... D' D E' E Indifferente Gonade Abb. 161 Differenzierung der Säugergo-naden (Mensch).... more ... D' D E' E Indifferente Gonade Abb. 161 Differenzierung der Säugergo-naden (Mensch). BE Hoden. B'E' Ovar. Verändert nach Langman (1981). Page 4. 2.2 Hoden und Spermien Der reife Hoden der Amniota enthält lange, schleifen-förmig gewundene Tubuli seminiferi (Abb. ...
In most animal species, brood size and body size exhibit some variation within and between popula... more In most animal species, brood size and body size exhibit some variation within and between populations. This is also true for burying beetles (genus Nicrophorus), a group in which the body size of offspring depends critically on the number of offspring competing for food due to the discrete nature of resource used for larval nutrition (vertebrate carcasses). In one species, brood size and body size are correlated with population density, and appear to be phenotypically plastic. We investigated potential proximate causes of between-population variation in brood size and body size in two species, Nicrophorus vespilloides and Nicrophorus defodiens. Our first experiment supported the notion that brood size is phenotypically plastic, because it was affected by environmental variation in adult nutritional condition. We found that the pre-breeding nutritional status of female N. vespilloides affected the number of eggs they laid, the number of surviving larvae in their broods, and the body size of their offspring. We do not know whether this plasticity is adaptive because greater offspring body size confers an advantage in contests over breeding resources, or whether starved females are constrained to produce smaller clutches because they cannot fully compensate for their poor pre-breeding nutritional status by feeding from the carcass. Our second experiment documents that brood size, specifically the infanticidal brood-size adjustment behavior, has undergone genetic differentiation between two populations of N. defodiens. Even under identical breeding conditions with identical numbers of first-instar larvae, females descended from the two populations produced broods of different size with corresponding differences in offspring body size.
Burying beetles tend their young on small vertebrate carcasses, which serve as the sole source of... more Burying beetles tend their young on small vertebrate carcasses, which serve as the sole source of food for the developing larvae. Single females are as proficient at rearing offspring as male‐female pairs, yet males opt to remain with their broods throughout most of the larval development. One potential benefit of a male's extended residency is that it affords him the opportunity of additional copulations with the female, which could ensure his paternity in a replacement brood should the female's first egg clutch fail to hatch. We tested this hypothesis by manipulating males' access to their mates during the production of replacement clutches, using genetic colour markers to determine the paternity of offspring. Females were induced to produce a replacement brood by removing their first clutch of eggs. In one experimental treatment, we removed the female's mate upon the removal of her first egg clutch (‘widowed’ females); in a second treatment, the female was permitt...
1. Burying beetles inter small vertebrate carcasses that ultimately serve as a food source for th... more 1. Burying beetles inter small vertebrate carcasses that ultimately serve as a food source for their developing young. The male remains with the female on the carcass after the brood has been produced, purportedly to aid in the feeding and protection of larvae. However, numerous laboratory experiments have failed to demonstrate a beneficial effect of the male on the growth and survival of offspring.2. A potential difficulty with laboratory studies is that beetles are typically held under relatively benign conditions, protected from the biotic and environmental challenges that they normally encounter. In nature, males may enhance offspring survival by aiding the female in ridding the carcass of mould, and by helping to preserve the carcass through the secretion of antibiotic substances in the beetles’ saliva. To examine more rigorously the potential benefits of male parental care, an experiment was conducted under field conditions in which the reproductive output of male–female pairs...
Our aim was to compare friction and traction forces between two burying beetle species of the gen... more Our aim was to compare friction and traction forces between two burying beetle species of the genus Nicrophorus exhibiting different attachment abilities during climbing. Specifically, the interaction of adhesive hairs and claws during attachment with respect to various surface properties was investigated by using a 2 × 3 experimental design. Traction force was measured for two different surface energies (hydrophilic vs hydrophobic) varying in roughness from smooth to micro-rough to rough. Nanotribometric tests on single legs were also performed. The external morphology of the attachment devices investigated by scanning electron microscopy suggested higher intra-specific (intersexual) than inter-specific differences. Whereas differences between the two species in traction force were high on smooth surfaces, no differences could be detected between males and females within each species. With claws intact, both species showed the highest forces on rough surfaces, although N. nepalensi...
