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Evidence that stress-induced changes in surface temperature serve a thermoregulatory function

Citation

Robertson, Joshua; Mastromonaco, Gabriela; Burness, Gary (2020), Evidence that stress-induced changes in surface temperature serve a thermoregulatory function, Dryad, Dataset, https://doi.org/10.5061/dryad.jsxksn05x

Abstract

Changes in body temperature following exposure to stressors have been documented for nearly two millennia, however, the functional value of this phenomenon is poorly understood. We tested two competing hypotheses to explain stress-induced changes in temperature, with respect to surface tissues. Under the first hypothesis, changes in surface temperature are a consequence of vasoconstriction that occurs to attenuate blood-loss in the event of injury and serves no functional purpose per se; defined as the Haemoprotective Hypothesis. Under the second hypothesis, changes in surface temperature reduce thermoregulatory burdens experienced during activation of a stress response, and thus hold a direct functional value; here, the Thermoprotective Hypothesis. To understand whether stress-induced changes in surface temperature have functional consequences, we tested predictions of the Haemoprotective and Thermoprotective hypotheses by exposing Black-capped Chickadees (n=20) to rotating stressors across an ecologically relevant ambient temperature gradient, while non-invasively monitoring surface temperature (eye region temperature) using infrared thermography. Our results show that individuals exposed to rotating stressors reduce surface temperature and dry heat loss at low ambient temperature and increase surface temperature and dry heat loss at high ambient temperature, when compared to controls. These results support the Thermoprotective Hypothesis and suggest that changes in surface temperature following stress exposure have functional consequences and are consistent with an adaptation. Such findings emphasize the importance of the thermal environment in shaping physiological responses to stressors in vertebrates, and in doing so, raise questions about their suitability within the context of a changing climate.

Usage Notes

## Readme

This note contains necessary descriptions for understanding and working with data used in the construction of Robertson et al, 2020 (Journal of Experimental Biology). Below,
we list each file name attached to this data repository, and descriptions of the data contained within each column of a data file if it is a .CSV. Information pertaining to our R code (which has been provided in this data repository) has not been provided within this readme note, because necessary descriptions for understanding our code are provided within the R code file itself.

Data files:

1) "All Combined Thermal Data.csv".

This CSV contains all ambient temperature and surface temperature measurements drawn from flight enclosures and individual Black-capped Chickadees (respectively) across each day of experimentation. Columns found within this data file are as follows:

Column 1: Row numbers (not used in our analyses, but are residual from previous raw data frames that were bound in the construction of this final, master data sheet).

Column 2: Dates from which ambient temperature and surface temperatures found in a row were drawn. Dates are in YYYYMMDD format and are treated as factors in our analyses.

Column 3: The time at which an ambient temperature and surface temperature measurement found in a row were drawn, as measured in seconds (integer), with second 0 equaling 12:00 AM of a given day. Time was measured in seconds as surface temperature measurements were captured at a frequency of one frame per second.

Column 4: Flight enclosure ID (a factor). This column contains the identity of a flight enclosure that the individual from which a surface temperature measurements was captured, was maintained. This experiment used 20 Black-capped Chickadees that were maintained across 4 flight enclosures (labelled by their cardinal position, with respect to other flight enclosures). Note that some enclosure IDs as labelled with their ID name, followed by "_2"; such IDs are found on rows that contain surface temperature measurements that were captured during a second filming session of that individual's enclosure in a given day. Specifically, we rotated our thermal imaging camera among flight enclosures each day. If an individual's surface temperature was captured during the second session of filming, it's respective flight enclosure was labelled, "FLIGHTID_2", where "FLIGHTID" is replaced with the true identity of the flight enclosure.       

Column 5: Flight enclosure ID abbreviated (a factor). This column contains the equivalent data to that described in column 4, however, second filming sessions are not labelled as distinct from first filming sessions. The enclosure identity column was used for all analyses described in our study.

Column 6: Maximum surface temperature of the eye region of a thermally imaged Black-capped Chickadee, in degrees Celsius (a continuous, numeric variable).

Column 7: Quality of the thermal image from which surface temperature measurements contained in column 6 were drawn. Thermal images of individual that were captured during movement, and were thus blurry, were labelled "Poor Eye", whereas those captured during moments with no movement, and were thus in focus, were labelled "Good". Rows containing surface temperature measurements that had quality values of "Poor Eye" were excluded from our analyses.

Column 8: Ambient temperature (a continuous, numeric variable) experienced during the time at which a surface temperature measurement contained in a given row was measured. Ambient temperature values were collected every 5 minutes, and were assumed to remain constant from the time of collection to the second before the next temperature measurement was drawn.

