Measuring thermal performance and reproductive success of the dung beetle Onthophagus vacca (Linnaeus, 1767)

We compare the pest status and age structure of bush fly,Musca vetustissima Walker, populations, and the abundance of native dung beetles at Uriarra, ACT, for five fly seasons before (1976–81) and three seasons after (1990–93) the exotic dung beetles Euoniticellus fulvus (Goeze) and Onthophagus taurus (Schreber) became established in the area during the late 1980s. Fly populations in all post-introduction seasons of 1990–93 were much older than in the pre-introduction seasons, indicating reduced levels of local fly breeding and higher proportions of immigrants. During the pre-introduction period, the fly annoyance index exceeded the ‘minimum discomfort’ threshold of 10.0 in parts of all seasons. The mean index was 11.3, and this did not differ significantly between seasons. The total dry weight of dung beetles at the time of the first influx of bush flies each year was consistently below 3 g/dung pad which was apparently too low to depress bush fly breeding below their replacement level of 3%. The mean annoyance index of 3.1 for the 1990–91 season was significantly lower than for the pre-introduction period and the total dry weight of beetles during November-December exceeded 3 g/dung pad on all sampling occasions. In the 1991–92 and 1992–93 seasons fly annoyance indices reverted to pre-introduction levels (seasonal means of 13.7 and 7.8 respectively) and total dry weight of beetles was again below 3 g/dung pad when the bush flies first appeared. Survival of immature bush flies in local dung pads remained below the replacement level of 3% during 1990–91, but exceeded 3% on two occasions during 1991–92. Apart from 1976–77, when mean catches of native dung beetles (O. australis and O. granulatus) were exceptionally high, mean catches of native dung beetles during pre- and post-introduction years were very similar, but the mean dung beetle biomass increased following the establishment of exotic species.

Viviparity is a very rare reproductive mode in nematodes, having been documented in only six species. Five of these species have been isolated among the dung beetles Onthophagus, suggesting that studying the environments associated with dung beetles may help shed light on why viviparity evolved in these particular species. Onthophagus atripennis is often closely associated with the viviparous nematode Tokorhabditis atripennis, as well as some other oviparous nematodes. Hence, the system involving T. atripennis and dung beetles could provide valuable insights into the adaptive significance of viviparity in nematodes. To explore this idea, it is essential to first gain a better understanding of the natural habitats of T. atripennis, which remain poorly understood. Therefore, we investigated the nematode communities associated with O. atripennis and identified potential habitats for T. atripennis in environments used by dung beetles. Nematodes associated with O. atripennis and those inhabiting its rearing cases were isolated from samples. Two Tokorhabditis species were isolated from the rearing cases of O. atripennis, suggesting that they inhabit environments used by O. atripennis. Regarding other oviparous nematodes, some appeared to have relatively strong associations with dung beetles, but more detailed studies are needed to confirm their specific habitats. Although further investigations are necessary, the fact that nematodes, including viviparous species, were isolated from environments used by dung beetles provides important information about the potential competitors or predators of T. atripennis in such environments.

Condition-Dependent Sex Ornaments and Field Tests of Sexual-Selection Theory

Dung beetles perform vital ecosystem functions, but their survival is threatened by parasiticide use in veterinary practices. Currently, it's unclear if parasiticides directly harm dung beetles or cause damage via secondary effects on crucial microbiome components. We investigated the impact of three commercial parasiticides (P1–levamisole and oxfendazole; P2–abamectin, levamisole and oxfendazole; P3–moxidectin) on Onthophagus binodis dung beetle gut and exoskeleton microbiomes. Dung beetles were subjected to parasiticides mixed with fresh dung for 14 days, and we used 16S rRNA genes to detect bacterial diversity changes. The tested parasiticides didn't alter dung beetle gut communities, but slightly affected the exoskeleton microbiota composition. No mortality difference was observed. Onthophagus binodis microbiomes are mainly diet-influenced, and their exoskeleton is more adaptable than their gut. Our study suggests that adjustable dung beetle microbiomes aren't susceptible to parasiticides due to their innate resilience.

