DOI: 10.5061/dryad.xgxd254sn
title: Seasonal activity and sexual selection in an urban dung beetle

description: 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.
description: # Seasonal activity and sexual selection in an urban dung beetle Dataset
 DOI: [10.5061/dryad.xgxd254sn](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.