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

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Parental behaviour in Copris lunaris (Coleoptera, Scarabaeidae): care and defence of brood balls and nest

Abstract. 1. Nesting female beetles righted brood balls (so as to replace the egg or larva in the uppermost position) and repaired damaged balls. This behaviour required the presence of an egg or larva in the ball, or of a short-lasting material found just after oviposition. The shape of the ball was also a righting stimulus since artificial ellipsoids were stood on end.
2. Balls containing dichloromethane extracts of C.lunaris brood were righted and repaired. Eggs and larvae of several other Scarabaeidae did not release these responses but were destroyed.
3. Righting behaviour was released when brood was absent from the top of the ball. The beetle then crawled vertically downwards and, if it encountered the displaced apex, a novel rolling action followed which automatically turned the ball towards the correct position.
4. An opening made in the nest was repaired with soil excavated from the chamber floor. Clunaris adults and Aphodius fossor larvae were attacked if they were encountered in the nest.     

The dispersal behaviour of the phoretic mite Poecilochirus carabi (Mesostigmata,Parasitidae): adaptation to the breeding biology of its carrier Necrophorus vespilloides (Coleoptera,Silphidae)

Summary When the phoretic mite Poecilochirus carabi reproduces in the brood chamber of its carrier Necrophorus vespilloides, a beetle with biparental brood care, the first deuteronymphs of the new mite generation aggregate on the male beetle. They do not use sex-specific traits to discriminate between male and female beetles in the brood chamber, but traits that are related to the beetles' behaviour and may be displayed by both parent beetles. When the male beetle departs, it carries virtually all deuteronymphs then present in the brood chamber. Deuteronymphs that develop later congregate on the female, which leaves the crypt some days after the male. Only those deuteronymphs that miss the female's departure disperse on the beetle larvae, meaning they have to wait in their pupal chambers until the beetles have completed their development. On average, 86% of the deuteronymphs leave the brood chamber on the parent beetles, thereby gaining the advantage of an early departure. As soon as their carrier arrives at one of the beetles' meeting places, the deuteronymphs can transfer between the beetles present. Choice experiments revealed that the deuteronymphs tend to even out density differences between congregating carriers, and prefer sexually mature to immature beetles. Therefore, transferring between beetles results in a dispersion of deuteronymphs on the sexually mature beetles of the population.     

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.     

Review. When to leave the brood chamber? Routes of dispersal in mites associated with burying beetles

Most nests of brood-caring insects are colonized by a rich community of mite species. Since these nests are ephemeral and scattered in space, phoresy is the principal mode of dispersal in mites specializing on insect nests. Often the mites will arrive on the nest-founding insect, reproduce in the nest and their offspring will disperse on the insect's offspring. A literature review shows that mites reproducing in the underground brood chambers of burying beetles use alternative routes for dispersal. For example, the phoretic instars of Poecilochirus spp. (Mesostigmata: Parasitidae) disperse early by attaching to the parent beetles. Outside the brood chamber, the mites switch host at carcasses and pheromone-emitting male beetles, where juvenile and mature burying beetles of several species congregate. Because they preferably switch to beetles that are reproductively active and use all species of burying beetles within their ranges, they have a good chance of arriving in a new brood chamber. Other mite associates of burying beetles (Alliphis necrophilus and Uropodina) disperse from the brood chamber on the beetle offspring. We suggest that these mites forgo the possible time gain of dispersing early on the parent beetles because their mode of attachment precludes host switching. Their phoretic instars, once attached, have to stay on their host and so only dispersing on the beetle offspring guarantees that they are present on reproducing burying beetles of the next season. The mites associated with burying beetles providean example of multiple solutions to one life history problem – how to find a new brood chamber for reproduction. Mites that have mobile phoretic instars disperse on the parent beetles and try to arrive in the next brood chamber by host switching. They are independent of the generation cycle of a single host and several generations of mites per host generation are possible. Mites that are constrained by their mode of attachment disperse on the beetle offspring and wait until their host becomes mature and reproduces. By doing this they synchronize their generation time with the generation time of their host species. Exp Appl Acarol 22: 621–631 © 1998 Kluwer Academic Publishers     

