DOI: 10.5061/dryad.tdz08kq94
title: Heat shock protein gene expression varies among populations but does not strongly track recent environmental conditions: implications for biomarker development

description: Global temperatures are rising, and scientists are mobilizing to uncover
 which birds are most affected by the problem of heat. Heat shock proteins
 (HSPs), for example, can shed light on this issue because they prevent
 damage and promote recovery from heat. However, few studies have
 investigated the relationship between HSPs and heat outside of
 experimental contexts. Here, we ask whether natural variation in HSP gene
 expression can serve as a biomarker of recent ambient conditions in wild
 nestling tree swallows (Tachycineta bicolor). We focused on HSP90AA1
 because this HSP increases mRNA abundance in avian blood after acute heat.
 Using blood samples collected across ten degrees of latitude, we tested
 for population differences in constitutive HSP90AA1 gene expression in
 12-day-old nestlings. To quantify the specific time period over which
 ambient conditions best predicted variation in HSP gene expression, we
 used a climate window analysis, evaluating the predictive value of maximum
 temperatures and maximum heat index in the hours and days from hatching
 until sampling. We found a significant population difference in
 constitutive HSP gene expression at the ends of our sampling range:
 nestlings in South Carolina had nearly double the HSP90AA1 mRNA abundance
 compared to nestlings in Massachusetts. There was no relationship between
 HSP90AA1 and heat index at any time (hours or days), meaning that baseline
 HSP gene expression is not a reliable biomarker for the combined effects
 of heat and humidity, at least not when applying the heat index developed
 for poultry. We found some evidence linking HSP90AA1 gene expression with
 maximum temperatures three to four days before sampling; however, a
 permutation test could not rule out the possibility of a false positive.
 Thus, HSP90AA1 mRNA abundance is not necessarily an effective biomarker of
 recent heat, and it may instead reflect other inherent population
 differences. As heat waves intensify, this conclusion could change, and
 other species could be more reactive to heat. We urge the avian biology
 community to continue biomarker testing and better analytical tools for
 estimating heat impacts on wild birds, as we seek to understand and
 predict their persistence in the future.
description: # Heat shock protein gene expression varies among populations but does not
 strongly track recent environmental conditions: implications for biomarker
 development Dataset DOI:
 [10.5061/dryad.tdz08kq94](10.5061/dryad.tdz08kq94) ### Author information 
 | Name  | Affiliation  | email  | ORCID  | | :----------------------- |
 :----------- |
 :----------------------------------------------------------- |
 :------------------- | | Mary J. Woodruff  | 1,2,3 |
 [mjowoodruff@gmail.com](mailto:mjowoodruff@gmail.com)  |
 0000-0003-0475-3811  | | Sarah E. Wolf  | 1,2,4  |
 [swolf2@ed.ac.uk](mailto:swolf2@ed.ac.uk) | 0000-0002-2620-8999  | | Ethan
 D. Clotfelter  | 5 |
 [edclotfelter@amherst.edu](mailto:edclotfelter@amherst.edu)  |
 0000-0002-6711-3873  | | Elizabeth P. Derryberry  | 6  |
 [liz@utk.edu](mailto:liz@utk.edu)  | 0000-0002-8248-9748  | | Mark T.
 Stanback | 7 | [mastanback@davidson.edu](mailto:mastanback@davidson.edu) 
 | 0000-0002-2786-6774  | | Kimberly A. Rosvall  | 1,2  |
 [krosvall@iu.edu](mailto:krosvall@iu.edu)  | 0000-0003-3766-9624  |
 **Affiliations:** 1 Department of Biology, Indiana University,
 Bloomington, IN, United States 2 Center for the Integrative Study of
 Animal Behavior, Indiana University, Bloomington, IN, United States 3
 Center for Epidemiology and Animal Health, US Department of Agriculture
 Animal and Plant Health Inspection Service, Fort Collins, CO, United
 States 4 Institute of Ecology and Evolution, School of Biological
 Sciences, University of Edinburgh, Edinburgh, United Kingdom 5 Department
 of Biology, Amherst College, Amherst, MA, United States 6 Department of
 Ecology and Evolutionary Biology, University of Tennessee Knoxville,
 Knoxville, TN, United States 7 Department of Biology, Davidson College,
 Davidson, NC, United States ## Description of the data and file structure 
 **File: Woodruff_TRES_HSP_By_Individual.csv** Nestling data quantified at
 the individual level. Missing values are indicated by “NA.” | \*\*Column
 Name \*\* | \*\*Description \*\* | | :----------------------- |
 :--------------------------------------------------------------------------------------------------------------------------- | | Band\_ID           | Individual ID from USGS band number, or for terminally collected individuals, the nest ID and “EUTH” to indicate “euthanized” | | State    | U.S. State associated with study population | | Date\_Collected          | Date the blood samples were collected | | Time    | Time of day the blood samples were collected | | Brood\_Size      | Number of nestlings in the nest | | Neslting\_DPH | Nestling days post hatch. Measured from the day the majority of nestlings hatched in the nest (D1). | | Sex       | Nestling sex, determined molecularly | | Log2\_HSP\_RQ | Log2 transformed blood relative gene expression of HSP90AA1 (2-Δ∆ct) | **Files: Woodruff_NOAA_Hourly_Climate.csv** Ambient temperature and heat index measures. Each row represents one hourly measurement. Missing values are indicated by “NA.” | **Column Name** | **Description** | | :---------------------------------------- | :------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | State    | U.S. State associated with study population | | Date    | Calendar date, climate data recorded | | Hour    | Hour climate data recorded; NOAA data recorded at the top of each hour | | Temperature (Degrees C)      | Temperature record for given hour in degrees Celsius. | | Heat Index (Zulovich and DeShazer (1990)) | Heat index formula sourced from Zulovich and DeShazer (1990) in which *Tdb* = dry bulb temperature in degrees Celsius and *Twb* = wet bulb temperature in degrees Celsius. |