Brood care in the dung beetle Onthophagus vacca (Coleoptera: Scarabaeidae): the effect of soil moisture on time budget, nest structure, and reproductive success

Under laboratory conditions brood care behaviour, nest structure and weight of dung supply in brood chambers of the dung beetle Onthophagus vcca proved to depend on water content of the soil beneath the dung. The substrate in a bucket beneath the dung pat was dry sand (4% water content) or moist sand (8% water content). Emigrating beetles were trapped and counted at 12 h intervals. In a total of 109 replicates one pair was released on an artificial 1000 g dung pat. From 95 replicates in which brood chambers were built the following results were derived: 1) Breeding females and resident males which helped the female stayed longer in dung pats on dry sand than in those on moist sand. 2) Nest architecture was influenced by substrate moisture: length of main tunnels did not differ between nests in dry and moist sand, but total length of side tunnels was shorter in dry sand. 3) Numbers of brood chambers were equal in both substrate types, weight of the dung supplies was larger in dry sand. 4) Offspring size was not only influenced by dung provision in the brood chambers. Beetles emerging from chambers in dry sand were smaller than those emerging from moist sand even if the amount of dung supply was equal.     

Evidence that sex‐specific signals may support mate finding and limit aggregation in the dung beetle Aphodius fossor

1. In temperate climates, dung is often colonised by several species of endocoprid (dwelling) dung beetles which use pats for feeding, shelter, and reproduction. 2. Endocoprid beetles aggregate even when offered patches (dung pats) of consistent age, size, and origin, suggesting that beetles themselves might influence the attractiveness of patches to members of their own species. Both pheromones, and physical changes to the structure of dung pats caused by colonising beetles have been suggested as mechanisms facilitating intraspecific aggregation, but neither of these hypotheses have been empirically tested. 3. Using a common European dung beetle (Aphodius fossor L.), we conducted a simple choice experiment designed to test whether (i) earlier colonisation by conspecifics could alter dung attractiveness and (ii) whether attraction was influenced by sex‐specific signals. 4. We found that female beetles are repelled by dung colonised by conspecific females and are attracted to dung colonised by conspecific males. Male beetles show no evidence of attraction or repellence for dung colonised by either sex. Neither in females nor males was uncolonised dung found to be significantly more or less attractive than predicted by non‐preference. 5. Our results suggest that for A. fossor male‐produced signals may support mate finding in patchy environments, and that female‐produced signals may serve to discourage subsequent colonisation by additional females.     

Spatial distribution, resource utilisation and intraspecific competition in the dung beetle Aphodius ater

Competitive interactions in northern temperate dung beetles are poorly understood. This investigation therefore comprises a series of field and experimental work on a dung beetle species common in northern Europe, Aphodius ater, with special focus on intraspecific competitive interactions. The between-pat distribution of adult A. ater in relation to the age of sheep dung pats was studied in the field. The distribution of both sexes was contagious in the fresh pats but became more regular with increasing pat age. The successional occurrence of males and females did not differ, but immature females tended to occur in fresh pats while mature females were mainly found in older pats. With increasing age of pats, the egg load of females also increased. Egg-laying behaviour of the beetles was studied in laboratory experiments. The mean number of eggs laid per female per dung pat decreased with increasing beetle density. Thus, density-dependent processes seem to regulate resource utilisation with regard to breeding behaviour, resulting in equal exploitation of the available pats. Survival and weight of recently hatched beetles decreased with increasing initial density of eggs. Hence, in A. ater, competition between larvae for food within pats does occur. Received: 4 February 1998 / Accepted: 20 April 1998     

Nest construction and larval behaviour of Bubas bison (L.) and Bubas bubalus (01.) (Coleoptera, Scarabaeidae)

Abstract.

• 1 Female beetles working alone or in cooperation with a male excavated vertical, tunnel-shaped brood chambers. Each chamber was filled with dung to form a cylindrical brood mass which contained two eggs, one near each pole.
• 2 To examine the possible relationship with other Onitini (which lay either one or several eggs per brood mass) factors that influence the two-egg programme were studied. Brood masses with only a single egg were formed if excavation was resumed prematurely. Conversely, when excavation was suppressed several oviposition programmes fused to produce a multi-egg brood mass.
• 3 The larvae repaired their chambers in the typical Scarabaeine manner by building a self-supporting wall formed from their own excrement. This behaviour also prevented direct contact and fighting between adjacent larvae in the same brood mass, and it allowed the larvae to survive inside artificial brood balls. Similar behaviour was observed in larvae of Onthophagus taunts and Ontho-phagus vacca (which develop in one-egg brood masses). The evolution of nesting habits that involve multi-egg brood masses or free-standing brood balls may depend on the pre-existence of this larval repair behaviour.

