The authors have declared that no competing interests exist.

Olive ridleys (

Global warming presents major challenges to organisms

One attempt to address this shortcoming is phenomenological, using climatic descriptions of contemporary ranges coupled with expected temperatures to predict future ranges

The extent of adaptive variation in heat-tolerance is likely to have important consequences for the resilience of many ectothermic species in a rapidly warming world

Recently, a general way to model sigmoidal embryo growth with variable incubation temperature during development obtained from

Olive Ridley sea turtles nest along all of the Pacific Coast of Guatemala. Egg collection for human consumption is authorized as long as 20% of the eggs of each collected nest is given to hatcheries located along all the littoral

Incubation time, longitudinal ttemperatures and 10 hatchling straight carapace lengths at the nearest 0.1 mm were registered for all monitored nests. Mean incubation temperatures and incubation durations were analysed using linear model

The variability of daily temperatures among nests was measured as the mean of the daily standard deviation of temperatures recorded in nests from each treatment (shading status and depth). Welch modified two-sample t-test with unequal variances were used to test the treatments effect (depth and shading)

The model of embryo growth integrates in a single framework both the growth rate dependency on temperature and the embryo growth

Biological temperature-dependent rate models based on Arrhenius’ and Eyring’s equations have been formulated by Sharpe and DeMichele

The early growth of embryos is modelled using a modification of the Gompertz model

Where X(0) is the size or mass at nesting time (time=0),

_{H} is the hatchling size and _{K}=2.09 is a constant used to slowdown growth at the end of incubation

The dynamic of

The gastrula is approximately a disk of 1.7 mm diameter and this size will be used as

Growth rate

Estimation of parameters was performed using maximum likelihood with an identity link and a Gaussian distribution of SCL. The standard error of parameters was estimated using the square-root of the inverse of the Hessian matrix which is an asymptotic approximation of the variance-covariance matrix

First, growth rate

The statistics

(Likelihood Ratio Test, with

Distribution of temperatures recorded in the 80 ^{-9}). Nests from hatchery were also significant cooler than the experimental ones (paired t-tests with Bonferonni correction, 1.32 °C difference between hatchery ^{-9} and 3.44 °C difference hatchery ^{-9}) (

Incubation duration ranged from 43 to 55 days (mean=49.86 days, sd=3.63). Significant effect of mean incubation temperature and shading status for experimental data was observed

Straight carapace length of hatchlings (mean 40.86 mm, sd=1.82) was significantly different for experimental data according to depth factor (deviance= 5.492, df=1, p<0.02) but not for any other factors (all p>0.05). Embryos incubated at 40 cm were smaller (40.22 mm, sd=1.54 mm) than those incubated at 60 cm (41.07 mm, sd=1.36 mm) (

An effect of shading at 40 cm (t = -6.7727, df = 9.15,p < 0.0001) and 60 cm (t = 5.0015, df = 11.441, p< 0.001) and depth for shade (t = -2.3516, df = 15.382, p-value < 0.04) and sun-exposed nests (t = 2.1895, df = 11.557, p < 0.05) were noticed on the daily standard deviation temperatures.

Parameters maximizing likelihood of observed hatchling size for each nest have been fitted first using the total set of 80 nests using the 4 and the 6-parameters equation describing instantaneous growth rate dependency to temperature. AIC for 4-parameters model was 380.97 whereas it was 390.05 for the 6-parameters model. Akaike weight gives a very strong support to retain the 4-parameters model (p=0.99). In a second step, parameters have been fitted separately for hatchery nests (Ln L=-97.83), for experimental nests (Ln L=-79.79) and for all nests together (Ln L=-186.55) with LRT being 1.90 (df=4, p=0.75). Thus, a single model for the two categories of nests was sufficient.

The fitted pattern of embryo growth for the 80 nests is shown in

The fitted instantaneous growth rate according to temperature is shown in

Temperature during incubation of ectothermic animals can have profound consequences on the fitness of individuals and then selection should act to adapt response of embryos to temperature.

The effect of shading on incubation temperature was anticipated based on several previous reports for turtles

Hatchlings from eggs incubated at 40 cm were significantly smaller than those from eggs incubated at 60 cm (

Here we do not detect an effect of temperature on size but an effect of depth of the nest. This effect could be mediated by moisture difference between two depths: it is possible that eggs incubated at 40 cm lost more water that those located at 60 cm, the latter being closer to the water table (sea water that infiltrates by porosity in sand)

The variability of temperatures among different nests incubated in same conditions was measured. We detect an effect of depth but much more an effect of shading (

We thank the hatchery of the Monterrico Natural Reserve for Multiple Uses and the authorities of Guatemala for authorization to use the eggs collected for this experiment. We thank two anonymous referees for their very valuable suggestions that have enhanced the clarity of this manuscript and we thank also the editor Adriana Cortés-Gómes for her help with this manuscript.