DOI: 10.5061/dryad.wpzgmsc0v
title: Suboptimal is good enough: Aligning thermal sensitivity to habitat temperature across season

description: Predicting organismal performance in changing environments is a global
 challenge. In ectotherms, organismal performance depends on how
 well-aligned the thermal sensitivities of fitness components are to body
 temperatures in natural habitat. It is frequently assumed that Topt
 (temperatures that maximize performance) for important fitness components
 have evolved to align with habitat temperatures. However, most organisms
 at temperate latitudes experience significant seasonal temperature
 variation, and therefore frequently operate at suboptimal temperatures.
 Importantly, seasonal performance patterns may differ among fitness
 components if those components have different thermal
 sensitivities.  The extent to which habitat temperature can
 deviate from Topt before an organism can no longer persist in its
 environment, and the role of seasonality in driving this deviation, are
 infrequently explored. Here, we assess how well-aligned the thermal
 sensitivity (thermal performance curves, or TPCs) of development, growth,
 and survival are to local habitat temperatures across two seasons using
 embryos of the marine gastropod Haminoea vesicula. We develop a
 mechanistic model by integrating thermal sensitivity for development,
 growth, and survival with habitat temperatures to predict embryo
 performance across seasons. Our results demonstrate that habitat
 temperatures mostly fall far below Topt for development and growth.
 Accordingly, in the cool spring, developmental periods are 20% longer and
 hatchling sizes are slightly (about 1%) smaller on average than in the
 summer. Survival risk intensifies in the summer due to an acute
 high-temperature event, indicating that seasonal temperature variation
 affects performance differently between fitness components. We
 horizontally shift TPC functions to assess how well-aligned the thermal
 sensitivity of each fitness component is to habitat temperatures.
 Simulations indicate that Topt for survival is well-aligned to habitat
 temperature, but Topt for development and growth would need to cold-shift
 by 11° and 16° C, respectively, to achieve optimal performance. However,
 cold-shifting TPCs to maximize development and growth results in sharp
 survival reductions due to summer heat spikes. Overall, Topt greatly
 exceed the most frequent habitat temperatures, leading to suboptimal
 performance most of the time. However, high Topt allow embryos to survive
 seasonally driven heat spikes. Sometimes “suboptimal” is good enough.
description: # Suboptimal is good enough: Aligning thermal sensitivity to habitat
 temperature across season Dataset DOI:
 [10.5061/dryad.wpzgmsc0v](10.5061/dryad.wpzgmsc0v) ## Description of the
 data and file structure ### Data Description This dataset contains code
 and data files that should allow replication of the workflow to model
 embryo thermal performance based on habitat temperature. Field data were
 collected at False Bay, San Juan Island, Washington, USA, and experimental
 data were generated at the University of Washington's Friday Harbor
 Laboratories, San Juan Island, Washington, USA.  ### Files and variables
 #### File: averagedtemps.csv **Description:** Habitat temperatures
 averaged across five different sites at each hourly time window at False
 Bay, San Juan Island, Washington, USA. Temperatures were recorded from
 April - September 2022.  ##### Variables * Temperature: Habitat
 temperature (in degrees Celsius). * Date:  Date and time in PST, to be
 converted to a POSIXct object (datetime object in R) in associated R
 script.  #### Files: FalseBay1Oct22.csv, FalseBay2Oct22.csv,
 FalseBay3Oct22.csv, FalseBay4Oct22.csv, FalseBay5Oct22.csv
 **Description:** Habitat temperatures from five different sensors at False
 Bay, San Juan Island, Washington, USA. Temperatures were recorded from
 April - September 2022.  ##### Variables * Temperature: Habitat
 temperature (in degrees Celsius). * Date:  Date and time in PST, to be
 converted to a POSIXct object (datetime object in R) in associated R
 script.  #### File: Dev_Size_Survival_ByDay.csv **Description:** A .csv
 containing experimentally-generated data on size and survival across each
 day of embryo development for embryos reared in laboratory conditions. 