     

Intraspecific female brood parasitism in the dung beetle Onthophagus taurus

Abstract.  1. Brood parasitism occurs when individuals parasitise each others' investment into parental care, and has been documented primarily as an interspecific interaction. Intraspecific brood parasitism, in contrast, is often difficult to detect and quantify, and evidence for it is comparatively scarce. The present study documents the occurrence of intraspecific brood parasitism by females of the tunnelling dung beetle Onthophagus taurus , and investigates the contributions of two variables to the propensity of female brood parasitism: female body size and dung desiccation rate.
2. Female O. taurus were found to routinely utilise brood balls made by conspecific females as food provisions for their own offspring.
3. Contrary to expectations, large and small females did not differ in the likelihood of engaging in brood-parasitic behaviour.
4. Dung desiccation rate appeared to influence likelihood of brood parasitism. Females that were given access to rapidly drying dung were significantly more likely to detect and utilise brood balls produced by conspecific females.
5. While interspecific brood parasitism has been documented in dung beetles before, the present study is among the first to present evidence for intraspecific brood parasitism as an alternative reproductive tactic of female dung beetles. Results are discussed in the context of the evolutionary ecology of onthophagine beetles.     

Do dung beetle larvae need microbial symbionts from their parents to feed on dung?

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Brood ball size but not egg size correlates with maternal size in a dung beetle,Onthophagus atripennis

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Male Horn Dimorphism and its Function in the Neotropical Dung Beetle <Emphasis Type="Italic">Sulcophanaeus velutinus</Emphasis>

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.     

Herbivore dung as food for dung beetles: elementary coprology for entomologists

1. How do dung beetles and their larvae manage to subsist on herbivore dung consisting of plant remains that are at least partly indigestible, mixed with various metabolic waste products? To clarify what is known and not known about this basic aspect of dung beetle biology, the present review summarises information on dung composition and discusses the feeding of beetles (food: fresh dung) and larvae (food: older dung) in relation to this information. 2. There is 70–85% water in typical fresh dung, and undigested lignocellulose or ‘fibre’ constitutes about 70% of the organic matter which also contains 1.5–3% N. About 75% of this is ‘metabolic faecal nitrogen’, mostly associated with dead and alive microbial biomass. As all essential amino acids and cholesterol are probably present, additional synthesis by microbial symbionts may not be needed by the beetles. 3. Beetles minimise the intake of lignocellulose by filtering fibre particles out of their food which is probably microbial biomass/debris with much smaller particle size. Excess fluid may be squeezed out of this material by the mandibles before ingestion. 4. All larvae are bulk feeders and unable to filtrate, but little is known about the composition of their food, i.e. older dung in pats or underground brood masses. Larvae in dung pats may depend on easily digestible dung components, probably microbial biomass, whereas the nutritional ecology of larvae in brood masses is still not understood. Unravelling the composition of their food might answer some of the so far unanswered questions.     

Effects of the veterinary antiparasitic drug eprinomectin on dung beetles (Coleoptera: Scarabaeidae), the non-pest fly Neomyia cornicina and pest fly Haematobia irritans (Diptera: Muscidae) in Japan

Effects of the antiparasitic drug eprinomectin were studied in the laboratory and field experiments in Hokkaido, Japan, by pour-on administrations (500 μg/kg) on the pest fly Haematobia irritans (Linnaeus), nontarget coprophagous fly Neomyia cornicina (Fabricius), and the dung beetles Caccobius jessoensis Harold and Liatongus minutus (Motschulsky). Eprinomectin excreted into cattle dung was highest at 3 days post-treatment in both experiments, then it declined rapidly at 7 days and was not detected on or after day 14 post-treatment. In laboratory experiments, pupation and emergence rates of H. irritans and N. cornicina were hampered from 1 to 14 days post-treatment. There were no significant differences in the numbers of brood balls constructed by C. jessoensis in dung from treated and control cattle. Adult emergence rates of C. jessoensis were significantly reduced on days 1 and 3 post-treatment in dung from treated cattle. There were no significant differences in the numbers of brood balls constructed by L. minutus in dung from treated and control cattle, but survival rates of larvae were significantly reduced on days 1 and 3 post-treatment. In field experiments, the numbers of brood balls by L. minutus recovered from beneath dung pats were significantly larger in number in dung from treated cattle, suggesting that adult beetles are attracted to dung pats from treated cattle. Survival rates of larvae in these brood balls of L. minutus were significantly reduced 1 day post-treatment in dung pats from treated cattle, and equivalent levels to the control were restored 7 days post-treatment. The results are discussed in relation to the effects of endectocides on nontarget insects in grazing pastures.     

