Inbreeding depression is the reduction in fitness caused by mating between related individuals. Inbreeding is expected to cause a reduction in offspring fitness when the offspring themselves are inbred, but outbred individuals may also suffer a reduction in fitness when they depend on care from inbred parents. At present, little is known about the significance of such intergenerational effects of inbreeding. Here, we report two experiments on the burying beetle Nicrophorus vespilloides, an insect with elaborate parental care, in which we investigated inbreeding depression in offspring when either the offspring themselves or their parents were inbred. We found substantial inbreeding depression when offspring were inbred, including reductions in hatching success of inbred eggs and survival of inbred offspring. We also found substantial inbreeding depression when parents were inbred, including reductions in hatching success of eggs produced by inbred parents and survival of outbred offspring that received care from inbred parents. Our results suggest that intergenerational effects of inbreeding can have substantial fitness costs to offspring, and that future studies need to incorporate such costs to obtain accurate estimates of inbreeding depression.

There is mounting evidence that inbreeding can have detrimental effects on the fitness of outbred individuals that interact with or depend on inbred individuals. However, little is currently known about the behavioral mechanisms by which interactions with inbred individuals induce fitness costs in outbred individuals. Here, we study effects of inbreeding on the behavioral dynamics of biparental cooperation in the burying beetle Nicrophorus vespilloides. To this end, we used a two-by-two factorial design, in which an inbred or outbred female was mated to an inbred or an outbred male and tested for effects on cooperation between male and female parents providing care for their joint offspring. We found no evidence that inbred parents provided less care than outbred parents. Nevertheless, partners of inbred parents increased the amount of care they provided, leading to overcompensation. Our study shows that inbreeding can have strong and complex effects on the behavioral dynamics of biparental cooperation and that these effects are mediated mainly through changes in the partner's behavior. We suggest that similar effects of inbreeding on outbred individuals may extend to other social contexts, such as cooperative breeding and mating.

Understanding the consequences of phenotypic variation in resource acquisition is an important problem in evolutionary ecology because such variation may impact on how parents balance resource investment in individual offspring against other life-history priorities. Here we investigate the effects of phenotypic variation in resource acquisition on the number and mass of offspring and the trade-off between the two in the burying beetle Nicrophorus vespilloides. We manipulate resource acquisition in adults by providing some females with a small mouse carcass (5-10 g) and other females with a large mouse carcass (15-20 g). We found that females breeding on larger carcasses produced both more and larger offspring than females breeding on smaller carcasses. Furthermore, an increase in brood size had a stronger negative effect on offspring mass in broods produced on smaller carcasses than in broods produced on larger carcasses. We conclude that phenotypic variation in resource acquisition had a strong effect on the number and mass of offspring and the trade-off between the two. Our study contributes to our understanding of phenotypic variation in resource acquisition by showing that females with more resources produce both more and larger offspring in situations where such variation is not associated with anatomical or physiological differences between females.

There is mounting evidence that inbreeding can have complex effects on social interactions among inbred and outbred individuals. Here, we investigate effects of offspring and maternal inbreeding on parent-offspring communication in the burying beetle Nicrophorus vespilloides. We find effects of the interaction between offspring and maternal inbreeding on maternal behavior. Outbred females provided more direct care toward inbred larvae, while inbred females provided similar levels of direct care toward inbred and outbred larvae. Furthermore, we find direct and indirect effects of offspring inbreeding on offspring begging and maternal behavior, respectively. Inbred larvae spent less time begging than outbred larvae, and (outbred) females provided more direct care and less indirect care toward inbred larvae. Finally, we find effects of the interaction between offspring and maternal inbreeding on larval body mass. Inbred and outbred offspring grew to a similar size when the female was outbred, while inbred offspring were of a smaller size when the female was inbred. Our results suggest that outbred females provided more care toward inbred offspring to compensate for their poor genetic quality. Our study advances our understanding of inbreeding by showing that inbreeding can have direct effects on the behavior of inbred individuals and indirect effects on the behavior of outbred individuals and that indirect effects on outbred individuals may in turn influence the fitness of inbred individuals.

Inbreeding avoidance reduces the probability that an individual will mate with a related partner, thereby lowering the risk that it produces inbred offspring suffering from inbreeding depression. Inbreeding avoidance can occur through several mechanisms, including active mate choice, polyandry and sex‐biased dispersal. Here, we focus on the role of active mate choice as a mechanism for inbreeding avoidance. Recent evidence suggests that the experimental design used in mate choice experiments (i.e. simultaneous versus sequential choice) can have a strong impact on the strength of the reported mating preferences. In this study, we examine whether similar effects of experimental design also apply in the context of inbreeding avoidance. To this end, we designed two experiments on the burying beetle Nicrophorus vespilloides that matched two different contexts under which females encounter potential mates in the wild; that is, when females encounter males simultaneously and sequentially. We found that females were as likely to mate with related and unrelated males regardless of whether they encountered male partners simultaneously or sequentially. Thus, our study provides no evidence for inbreeding avoidance in this species, and suggests that the number of mates present did not influence the degree of inbreeding avoidance. We discuss potential explanations for the lack of inbreeding avoidance through mate choice, including lack of mechanisms for recognizing close relatives, low costs and/or low risks of inbreeding and the presence of other inbreeding avoidance mechanisms, such as sex‐biased dispersal and polyandry coupled with post‐copulatory mate choice.