BackgroundMaternal effects are environmental influences on the phenotype of one individual that are due to the expression of genes in its mother, and are expected to evolve whenever females are better capable of assessing the environmental conditions that their offspring will experience than the offspring themselves. In the dung beetle Onthophagus taurus, conditional male dimorphism is associated with alternative reproductive tactics: majors fight and guard females whereas minors sneak copulations. Furthermore, variation in dung beetle population density has different fitness consequences for each male morph, and theory predicts that higher population density might select for a higher frequency of minors and/or greater expenditure on weaponry in majors. Because adult dung beetles provide offspring with all the nutritional resources for their development, maternal effects strongly influence male phenotype.ResultsHere we tested whether female O. taurus are capable of perceiving population density, and responding by changing the phenotype of their offspring. We found that mothers who were reared with other conspecifics in their pre-mating period produced major offspring that had longer horns across a wider range of body sizes than the major offspring of females that were reared in isolation in their pre-mating period. Moreover, our results indicate that this maternal effect on male weaponry does not operate through the amount of dung provided by females to their offspring, but is rather transmitted through egg or brood mass composition. Finally, although theory predicts that females experiencing higher density might produce more minor males, we found no support for this, rather the best fitting models were equivocal as to whether fewer or the same proportions of minors were produced.ConclusionsOur study describes a new type of maternal effect in dung beetles, which probably allows females to respond to population density adaptively, preparing at least their major offspring for the sexual competition they will face in the future. This new type of maternal effect in dung beetles represents a novel transgenerational response of alternative reproductive tactics to population density.

Horned beetles are emerging models in the study of coevolution between novel morphologies and behavior. In Onthophagus beetles, large males use horns to fight other males in brood tunnels while small males with higher mobility sneak around the large males to gain access to females. Mating tactics have rarely been described in other dung beetle genera. We studied the horned dung beetle Sulcophanaeus velutinus that exhibits two parallel horns on the prothorax and one on the head. We put two males of different horn lengths, but similar mass, in observation chambers and found that the large male with longer horns won access to the female in physical competition. Speed tests in artificial tunnels show that locomotion is impeded in large males, suggesting an advantage in mobility for males with small horns. This work contributes to the limited existing evidence on the function of alternative morphologies in horned dung beetles taxa.

Host-associated microbes facilitate diverse biotic and abiotic interactions between hosts and their environments. Experimental alterations of host-associated microbial communities frequently decrease host fitness, yet much less is known about if and how host-microbiome interactions are altered by natural perturbations, such as introduction events. Here, we begin to assess this question in Onthophagus dung beetles, a species-rich and geographically widely distributed genus whose members rely on vertically transmitted microbiota to support normal development. Specifically, we investigated to what extent microbiome community membership shifts during host introduction events and the relative significance of ancestral associations and novel environmental conditions in the structuring of microbial communities of introduced host species. Our results demonstrate that both evolutionary history and local environmental forces structure the microbial communities of these animals, but that their relative importance is shaped by the specific circumstances that characterize individual introduction events. Furthermore, we identify microbial taxa such as Dysgonomonas that may constitute members of the core Onthophagus microbiome regardless of host population or species, but also Wolbachia which associates with Onthophagus beetles in a species or even population-specific manner. We discuss the implications of our results for our understanding of the evolutionary ecology of symbiosis in dung beetles and beyond.

Reproduction is costly and individual decisions about when and how much to invest in reproduction will relate to potential benefits in terms of offspring survivorship or mating success. For those organisms that can reproduce more than once, individuals should invest relatively more in reproduction when the potential benefits are high. If females gain directly or indirectly from choosing attractive, highly ornamented males, then it could be predicted that females mated to these males should invest more in reproduction. Here we report the first test of this prediction for a lekking species, peafowl (Pavo cristatus), in which males do not provide resources for offspring, and females prefer to mate with those males that possess the most elaborate trains. We find that peahens randomly mated to males that vary in the degree of ornament produce more eggs for those peacocks with more elaborate trains. We could find no evidence to support the possibility that this difference arises as a result of difference between males in their ability to fertilize eggs.