Proceedings of the Royal Society B: Biological Sciences, 2008
Proximate mechanisms underlying reproductive skew are obscure in many animals that breed communal... more Proximate mechanisms underlying reproductive skew are obscure in many animals that breed communally. Here, we address causes of reproductive skew in brood-parasitic associations of burying beetles ( Nicrophorus vespilloides ). Male and female burying beetles feed and defend their larvae on buried carcasses. When several females locate the same small carcass, they engage in violent physical altercations. The subordinate then acts as an intraspecific brood parasite, laying eggs, but not providing care. The dominant female largely monopolizes access to the carcass; she alone provides parental care and her share of the brood is much larger than the subordinate's. On larger carcasses, subordinates have greater access to the carcass than on small ones, and reproductive skew is reduced. Differential fecundity, ovicide and larvicide have been suggested as causes of skew on small carcasses. Here, we report the results of the experiments pertaining to the first two of these potential mech...
Proceedings of the Royal Society B: Biological Sciences, 2008
The ability to recognize individuals is an important aspect of social interactions, but it can al... more The ability to recognize individuals is an important aspect of social interactions, but it can also be useful to avoid repeated matings with the same individual. The Coolidge effect is the progressive decline in a male's propensity to mate with the same female combined with a heightened sexual interest in new females. Although males that recognize previous partners and show a preference for novel females should have a selective advantage as they can distribute sperm evenly among the females they encounter, there are few invertebrate examples of the Coolidge effect. Here we present evidence for this effect in the burying beetle Nicrophorus vespilloides and examine the mechanism underlying the discrimination between familiar and novel mates. Burying beetles feed and reproduce on vertebrate carcasses, where they regularly encounter conspecifics. Males showed greater sexual interest in novel females (virgin or mated) than in females they had inseminated before. The application of id...
The necrophagous burying beetle Nicrophorus vespilloides reproduces on small carcasses that are b... more The necrophagous burying beetle Nicrophorus vespilloides reproduces on small carcasses that are buried underground to serve as food for their offspring. Cadavers that are too large to bury have previously been postulated to be important food sources for newly emerged beetles; however, the attractiveness of distinct successive stages of decomposition were not further specified. Therefore, we investigated the potential preference of newly emerged N. vespilloides females for odour bouquets of piglet cadavers at specific stages of decomposition. Analyses of walking tracks on a Kramer sphere revealed a significantly higher mean walking speed and, consequently, a higher mean total track length when beetles were confronted with odour plumes of the decomposition stages 'post-bloating', 'advanced decay' or 'dry remains' in comparison with the solvent control. Such a change of the walking speed of newly emerged N. vespilloides females indicates a higher motivation to locate such food sources. In contrast to less discriminating individuals this behaviour provides the advantage of not wasting time at unsuitable food sources. Furthermore, in the advanced decay stage, we registered a significantly higher preference of beetles for upwind directions to its specific odour plume when compared with the solvent control. Such a change to upwind walking behaviour increases the likelihood that a large cadaver will be quickly located. Our findings are of general importance for applied forensic entomology: newly emerged N. vespilloides females on large cadavers can and should be regarded as potential indicators of prolonged post mortem intervals as our results clearly show that they prefer emitted odour bouquets of later decomposition stages.
The behaviour of female Necrophorus vespilloides whose clutches had been removed partially or com... more The behaviour of female Necrophorus vespilloides whose clutches had been removed partially or completely was tested in laboratory experiments. If the reproductive activities can proceed without disturbances, the first larvae reach the carcass 56 h after the start of egg-laying. If no larvae come to the carcass, all females resume egg-laying within five days. The second clutch ('replacement clutch') is, on average, smaller than the first one. If the eggs from the replacement clutches are also removed, the females produce new clutches until no more carrion is available. O n e larva coming to the carcass prevents production of replacement clutches with 20 70 of the females. 5 and 10 larvae prevent a higher proportion of females from producing new clutches; the reaction of the female depends on the size of the carcass offered and on the number of larvae present on the carcass. There are two behavioural options for the females with respect to time when egg-laying is resumed. Some females produce a replacement clutch while the larvae are still at the carcass; other females wait until the larvae leave the carcass. In the presence of only a few larvae at the carcass most females show both forms of behaviour under experimental conditions.
Few studies have attempted to distinguish between cues and signals in the context of chemical com... more Few studies have attempted to distinguish between cues and signals in the context of chemical communication. A number of chemical substances have been shown to vary with physiological state, such as stage of oestrus cycle, fertility, dominance status or nutritional condition, but little is known about whether this variation is incidental or adaptive. Here, we provide evidence of a substance whose emission varies with breeding state, but is not merely an incidental by-product of physiological state, but rather, an evolved signal. Breeding females of the facultative biparental burying beetle, Nicrophorus vespilloides , release methyl geranate, a substance that helps males to identify breeding status and to distinguish between their female partners and non-breeding intruders. We demonstrate that females respond flexibly to their social environment and emit high amounts of methyl geranate only in the presence of a male partner, i.e. a receiver. In contrast, cuticular hydrocarbons, which...
