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| Effects of carcass mass on brood size at dispersal (A) and mean larval mass at dispersal (B). Filled circles represent individual data points; lines represent a linear regression line in panel (A) and a polynomial regression line in panel (B), and shaded ribbons the 95% confidence intervals.
Source publication
In species where both parents cooperate to care for their joint offspring, one sex often provides more care than the other. The magnitude of such sex differences often varies both between and within species and may depend on environmental conditions, such as access to resources, predation risk and interspecific competition. Here we investigated the...
Contexts in source publication
Context 1
... was no significant effect of carcass mass on the average time spent begging by individual larvae ( Table 2). However, brood size at dispersal increased by approximately 2 larvae for each additional 10 g of carcass ( Table 2 and Figure 4A; estimate = 0.016, SE = 0.006, z = 2.51, P = 0.012) and, for smaller carcasses (i.e., below 10 g), mean larval mass at dispersal increased by approximately 0.026 g for each additional 10 g of carcass ( Table 2 and Figure 4B; estimate = 0.025, SE = 0.006, t = 4.00, P < 0.001). There were significant effects of both the quadratic (χ 2 = 8.89, df = 1, P = 0.0028) and the cubic (χ 2 = 5.52, df = 1, P = 0.018) terms of carcass mass on mean larval mass at dispersal. ...
Context 2
... was no significant effect of carcass mass on the average time spent begging by individual larvae ( Table 2). However, brood size at dispersal increased by approximately 2 larvae for each additional 10 g of carcass ( Table 2 and Figure 4A; estimate = 0.016, SE = 0.006, z = 2.51, P = 0.012) and, for smaller carcasses (i.e., below 10 g), mean larval mass at dispersal increased by approximately 0.026 g for each additional 10 g of carcass ( Table 2 and Figure 4B; estimate = 0.025, SE = 0.006, t = 4.00, P < 0.001). There were significant effects of both the quadratic (χ 2 = 8.89, df = 1, P = 0.0028) and the cubic (χ 2 = 5.52, df = 1, P = 0.018) terms of carcass mass on mean larval mass at dispersal. ...
Context 3
... were significant effects of both the quadratic (χ 2 = 8.89, df = 1, P = 0.0028) and the cubic (χ 2 = 5.52, df = 1, P = 0.018) terms of carcass mass on mean larval mass at dispersal. Thus, mean larval mass increased with carcass mass when carcasses were relatively small and plateaued as carcass mass approached the upper end of the range of carcasses used in our experiment ( Figure 4B). In addition, the duration of biparental care had a positive effect on brood size at dispersal (χ 2 = 5.91, df = 1, P = 0.015), increasing by approximately 0.8 larvae for each additional day of biparental care. ...
Similar publications
Parental care directly affects the fitness of individuals because it increases the probability of offspring survival. Therefore, it is expected that parents be particularly motivated to return (i.e., exhibit homing behavior) and resume care if they are moved away from offspring by disturbances. Yet, despite several studies on the behavioral ecology...
Citations
... When caring biparentally, females predominantly provide direct care Smiseth et al., 2005;Smiseth & Moore, 2004b;Walling et al., 2008), whereas males often focus on indirect care i.e., carcass maintenance and defense (Fetherston et al., 1990;Trumbo, 1991Trumbo, , 2007. Additionally, it is known that males usually desert earlier than females (Bartlett, 1988;Fetherston et al., 1990;Müller et al., 2007;Parker et al., 2015;Ratz et al., 2021;Royle et al., 2014;Scott, 1998a;Ward et al., 2009). However, if the female deserts or dies, males are able to compensate for the loss of their partner (Bartlett, 1988;Jenkins et al., 2000;Müller et al., 1998;Scott, 1989;Smiseth et al., 2005;Trumbo & Fernandez, 1995). ...
... Large carcasses, on the other hand, might be very costly to maintain and defend, making it unprofitable to raise broods of small sizes. That larger carcasses are more costly to prepare was also suggested in previous studies (de Gasperin & Kilner, 2015;Ratz et al., 2021;Xu & Suzuki, 2001). For example, de Gasperin and Kilner (2015) found that the preparation of larger carcasses resulted in a reduced lifespan of male beetles. ...
