Species with environmental sex determination (ESD) have persisted through deep time, despite massive environmental perturbation in the geological record. Understanding how species with temperature-dependent sex determination (TSD), a type of ESD, persist through climate change is particularly timely given the current climate crisis, as highly biased sex ratios and extinction are predicted. Since 1982, we have studied primary sex ratios of a reptile with TSD (Chelydra serpentina). Primary sex ratios remained unchanged over time, despite warming in the environment. Resilience of the primary sex ratio occurred via a portfolio effect, realized through remarkable intra-annual variation in nest-level sex ratios, leading to a relatively consistent mean annual sex ratio. Intra-annual variation in nest-level sex ratios was related to variation in egg burial depth coupled with large clutch sizes, creating thermal gradients in the nest, and promoting mixed-sex clutches. Further, both locally and globally, sustained increases in nighttime air temperature contribute more to warming than increases in daily maximum temperature, but development rate was affected more strongly by maximum daily air temperature, conferring additional resilience to overall warming. Our study suggests that some TSD species may be resilient to warming and provides an example of how ESD may persist under environmental change.

Data file description:

Nest Temperatures: Hourly nest temperature records from nests that were laid on the dam or translocated there shortly after laying. Missing values indicate temperature logger failure. There is a file for each year between 1985 and 1998. Within each of these files:

DATE - indicates the date that the nest temperature was measured on. Each date appears in this column 24 times as nest temperatures were measured hourly. 

The following coloumns are nest temperatures - the names of the column indicate the turtle ID of the female that laid the nest. 

AirTemp: These are daily air temperature records downloaded from https://climate.weather.gc.ca/historical_data. They span January 1st 1965-October 20th 2020

Date - the date in format d/m/y

Year - year of measurement extracted from Date column

Day - day of the month extracted from Date column

Max.Temp - daily maximum temperature measured at the weather station

Min.Temp - daily minimum temperature measured at the weather station

Mean.Temp - daily mean temperature measured at the weather station

SexRatio: contains nest dates, and sex ratios (where applicable - NAs where nest sex ratio was not measured) for all nests laid naturally on the Sas Dam between 1973 and 2020.

Individual - the unique individual identifier of nesting females (1-124)

Year - the year that the nest was laid in

NestDate - the date that the nest was laid in Y-m-d format

n.female - the number female hatchlings that emerged from the eggs of that clutch that were taken to the laboratory

n.male - the number male hatchlings that emerged from the eggs of that clutch that were taken to the laboratory

ClutchSize - the total number of eggs laid in that nest. n.female + n.male does not necessarily equal clutch size because often only a subset of eggs were taken to be sexed.

EggDepth: This contains egg depth measures from 2018, along with maternal ID, egg number, and sex

Maternal ID - the unique individual identifier of nesting females (1-5). Female 1 in this dataset is not the same as Individual 1 in the Clutch Data.

EggNumber - the position of the egg within the clutch. As researchers excavate the nest after laying eggs are given a number based on the order that they are removed (1st removed = last laid = egg number 1, last removed = first laid egg = egg number n).

Depth - the depth of the egg from the substrate surface in centimeters.

Sex - the sex of the embryo that hatched from the egg

SexEmb - a numeric version of the previous column (0 = female, 1 = male).

EggOrder: This contains the sex of hatchlings, their egg number, maternal ID, and year. This is for nests laid naturally on the dam between 1983 and 1997. 

Maternal ID - the unique individual identifier of nesting females (1-53). Female 1 in this dataset is not the same as Female 1 in the Egg Depth Data or Individual 1 in the Clutch Data.

Year - the year the nest was laid in

EggNo - the position of the egg within the clutch. As researchers excavate the nest after laying eggs are given a number based on the order that they are removed (1st removed = last laid = egg number 1, last removed = first laid egg = egg number n).

Clutch ID - indicated eggs that came from the same clutch (1-195). 

Sex - the sex of the embryo that hatched from the egg

SexEmb - a numeric version of the previous column (0 = female, 1 = male).

NestDepth: This contains the measures of depth of top and bottom of nest cavity for 31 nests laid on the dam or alternate sites in 2020. Maternal ID and nest site (dam/alt) are included.

maternalID - the unique individual identifier of nesting females (1-53). Female 1 in this dataset is not the same as Female 1 in the Egg Depth/Order Data or Individual 1 in the Clutch Data.

MaxDepth - the depth of the bottom of the nest chamber from the substrate surface (0cm).

TopNest - the depth of the top of the nest chamber from the substrate surface (0cm).

orig.site - the location of the nest site (dam/ALT). dam = Lake Sasajewun dam, alt = alternate site but from the same watershed. 

Staging: This contains data on ED20 stage of eggs laid naturally on the dam between 1983 and 1995. ED20 stage is the average stage of all eggs collected on the specified date. Maternal ID is also included.

Year - the year the nest was laid

Individual - the maternal ID of the turtle that laid the nest

Date.Collected - the date that the egg was removed from the nest for staging. Eggs were either staged immediately or frozen immediated after collection

ED20.Stage - the stage of the embryo in equivalent development at 20 degrees.

R-file description:

Scripts must be run in the order displayed here as each builds on the previous. I also assume here that all data and script files are downloaded within a single project.

1) development1: Script for determining daily within nest development from nest temperatures and Schoolfield model (Appendix 1)

2) development2: Regression of within nest air temperature on daily development (Appendix 1)

3) validation: Regressing predicted egg stage from our model on measured egg stage data & applying Rollinson et al 2018 correction.

4) mainanalyses: All regressions in main text and appendix 2

5) figures: All figures from main text and appendix