Dung Beetle Assemblages Attracted to Cow and Horse Dung: The Importance of Mouthpart Traits, Body Size, and Nesting Behavior in the Community Assembly Process.

Victoria C. Giménez Gómez,José R. Verdú,Fernando Casanoves,Mario Zunino,Mattia Tonelli

doi:10.3390/life11090873

Abstract

Dung beetles use excrement for feeding and reproductive purposes. Although they use a range of dung types, there have been several reports of dung beetles showing a preference for certain feces. However, exactly what determines dung preference in dung beetles remains controversial. In the present study, we investigated differences in dung beetle communities attracted to horse or cow dung from a functional diversity standpoint. Specifically, by examining 18 functional traits, we sought to understand if the dung beetle assembly process is mediated by particular traits in different dung types. Species specific dung preferences were recorded for eight species, two of which prefer horse dung and six of which prefer cow dung. Significant differences were found between the functional traits of the mouthparts of the dung beetles attracted to horse dung and those that were attracted to cow dung. Specifically, zygum development and the percentage of the molar area and the conjunctive area differed between horse and cow dung colonizing beetles. We propose that the quantitative differences in the mouthpart traits of the species attracted to horse and cow dung respectively could be related to the differential capacity of the beetles to filtrate and concentrate small particles from the dung. Hence, the dung preference of dung beetles could be related to their ability to exploit a specific dung type, which varies according to their mouthpart traits. Moreover, we found that larger and nester beetles preferred cow dung, whereas smaller and non-nester beetles preferred horse dung. This finding could be related to the tradeoff between fitness and parental investments, and to the suitability of the trophic resource according to the season and species phenology.

Highlights

We sought to answer two main questions: (i) Are there species which have a preference for cow or horse dung? (ii) Are there some traits linked to a specific dung type? To answer these questions, we focused on multiple (N = 18) species traits related to body morphology, mouthpart morphology, and behavior, seeking to ascertain if the assembly process in different dung types is mediated by these particular traits
90,480 individuals belonging to 50 species were collected (three exclusive species: Amidorus thermicola (Sturm, 1800), Euorodalus paracoenosus (Balthasar & Hrubant, 1960), Limarus zenkeri (Germar, 1813)), whereas in the cow dung, 66,456 individuals belonging to 55 species were collected (eight exclusive species: Melinopterus stolzi (Reitter, 1906), Nialus varians (Duftschmid, 1805), Calamosternus mayeri (Pilleri, 1953), Bodiloides ictericus (Laicharting, 1781), Biralus mahunkaorum (Ádám, 1983), Acrossus rufipes (Linnaeus, 1758), Agrilinus constans (Duftschmid, 1805), Planolinus fasciatus (Olivier, 1789)) (Table 2)
We found quantitative differences in some mouthpart traits between dung beetles attracted to horse dung and those attracted to cow dung

Summary

Introduction

Dung beetles (Scarabaeidae: Scarabaeinae, Aphodiinae; Geotrupidae) are distributed in all biogeographic regions and include more than 8000 species [1]. They are mainly coprophagous, a feeding habit which arose from saprophagy in the Cretaceous, leading to a species radiation during mammal diversification in the Cenozoic [2,3]. In other places (e.g., tropical and subtropical habitats), dung beetles became more generalist species associated with the greater diversity and abundance of other types of resource, such as omnivorous dung, vertebrate and invertebrate carrion, fungi, and fruits [5,6]. In places where dung is the main source of food, dung beetles use this resource throughout their ontogenetic development, from larval to adult stages [7]. The trophic predilection of dung beetles for certain dung types has often been reported [5,16,17,18,19,20,21,22,23,24], this preference seems to vary geographically, suggesting that it may not depend on a fixed species trait [25]

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