Sexual shape dimorphism accelerated by male–male competition,but not prevented by sex-indiscriminate parental care in dung beetles (Scarabaeidae)

Dimorphic sexual differences in shape and body size are called sexual dimorphism and sexual size dimorphism, respectively. The degrees of both dimorphisms are considered to increase with sexual selection, represented by male–male competition. However, the degrees of the two dimorphisms often differ within a species. In some dung beetles, typical sexual shape dimorphisms are seen in male horns and other exaggerated traits, although sexual size dimorphism looks rare. We hypothesized that the evolution of this sexual shape dimorphism without sexual size dimorphism is caused by male–male competition and their crucial and sex-indiscriminate provisioning behaviors, in which parents provide the equivalent size of brood ball with each of both sons and daughters indiscriminately. As a result of individual-based model simulations, we show that parents evolve to provide each of sons and daughters with the optimal amount of resource for a son when parents do not distinguish the sex of offspring and males compete for mates. This result explains why crucial and sex-indiscriminate parental provisioning does not prevent the evolution of sexual shape dimorphism. The model result was supported by empirical data of Scarabaeidae beetles. In some dung beetles, sexual size dimorphism is absent, compared with significant sexual size dimorphism in other horned beetles, although both groups exhibit similar degrees of sexual shape dimorphism in male horns and other exaggerated traits.     

Does resource availability affect offspring begging and parental provisioning in a partially begging species?

In species where parents repeatedly provide their offspring with food, the offspring often communicate their need to the parents. Burying beetles, which breed on a wide size range of carcasses of small vertebrates, are interesting model systems to test theories on begging, because the larvae show partial begging, that is, they obtain food through both signalling to their parents (begging) and feeding directly from the carcass. We manipulated resource availability inNicrophorus vespilloides by providing parents with mouse carcasses spanning a wide size range, and allowing them to rear the larvae that hatched, so that both the amount of resources and the number of siblings varied. Time spent begging by each larva was strongly influenced by the time parents spent near the larvae. Brood size had a nonlinear effect on larval begging, with begging increasing with brood size for relatively smaller broods and decreasing again for larger broods. Carcass size and number of parents present had no effect on begging. Time spent provisioning the larvae by the parents was strongly associated with the time spent begging by each larva. Parents spent more time provisioning under biparental care than under uniparental care, while brood size and carcass size had no significant effect. These findings suggest that the larvae adjust their begging to the behaviour of their parents and the number of siblings, but not to the amount of resources. Furthermore, parents adjust the time spent provisioning to the average amount of begging by each larva in the brood, and not to the availability of resources.     

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.     

Habitat selection and offspring survival rate in three paracoprid dung beetles: the influence of soil type and soil moisture

Paracoprid dung beetles build brood chambers in the soil beneath a dung pat and provide them with dung Onthophagus species lay one egg into each chamber This paper deals with the influence of soil type and soil moisture on micro-habitat selection and survival of offspring m three middle-European Onthophagus-species ( O coenobita, O fracticonis and O vacca) Discrimination between sandy soils with three different loam contents (0%, 20%, 40%) and four different water contents (4%, 8%, 12%, 16%) was tested in the laboratory During the first 24 h of each replicate beetles which colonized one of the patches did not distinguish between different soil conditions Emigration rates, measured as time when 50% of all individuals had left the patch, and numbers of brood chambers proved to be species specific and depended on soil moisture and soil type Survival rates of the larvae in the brood chambers were influenced nearly exclusively by soil moisture The results are discussed in relation to the ecology of the three species and in context with optimal foraging theories     

Subsocial behaviour in Oniticellus cinctus (Coleoptera, Scarabaeidae): effect of the brood on parental care and oviposition

ABSTRACT. In Oniticellus cinctus (F.) the nest chambers each contain about twenty brood balls. Females enlarge the brood balls during the egg and larval stages and remain in the chamber for the whole period of brood development (1 month); they then make a new nest after 1 week. The presence of the brood releases parental care and ensures that the mother remains in the nest: she repairs defects in the brood balls and the nest, and expels other O. cinctus females. A new ball is formed around a naked O. cinctus larva, but larvae of other species are killed. In addition, the brood inhibits oviposition: removal (or addition) of brood balls stimulates (or inhibits) egg laying. In inhibited ovarioles, existing follicles are resorbed and production of new ones ceases. Control of clutch size by the brood is an adaptation to the nest structure and life history of O. cinctus. It may have an important role in the reproductive strategy of other insects with parental care.     

