Seasonal activity and sexual selection in an urban dung beetle
Data files
Sep 11, 2025 version files 57.27 MB
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orpheus_fight1.mp4
13.62 MB
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orpheus_fight2.mp4
43.59 MB
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orpheus_seasonality2024_raw_data.xlsx
39.55 KB
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orpheus_seasonality2024.csv
8.86 KB
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README.md
2.47 KB
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seasonality.R
7.66 KB
Abstract
Onthophagus orpheus Panzer (Coleoptera: Scarabaeidae) is the most abundant dung beetle in urban forests in central Massachusetts, but little is known about its behavioral ecology. We measured individuals throughout the breeding season to characterize male horn allometry and track seasonal variation in population abundance, adult sex ratio, and male morph ratio. Large major males have a forked thoracic horn that they use in male-male fights over ownership of breeding tunnels; small minor males have rudimentary horns; and females are hornless. Unlike many onthophagine dung beetles that exhibit sigmoidal horn allometries with distinct horned and hornless male morphs, O. orpheus exhibits a segmented horn allometry in which many males have intermediate-sized horns. Abundance peaked in July, and average densities were comparable to those observed for other horned Onthophagus species that experience intense male-male competition. The season-wide adult sex ratio was significantly female-biased, and males exhibited size-dependent seasonal activity. These ecological conditions are likely to promote a highly competitive, defense-based mating system that favors the development of sexually selected horns. Because of its prevalence in urban forests across the eastern United States and the expected increases in resource availability (i.e., dog dung) in urban environments, we highlight O. orpheus as an emerging model species for investigating the effects of urbanization on mating dynamics.
Dataset DOI: 10.5061/dryad.xgxd254sn
Files and variables
This dataset contains two Excel files, one R file, and two videos.
File: seasonality.R
Description: complete R code used for analyses and plotting figures.
File: orpheus_seasonality2024.csv
Description: complete morphological dataset that was used in the analyses of male horn allometry and male size-dependent seasonal activity.
Variables
- ID: Individual ID for each male collected
- PW: Prothorax width (measured in mm)
- HW: Horn width (measured in mm)
- HL: Horn length (measured in mm)
- Date: Month in which the male was collected
- Notes: Additional description of two individuals with broken weapons. We were unable to measure horn width for S_August23_MH18 (line 145) because it had a broken tine, so we left that blank.
File: orpheus_seasonality2024_raw_data.xlsx
Description: compiled dataset on seasonal activity and contains four spreadsheets:
“independent_measurements” reports the independent measurements of body size, horn width, and horn length that were taken by three separate researchers (Bea, Luna, and Maddie). The final columns calculate the averages that were used in the analyses. We were unable to measure horn width for S_August23_MH18 (line 145) because it had a broken tine, so we left those cells blank;
“orpheus_seasonality2024” reports the averaged body size, horn width, and horn length measurements from the “independent measurements” spreadsheet described above. We were unable to measure horn width for S_August23_MH18 (line 145) because it had a broken tine, so we left that cell blank. This file was saved as a separate CSV file and used in the analyses in R;
“morph ratio” reports the number of major and minor males collected each month;
“sex ratio” reports the number of males and females collected each month.
File: orpheus_fight1.mp4
Description: video of two males fighting in an artificial tunnel. One male wedges his head (clypeus) underneath the opponent’s horn and rapidly jerks his head upward to pry the opponent of the tunnel wall.
File: orpheus_fight2.mp4
Description: another video of two males fighting in an artificial tunnel. Males interlock their horn tines and engage in a head-to-head pushing match to shove the opponent down or out of the tunnel.