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Regulation of brood size by male parents and cues employed to assess resource size by burying beetles

Authors:
  • University of Connecticut-Waterbury

Abstract

Burying beetles prepare small vertebrate carcasses as a resource for their young and adjust the size of their brood to match the size of the resource. We tested whether single males of N. orbicollis can regulate brood size in the absence of clutch or brood size adjustments by females, and whether parents use mass- or volume-related cues to estimate resource potential. When provided with 25 first instar larvae, single males reared significantly more young on larger carcasses than on smaller carcasses (18.5 versus 11.4). Mortality of young occurred almost exclusively during the early stages of parental care, and therefore was unrelated to depletion of the resource. The mean mass of individual larvae at dispersal did not vary with resource size, and was consistent with 15 previous experiments utilizing N. orbicollis, suggesting that regulation of brood size had occurred. Examination of previous experiments also suggested that the number and mean mass of young was not affected by whether one or two parents provide care. Mass and volume of carcasses were manipulated to examine possible cues that burying beetles might employ to assess resource size. The addition of lead weights into the body cavity of a mouse corpse (mean increase in mass of 64%) did not alter the number of young produced by male-female pairs. When volume of a corpse was experimentally increased using hollow plastic tubes (mean increase of 21%), however, pairs reared 17% more offspring than on control carcasses. Mean mass of individual offspring on volume-enhanced carcasses was significantly less (– 18%) than on control carcasses. This suggests that burying beetles use a volume- but not a mass-related cue to assess resource potential. We also present evidence that increased handling time of a carcass during nest preparation may lead to deterioration in resource quality.
... In common with many other taxa, N. vespilloides parents kill surplus offspring through partial filial cannibalism (Klug & Bonsall, 2007;Manica, 2002). Partial filial cannibalism potentially increases the fitness of remaining offspring when resources are limiting (Bartlett, 1987;Schrader et al., 2015a;Trumbo & Fernandez, 1995) because there is a marked trade-off between brood size and larval size at dispersal in burying beetles. Eliminating some offspring thus promotes larval mass at dispersal, which is a strong predictor of future fitness (Bladon et al., 2020;Lock et al., 2004;Pascoal et al., 2018) while also providing an energetic benefit to parents. ...
... Females crudely adjust the number of eggs they lay to match the size of the dead body and generally lay more eggs when breeding upon a larger corpse Trumbo & Fernandez, 1995). After hatching, brood size is more carefully matched to the resources upon the carcass through partial filial cannibalism, when parents consume excess 1 st instar larvae (Bartlett, 1987;Müller, Eggert, & Furlkröger, 1990;Trumbo & Fernandez, 1995). ...
... Females crudely adjust the number of eggs they lay to match the size of the dead body and generally lay more eggs when breeding upon a larger corpse Trumbo & Fernandez, 1995). After hatching, brood size is more carefully matched to the resources upon the carcass through partial filial cannibalism, when parents consume excess 1 st instar larvae (Bartlett, 1987;Müller, Eggert, & Furlkröger, 1990;Trumbo & Fernandez, 1995). Parents have been found to consume up to half of the larvae to optimize the brood size to the carcass (Bartlett, 1987), and brood size has an important bearing on the fitness attained by individual larvae. ...
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The overproduction of offspring is commonly associated with high hatching failure and a mechanism for dispensing with surplus young. We used experimental evolution of burying beetle populations Nicrophorus vespilloides to determine causality in these correlations. We asked does eliminating the mechanism for killing “spare” offspring cause the evolution of a more restrained clutch size and consequently select for reduced hatching failure? N. vespilloides typically overproduces eggs but kills 1st instar larvae through partial filial cannibalism during brood care. We established replicate evolving populations that either could practice filial cannibalism (Full Care) or could not, by removing parents before their young hatched (No Care). After 20+ generations of experimental evolution, we measured clutch size and hatching success. We found that No Care females produced fewer eggs than Full Care females when allowed to breed on a small corpse, a finding not explained by differences in female quality. On larger corpses, females from both populations laid similar numbers of eggs. Furthermore, hatching success was greater in the No Care populations on small corpses. Our results suggest that the adaptive overproduction of offspring depends on a mechanism for eliminating surplus young and that killing offspring, in turn, relaxes selection against hatching failure. The overproduction of offspring is commonly associated with high hatching failure and a mechanism for dispensing with surplus young. We used experimental evolution of burying beetle populations Nicrophorus vespilloides to ask whether eliminating the mechanism for killing “spare” offspring caused the evolution of a more restrained clutch size and consequently select for reduced hatching failure. Our results suggest that the adaptive overproduction of offspring depends on a mechanism for eliminating surplus young and that killing offspring, in turn, relaxes selection against hatching failure.
