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Social hierarchy reveals thermoregulatory trade-offs in response to repeated stressors

Citation

Robertson, Joshua (2020), Social hierarchy reveals thermoregulatory trade-offs in response to repeated stressors, Dryad, Dataset, https://doi.org/10.5061/dryad.rfj6q5774

Abstract

Coping with stressors can require substantial energetic investment, and when resources are limited, such investment can preclude simultaneous expenditure on other biological processes. Among endotherms, energetic demands of thermoregulation can also be immense, yet our understanding of whether a stress response is sufficient to induce changes in thermoregulatory investment is limited. Using the black-capped chickadee as a model species, we tested a hypothesis that stress-induced changes in surface temperature (Ts), a well-documented phenomenon across vertebrates, stem from trade-offs between thermoregulation and stress responsiveness. Because social subordination is known to constrain access to resources in this species, we predicted that Ts and dry heat loss of social subordinates, but not social dominants, would fall under stress exposure at low ambient temperatures (Ta), and rise under stress exposure at high Ta, thus permitting a reduction in total energetic expenditure toward thermoregulation. To test our predictions, we exposed four social groups of chickadees to repeated stressors and control conditions across a Ta gradient (n=30 days/treatment/group), whilst remotely monitoring social interactions and Ts. Supporting our hypothesis, we show that: (1) social subordinates (n=12), who fed less than social dominants and alone experienced stress-induced mass-loss, displayed significantly larger changes in Ts following stress exposure than social dominants (n=8), and (2) stress-induced changes in Ts significantly increased heat conservation at low Ta and heat dissipation at high Ta among social subordinates alone. These results suggest that chickadees adjust their thermoregulatory strategies during stress exposure when resources are limited by ecologically relevant processes.

 

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, 223, jeb229047). 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) "Digital Bird with RT.csv".

This CSV contains data used for analyses of feeding rate and social status of 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 and social status determination. 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.     

 

3) "Effects of Social Status on Stress-induced Changes in Surface Temperature of Chickadees.R".

This file contains all necessary code for reproducing analyses that were conducted in Robertson et al (2020; Journal of Experimental Biology, 223, jeb229047).

 

Funding

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