Recent advances on the estimation of the thermal reaction norm for sex ratios

Abstract

Temperature-dependent sex determination, or TSD, is a widespread phenomenon in reptiles. The shape of the relationship between constant incubation temperature and sex ratio defines the TSD pattern. The TSD pattern is considered a life-history parameter important for conservation because the wider the range of temperatures producing both sexes, the more resilient the species is to climate change impacts. We review the different published equations and methodologies that have been used to model TSD patterns. We describe a new flexible model that allows for an asymmetrical pattern around the pivotal temperature, which is the constant temperature producing both sexes in equal proportions. We show that Metropolis-Hastings with Markov chain produced by a Monte Carlo process has many advantages compared to maximum likelihood and is preferred. Finally, we apply the models to results from incubation experiments using eggs from the marine turtle Lepidochelys olivacea originating in Northeast Indian, East Pacific, and West Atlantic Regional Management Units (RMUs) and find large differences in pivotal temperatures but not in transitional ranges of temperatures.

Hatching Success Rather Than Temperature-Dependent Sex Determination as the Main Driver of Olive Ridley (Lepidochelys olivacea) Nesting Activity in the Pacific Coast of Central America

“…Incubation temperature influences both hatching success and sex ratio. The fitting of the sex ratio thermal reaction norm for the East Pacific RMU was published in Abreu-Grobois et al [ 37 ]. The methodology is recalled here briefly.…”

“…Data on the number of males and females produced for incubations at 17 constant temperatures were used. The relationship between constant incubation temperature and sex ratio was fitted using the logistic equation [ 38 ], and the credible interval was fitted using the Metropolis-Hastings algorithm with a Monte Carlo Markov chain in Bayesian analyses with uniform priors see [ 37 ] for more details.…”

Variation in thermal traits describing sex determination and development in Western Australian sea turtle populations

“…To determine the relationship between incubation temperature and sex, the EmbryoGrowth package for r (Girondot & Kaska, 2014) was used to model the TSD reaction norm for each rookery. This method allowed for up to five threshold models (Logistic, A‐Logistic, Hill, Flexit and a model that assumed genotypic sex determination [GSD]) using maximum likelihood scenarios, and required that at least two incubation temperatures produced mixed sexes (Abreu‐Grobois et al., 2020; Girondot, 1999). Confidence intervals (95%;) were calculated using the Metropolis‐Hastings method of Markov chain Monte Carlo (MCMC) simulations, with three chains of 10,000 iterations used, assuming the maximum likelihood outputs for each model as priors.…”

“…Flexit and a model that assumed genotypic sex determination [GSD]) using maximum likelihood scenarios, and required that at least two incubation temperatures produced mixed sexes (Abreu-Grobois et al, 2020;Girondot, 1999). Confidence intervals (95%) were calculated using the Metropolis-Hastings method of Markov chain Monte Carlo (MCMC) simulations, with three chains of 10,000 iterations used, assuming the maximum likelihood outputs for each model as priors.…”

Short Communication: Antimicrobial properties in cloacal fluid of olive ridley sea turtle (Lepidochelys olivacea)

“…The olive ridley sea turtle (Lepidochelys olivacea) is threatened by fisheries bycatch, habitat degradation, and the unsustainable harvest of eggs and is listed by the IUCN as a vulnerable species (Abreu-Grobois et al 2020). Bacteria and fungi contamination have been reported to reduce the hatchling success of sea turtle nests worldwide (Bezy et al 2015;Caron et al 2018;Gifari et al 2018;Candan and Candan 2020;Hoh et al 2020).…”