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1. Bateman’s principle, stating that female fitness is maximised by increasing longevity, suggests females are likely to exhibit a stronger immune response than males. Applying these ideas to maturation, we predict that immature beetles will also show enhanced immunity. This study looks at how life-history strategies interplay with infection responses in a well-established immunological model, the burying beetle, Nicrophorus vespilloides, and a pathogenic bacteria, Photorhabdus luminescens. 2. To test this, the immune enzyme phenoloxidase (PO) and bacterial loads in sexually mature and immature beetles were tested over time after injection with P. luminescens, and survival was monitored. Breeding after infection was also tested. 3. Bacterial loads were lower in females than males, and clearance seems more prolonged in immature than mature beetles, and both these groups show increased survival, supporting the application of Bateman’s principle to the effects of maturation and sex on immunity. 4. Mature beetles were found to undergo a shorter period of PO suppression after injection with bacteria. However, whilst high PO was beneficial up to 20 hours post-infection, it became detrimental thereafter. This temporal factor has rarely been investigated but is shown here to be influential on the interpretation of PO activity, which is generally perceived as beneficial after infection. 5. A trade-off between reproduction and immunity was also found, revealed only by a highly pathogenic infection. This contrasts with the effects found in studies using non-pathogenic bacteria, suggesting an enforced, resource-based trade-off is the driving force behind the change, rather than an adaptive strategy.

1. In burying beetles (Nicrophorinae), body size is known to provide both a fecundity advantage (in females) and successful resource defence (in males and females). Despite this, considerable variation in body sizes is observed in natural populations. 2. A possible explanation for the maintenance of this variation, even with intra- and inter-specific resource competition, is that individuals might assort according to body size on different-sized breeding resources. 3. We tested prediction that ‘bigger is always better’, in the wild and in the laboratory, by experimentally manipulating combinations of available breeding-resource size (mouse carcasses) and competitor's body size in Nicrophorus vespilloides (Herbst 1783). 4. In the field, large female beetles deserted small carcasses, without breeding, more often than they did larger carcasses, but small females used carcasses indiscriminately with respect to size. In the laboratory, large beetles reared larger broods (with more offspring) on larger carcasses than small beetles, but on small carcasses small beetles had a reproductive advantage over large ones. Offspring size covaried with carcass size independently of parental body size. 5. The present combined results suggest breeding resource value depends on an individual's body size, and variation in body size is environmentally induced: maintained by differences in available carcass sizes. This produces a mechanism by which individual specialisation leads to an increase in niche variation via body size in these beetles.

1. We provide evidence for social immunity in offspring of a sub-social species, the burying beetle, Nicrophorus vespilloides. 2. N. vespilloides is a carrion breeder, and in a similar fashion to the adult beetles, the offspring produce exudates that exhibit lytic activity, which are used to coat the breeding resource. This strategy defends against the microbial community. 3. The lytic activity in larval exudates declines as the brood develops, perhaps being most beneficial at the start of the breeding bout. 4. Changing levels of parental care through widowing/orphaning affects lytic activity in the larval exudates, with levels decreasing in the absence of both parents.

1. Interactions between species can vary from mutually beneficial to evolutionarily neutral to antagonistic, even when the same two species are involved. Similarly, social interactions between members of the same species can lie on a spectrum from conflict to cooperation. 2. The aim of the present study was to investigate whether variation in the two types of social behaviour are interconnected. Is the fitness of the various classes of social partner within species (such as parent and offspring, or male and female) differently affected by interactions with a second species? Moreover, can inter‐specific interactions influence the outcome of social interactions within species? 3. The present experiments focus on the interactions between the burying beetle Nicrophorus vespilloides Herbst and the phoretic mite Poecilochirus carabi G. Canestrini & R. Canestrini. The approach was to measure the fitness of burying beetle mothers, fathers, and offspring after reproduction, which took place either in the presence or absence of mites. 4. We found that male, female, and larval burying beetles derive contrasting fitness costs and benefits from their interactions with the mite, despite sharing a common family environment. From the mite's perspective, its relationship with the burying beetle can, therefore, be simultaneously antagonistic, neutral, and possibly even mutualistic, depending on the particular family member involved. We also found that mites can potentially change the outcome of evolutionary conflicts within the family. 5. We conclude that inter‐specific interactions can explain some of the variation in social interactions seen within species. It is further suggested that intra‐specific interactions might contribute to variation in the outcome of interactions between species.

1. In many undisturbed watersheds along the Pacific Rim, anadromous salmon (Oncorhynchus spp.) provide a predictable source of carrion to the riparian zone, largely due to horizontal transfer of salmon carcasses by bears (Ursus spp.) and other vertebrates. 2. Burying beetles are important members of the north-temperate carrion fauna, and may utilise salmon carcasses and remnants for breeding. In this study, isotopic and observational data are reported that demonstrate previously unrecognised Nicrophorus investigator (Zetterstedt) reproduction on large salmon carcasses from five watersheds in coastal British Columbia. 3. Stable isotope signatures (δ15N and δ13C) of adult beetles collected in autumn indicate a diet of salmon origin in all but one individual from all watersheds, suggesting that this beetle–salmon association is widespread. Comparison of autumn isotope signatures to individuals collected randomly in summer suggests that isotope signatures represent the larval carrion source from the previous autumn rather than immediate adult diet. 4. In a survey of N. investigator use of salmon carcasses from two watersheds, 35 broods were observed on chum and pink salmon carcasses, including 16 natural brood complexes containing over 100 larvae, and five ranging from 250 to 750 larvae. 5. Overall, north-coastal populations of N. investigator breed on the rich and reliable salmon resource and may exhibit a system of communal breeding on these carcasses. This is most relevant when the dramatic reduction in salmon spawning biomass over the last century is considered.