Adjustment of parental expenditure in sympatric <Emphasis Type="Italic">Onthophagus</Emphasis> beetles (Coleoptera: Scarabaeidae)

Many organisms adjust their parental expenditure to offspring in response to resource quality. However, the mechanisms underlying the adjustment in parental expenditure are not well understood. We examined the adjustments in parental expenditure and subsequent offspring performance in two sympatric, closely related dung beetles, Onthophagus ater and O. fodiens, that were provided either monkey, deer, horse, or cow dung. The egg contained within each dung brood mass provisioned by the parent beetles develops to adulthood underground. Thus, the size of the brood mass roughly represents the amount of parental expenditure. The brood mass size differed between the two species and among the four dung types. Results of offspring performance suggested that O. ater parents optimally adjusted the brood mass size in response to dung quality, whereas O. fodiens parents did not. We hypothesized that brood mass size in O. ater may increase with prolonged egg maturation caused by the lower nutrition level of cow dung. In addition, our complex results may be explained in part by the specific threshold concept of dung quality (i.e., water content and nutritional level).     

Dung beetle community composition affects dung turnover in subtropical US grasslands

1. An important service in many ecosystems is the turnover and degradation of dung deposited by cattle. Dung beetles are the primary group of insects responsible for dung turnover, and factors affecting their abundance and distribution thus impact dung degradation. Lands lost to grazing due to dung buildup and pasture contamination total millions of acres per year in US pastures.
2. We evaluated the structural differences in dung beetle assemblages in natural grasslands versus a managed agroecosystem in subtropical southeastern Florida (USA). We measured the direct effect of dung longevity when dung beetle fauna normally inhabiting dung pats were excluded.
3. Our results indicate dung beetle abundance, functional diversity, and species richness have a substantial impact on the rate of dung turnover in subtropical pastoral lands with ~70% of dung removed from the soil surface after three months. Functional diversity and evenness did not have a significant positive effect on dung removal in managed, versus natural grasslands demonstrating a strong relationship between dung beetle assemblage composition and delivery of a key ecological process, dung degradation.
4. We suggest the importance of trees, which provide a thermal refuge for beetles, should be dispersed within matrixes of open pasture areas and within proximity to adjacent closed‐canopy hammocks to facilitate the exchange of dung beetles between habitats and therefore maintain the provisioning of dung degradation services by dung beetle assemblages.

     

Differences in temporal utilization patterns of dung pats among three scarabaeid dung beetles

1. Differences in the temporal utilization patterns of dung pats were investigated among three dung beetle species, Aphodius haroldianus, Onthophagus lenzii and Liatongus phanaeoides, and density effects of three species on emigration from a dung pat were compared.
2. A. haroldianus preferred fresh dung pats, immigrated to fresh pats and then emigrated from those pats quickly (mean duration of residence 48.4 h), whereas L. phanaeoides immigrated to older dung pats (over 7 days after deposition) as well as fresh ones and remained in the pats for the longest time (165.6 h).O. lenzii showed intermediate behavior in this respect (63.3 h).
3. In A. haroldianus, the presence of conspecifics induced faster emigration than presence of the other two species. L. phanaeoides showed the opposite relationship. In O. lenzii, the response to conspecifics was intermediate to those of the other two species.

     

The evolution of parental behaviour in Scarabaeinae (Coleoptera, Scarabaeidae): an experimental approach

ABSTRACT.

• 1 Dung beetle lifestyles are reviewed. Most Scarabaeinae lay their eggs in dung masses that are packed into underground chambers, but Coprini and Scarabaeini typically lay their eggs in free-standing brood balls and it is in these tribes that parental care of the brood has evolved.
• 2 Brood balls are constructed by aggregating fragments of dung. This technique is derived from the method of gathering dung at the surface. Larvae developing in brood balls are better protected against dehydration and parasite attack. The repair technique of Scarabaeine larvae preadapts them to life in brood balls.
• 3 Parental care by Copris lunaris depends on appropriate responses by the female to the brood, and it has the selective advantage of protecting the brood against parasites. Preadaptations for parental care in‘non-brooding’Coprini are discussed.
• 4 Variations in the basic Copris nesting behaviour are summarized. Similar variations can occur spontaneously in C.lunaris and can also be released by unusual circumstances.
• 5 C.lunaris females could in principle cooperate but certain factors have prevented this social evolution. The significance of the transient cooperation with the male beetle is discussed.

