Adaptation of sea turtles to climate warming: will phenological responses be sufficient to counteract changes in reproductive output?

README: Supplementary Information

In this document, we list the supplementary material that supports our results and conclusions and we provide a description of what each file contains.

Supplementary Tables

Supp. Info. Table S1: metadata

This file contains various information about the nesting sites studied, including their location and respective Regional Management Unit (RMU, as per Wallace, B. P., et al. 2010. "Regional management units for marine turtles: a novel framework for prioritizing conservation and research across multiple scales." PLoS One 5(12): e15465), the number of nesting seasons with nest count data and how monitoring is conducted, the number of temperature loggers deployed, their type and where they were placed in the clutch, hatchling measurements in terms of straight carapace length (SCL in mm), and whether data from the literature (incubation experiments at constant temperature) was available at the RMU level to estimate thermal tolerance curves (see the column labeled ‘hatching success lab. data for this RMU (literature)’) and sex ratio thermal reaction norms (see the column labeled ‘sex ratio lab. data for this RMU (literature)’).

The file also summarizes the parameters used to reconstruct nest temperature following the method in Monsinjon, J. R., et al. (2019) "The climatic debt of loggerhead sea turtle populations in a warming world." Ecological Indicators 107: 105657: mean diel thermal amplitude in °C (daily maxima minus daily minima), average time of daily min. temperatures in decimal hours, average time of daily max. temperatures in decimal hours, number of days lagged with sea surface temperature (SST), number of days lagged with two-meter air temperature (T2M), GLM coefficient of the Intercept, GLM coefficient of the relationship with SST, GLM coefficient of the relationship with T2M, GLM coefficient of the relationship with the proportion of incubation time used to infer metabolic heating (MH), and standard deviation of the coefficients of the nests from the GLMM random effect used to estimate the thermal heterogeneity.

IPCC regions from which predicted increases in air and sea temperatures were extracted are indicated along with the values extracted for the future changes in temperature (median). The settings selected to extract the warming scenarios from the online interface are given below:

IPCC's atlas: https://interactive-atlas.ipcc.ch/regional-information

Dataset = CMIP6 (Model projections)

Variable = Mean temperature (T) and Sea Surface Temperature (SST) anomalies (change in deg C)

Region set = WGI reference-regions (or Small islands for Tetiaroa, French Polynesia)

Uncertainty = Advanced

Baseline period = 1981-2010

Future period = 2081-2100

Season = Annual

Scenario “Middle of the road” (SSP2-4.5): Approximately in line with the upper end of combined pledges under the Paris Agreement. The scenario “deviates mildly from a ‘no-additional climate-policy’ reference scenario, resulting in a best-estimate warming around 2.7°C by the end of the 21st century”.

The remaining columns show the shift (number of days) in nesting phenology estimated for the IPCC regions according to seawater warming scenarios, and using either the mean or the extreme (max.) coefficient of the negative linear relationship between nesting dates and sea water temperature (using the literature data presented in Supp. Info. Table S6).

Supp. Info. Table S2: hatching success literature data

This file contains the literature data on hatching success from incubation experiments conducted at various constant temperatures. For each species, the Regional Management Unit (RMU) is specified.

Supp. Info. Table S3: mean temperature and hatching success

This file contains in-situ hatching success data and associated mean temperatures during the whole incubation period. Data are from the literature and the present study (refer to Supp. Info. Table S1 for the 3-letter beach codes). Note that the nesting season is specified only for the present study.

Supp. Info. Table S4: sex ratio literature data

This file contains the literature data on sex ratio from incubation experiments conducted at various constant temperatures. For each species, the Regional Management Unit (RMU) is specified.

Supp. Info. Table S5: in situ hatching success

This file contains in-situ hatching success data measured at 19 of our 24 study sites encompassing the four species considered for this study: Caretta caretta, Chelonia mydas, Eretmochelys imbricata, and Lepidochelys olivacea (refer to Supp. Info Table S1 for the 3-letter beach codes). When the number of eggs was not available, we calculated the number that hatched by multiplying the survival proportion by 100 and rounding the value. And we calculated the number of eggs that did not hatch by subtracting the number that hatched from 100.

Supp. Info. Table S6: phenological shifts

This file contains the literature data on the relationship between nesting dates and thermal environmental cues. The grey rows (*) indicate cases that were not considered because the study reported either non-significant relationships or positive relationships between the proxy for nesting phenology and the environmental cue (i.e., a delay of nesting dates with increasing temperatures instead of a shift earlier as assumed in the present study).

Supp. Info. Table S7: required phenological shifts earlier and later in the nesting season

This file contains the estimated required phenological shifts (number of days earlier or later in the season to stay within present-day conditions) and associated rates (number of days earlier or later per 1°C increase in sea surface temperature) that would be necessary to achieve required shifts. Rates were calculated by dividing the required shifts by projected increases in sea surface temperature at our sites (see Supp. Info. Table S1). Required shifts and rates were calculated for our indicators of incubation temperature (IT in column labels; phenological shifts required for the future median incubation temperature index to remain below the 75th percentile of current conditions), hatching success (HS in column labels; phenological shifts required for the future median hatching success index to remain above the 25th percentile of current conditions), and sex ratio (SR in column labels; phenological shifts required for the future median sex ratio index, in proportion of males, to remain above the 25th percentile of current conditions). NAs mean that no shift was found to remain within present-day conditions. Refer to Supp. Info Table S1 for the 3-letter beach codes.

