carstairs et al., 2019 Tetzlaff et al., 2019), which may increase survival rates in the wild ( Rollinson and Rowe, 2015).Īrtificial incubation is an integral part of many conservation initiatives for reptiles. Another common initiative undertaken by zoos, parks, conservation authorities and even private individuals involves incubation of reptile eggs in an ex-situ setting ( Eckert et al., 1999), followed by the release of hatchlings or juveniles. At present, 56.3% of data sufficient species (51.9% of all recognized species) are considered critically endangered, endangered or vulnerable by the International Union for Conservation of Nature ( Rhodin et al., 2018).Ĭommon turtle conservation initiatives include protecting nesting turtles from natural predation and poachers ( Eckert et al., 1999), rehabilitation programs at trauma centers ( Feck and Hamann, 2013), education initiatives ( Hassan et al., 2017) and captive breeding ( Bowkett, 2009). Elevated adult mortality of turtles arising from road collisions ( Steen and Gibbs, 2004), fishing gear entrapment ( Lewison et al., 2004 Bolten et al., 2011), predation ( Bolten et al., 2011) and direct consumption as a food source ( Conway-Gómez, 2007 Hancock et al., 2017) has therefore resulted in dramatic population declines. Kondo et al., 2017) and low genetic diversity ( Romiguier et al., 2014), populations are unable to adapt to environmental change on the time scale of anthropogenic impacts ( Hawkes et al., 2009). ![]() Natural rates of replacement and population growth are low in most turtle species, and because of high juvenile mortality, slow life histories (e.g. ![]() Turtles, for example, are among the most imperiled group of vertebrates in the world ( Rhodin et al., 2018 Gibbons and Lovich, 2019 Stanford et al., 2020). Of equal importance, we provide insight into the enigmatic evolution of TSD in chelonians, by providing support to the hypothesis that TSD evolution is related to the quality of the phenotype conferred by incubation temperature, with males produced in high-quality incubation environments.ĭespite recent and widespread interest in reptile conservation ( Roll et al., 2017), reptile populations are declining globally ( Todd et al., 2010). Indeed, our models predict that, on average, a sex ratio of >75% females can generally be achieved by incubating eggs only 1☌ above TPiv. If patterns of temperature-sensitive embryonic mortality are also indicative of chronic thermal stress that occurs post-hatching, then conservation programs may benefit from incubating eggs close to species-specific TPivs, thus avoiding high-temperature incubation. Further, we find some evidence that pivotal temperatures (TPiv, the temperature that produces a 1:1 sex ratio) may exhibit a correlated evolution with embryonic thermal tolerance. We find several lines of evidence suggesting that warm, female-producing temperatures are more stressful than cool, male-producing temperatures. We synthesize data from 28 studies to investigate how constant temperature incubation affects embryonic mortality in chelonians with TSD. We predict that female-producing temperatures, which comprise relatively high incubation temperatures in chelonians and crocodilians, are relatively stressful for embryos and subsequent life stages. It follows that males benefit more than females from incubation environments that confer high-quality phenotypes, and hence high-condition individuals. Here, we revisit classic sex allocation theory and hypothesize that TSD evolved in some reptile groups (specifically, chelonians and crocodilians) because male fitness is more sensitive to condition (general health, vigor) than female fitness. Temperature-dependent sex determination (TSD) occurs in most chelonians, permitting conservation managers to bias sex ratios towards females by incubating embryos at high temperatures, ultimately allowing the introduction of more egg-bearing individuals into populations. A common reptile conservation strategy involves artificial incubation of embryos and release of hatchlings or juveniles into wild populations. ![]()
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