     

Effects of dung beetles on seedling emergence from herbaceous seeds in the dung of sika deer (<Emphasis Type="Italic">Cervus nippon</Emphasis>) in a temperate Japanese grassland ecosystem

The effects of dung form and condition and of dung beetles on the emergence of seedlings from herbaceous seeds in sika deer dung were examined in a temperate grassland ecosystem dominated by Zoysia japonica and Hydrocotyle maritima. I conducted field experiments to compare seedling emergence between dung exposed to dung beetles and intact dung using both dung pellets and pats during a typical rainy month (June) and the hottest, drier month (August), when large numbers of seeds of the dominant species were present in the dung. The exposed dung was immediately attacked and broken up by dung beetles, whereas dung protected from the beetles remained intact. In June, at least 12 herbaceous species, including Z. japonica, H. maritima, Mazus pumilus, and Plantago asiatica, emerged from the dung, versus at least six species in August. Decomposition rates of the pellets in June and decomposition scores of the pats in June and August were positively correlated with the number of emerging seedlings, suggesting that the acceleration of decomposition by dung beetles can positively affect seed germination. In this system of interactions among sika deer, herbaceous plants, and dung beetles, sika deer dung prevented seeds from germinating, and beetles had an indirect positive effect on seedling emergence by accelerating decomposition of the dung, although the extent of the effect may depend on the dung type, plant species, and environmental factors.     

Dung burial strategies in some South African coprine and onitine dung beetles (Scarabaeidae: Scarabaeinae)

ABSTRACT.

• 1 The dung colonization and dung burial behaviour of twelve crepuscular/nocturnal tunnelling (paracoprid) species of beetles were examined in order to identify mechanisms which might facilitate resource (dung) partitioning. The species were selected from a diverse assemblage of dung beetles, the members of which coexist in the sandy-soil regions of Natal, South Africa.
• 2 The pattern of dung colonization in relation to dung age was examined in the field using baited pitfall traps. Some species, e.g. Onitis deceptor Peringuey, Catharsius tricornutus De Geer and Copris elphenor Klug, showed a marked preference for fresh dung (1–2 days old) whereas other species, e.g. O. viridulus Boheman and Copris fallaciosus Gillet, preferred older dung (3–7 days old).
• 3 Two distinct patterns of dung burial were recognized. In the Coprini, dung burial was complete within 24–48h of pad colonization, and the level of dung burial was similar in the laboratory and in the field. In the Onitini, dung burial occurred progressively over a 12-day period, although the timing of initiation of dung burial varied between species: in O. deceptor nearly all individuals had begun burial within 2 days of pad colonization, whereas only 20% of O. viridulus had commenced dung burial by that time. However, nearly all O. viridulus had buried substantial quantities of dung by day 12.
• 4 The mass of dung buried per pair by the larger coprine beetles (100–300 g) and onitine beetles (400–1000 g) suggests that there is potential for inter- and intraspecific competition, even in pads colonized by relatively few beetles. The colonization and use of dung of different ages are discussed as means of resource partitioning in relation to the relative abilities of species to compete for dung.

     

An analysis of the nesting behaviour of Geotrupes spiniger Marsham (Coleoptera, Scarabaeidae)

Abstract. 1. Female G.spiniger adults working alone made nests each consisting of a vertical shaft leading to a series of horizontal brood chambers filled with dung brood masses. Oviposition near the tip of the brood mass occurred while the egg cell was being completed over the expanded ovipositor. The shaft above each brood mass was filled with soil excavated from the next brood chamber. A similar response also filled artificial diverticula. An avoidance reaction towards buried dung prevented damage to pre-existing brood masses. 2. Virgin females did not make nests and did not avoid buried dung, but after mating (at about 4 weeks after eclosion) both types of behaviour were released within a few hours. 3. The presence of dung was required to initiate but not to maintain nesting behaviour. If dung was removed after oviposition the chamber was filled with soil produced by renewed excavation. Cellulose pulp could substitute for dung in brood mass formation. 4. Beetles interchanged between burrows at different stages before oviposition readily repeated all pre-oviposition behaviour. They appeared to respond to the length of the shaft and of the brood chamber since they extended short shafts and short brood chambers considerably more than those of normal length. After oviposition the beetles continued to make brood masses even under abnormal conditions. 5. Tilting the cage through 90° caused beetles before oviposition to re-orientate their burrowing direction, but tilting just after oviposition caused them to make vertical brood masses. Placing the shaft in a horizontal position towards the end of brood mass formation postponed the termination of this phase. 6. Beetles repeatedly excavated shafts and chambers when transferred to new cages. Conversely they repeatedly made brood masses when maintained in preformed plaster-of-Paris burrows. 7. This nesting behaviour can be described as a reaction chain in which each action generates its own terminating stimulus and initiates the subsequent response. The behaviour before oviposition could be omitted or repeated as required by the environment, but after oviposition there was little response to external interference. These characteristics have direct relevance to the survival of the larvae.     