 ##### Variables * category: Categorical variable describing the
 temperature treatment, where "lo" = 10 degrees Celsius,
 "med" = 20 degrees Celsius, and "hi" = 26 degrees
 Celsius * temperature: Treatment temperature (in degrees Celsius).  * day:
 Days since birth.  * stage: Developmental stage.  * size: Embryo size (in
 microns). * survival: Proportion of embryos that are alive at each
 developmental day. * se_stage: Standard error of developmental stage
 across replicate egg ribbons. * se_size_prelim: Standard error of embryo
 size  across replicate embryos and egg ribbons. * se_size: Standard error
 of the mean embryo size across replicate egg ribbons. #### File:
 Haminoea_ThermalSensitivity_Summary.csv **Description:** A summary of
 experimentally generated values for mean embryo development, growth, and
 survival rates across all of embryonic development during exposure to
 different temperature treatments.  ##### Variables * Spp: String variable
 representing species, where "HV" = *Haminoea vesicula*, the
 focal species of the study. * Temperature: The temperature at which
 embryos were experimentally reared, in degrees Celsius * Replicate: A
 numerical identifier for each whole egg ribbon replicate per temperature
 treatment (n = 3 whole egg ribbons per temperature treatment). * Growth
 Rate: Mean embryo growth rate in microns per day * Developmental Rate:
 Mean embryo developmental rate in developmental stages per day.  *
 Survivorship: Mean survival, the % of embryos that survived to hatch ####
 File: Mechanistic_Modelling.R **Description:** R script used to generate
 predictions of time to hatch, size at hatch, and survival of embryos in
 natural habitat.  #### File: TPC_Fitting.R **Description:** R script used
 to fit thermal performance curves for embryo development, growth, and
 survival to raw experimental data.  #### File:
 ToptShift_MechanisticModel_OutputSummary.csv **Description:** A tabular
 summary of predicted embryo performance in habitat with cold and
 hot-shifted thermal performance curves. Generated by running the
 mechanistic model (detailed in mechanistic file R script) after shifting
 the position of all thermal performance curves left or right in one degree
 Celsius increments.  ##### Variables * shift: Amount that thermal
 performance curves have been shifted in degrees Celsius, where negative
 values represent cold (left) shifts, and positive values represent warm
 (right) shifts.  * Reprodhours: Total number of hours during the
 reproductive season during which embryos could be born and complete
 embryonic development without succumbing to heat death.  * Growthmean:
 Cumulative arithmetic mean of growth rates (in microns per day) of embryos
 born at every hour across the entire reproductive season.  *
 Growthscaledmean: The same as the column "Growthmean" but scaled
 to a maximum value of 1. * Survivmean: Cumulative geometric mean of
 survival rates (as a fraction of 1) of embryos born at every hour across
 the entire reproductive season. * Fitnessmean: Product of growth and
 survival means, not representative of true fitness, but rather a loose,
 exploratory estimate for embryos. * Devmean: Cumulative arithmetic mean of
 developmental rates (in developmental stages per day) of embryos born at
 every hour across the entire reproductive season.  * daysmean: Mean time
 to hatch (in days) for embryos born at every hour across the entire
 reproductive season. * sizemean: Mean size at hatch (in microns, measured
 as the longest dimension of the larval shell, from the apical tip to the
 dorsal/posterior end) of embryos born at every hour across the entire
 reproductive season. * nodeathdaysmean: Mean time to hatch (in days)
 for embryos born at every hour across the entire reproductive season,
 **excluding embryos that did not survive to hatch.** * nodeathsizemean:
 Mean size at hatch (in micros) for embryos born at every hour across the
 entire reproductive season, **excluding embryos that did not survive to
 hatch.** #### File: TimetoHatch_DaystoHatch_Survival_MechanisticModel.csv
 **Description:** A mechanistic model that combines thermal performance
 curves and habitat temperature in order to predict embryo days to hatch,
 size at hatch, and survival to hatch in natural habitat.  ##### Variables
 * Temperature: Temperature (in degrees Celsius) in egg-laying habitat,
 averaged across 6 sites at hourly time windows across the duration of
 reproductive season (April - September). * Date: Date and time in PST, to
 be converted to a POSIXct object (datetime object in R) in associated R
 script.  * growthrate_daily: Growth rate (in microns **per day**) derived
 from aligning habitat temperature with thermal performance curve for
 embryo growth.  * devrate_daily: Development rate (in stages **per day**)
 derived from aligning habitat temperature with thermal performance curve
 for embryo development.  * survivorship: Survival (as a fraction of 1)
 derived from aligning habitat temperature with thermal performance curve
 for embryo survival.  * growthrate_hourly: Amount of growth (in microns
 **per hour**) derived from aligning habitat temperature with thermal
 performance curve for embryo growth.  * devrate_hourly: Developmental rate
 (in stages **per hour**) derived from aligning habitat temperature with
 thermal performance curve for embryo development.  * status:
 "hatch" if an embryo born at the time in that row will survive
 to hatch, and "died" if it succumbs to heat death before
 hatching * days: Time to hatch (in days) for an embryo born on the date
 and time specified in the row.  * finalsize: Size at hatch (in
 microns) for an embryo born on the date and time specified in the row *
 meansurvivorship: Geometric mean survival (as a fraction of 1) of all 
 survival values at each hourly time window during embryonic development
 for an embryo born on the date and time specified in the row.  * meandev:
 Arithmetic mean developmental rate (in developmental stages per day) of
 development rates at each hourly time window during embryonic development
 for an embryo born on the date and time specified in the row.  *
 meangrowth: Arithmetic mean growth rate (in microns per day) of growth
 rates at each hourly time window during embryonic development for an
 embryo born on the date and time specified in the row.  *
 meangrowthscaled: Arithmetic mean growth rate (in microns per day) of
 growth rates at each hourly time window during embryonic development for
 an embryo born on the date and time specified in the row, scaled to a
 maximum value of 1. * scaledfitness: The product of arithmetic mean growth
 and geometric mean survival, representing a loose, exploratory estimate of
 fitness for an embyro.  ## Code/software ## Relationship between data
 files and scripts Data scripts are listed in roughly the order necessary
 for the analysis to be replicated from starting with a data file
 containing habitat temperature data through generating mechanistic model
 outputs and summarizing outputs. We describe which files are used as input
 for each script, as well as the expected output. * R script to fit TPCs to
 experimental data: "TPCFitting.R" * Files used:
 "Haminoea_ThermalSensitivity_Summary.csv" * R script to predict
 embryo time to hatch, size at hatch, and survival in natural habitat:
 "Mechanistic_Modelling.csv" * Files used:
 "averagedtemps.csv" * Files output:
 "TimetoHatch_DaystoHatch_Survival_MechanisticModel.csv" *
 Summary stats of mechanistic model output:
 "ToptShift_MechanisticModel_OutputSummary.csv" follow R script
 to shift TPCs in order to generate these outputs.