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.

     

Oviposition and development of the immature stages of Tomicus minor (Coleoptera, Scolytidae)

1 This paper describes the construction process of the brood gallery of Tomicus minor and its total length as well as the length of each arm, the fertile part where the female lays her eggs and also, the infertile part. >2 The presence of the parents during the process and their position in the brood gallery (arms or mating chamber) is studied and how it influences the number of eggs laid. Both the first brood galleries and those burrowed by the repenetrating females were observed. 3 The development and duration of the immature stages of the insect in the 3-year study period, from laying to the emergence of the young beetles from the F₁ generation, were also studied.     

Nest construction and larval behaviour of Onitis belial and Onitis ion (Coleoptera, Scarabaeidae)

Abstract. 1. Female beetles working alone or in cooperation with a male buried dung to make brood masses. O.belial brood masses were packed close together in clusters; each mass was constructed as a horizontal thick-walled tube of dung which was filled with a dung sausage containing two to six eggs. O.ion made vertical sausage-shaped brood masses with one to four eggs.
2. The larvae of both species were able to survive in artificial brood balls as well as in multi-egg brood masses because of their ability to repair larval chambers with their own excrement.
3. The multi-egg brood mass of Onitis has probably evolved from a simple one-egg brood mass. It does not resemble the underground dung mass from which brood balls are made by certain Coprini.     

Survival of parent and brood adult bark beetles, Ips typographus, in relation to size, lipid content and re-emergence or emergence day

ABSTRACT. This study investigated a possible trade-off between bark beetle reproductive effort and future survival. Parent adult Ips typographus (L.) (Coleoptera: Scolytidae) were collected when they re-emerged from a laboratory culture after completing their first brood and held at constant temperatures of 4 or 25^oC. As a comparison, emerging brood adults were collected and held at 25^oC. The longevity of the beetles was related to when they re-emerged or emerged (measured in days since parent introduction) and to their size (pronotal width), fresh weight and lipid content at collection, by multiple regression analysis. The expression (fresh weight x pronotal width ^-2.6), used as an estimate of lipid content of the living beetles, was significantly correlated (r=0.67, P<0.001) with the actual (extracted) lipid content. At 25^oC, fat content was the variable most strongly correlated with survival time in all beetle groups except parent females. In both parent and brood females, re-emergence or emergence day, respectively, contributed significantly to the explanation of survival time, whereas pronotal width and fresh weight never contributed significantly to the regression equation. At 4^oC, fat content was not estimated but, re-emergence day was negatively correlated with survival time. In conclusion, beetles with high fat content and re-emerging or emerging early have longer expected survival than beetles leaving the log later or containing less fat. This means that females laying a large first brood might suffer a somewhat higher mortality than females laying a smaller brood.     

Brood Ball-Mediated Transmission of Microbiome Members in the Dung Beetle,Onthophagus taurus (Coleoptera: Scarabaeidae)

Insects feeding on plant sap, blood, and other nutritionally incomplete diets are typically associated with mutualistic bacteria that supplement missing nutrients. Herbivorous mammal dung contains more than 86% cellulose and lacks amino acids essential for insect development and reproduction. Yet one of the most ecologically necessary and evolutionarily successful groups of beetles, the dung beetles (Scarabaeinae) feeds primarily, or exclusively, on dung. These associations suggest that dung beetles may benefit from mutualistic bacteria that provide nutrients missing from dung. The nesting behaviors of the female parent and the feeding behaviors of the larvae suggest that a microbiome could be vertically transmitted from the parental female to her offspring through the brood ball. Using sterile rearing and a combination of molecular and culture-based techniques, we examine transmission of the microbiome in the bull-headed dung beetle, Onthophagus taurus. Beetles were reared on autoclaved dung and the microbiome was characterized across development. A ~1425 bp region of the 16S rRNA identified Pseudomonadaceae, Enterobacteriaceae, and Comamonadaceae as the most common bacterial families across all life stages and populations, including cultured isolates from the 3^rd instar digestive system. Finer level phylotyping analyses based on lepA and gyrB amplicons of cultured isolates placed the isolates closest to Enterobacter cloacae, Providencia stuartii, Pusillimonas sp., Pedobacter heparinus, and Lysinibacillus sphaericus. Scanning electron micrographs of brood balls constructed from sterile dung reveals secretions and microbes only in the chamber the female prepares for the egg. The use of autoclaved dung for rearing, the presence of microbes in the brood ball and offspring, and identical 16S rRNA sequences in both parent and offspring suggests that the O. taurus female parent transmits specific microbiome members to her offspring through the brood chamber. The transmission of the dung beetle microbiome highlights the maintenance and likely importance of this newly-characterized bacterial community.     