... In general, our results highlight that males are able to evaluate resource size and are consistent with the results of previous studies that examined male care behavior under biparental care. Bartlett (1988), Kishida and Suzuki (2010) and Ratz et al. (2021), for example, found that males are sensitive to carcass size and leave the brood earlier as carcass mass decreases. Males of other species are also known to monitor resource availability (e.g., Barbasch et al., 2020) or other non-social environmental factors (e.g., Green & McCormick, 2004) and adjust care behavior accordingly. ...
Parental care strategies do not only vary greatly across species, but also within species there can be substantial between- and within-individual variation in parental care behavior. To better understand the evolution of care strategies, it is crucial to determine how and when parents modify their behavior in response to internal as well as environmental factors. Here, we investigated the effect of brood size, resource size and an individual's quality on care strategies of uniparental males and examined the downstream consequences on offspring performance in the burying beetle Nicrophorus vespilloides. Burying beetles breed on small vertebrate cadavers and, on average, males invest much less in care than females. Nevertheless, we found that uniparentally caring males were responsive to their social and non-social environment and adjusted the amount as well as the type of care to the size of the brood, the size of the cadaver and their own body size. Additionally, we show that the care strategies affected offspring performance. Specifically, males that cared longer had larger and more surviving larvae. Our results add to our understanding of plastic parenting strategies by showing that even the sex that provides less care can evolve a very flexible care behavior.
... This increase in competition could eventually lead to a selection of uniparental care over biparental care when resource availability is low during breeding. Indeed, this notion aligns with the results of Ratz et al. (2021) and Kishida and Suzuki (2010) who found that males left earlier on smaller than on larger carcasses. ...
Harsh environmental conditions in form of low food availability for both offspring and parents alike can affect breeding behavior and success. There has been evidence that food scarce environments can induce competition between family members, and this might be intensified when parents are caring as a pair and not alone. On the other hand, it is possible that a harsh, food-poor environment could also promote cooperative behaviors within a family, leading, for example, to a higher breeding success of pairs than of single parents. We studied the influence of a harsh nutritional environment on the fitness outcome of family living in the burying beetle Nicrophorus vespilloides. These beetles use vertebrate carcasses for reproduction. We manipulated food availability on two levels: before and during breeding. We then compared the effect of these manipulations in broods with either single females or biparentally breeding males and females. We show that pairs of beetles that experienced a food-poor environment before breeding consumed a higher quantity of the carcass than well-fed pairs or single females. Nevertheless, they were more successful in raising a brood with higher larval survival compared to pairs that did not experience a food shortage before breeding. We also show that food availability during breeding and social condition had independent effects on the mass of the broods raised, with lighter broods in biparental families than in uniparental ones and on smaller carcasses. Our study thus indicates that a harsh nutritional environment can increase both cooperative as well as competitive interactions between family members. Moreover, our results suggest that it can either hamper or drive the formation of a family because parents choose to restrain reproductive investment in a current brood or are encouraged to breed in a food-poor environment, depending on former experiences and their own nutritional status.
... We first tested for damage to the dead intruders to verify that our experimental treatment had the intended effect. We next tested for shifts in the balance between cooperation and conflict detected as changes in the duration of biparental care relative to uniparental care (Pilakouta et al., 2018;Ratz et al., 2021). We predicted that the presence of conspecific intruders would be associated with a shift towards greater levels of cooperation, detected as an increase in the duration of biparental care relative to uniparental care, given that two parents are better at defending the resource and the brood against such intruders than single parents (e.g. ...
... We scored the male and the female as being absent, and having deserted the brood, if they were neither on the carcass nor in the crypt on 2 consecutive days, in line with established protocols for this species (e.g. Pilakouta et al., 2018;Ratz et al., 2021). We removed any parent that was scored as having deserted the brood and weighed it to record information on weight change during breeding (see below). ...