... In the present study, we investigated the parenting mode and its consequences in the North American burying beetle species N. orbicollis Say. Mate removal studies found no obvious benefits to offspring from biparental care (Trumbo & Fernandez, 1995). However, alternative approaches may be informative. ...
... observ.). Brood size is known to be a consequence of parental culling behaviour during the first larval instar (Trumbo & Fernandez, 1995). ...
... Previous work in N. orbicollis (Trumbo & Fernandez, 1995) suggested that biparental care in this species evolved largely as a result of task specialization, with males primarily functioning to defend the carcass (Trumbo, 2006). The results of the present study also suggest that biparental care can sometimes have direct effects on parental fitness. ...
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Parenting strategies can be flexible within a species and may have varying fitness effects. Understanding this flexibility and its fitness consequences is important for understanding why parenting strategies evolve. In the present study, we investigate the fitness consequences of flexible parenting in the burying beetle Nicrophorus orbicollis, a species known for its advanced provisioning behaviour of regurgitated vertebrate carrion to offspring by both sexes. We show that, even when a parent is freely allowed to abandon the carcass at any point in time, biparental post-hatching care is the most common pattern of care adopted in N. orbicollis. Furthermore, two parents together raised more offspring than single parents of either sex, showing that the presence of the male can directly influence parental fitness even in the absence of competitors. This contrasts with studies in other species of burying beetle, where biparental families do not differ in offspring number. This may explain why biparental care is more common in N. orbicollis than in other burying beetles. We suggest how the fitness benefits of two parents may play a role in the evolution and maintenance of flexible biparental care in N. orbicollis.
... trupla miši ali manjših ptic, s čimer se grobarji znebijo tekmecev, predvsem pa s tem zmanjšajo predacijo jajc in ličink, ki se razvijajo na zakopanih kadavrih (Jakubec 2015). Najdeno truplo zakopljeta samec in samica, ki potem tudi skrbita za razvijajoče se ličinke, kar je posebnost med hrošči (Trumbo & Fernandez 1995). Poleg nekrofagov so mrharji tudi plenilci, ki plenijo po kadavrih ali gnilih gobah druge žuželke in njihove ličinke, nekatere vrste, kot sta četveropikasti (Dendroxena quadrimaculata) in polžji mrhar (Phosphuga atrata), pa sta izključno specializirana plenilca (Dekeirsschieter s sod. ...
... carcasses of mice or small birds, to get rid of competitors and, most importantly, reduce the predation of eggs and larvae developing on these buried corpses (Jakubec 2015). The carcass found is buried by male and female, which then also take care of the developing larvae, which is a special habit among beetles (Trumbo & Fernandez 1995). Besides being necrophagous, Carrion Beetles are also predators preying on insects and their larvae on carcasses or rotten fungi, and some species, such as Dendroxena quadrimaculata and Phosphuga atrata, are truly specialized predators . ...
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A catalogue of the Carrion Beetle (Silphidae) fauna was prepared based on the collected data from the literature, entomological collections and three databases, which include data from Slovenia from the period between 1763 and 2020. The presence of 23 species was ascertained, two of which are already extinct (Nicrophorus germanicus, N. sepultor), one species is believed to be extinct (Aclypea opaca), four species have not been found in the last 20 years (Aclypea undata, Thanatophilus dispar, Nicrophorus sepulchralis, N. vestigator), while Silpha tyrolensis stands out among the rarer species. The species with the most data (over 10% of all collected data) are Oiceoptoma thoracicum, Phosphuga atrata, Nicrophorus vespillo and N. vespilloides. The catalogue of species presents the species distribution in Slovenia in three periods (before 1950, 1950-1999 and after 2000), the altitudinal and seasonal distribution of collected data, a review of Slovenian literature, and a list of collected data. The article also brings a proposal for the Slovenian nomenclature of all European Carrion Beetle species and a proposal for a new classification of the Carrion Beetle species in the Red list of Endangered Species of Slovenia.