Column 9: Experimental treatment (a factor). Rows containing surface temperature measurements that were captured from individuals experiencing control treatments are labelled "Rest", while those captured from individuals experiencing stress exposed treatments are labelled "Stress".

Column 10: Bird identity (a factor). The individual from which a surface temperature measurement in a given row was collected is identified by it's unique coloured leg-band combination here.

2) "Full_Thermal_Data_With_Sexes.csv".

This CSV contains identical data to that found within "All Combined Thermal Data.csv", however, additional factorial data pertaining to individuals from which surface temperature measurements were bound is also found within. Columns found within this data file are as follows:

Columns 1 through 10: All data is as described for "All Combined Thermal Data.csv".

Column 11: Location of capture (a factor). The region that a given individual, from which a surface temperature measurement contained in a given row was captured, was collected from. All Black-capped Chickadees were captured across 6 different regions, and the regional name of each location of capture are found within this column.

Column 12: Category of an individual's capture location (a factor). This column was not used in our analysis, but categorizes that capture locations found in column 11 as either "Urban" or "Rural".

Column 13: Sex of an individual from which a surface temperature measurement in a given row was drawn (a factor); either "Male" or "Female".

3) "Condition_Data.csv".

This CSV contains relevant measurements of individuals used for analysing change in condition experienced by a Black-capped Chickadee across control and stress exposure treatments. Columns found within this data file are as follows:
        
Column 1: Row number (unused in our analysis, and residual from master data frame construction).

Column 2: Individual identity of a given bird (factor), as defined by a unique coloured leg-band combination. Note that Chickadees were measured before and after each experimental treatment (stress exposure and control), and as such, four rows should be found for each individual.

Column 3: Flight enclosure identity (factor). The flight enclosure from which an individual (whose data is represented in a given row) was maintained during experimentation.    

Columns 4-6: Equivalent to columns 11-13 in "Full_Thermal_Data_With_Sexes.csv".

Column 7: Right wing chord measurement of a given individual defined within column 2 of the data row. Measured in mm.

Column 8: Back of head to tip of bill measurement of a given individual defined within column 2 of the data row. Measured in mm.

Column 9: Right tarsus measurement of a given individual defined within column 2 of the data row. Measured in mm.

Column 10: Mass measurement of a given individual defined within column 2 of the data row. Measured in g.

Column 11: Time-point at which measurements within a given row were collected (a factor), with respect to the beginning or end of a treatment (e.g. "Start" or "End"), and with respect to the treatment type (whereby control treatments are labelled as "Rest", and stress exposure treatments as labelled as "Stress").

4) "Digital Bird with RT.csv".

Lastly, this CSV contains data used for analyses of feeding rate according to experimental treatment among our Black-capped Chickadees, and for analyses of whether feeding rate correlates with surface temperature in our Black-capped Chickadees. It contains surface temperature measurements of Chickadees across dates, times, and experimental treatments, and contains an enumerated presence and absence column for use in feeding rate analyses. Columns within this data file are as follows:

Columns 1-2: Equivalent to columns 2-3 in "All Combined Thermal Data.csv".

Column 3: Equivalent to column 4 in "All Combined Thermal Data.csv".    

Column 4: Time at which a surface temperature measurement contained within a given row was collected, as written in HHMMSS format, rather than absolute seconds format. This column is not used in our analyses, and is contained for simple visualization purposes.

Columns 5-7: Equivalent to columns 6-8 in "All Combined Thermal Data.csv".

Column 8: Equivalent to column 5 in "All Combined Thermal Data.csv".    

Column 9: Equivalent to column 9 in "All Combined Thermal Data.csv".    

Column 10: A duplication of column 1, but with a truncated column name for simplicity. Date from which a surface temperature measurement in a given row was captured.

Column 11: Equivalent to column 5 in "All Combined Thermal Data.csv".

Column 12-16: Columns describing the presence (1) or absence (0) of a given individual (defined by the column name), at a given second of an experimental day, as defined by columns 1 and 2 of a given row. This experiment was conducted across 4 flight enclosures, with 5 individuals held within each flight enclosure; each column therefore pertains to the presence of absence of one specific individual in the flight enclosure identified in columns 3 and 11 for a given row. Note that the identities of individuals defined in each column, with respect to their unique coloured-leg band combinations, are identified within the attached r code. Importantly, not all rows containing a presence value (1) also have a corresponding surface temperature value, because the eye region of birds that were feeding could not always be viewed.

Column 17: A column defining the global presence (1) or absence (0) of any feeding birds (as identified in digital video), at any given time.     

 

Funding

Natural Sciences and Engineering Research Council of Canada, Award: RGPIN-04158-2014