The non-indigenous dung beetle (Onthophagus nuchicornis) can effectively reproduce using the dung of indigenous eastern North American mammals

Abstract

Non-indigenous dung beetle (Coleoptera: Scarabaeoidea) species in North America are important contributors to ecosystem functions, particularly in pasture-based livestock systems. Despite the significant body of research surrounding non-indigenous (and often invasive) dung beetles in agricultural contexts, there has been minimal study concerning the impact that these species may have on indigenous dung beetle populations in natural environments. Here we examine the possible impact of the introduced dung beetle Onthophagus nuchicornis on indigenous dung beetle populations via use of indigenous mammal dung. Using a controlled laboratory experiment, we quantified how readily beetles could use dung from bobcat (Lynx rufus), red fox (Vulpes vulpes), moose (Alces alces), raccoon (Procyon lotor), and domestic sheep (Ovis aries). To determine the suitability of each dung type for reproduction, we measured offspring abundance and fitness. While the number of developed offspring was significantly different among treatments, offspring fitness did not vary significantly across dung types. Our results demonstrate the generalist feeding habits of the non-indigenous dung beetle O. nuchicornis can allow this species to use the dung of various wild animals indigenous to eastern North America.

Keywords: Agroecology; Coleoptera; Dung; Dung beetle; Dung decomposition; Indigenous species; Invasive; Onthophagus; Reproduction.

Figure 1. Fresh dung of four species indigenous to eastern North America, and domestic sheep.

(A) Bobcat. (B) Fox. (C) Moose. (D) Raccoon. (E) Texel Sheep. Image credits: Photo of the sheep was taken by Paul Manning; animal dung photos were taken by Katelyn Stokes. All other photos are in the public domain, licensed under the Creative Commons CC0 license, and were retrieved from Wikimedia Commons.

Figure 2. Box and whisker plot visualizing the median number of days since experiment start to 50% F0 beetle emergence for females and males.

The horizontal line inside each box represents the median time in days (female bobcat = 14, male bobcat = 20, female fox = 18, male fox = 28.5, female moose = 16.5, male moose = 27, female raccoon = 10, male raccoon = 11, female sheep = 31.5, male sheep = 30.5). The upper and lower boundaries of the coloured boxes show the inter-quartile range (IQR). The whiskers extending from the boxes show maximum and minimum values for data within 1.5x the IQR; any observations beyond this range are represented as a point.

Figure 3. Mean number and standard error (SE) of F1 beetles that successfully reached full development across n = 4 replicates per dung treatment.

F0 beetles using fox (2.25 ± 0.85) and racoon dung (2 ± 0.91), produced significantly fewer F1s than beetles using sheep (9.75 ± 2.25), moose (6 ± 1.58), or bobcat (6.75 ± 1.70) dung.

Figure 4. Box and whisker plot visualizing the mean pronotal width for female, major male, and minor male F1 beetles across dung treatments.

The horizontal line inside each box represents the median. The upper and lower boundaries of the coloured boxes show the inter-quartile range (IQR). The whiskers extending from the boxes show maximum and minimum values for data within 1.5x the IQR; any observations beyond this range are represented as a point.

Figure 5. (A) Box and whisker plot visualizing the proportion of emerged F1 beetles that were female. (B) Box and whisker plot visualizing the mean proportion of major males to total males across dung treatments.

A value of 1 indicates 100% of male F1s produced were major males. The horizontal line inside each box represents the mean (A: bobcat = 0.57, fox = 0.33, moose = 0.56, raccoon = 0.72, sheep = 0.44; B: bobcat = 0.19, fox = 0.83, moose = 0.65, raccoon = 1, sheep = 0.75). The upper and lower boundaries of the coloured boxes show the inter-quartile range (IQR). The whiskers extending from the boxes show maximum and minimum values for data within 1.5x the IQR; any observations beyond this range are represented as a point.