Burying beetles (genus Nicrophorus) are known for their elaborate parental care. Two or more cons... more Burying beetles (genus Nicrophorus) are known for their elaborate parental care. Two or more conspecific females may reproduce on the same carcass, especially when the carcass is large. Here we present the results of experiments in which we observed patterns of larval hatching and parental care in unmanipulated cobreeders, manipulated hatching synchrony between cobreeders, and compared patterns of oviposition in cobreeding and single females. Our results show that in these cobreeding associations, one of the females may or may not monopolize the carcass during the period of larval hatching. We present evidence that in either case, infanticide based on temporal cues constitutes an important proximate mechanism underlying the observed reduction in average reproductive success in cobreeding females. Females with higher synchrony (i.e., greater overlap between their oviposition patterns) produce larger broods with lower reproductive skew. Cobreeding females oviposit later and less synchronously than single breeders. Such delayed oviposition may reduce the risk that a female's larvae fall victim to cannibalistic acts committed by her cobreeder or maximize her own opportunity to selectively kill her cobreeder's larvae.
Burying beetles use small vertebrate carcasses as food for their larvae and defend these carcasse... more Burying beetles use small vertebrate carcasses as food for their larvae and defend these carcasses against intra-and interspecific competitors. Breeding associations on carcasses can consist of single females, heterosexual pairs, or various combinations of males and females. When a heterosexual pair collaborate in a breeding attempt, they do not typically exhibit aggressive behavior toward each other, but do attack newly arrived conspecifics that attempt to usurp the carcass. We investigated the cues involved in discrimination between breeding partners and intruders by female burying beetles. We found that resident females tolerate males that have cared for a brood, as well as males that have not cared for a brood but have been on a carcass for a day or two. Males that have had no prior contact with a carcass are attacked. Females appear to use a chemical cue, the ''breeder's badge,'' an apolar substance on the male's cuticle that can be removed by washing with pentane. This cue is reliably correlated with recent male experience with a carcass that is suitable for reproduction. The breeder's badge develops as a result of prolonged contact with such a carcass, and disappears on removal from the carcass; its presence does not require contact with a female or with larvae. Female recognition of their male partners in burying beetles thus does not involve individual recognition, but rather recognition of reproductive condition.
... D' D E' E Indifferente Gonade Abb. 161 Differenzierung der Säugergo-naden (Mensch).... more ... D' D E' E Indifferente Gonade Abb. 161 Differenzierung der Säugergo-naden (Mensch). BE Hoden. B'E' Ovar. Verändert nach Langman (1981). Page 4. 2.2 Hoden und Spermien Der reife Hoden der Amniota enthält lange, schleifen-förmig gewundene Tubuli seminiferi (Abb. ...
In most animal species, brood size and body size exhibit some variation within and between popula... more In most animal species, brood size and body size exhibit some variation within and between populations. This is also true for burying beetles (genus Nicrophorus), a group in which the body size of offspring depends critically on the number of offspring competing for food due to the discrete nature of resource used for larval nutrition (vertebrate carcasses). In one species, brood size and body size are correlated with population density, and appear to be phenotypically plastic. We investigated potential proximate causes of between-population variation in brood size and body size in two species, Nicrophorus vespilloides and Nicrophorus defodiens. Our first experiment supported the notion that brood size is phenotypically plastic, because it was affected by environmental variation in adult nutritional condition. We found that the pre-breeding nutritional status of female N. vespilloides affected the number of eggs they laid, the number of surviving larvae in their broods, and the body size of their offspring. We do not know whether this plasticity is adaptive because greater offspring body size confers an advantage in contests over breeding resources, or whether starved females are constrained to produce smaller clutches because they cannot fully compensate for their poor pre-breeding nutritional status by feeding from the carcass. Our second experiment documents that brood size, specifically the infanticidal brood-size adjustment behavior, has undergone genetic differentiation between two populations of N. defodiens. Even under identical breeding conditions with identical numbers of first-instar larvae, females descended from the two populations produced broods of different size with corresponding differences in offspring body size.
Burying beetles tend their young on small vertebrate carcasses, which serve as the sole source of... more Burying beetles tend their young on small vertebrate carcasses, which serve as the sole source of food for the developing larvae. Single females are as proficient at rearing offspring as male‐female pairs, yet males opt to remain with their broods throughout most of the larval development. One potential benefit of a male's extended residency is that it affords him the opportunity of additional copulations with the female, which could ensure his paternity in a replacement brood should the female's first egg clutch fail to hatch. We tested this hypothesis by manipulating males' access to their mates during the production of replacement clutches, using genetic colour markers to determine the paternity of offspring. Females were induced to produce a replacement brood by removing their first clutch of eggs. In one experimental treatment, we removed the female's mate upon the removal of her first egg clutch (‘widowed’ females); in a second treatment, the female was permitt...