Genetically modified (GM) Bt plants currently represent a highly adopted alternative for pest control in agricultural crops. However, their safety to non‐target organisms has been an unsolved issue. Non‐target organisms associated to nutrient cycling in natural and agricultural systems, such as dung beetles, use faeces of mammals as a food resource and could be exposed to Bt‐plant material through faeces of livestock fed with Bt‐crops. The aim of this study was to assess whether indirect exposure to transgenic Bt maize MON810 can reduce fitness in dung beetles. Four dung beetles species, Canthon angularis, Canthon rutilans cyanescens, Coprophanaeus saphirinus and Phanaeus splendidulus, were reared under laboratory conditions and fed with pig faeces using two treatments/diets: faeces of pigs fed transgenic maize and of pigs fed conventional maize. The behaviour of insects was tested by experiments on the incorporation of organic matter in the soil and nesting, and experiments of foraging behaviour with olfactometry measures. Organic matter incorporation in the soil per male–female pairs of C. rutilans was similar between GM and conventional treatments, as was their reproductive success, but beetles fed with faeces from transgenic maize produced more brood balls. In another trial regarding the incorporation of organic matter in the soil, C. saphirinus fed with faeces derived from conventional maize showed greater ability to bury food resource in comparison with GM fed ones. In an olfactometer test, the time to reach the food source was longer for individuals of C. rutilans, previously fed with transgenic faeces during 1 month, than individuals fed with conventional faeces. Our results suggest that differences found in dung beetles’ ability represent potential indirect effects of transgenic maize through the food chain and may also affect ecological functions of these organisms in natural habitats, by means of reduced beetle efficiency in removal and burial of faecal masses.

A "Good-Sperm" Model Can Explain the Evolution of Costly Multiple Mating by Females

Territoriality, referring to the defense of a designated area, is one of the common animal behaviors observed in many insect species. In insects, territorial behavior contributes to survival and reproductive success by ensuring resource availability. Beetles (Coleoptera: Hexapoda) comprise one of the largest insect groups, with approximately 0.4 million estimated species. This study critically reviews the published literature collected from journals, books, magazines, and other resources to explore the use of aggressive behavior shown by the dung beetles, blister beetles, burying beetles, bombardier beetles, and bark beetles in territorial defense. In many Coleopterans, aggression has been observed as a behavioral tool of paramount importance in territorial defense (marking and protecting areas), leading ultimately to their continuity and reproductive success. To protect their territory, beetles show aggression using various chemicals, such as cantharidin (blister beetles), pygidial secretions (dung beetles), aggression pheromones like turpentine (bark beetles), and other noxious substances (bombardier beetles), along with the use of elytra (burying beetles). These chemicals play an important part in the success of aggressive behavior in beetles by repelling potential competitors or predators. Beetles in various families also use other behavioral tools, such as dung rolling and storage (as nesting behavior) used by dung beetles. Visual and acoustic signals also contribute significantly to territorial defense. Territorial ownership influences the intensity of aggression among beetles which helps them to deter rivals, sustain their territory, and access crucial resources including food, mate, and shelter without risk.

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.

Fifty-five species of exotic dung beetles have been introduced into Australia and in many areas, several species are now established and often abundant. Controversy exists in the dung beetle literature concerning the use of ivermectin as an anthelmintic treatment for livestock and its subsequent lethal and sub-lethal effects on adult dung beetles. A study was conducted in the field exposing replicate dung pats containing residues of ivermectin excreted 0–15 days post-injection. At the time of the study, the introduced species of dung beetle Onthophagus taurus (Schreber) was present in high numbers (>1000 beetles per pat). After 24 h exposure, dung pats collected from cattle treated 7 and 10 days earlier with ivermectin were dispersed significantly less than untreated dung. A similar pattern was evident in the numbers of dung beetles present in each pat. This study is discussed in the context of anthelmintic usage in cattle and their potential ecotoxic effects against dung beetles.

The expanded use of macrocyclic lactones (ML) to treat endo- and ectoparasites in cattle in tropical regions, can reduce dung beetle populations, and thus interrupt the dung removal process in cattle pasture ecosystems. During the reproductive period (the rainy season) of two functional groups of dung beetles (paracoprid and telocoprid Scarabaeinae), we compared dung removal amount in ranches where ML are and are not used in Yucatan, Mexico, through exclusion traps baited with 500 g of ML-free cow dung. On each ranch, two transects (separated by 500 m) with six traps each, were set up for 24 hours. After this time, all the dung remnants in each trap were obtained and weighed in order to record the dung removal. Results showed that dung removal amounts were similar in ranches with and without ML use. Dung beetles removed 40.1 % of all cow dung weighed. Paracoprids removed 87.46 % and telocoprids 12.54 % of all the dung that was removed. Our results indicated that the ecological function of dung beetles in the pastures studied, does not seem to be affected by the ML use, and that paracoprid species removed most of the dung. For both types of ranch, further studies that take into account the population dynamics and movement of the most important dung beetle species in the region are required, coupled with laboratory studies evaluating the effect of ML on their reproductive success. This could give some light on the effect of ML on the ecological function of this important insect group in the sustainability of cattle production systems.

The influence of slope aspect and soil type on immigration and emergence of some northern temperate dung beetles