... Adult burying beetles use the carcasses of small vertebrates, such as mice, as a resource to provision offspring, the availability and quality of which are highly stochastic in the wild (Royle & Hopwood, 2017;Scott, 1998). The number and size of offspring that they produce strongly depend on the size of the carcass that they breed on (Bartlett, 1987;Creighton, 2005;Creighton et al., 2009;Trumbo & Fernandez, 1995). In addition, when individuals breed more than once on carcasses of different sizes the order of presentation of the carcasses affects reproductive output with females breeding on small then large carcasses investing more in their second brood than females breeding in other order combinations (large then small, small then small or large then large; Billman, Creighton, & Belk, 2014). ...
... This repeated measures crossover design allowed us to examine order effects on patterns of investment in relation to age. At larval dispersal, offspring number and brood mass were measured to analyse individual adjustments in brood size to carcass size (Creighton, 2005;Trumbo & Fernandez, 1995). Mean larval mass was calculated by dividing brood mass by the number of larvae in the brood to enable us to assess potential offspring numberesize trade-offs ( ...
Article
Phenotypic plasticity is an important mechanism facilitating adaptation to environmental change that often varies among individuals. One reason for this individual variation is that plasticity may depend on state variables, such as size, condition or age, which affect the costs and benefits of plasticity. Recent theoretical work predicts that plasticity will decrease as an organism ages because costs of plasticity mean that flexible phenotypic adjustments by individuals to environmental change will be less beneficial as age-related survival prospects decrease. Here we used Nicrophorus vespilloides burying beetles to test this prediction in the context of parental care. Burying beetles use the carcasses of small vertebrates as resources for breeding and have complex, extended, flexible parental care. Our experiment manipulated female age and (the order of presentation of) carcass size in a repeated-measures design to test the prediction that older beetles are less plastic than younger beetles in parental care. We found evidence in support of our central prediction: young females showed greater mean levels of plasticity than older beetles for all traits (parental care, number of offspring, brood mass) except mean larval mass (i.e. size of offspring), with the response to changes in carcass size dependent on the order of carcass presentation for young females but not for older females. Between-trait correlation analysis revealed age-related trade-offs between the size and number of offspring for older, but not young, mothers. The three age-dependent traits, which were intercorrelated, were also repeatable, indicating potential for coevolutionary responses to selection.
... It has been reported that parental care improves larval fitness (brood size, survival, and growth rate) in Nicrophorus spp. . However, many studies have shown that a second parent provides no additional benefit (Trumbo & Fernandez, 1995;Sakaluk et al., 1998;Smiseth et al., 2005;Trumbo, 2006) and Pilakouta et al (2018) showed that biparental care in N. vespilloides improved the larval mass but males provided less care when working with a partner. Why males provide care to their young in burying beetles is still unknown. ...
Article
In species showing biparental care, parents often adjust their level of care facultatively. Partners can potentially monitor each other directly (modify their effort sequentially in direct response to the prior effort of their mate) or indirectly (parents modify their effort through the begging rates of their offspring). This study examined whether partner negotiation or begging by larvae best explains male provisioning in Nicrophorus quadripunctatus . The frequency of males approaching larvae to feed did not increase with either female removal or female handicapping. However, larval begging toward males increased with female removal, but not with female handicapping. This suggests that larvae are not affected by the change of female investment in care but larvae reacted to the absence of a female parent. Although larvae begged more towards the male when the female was removed, my findings show that males did not respond by increasing their care, which suggests that males are insensitive to variation in their partner’s state or offspring behaviour in N. quadripunctatus .
... This behaviour is thought to be related to resource utilization such that surviving larvae reach dispersal at an optimal size (Bartlett, 1987). Burying beetles assess the volume of the carcass resource prior to reproduction (Trumbo & Fernandez, 1995), and they appear to make brood size decisions based on initial assessment of carcass size (Trumbo, 1990a(Trumbo, , 1990b(Trumbo, , 1992Bartlett & Ashworth, 1988;Nagano & Suzuki, 2007;) along with other environmental cues related to food availability and conspecific competition (Woelber et al., 2018). Seismic noise may have disrupted the parent beetles' ability to properly assess carcass size, leading to an increase in larval culling and underproduction of offspring. ...
