Effects of Incubation Conditions on Sex Determination, Hatching Success, and Growth of Hatchling Desert Tortoises, Gopherus agassizii

Effect of tidal overwash on the embryonic development of leatherback turtles in French Guiana

“…Hatching success for organisms that lay eggs in a nest, such as sea turtles, is believed to be influenced by numerous biotic and abiotic factors such as predation, type of substrate, porosity, temperature, moisture content, salinity, slope of the beach, nest elevation, rainfall and tidal inundation (Mortimer, 1990;Horrocks and Scott, 1991;Ackerman, 1997;Wood and Bjorndal, 2000;Allen et al, 2001;Bilinski et al, 2001;Donlan et al, 2004;Foley et al, 2006). In many oviparous reptiles, however, environmental factors not only influence embryo survivorship (Horrocks and Scott, 1991;Resetarits, 1996), but also hatchling size (Packard and Packard, 1988), performance (Janzen, 1993), growth (Bobyn and Brooks, 1994), behaviour (Burger, 1991), and sex determination (Spotila et al, 1994). After the emergence of hatchling turtles, their survival may be strongly related to the distance at which the nest is laid from the sea and from supra-littoral vegetation behind the beach (Mrosovsky, 1983).…”

Temperature-Dependent Sex Determination in Vertebrates

“…Although new data, as well as definition of T piv s by probit, reduce the estimated values for G. versa (to 29.7˚C), G. caglei (to 29.6˚C), and G. barbouri (to 28.1˚C), the trend persists. Confirming a prediction of Spotila and Standora (1986), Gopherus agassizii has a higher T piv (31.0˚C; see Spotila et al 1994;Lewis-Winokur and Winokur 1995) than G. polyphemus (29.2˚C;see Demuth 2001). In general, T piv s of species of the western United States and Mexico appear somewhat higher that in related forms in the east ; see below).…”

“…Whereas temperature effects on certain traits may be mediated by temperature-induced variation is sex steroid levels in some species, studies in snapping turtles indicate 96 T. Rhen and J. W. Lang McKnight and Gutzke 1993Bobyn and Brooks 1994Spotila et al 1994Roosenburg 1996Roosenburg and Kelley 1996Foley 1998Demuth 2001Janzen and Morjan 2002 that temperature can have effects mediated via alternative mechanisms. In experiments described earlier, snapping turtle embryos were treated with exogenous estrogen or a potent aromatase inhibitor at the beginning of the thermosensitive period (TSP).…”

Weather and sex ratios of head-started Agassiz’s desert tortoise Gopherus agassizii juveniles hatched in natural habitat enclosures

“…The 3-parameter sigmoidal model (1) y a where y is % females, x is air temperature in °C, a is the curve's maximum or asymptote (approaching 100% females), x 0 is the x value at the middle of the sigmoid (or inflection point) and b is the steepness of the sigmoid regression, was the simplest model, and provided nearly identical results to higher parameter models, including logistic, Weibull, Gompertz and other models. The sigmoidal model also accurately estimated the pivotal temperature (x 0 ; 31.3°C) for the incubation data summarized in Table 6.1 of Rostal & Wibbels 2014 (original data from Spotila et al 1994, Rostal et al 2002. We also summarized the long-term air temperatures for this weather station.…”

“…In reptiles with TSD, such as many turtles and tortoises, it is the temperatures of the embryos during development, rather than the embryos' chromosomes, that determine the sex of the offspring (Pieau 1976, Bull & Vogt 1979, Janzen & Paukstis 1991, Spotila et al 1994, Rostal & Wibbels 2014). This phenomenon may lead to problems in otherwise well-intended efforts to aid declining populations by protecting nests and eggs using predator-resistant natural field enclosures, or indoor incubation of eggs collected from the nests (e.g.…”