1. Under natural conditions in Kyoto, Japan, the reproductive activities of Nicrophorus quadripunctatus Kraatz (Coleoptera: Silphidae) decreased in summer and the species showed a bimodal life cycle. 2. In the laboratory, most adult pairs raised at 20 degrees C under a LD 12:12 h regime reproduced when provided with a piece of chicken. In adults raised at 20 degrees C under a LD 16:8 h regime, however, both reproductive behaviour and ovarian development were reduced. It is concluded that these adults entered a reproductive summer diapause. 3. High temperature (25 degrees C) also suppressed the reproductive behaviour even under a favourable LD 12:12 h regime. In the field, therefore, adults reduce their reproductive activity in summer because of diapause induced by long-day photoperiods and direct inhibition of reproduction by high temperatures. 4. When the temperature was changed from 20 degrees C to 25 degrees C immediately after hatching of larvae, they reached the wandering stage in 95% of adult pairs. When the temperature was changed from 20 degrees C to 25 degrees C immediately after oviposition, however, no larvae hatched in 85% of pairs. Egg mortality was significantly higher at 25 degrees C than at 20 and 22.5 degrees C; no eggs hatched at 27.5 degrees C. The physiological mechanisms for reducing reproduction probably prevent the beetles from inefficient oviposition in summer.

1. Female burying beetles behave differently towards males of different sizes, avoiding mating with large males that are not defending resources but mating with small males regardless of the presence of resources. Females of the burying beetle Nicrophorus orbicollis were therefore examined to determine whether they discriminate among males using only pheromonal signals. The influence of female size on its own mate choice was also examined. 2. Females do use male pheromonal signals to discriminate among males and these signals do appear to convey information about male body size to females. Overall, females were more likely to be attracted to larger males than to smaller males. 3. Female choice of a male was influenced by both the female's own body size and the size of the female relative to the size of the two males available to it. 4. While there is an overall mating advantage for larger males, resulting from female preferences based on odour cues, smaller males are also attractive to some females under some circumstances. 5. It is argued that there are different costs and benefits of mating with different sized males, leading to the evolution of context-dependent mate choice for females and the need to be able to discriminate males of different sizes from a distance.

Summary 1. Beetles of the genus Nicrophorus reproduce on small vertebrate carcasses that they bury in the soil to provide the larvae with food. Usually, both parents cooperate in brood care by feeding and guarding their progeny. 2. In pairs of the common European species N. vespillo, the duration of care depended on the time of year when the beetles reproduced. Both in 1990 and in 1991, male and female parents stayed longer with their broods when reproduction started in spring than when reproduction started in early or late summer. This was probably due to the longer development time of the larvae caused by lower temperatures in spring, because laboratory experiments suggested a strong influence of temperature on both the duration of brood care and offspring development. 3. The number of adult offspring produced by a beetle pair did not vary among different times of the year. 4. The median time required for offspring development, measured as time from burial of the carcass to emergence of young adults, was between 62 and 84 days. When the beetles reproduced in late summer, only about three-quarters of the offspring left the soil and hibernated as adults. The remaining offspring stayed underground and adults appeared on the soil surface the following spring. They still showed the flexible cuticle typical of newly-hatched beetles, suggesting that they may have overwintered in a pre-adult stage.

1 To investigate the range of resource size that burying beetles (Nicrophorus) exploit, small (21–33 g), medium (50–90 g) and large (120–210g) carcasses, were placed in the field and then exhumed after 1, 4, 8, 12 or 18 days. 2 Nicrophorus attempts to utilize carcasses over this entire size range but has greater success on smaller carcasses. 3 Larger carcasses were more difficult to exploit because: (a) they took longer to conceal beneath the leaf litter; (b) they were less likely to be rounded into brood balls; (c) they were more likely to be utilized by dipterans; and (d) they were occupied by greater numbers of congeners. 4 Larger carcasses, however, did support greater numbers of larvae and contained broods of greater total mass than smaller carcasses. 5 Beetles sometimes bred communally on larger carcasses in the field and same-sex adults were observed to feed young. 6 Two follow-up experiments were conducted in the laboratory. On a large carcass N.defodiens, N.tomentosus or N.orbicollis can raise a maximum of 35–50 young. Nicrophorus pustulatus, in contrast, appears to be unique among Nicrophorus in that it can raise nearly 200 young on larger carcasses. 7 Nicrophorus orbicollis and Nicrophorus sayi are extremely dependent on parental regurgitations and young fail to survive to the second instar if parents are removed. Young of Nicrophorus defodiens, N.tomentosus and N.pustulatus can develop normally without parental regurgitations. 8 I discuss these results in the context of reproduction on carcasses of different size and hypothesize that this breeding system is facultatively quasisocial.

Burying beetles are carrion feeders that specialize on small carcasses. We investigated interactions among congeners at two sites in Michigan, U.S.A., that differ in both number and relative proportion of species. 2. Intra- and interspecific competition for carcasses is intense. The majority of carcasses are found within 24 h of their placement. 3. Competition between N.arbicollis and N.defodiens is temperature depen- dent. Not-bicoflis can displace N.defodiens on single carcasses, but requires warm temperatures to find the carcasses. Cool weather therefore serves as a refuge for N.defadiens. 4. The southern edge of Ndefodien's geographical range is probably deter- mined by competition with N.orbicoNis. 5. Nmyi and N.tomenrosus are spring and autumn breeders respectively, and rarely interact with each other or the other two species. Nevertheless, inter- specific competition is the most likely evolutionary force leading to seasonal segregation.