1. Burying beetles inter small vertebrate carcasses that ultimately serve as a food source for th... more 1. Burying beetles inter small vertebrate carcasses that ultimately serve as a food source for their developing young. The male remains with the female on the carcass after the brood has been produced, purportedly to aid in the feeding and protection of larvae. However, numerous laboratory experiments have failed to demonstrate a beneficial effect of the male on the growth and survival of offspring.2. A potential difficulty with laboratory studies is that beetles are typically held under relatively benign conditions, protected from the biotic and environmental challenges that they normally encounter. In nature, males may enhance offspring survival by aiding the female in ridding the carcass of mould, and by helping to preserve the carcass through the secretion of antibiotic substances in the beetles’ saliva. To examine more rigorously the potential benefits of male parental care, an experiment was conducted under field conditions in which the reproductive output of male–female pairs...
Our aim was to compare friction and traction forces between two burying beetle species of the gen... more Our aim was to compare friction and traction forces between two burying beetle species of the genus Nicrophorus exhibiting different attachment abilities during climbing. Specifically, the interaction of adhesive hairs and claws during attachment with respect to various surface properties was investigated by using a 2 × 3 experimental design. Traction force was measured for two different surface energies (hydrophilic vs hydrophobic) varying in roughness from smooth to micro-rough to rough. Nanotribometric tests on single legs were also performed. The external morphology of the attachment devices investigated by scanning electron microscopy suggested higher intra-specific (intersexual) than inter-specific differences. Whereas differences between the two species in traction force were high on smooth surfaces, no differences could be detected between males and females within each species. With claws intact, both species showed the highest forces on rough surfaces, although N. nepalensi...
Proceedings of the Royal Society B: Biological Sciences, 2008
Proximate mechanisms underlying reproductive skew are obscure in many animals that breed communal... more Proximate mechanisms underlying reproductive skew are obscure in many animals that breed communally. Here, we address causes of reproductive skew in brood-parasitic associations of burying beetles ( Nicrophorus vespilloides ). Male and female burying beetles feed and defend their larvae on buried carcasses. When several females locate the same small carcass, they engage in violent physical altercations. The subordinate then acts as an intraspecific brood parasite, laying eggs, but not providing care. The dominant female largely monopolizes access to the carcass; she alone provides parental care and her share of the brood is much larger than the subordinate's. On larger carcasses, subordinates have greater access to the carcass than on small ones, and reproductive skew is reduced. Differential fecundity, ovicide and larvicide have been suggested as causes of skew on small carcasses. Here, we report the results of the experiments pertaining to the first two of these potential mech...
Proceedings of the Royal Society B: Biological Sciences, 2008
The ability to recognize individuals is an important aspect of social interactions, but it can al... more The ability to recognize individuals is an important aspect of social interactions, but it can also be useful to avoid repeated matings with the same individual. The Coolidge effect is the progressive decline in a male's propensity to mate with the same female combined with a heightened sexual interest in new females. Although males that recognize previous partners and show a preference for novel females should have a selective advantage as they can distribute sperm evenly among the females they encounter, there are few invertebrate examples of the Coolidge effect. Here we present evidence for this effect in the burying beetle Nicrophorus vespilloides and examine the mechanism underlying the discrimination between familiar and novel mates. Burying beetles feed and reproduce on vertebrate carcasses, where they regularly encounter conspecifics. Males showed greater sexual interest in novel females (virgin or mated) than in females they had inseminated before. The application of id...
The necrophagous burying beetle Nicrophorus vespilloides reproduces on small carcasses that are b... more The necrophagous burying beetle Nicrophorus vespilloides reproduces on small carcasses that are buried underground to serve as food for their offspring. Cadavers that are too large to bury have previously been postulated to be important food sources for newly emerged beetles; however, the attractiveness of distinct successive stages of decomposition were not further specified. Therefore, we investigated the potential preference of newly emerged N. vespilloides females for odour bouquets of piglet cadavers at specific stages of decomposition. Analyses of walking tracks on a Kramer sphere revealed a significantly higher mean walking speed and, consequently, a higher mean total track length when beetles were confronted with odour plumes of the decomposition stages 'post-bloating', 'advanced decay' or 'dry remains' in comparison with the solvent control. Such a change of the walking speed of newly emerged N. vespilloides females indicates a higher motivation to locate such food sources. In contrast to less discriminating individuals this behaviour provides the advantage of not wasting time at unsuitable food sources. Furthermore, in the advanced decay stage, we registered a significantly higher preference of beetles for upwind directions to its specific odour plume when compared with the solvent control. Such a change to upwind walking behaviour increases the likelihood that a large cadaver will be quickly located. Our findings are of general importance for applied forensic entomology: newly emerged N. vespilloides females on large cadavers can and should be regarded as potential indicators of prolonged post mortem intervals as our results clearly show that they prefer emitted odour bouquets of later decomposition stages.