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.     

Reemergence and second brood in the bark beetle Ips typographus

The knowledge about reemergence of parent spruce bark beetles Ips typographus . their dispersal, and production of a second brood is reviewed. A majority of the beetles reemerge after their first brood. The process is mainly determined by temperature but high breeding density decreases the average time spent in the tree. The difference between males and females in reemergence seems to be small. In the field, a positive relationship between residence time and fat content at reemergence seems to exist, whereas the opposite tendency is found under laboratory conditions. In the laboratory, the survival of beetles reemerging late is on the average lower than that for early reemerging beetles. The time of reemergence and size of the first brood do not, however, seem to influence the production of a second brood. A large proportion of the reemerging beetles are able to establish a new brood in the laboratory, but calculations based on the number of attacked trees and estimated reemergence in forests in South Norway suggest that only about one third of the beetles actually produce a second brood. In northern Europe, successful colonization of new trees by the reemerging beetles seems to require a period of several warm days during the main reemergence period.     

Ultrastructural Observations on the Larva of Loxosoma pectinaricola Franzén (Entoprocta,Loxosomatidae)

The larva of Loxosoma pectinaricola Franzén has been studied using scanning and transmission electron microscopy. The embryo develops surrounded by an egg envelope attached to the brood chamber. The newly released larva measures about 100 μm in length and is characterized by a prominent apical organ, stalked vesicles, paired lateral sense organs and a prototroch. The apical organ consists of at least four cell types: (1, 2) two types of ciliated cells, (3) vacuolated cells and (4) myoepithelial cells. The apical organ and frontal ganglion are tightly juxtaposed in the upper tier of the episphere. The stalked vesicles each consisting of two cells are unique evaginations of the epidermis. There are about twenty stalked vesicles with a maximum diameter of about 20.0 μm. The ciliated, knob-shaped, paired lateral sense organs are situated fronto-laterally on the episphere. The prototroch is comprised of a row of contiguous prototroch cells each containing about eighteen long cilia. The apical organ, frontal ganglion and paired lateral sense organs are suggested to be sensory structures that play an important role in active locomotion, settlement site selection and metamorphosis.     

Competition between the oligolectic beePtilothrix plumata (Anthophoridae) and the flower closing beetlePristimerus calcaratus (Curculionidae) for floral resources ofPavonia cancellata (Malvaceae)

The flowers ofPavonia cancellata, a creeping ruderal half-shrub of northeastern Brazil, open synchronously at 6:00 h with all anthers already dehisced. The oligolectic beePtilothrix plumata was the most effective pollinator. During 90—180 min, female bees make up to 40 brief pollen collection trips to provision their brood cells. The pollen of about 40 flowers ofP. cancellata is needed to feed one bee larva. The most frequent flower visitors, however, are the specialized curculionid beetlesPristimerus calcaratus, which do not crosspollinate the flowers. They perforate the epidermis with their mouthparts, provoking dehydration, and then actively close the loose petals with their legs. Two hours after opening, half of the flowers had already been closed by the beetles. We interpret the fast, uninterrupted pollen foraging ofPtilothrix plumata bees as a strategy adapted to synchronous pollen presentation ofPavonia and to competition withPristimerus calcaratus: the female bees have to provision their brood cells before the beetles succeed in closing the flowers.     

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

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