Host-searching and mating in an outbreeding parasitoid wasp

Abstract.

• 1 Female parasitoid wasps (Hymenoptera) must search for hosts to reproduce, but only require mates if their broods are to contain female progeny. In outbreeding species, females locate mates after dispersal from the emergence site. Unmated females may therefore face a trade-off between searching for hosts and searching for mates, if hosts and mates are spatially separated.
• 2 In the outbreeding parasitoid Bracon hebetor Say (Hymenoptera: Braconidae), males and females are spatially segregated in the field. Females are found primarily below the surface of stored corn where they search for hosts, whereas males are found on or above the surface.
• 3 Wasps placed in laboratory observation chambers designed to mimic B.hebetor's stored corn habitat distributed themselves in a manner consistent with field observations. Males remained on the surface of the grain, whereas females moved below the surface to attack hosts.
• 4 In the laboratory, female distribution was influenced by their mating status, the presence of males or hosts, and female age. Virgin females were more reluctant to move into the corn than were mated females, younger females foraged deeper than older females, and all females moved deeper into the com when males were present.
• 5 10% of all females did not mate even when males were present in the chambers, a percentage consistent with previous observations from the field. If B.hebetor faces a trade-off between host-searching and mate-searching, the trade-off seems to be part of 'split sex ratio strategies', with some females remaining constrained to producing only male offspring.

     

Maternal and paternal effects on offspring phenotype in the dung beetle Onthophagus taurus

Abstract.— Parents often have important influences on the development of traits in their offspring. One mechanism by which parents are able to influence offspring phenotype is through the level of care they provide. In onthophagine dung beetles, parents typically provision their offspring by packing dung fragments into a brood mass. Onthophagus taurus males can be separated into two discrete morphs: Large, "major" males have head horns, whereas "minor" males are hornless. Here we show that a switch in parental provisioning strategies adopted by males coincides with the switch in male morphology. Male provisioning results in the production of heavier brood masses than females will produce alone. However, unlike females in which the level of provisioning increases with body size in a continuous manner, the level of provisioning provided by males represents an "all-or-none" tactic with all major males providing a fixed level of provisioning irrespective of their body size. Offspring size is determined largely by the quantity of dung provided to the developing larvae so that paternal and maternal provisioning affects the body size and horn size of offspring produced. The levels of provisioning by individual parents are significantly repeatable, suggesting paternal and maternal effects as candidate indirect genetic effects in the evolution of horn size in the genus Onthophagus .     

Reproductive properties of two sympatric dung beetles,Aphodius haroldianus andA. Elegans (Coleoptera: Scarabaeidae)

1. Reproductive properties of two sympatric dung beetles, Aphodius haroldianus and A. elegans, were studied at a pasture in the central Japan.
2. Overwintered adults of A. haroldianus came flying to dung pats from May to early August and bred from June to July. A. elegans overwintered as larvae, new adults came to dung pats from mid May to mid June. After aestivation, they reproduced from October to November.
3. A. haroldianus was a species with low fecundity and large food reserve for larvae. Female of this species had short duration of residence and laid fewer number of eggs in one dung pat. On the other hand, A. elegans was a species with high fecundity and small food reserve for larvae. Female of this species had long duration of residence and laid larger number of eggs in one dung pat.
4. The daily egg production in A. haroldianus reached a peak (0.40 eggs/female/day) at middle of oviposition period, but, that in A. elegans reached a peak (6.49 eggs/female/ day) at the beginning of oviposition period. The mortality of A. haroldianus female occurred after the daily egg production reached a peak and then rapidly increased, whereas that of A. elegans began soon after the beginning of oviposition and then gradually increased.