The behaviour of female Necrophorus vespilloides whose clutches had been removed partially or com... more The behaviour of female Necrophorus vespilloides whose clutches had been removed partially or completely was tested in laboratory experiments. If the reproductive activities can proceed without disturbances, the first larvae reach the carcass 56 h after the start of egg-laying. If no larvae come to the carcass, all females resume egg-laying within five days. The second clutch ('replacement clutch') is, on average, smaller than the first one. If the eggs from the replacement clutches are also removed, the females produce new clutches until no more carrion is available. O n e larva coming to the carcass prevents production of replacement clutches with 20 70 of the females. 5 and 10 larvae prevent a higher proportion of females from producing new clutches; the reaction of the female depends on the size of the carcass offered and on the number of larvae present on the carcass. There are two behavioural options for the females with respect to time when egg-laying is resumed. Some females produce a replacement clutch while the larvae are still at the carcass; other females wait until the larvae leave the carcass. In the presence of only a few larvae at the carcass most females show both forms of behaviour under experimental conditions.
Few studies have attempted to distinguish between cues and signals in the context of chemical com... more Few studies have attempted to distinguish between cues and signals in the context of chemical communication. A number of chemical substances have been shown to vary with physiological state, such as stage of oestrus cycle, fertility, dominance status or nutritional condition, but little is known about whether this variation is incidental or adaptive. Here, we provide evidence of a substance whose emission varies with breeding state, but is not merely an incidental by-product of physiological state, but rather, an evolved signal. Breeding females of the facultative biparental burying beetle, Nicrophorus vespilloides , release methyl geranate, a substance that helps males to identify breeding status and to distinguish between their female partners and non-breeding intruders. We demonstrate that females respond flexibly to their social environment and emit high amounts of methyl geranate only in the presence of a male partner, i.e. a receiver. In contrast, cuticular hydrocarbons, which...
Burying beetles (genus Nicrophorus) are known for their elaborate parental care. Two or more cons... more Burying beetles (genus Nicrophorus) are known for their elaborate parental care. Two or more conspecific females may reproduce on the same carcass, especially when the carcass is large. Here we present the results of experiments in which we observed patterns of larval hatching and parental care in unmanipulated cobreeders, manipulated hatching synchrony between cobreeders, and compared patterns of oviposition in cobreeding and single females. Our results show that in these cobreeding associations, one of the females may or may not monopolize the carcass during the period of larval hatching. We present evidence that in either case, infanticide based on temporal cues constitutes an important proximate mechanism underlying the observed reduction in average reproductive success in cobreeding females. Females with higher synchrony (i.e., greater overlap between their oviposition patterns) produce larger broods with lower reproductive skew. Cobreeding females oviposit later and less synchronously than single breeders. Such delayed oviposition may reduce the risk that a female's larvae fall victim to cannibalistic acts committed by her cobreeder or maximize her own opportunity to selectively kill her cobreeder's larvae.
Burying beetles use small vertebrate carcasses as food for their larvae and defend these carcasse... more Burying beetles use small vertebrate carcasses as food for their larvae and defend these carcasses against intra-and interspecific competitors. Breeding associations on carcasses can consist of single females, heterosexual pairs, or various combinations of males and females. When a heterosexual pair collaborate in a breeding attempt, they do not typically exhibit aggressive behavior toward each other, but do attack newly arrived conspecifics that attempt to usurp the carcass. We investigated the cues involved in discrimination between breeding partners and intruders by female burying beetles. We found that resident females tolerate males that have cared for a brood, as well as males that have not cared for a brood but have been on a carcass for a day or two. Males that have had no prior contact with a carcass are attacked. Females appear to use a chemical cue, the ''breeder's badge,'' an apolar substance on the male's cuticle that can be removed by washing with pentane. This cue is reliably correlated with recent male experience with a carcass that is suitable for reproduction. The breeder's badge develops as a result of prolonged contact with such a carcass, and disappears on removal from the carcass; its presence does not require contact with a female or with larvae. Female recognition of their male partners in burying beetles thus does not involve individual recognition, but rather recognition of reproductive condition.
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Papers by Josef Müller