Supp. Info. Table S8: hatching success and sex ratio ranges per site

This file contains statistics (minimum, median, and maximum) on hatching success (HS in survival proportion) and sex ratio (SR in male proportion) for each study site, and the climate (SSP2-4.5) and phenology (no shift, mean shift, and max. shift) scenarios presented in the core manuscript. For each study site (see Supp. Info. Table S1 for the 3-letter beach codes in the first column), ranges are calculated between 2007-2020 for the present conditions and between 2059-2100 for the future conditions.

Supplementary Figures

Supp. Info. Figure S1: hatching success and sex ratio reaction norms

This figure shows the hatching success and sex ratio thermal reaction norms estimated using literature data at controlled incubation temperatures (see data in Supp. Info. Table S2 and Supp. Info. Table S4) for the four species considered here: Caretta caretta, Chelonia mydas, Eretmochelys imbricata, and Lepidochelys olivacea. Points are observations and error bars are their confidence intervals. Continuous lines are estimated curves with shades of grey being the confidence intervals. Reaction norms were fitted using data at the species-level (black) and the RMU-level (red) when available.

Supp. Info. Figure S2: output examples in 2018-2020

This figure shows five successive panels for each study site. In the first panel, we show reconstructed nest temperature without metabolic heating under present (black) and future (SSP2-4.5 in red) scenarios. The blue line shows the estimated pattern of nesting activity assuming no change in phenology and the purple and pink ones corresponds to those assuming a maximum shift (i.e., -18.85 d.°C-1) and a mean shift (i.e., -6.86 d.°C-1), respectively, in nesting dates under the SSP2-4.5 warming scenario (see median values in Supp. Info. Table S1). The following panels show the outputs for hatching success and sex ratio under the present and SSP2-4.5 climate scenarios. Information on the study sites is shown in the title (species, location, 3-letter beach codes).

Supp. Info. Figure S3: required shift for incubation temperature

This figure shows the backward (earlier nesting) and forward (later nesting) phenological shifts required (vertical arrows) for the future median incubation temperature index (the black continuous line, with grey shaded areas representing the 25th and 75th percentiles) to remain below the 75th percentile of current conditions. The black rectangle represents the 25th and 75th percentiles of current conditions and the black point is the median. The red point shows the median of future conditions under the SSP2-4.5 warming scenario assuming no phenological shift, the blue point according to the mean phenological shift, and the green point according to the maximum phenological shift. Refer to Supp. Info. Table S1 for the 3-letter beach codes.

Supp. Info. Figure S4: required shift for hatching success

This figure shows the backward (earlier nesting) and forward (later nesting) phenological shifts required (vertical arrows) for the future median hatching success index (the black continuous line, with grey shaded areas representing the 25th and 75th percentiles) to remain above the 25th percentile of current conditions. The black rectangle represents the 25th and 75th percentiles of current conditions and the black point is the median. The red point shows the median of future conditions under the SSP2-4.5 warming scenario assuming no phenological shift, the blue point according to the mean phenological shift, and the green point according to the maximum phenological shift. Refer to Supp. Info. Table S1 for the 3-letter beach codes.

Supp. Info. Figure S5: required shift for sex ratio

This figure shows the backward (earlier nesting) and forward (later nesting) phenological shifts required (vertical arrows) for the future median sex ratio index, in proportion of males (the black continuous line, with grey shaded areas representing the 25th and 75th percentiles), to remain above the 25th percentile of current conditions. The black rectangle represents the 25th and 75th percentiles of current conditions and the black point is the median. The red point shows the median of future conditions under the SSP2-4.5 warming scenario assuming no phenological shift, the blue point according to the mean phenological shift, and the green point according to the maximum phenological shift. Refer to Supp. Info. Table S1 for the 3-letter beach codes.

Supp. Info. Figure S6: incubation temperature fit quality for each site

This figure shows the predicted vs observed daily mean incubation temperatures (individually for each site). The grey dashed line is the line of equality, and the red line shows the orthogonal regression. Refer to Supp. Info. Table S1 for the 3-letter beach codes.

Supp. Info. Figure S7: sensitivity analysis

This figure shows the differences in hatching success (survival proportion) and sex ratio (male proportion) when predicted using laboratory data (from constant temperature experiments found in the literature: see Supp. Info. Table S2 and Supp. Info. Table S4) either at the species level or at the Regional Management Unit (RMU) level. Differences are plotted for two climate scenarios (present and SSP2-4.5) and three phenology scenarios (no shift, mean shift, max. shift: see values in number of days shifted earlier in Supp. Info. Table S1). We considered only predictions for Caretta caretta (Cc in orange), Eretmochelys imbricata (Ei in yellow) and Lepidochelys olivacea (Lo in green). Data at the RMU level were not available at our study sites for Chelonia mydas. Black dashed lines represent the line of equality.