Article
Anthropogenic noise pollution is known to alter the behaviour of acoustically sensitive animals. Many animals also sense vibrations through solid substrates and use substrate-borne vibrations in conspecific communication. The effects of substrate-borne noise pollution, however, remain largely unknown. Here, we investigate the potential for seismic (soil-borne) noise to alter the reproductive behaviour of the burying beetle Nicrophorus marginatus, a species that breeds below the soil surface on vertebrate carcasses and provides biparental care to offspring. Nicrophorus marginatus beetles produce sound using stridulatory structures on the elytra and abdomen, but no ears have been identified in these beetles, suggesting that stridulation might function to produce substrate-borne signals. We examined the timing of stridulation during reproduction, measured neural responses of beetles to substrate-borne vibrations, and measured beetle reproduction in the presence and absence of seismic noise. We found that parental beetles stridulate throughout carcass preparation and the burial process and confirmed that adult beetles are sensitive to low-frequency seismic vibrations. Variables related to brood size were affected in treatments with seismic noise, with burying beetles producing smaller broods with lower total mass than those in control treatments, providing support for the hypothesis that substrate-borne noise may impose fitness costs for soil-dwelling animals. The precise mechanisms leading to reduced brood size remain unknown but may relate to disruption of seismic communication or inaccurate assessment of resource size. Additional investigations are required to understand the degree to which human-generated seismic noise in natural settings influences other edaphic species, and whether these behavioural impacts lead to shifts in edaphic community structure or function.
... Alternatively, females may not assess the size of the carcass until after mating. For example, in Nicrophorus orbicollis, a congener to our study species, females assess the size of the carcass while preparing and burying it (Trumbo & Fernandez, 1995), which typically happens after mating has taken place. ...
Article
Theory predicts that the outcome of mating interactions should be influenced by the condition of both males and females. First, females should base their mating decisions on reliable cues about male quality, which are often condition dependent. Second, the costs and/or benefits of being choosy during mating may depend on the female's own condition. Finally, when males divide their time between different mating tactics, investment in alternative mating tactics may depend on male condition. Here we examined the effects of male and female nutritional condition on mating behaviour in the burying beetle Nicrophorus vespilloides. We manipulated male and female nutritional condition either during sexual maturation or at the time of mating and monitored female mate choice and male mating tactics. We found that females in poor condition (i.e. starved either during sexual maturation or at the time of mating) preferred to mate with males in good condition over males that were starved at the time of mating. In contrast, well-fed females showed no such preference. Furthermore, males that were starved during sexual maturation increased their investment in alternative mating tactics by spending more time signalling for females. Our results add to evidence suggesting that females in poor condition bias mating towards males in good condition although it is currently unclear why these females are choosier in this species. Ours is the first study to demonstrate that nutritional condition during sexual maturation can influence mating behaviour, which may have implications for the rate and direction of sexual selection.
... In addition, burying beetle parents may influence offspring performance by actively tailoring offspring number to carcass size through regulation of the number of eggs laid and postnatal filial cannibalism (Bartlett, 1987;Trumbo, 1990a). When carcasses do not vary substantially in size, parents can tailor offspring number sufficiently accurately to maintain larval size across the range of carcasses, at least in some species (Trumbo, 1990b;Trumbo & Fernandez, 1995;Wilson & Fudge, 1984). Such behaviors are plastic and may have a genetic basis (Steiger, Richter, M€ uller, & Eggert, 2007). ...
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Among-individual variation in behavioral plasticity—the modification of behavior in response to changes in environment experienced by individuals—is increasingly recognized as an important, but relatively poorly understood, feature of organisms that facilitates adaptation to environmental change. It is expected to evolve when there is rapidly fluctuating or directional environmental change during the lifetime of individuals. This is particularly likely to occur in the context of reproductive behaviors, when the outcomes of unpredictable social interactions with other individuals during mating and parental care determine how selection acts on males and females and mating systems evolve. To better understand patterns of mating and parental care and organismal adaptation to environmental change, we need to know why there is so much variation in behavioral plasticity between and within species. Here we address this question using burying beetles as a model. Burying beetles have unusually variable, facultatively expressed, modes of parental care and variation between the sexes and among individuals in the plasticity of reproductive behaviors. We present evidence to show that variation in male plasticity of mating behavior is a key driver of the evolution of patterns of parental care in Nicrophorus vespilloides burying beetles. More generally, we conclude that behavioral plasticity in burying beetles, and likely other taxa, has evolved as a consequence of a resource requirement bottle-neck (niche specialization) in combination with highly unpredictable availability of such suitable resources and the social unpredictability that arises as a result: constraint is the mother of plastic invention.
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