Data from: Surviving in the mountains: Temperature and elevation have contrasting physiological effects and no effect on morphology of the hoverfly Eristalis tenax in the Himalayas

Gharpure, Gauri 1 ; Vedamurthy, Jagath1; Priya, Sakshi; Prabhakar, Sunil1; Thimmegowda, Geetha G.1; Olsson, Shannon B.1

Published Jan 12, 2026 on Dryad. https://doi.org/10.5061/dryad.83bk3jb6t

Data files

Jan 12, 2026 version files 8.16 GB

Abstract

Insect populations are experiencing a global decline due to a variety of human-linked environmental changes. Among these changes, the potential impact on insect physiology of predicted upslope migration due to climate change is unknown. Being ectotherms, insect physiology is influenced by abiotic factors such as ambient temperature, which changes with elevation. Here, we performed in situ experiments to assess the sensory and cardiac physiology of an important generalist pollinating hoverfly Eristalis tenax (Diptera: Syrphidae), across different elevations in the eco-sensitive and biodiverse Himalayan mountains. We built a portable physiology setup and measured hoverfly antennal responses towards common floral volatiles at 3600 masl and 4200 masl. We also recorded their heart rate at 3000 masl, 3500 masl, and 4000 masl. We also performed tissue morphometric measurements on wild-caught E. tenax using micro-CT. To our knowledge, we report the first in situ physiology experiments performed in the high-altitude Himalayas and the first measurements of internal structures of wild-caught E. tenax. Our results show a contrasting impact of elevation and temperature on the sensory and cardiac physiology of hoverflies, with antennal olfactory sensitivity decreasing with increasing elevation, while average heart rate increased with temperature, independent of elevation. However, elevation did not show an impact on morphometric parameters like body size and flight musculature. With upslope migration and climate warming, consequent sensory mismatches and potential cardiac stress could have deleterious effects on the health of both hoverflies and the vulnerable Himalayan ecosystem.

Dataset DOI: 10.5061/dryad.83bk3jb6t

Description of the data and file structure

Measurement of antennal olfactory sensitivity and threshold for stimulus detection: We standardized a portable electrophysiology (pEAG) rig to perform electroantennograms to measure the antennal response towards the given olfactory stimuli at each site.

Measurement of heart rate: We performed dissections to record the heart rate at each site using a modified protocol.

Wild-caught individuals of Eristalis tenax were used for all experiments.

Whole insect preparation was used to perform electroantennograms at different elevations (3600 and 4200 masl) in the Himalayas and the lab in Bengaluru (900 masl).
Individuals were dissected to reveal the beating heart, which was video recorded for 5 minutes, at different elevations (3000, 3500, 3600, 4000, 4200 masl) in the Himalayas and the lab in Bengaluru (900 masl).

Files and variables

File: eag_data_zipped_.zip

Description: The EAG, ASC and CSV files of electroantennograms of E. tenax at all sites

File: heartrate_videos.zip

Description: The video files of heartrate recordings of E. tenax at all sites

Code/software

eag_data_zipped_.zip

Each recording for EAG has three files: (1) .eag files - can be opened using EAG2000 software; (2) .asc files - can be opened using Notepad and similar programs/software and (3) .csv files - can be opened using MS Excel and similar programs/software.

heartrate_videos.zip

The heartrate files (extension .mp4) can be opened with any media player.

Some notes about extracting data for the electroantennogram (EAG) recordings:

For each EAG recording, there are 3 files:

(1) EAG file – open using EAG2000 software (though proprietary one but the data are also available in the following ASC and CSV files)

(2) ASC file – open using Notepad

(3) CSV file – open using MS Excel

Procedure to extract data:

1. Open CSV file using MS Excel. There are four sheets: ‘data’ ‘chemicals’, ‘sorting’ and ‘max deflections’.

2. In ‘data’ sheet, values in column B are the values of electric potential measured at that time in that recording. These data have to be extracted. The numbers “1, 2, 3…” in column A indicate the stimulus number. These demarcate different stimuli given.

3. First, in a new sheet (‘chemicals’ in this Excel document), copy and paste each stimulus and corresponding electric potential values. There should be one column with the potential values for each stimulus presented (henceforth called ‘mV column’). Each such column corresponds to one chemical stimulus, whose name should be written above the columns.

4. Next, insert two columns before the mV column. In first of those columns, write the serial numbers from 1, 2, 3 .. until the last entry in the mV column (henceforth ‘S. no. column). There should be between 250 to 256 entries for each stimulus.

5. Next, in the second column, we will calculate the time of stimulus presentation. The entire recording last for 10 seconds. That means the electric potential in mV column have been recorded over 10 seconds. In order to calculate the exact time for each entry in mV column, we will use the formula – 10/(value in serial number column). These values should be calculated and inserted in the second column, in front of each of the mV column; this column will be henceforth called ‘Time column’. This last entry in this column should be ‘10’, indicating the value of electric potential at the 10-second time point for each presented stimulus.

6. Next, we make a copy of this sheet, called ‘sorting’ in this Excel document. Here, we will consider values only until 4 seconds, which is when the stimulus is presented. Hence, only retain the values until 4-second timepoint and discard the rest. Repeat for each presented stimulus.

7. In the retained dataset, sort the values in mV column from lowest to highest. The lowest value will be the value of maximum deflection for each presented stimulus.

8. Take this value for each stimulus and tabulate it for each recording. This is represented in the sheet ‘max deflections’ in the document.

9. Repeat for each individual recording (which in our case, is from one individual). Compile the maximum deflection values for each stimulus for each individual and proceed for further analyses.

Legend: (i) mV = milliVolts; (ii) CHA = cis-3-hexenyl-acetate; (iii) cym = p-cymene; (iv) pin = alpha-pinene; (v) PF = 2-pentylfuran; (vi) 10 ^-1, 10 ^-2, 10 ^-3, 10 ^-4, 10 ^-5 = serial dilutions of the chemical stimulus (percent volume/volume) representing 0.1, 0.001, 0.0001, 0.00001 and 0.00001 times (respectively) the concentration of the pure chemical stimulus; (vii) MO = mineral oil (solvent control); (viii) SKP = Sikkim Positive stimulus (positive control stimulus obtained from Mishra et al. (2025).