... However, this seems unlikely given that parents respond to the presence of conspecifics by adjusting their acceptance threshold such that they become more aggressive towards new intruders (Steiger & Müller, 2010) and by providing more care towards the current brood (Georgiou-Shippi et al., 2018). Thus, parents respond to the presence of conspecifics as expected if they used these as cues about the level of intraspecific competition (Hopwood et al., 2015) or the availability of resources (Bartlett, 1988;Ratz et al., 2021). Thus, one avenue for future work is to examine the conditions under which parents respond to the presence of conspecific intruders and the type of responses mounted by residents (i.e. ...
Biparental care occurs when males and females cooperate to care for their joint offspring. It is associated with sexual conflict because the benefits stem from the combined effort of both parents, while any costs depend on each parent's own effort. Thus, biparental care involves a delicate balance between cooperation and conflict. Shifts in this balance are likely to be driven by environmental conditions that alter the costs and benefits to males and females. Here, we used the burying beetle Nicrophorus vespilloides to investigate whether the presence of conspecific intruders shifts the balance towards cooperation (detected as an increase in the duration of biparental care relative to uniparental care) or alters the magnitude of sex differences in care, and whether any such effects are dependent on resources available for breeding. We found that the presence or absence of conspecific intruders had no effect on the duration of biparental care relative to uniparental care. Thus, there was no evidence that the presence of intruders caused a shift towards more cooperation. Females, but not males, responded to the presence of conspecific intruders by increasing their time spent providing one form of care, but only when breeding on larger resources. Thus, there was some evidence that the presence of intruders altered the magnitude of sex differences in care and that this was conditional upon the amount of resources available for breeding. Overall, our results show that threats from conspecific intruders alters sex differences in parental care, while not changing the balance between cooperation and conflict.
... In further studies, a more direct estimate, such as vegetation growth in the breeding site and the distribution of animal food during the breeding season, will be valuable to justify our conclusions. Furthermore, a recent experimental study on the burying beetle (Nicrophorus vespilloide) demonstrates that high abundance of food promotes instead of reducing cooperation between parents (Ratz et al. 2021). It would be worthwhile to test the generality of this finding using large-scale databases on insects. ...
In animals, species differ remarkably in parental care strategies. For instance, male-only care is prevalent in teleost fishes, while biparental care predominates in birds and female-only care is widespread in mammals. Understanding the origin and maintenance of diversified parental care systems is a key challenge in evolutionary ecology. It has been suggested that ecological factors and life-history traits play important roles in the evolution of parental care, but the generality of these predictions has not been investigated across a broad range of taxa. Using phylogenetic comparative analyses and detailed parental care data from 1101 avian species that represent 119 families of 26 orders, here we investigate whether parental strategies are associated with ecological variables (i.e., food type, nest structure, and coloniality) and life-history characteristics (i.e., chick development mode and body size). We show that parental care strategies are in relation to coloniality (solitary, semi-colonial, colonial) and chick development mode (altricial vs. precocial). Colonial and altricial species provide more biparental care than solitary and precocial species, respectively. In contrast, food type (plant, invertebrate, vertebrate), nest structure (open vs. closed), and body size do not covary systematically with parental care patterns in birds. Taken together, our results suggest that living in groups and/or having high-demand offspring are strongly associated with biparental care. Towards the end, we discuss future research directions for the study of parental care evolution.
Significance statement
Animal species differ remarkably in the amount of care parents provide to their offspring and in the distribution of care tasks over the parents. In birds, for example, the young of some species are quite independent from the start, while the young of other species are helpless after hatching, requiring a lot of care. Moreover, either the female or the male does most of the caring in some species, while the parental tasks are shared equally in still other species. To understand the diversified parental care patterns, we applied advanced comparative methods to a large data set comprising over 1000 bird species. The analysis reveals that the parents tend to share their care duties equally when they live in groups and/or have offspring that are born helpless, and that parental care patterns are not associated with diet, nest type or body size. Hence, living in groups and having high-demand offspring seem to play important roles in the evolution of parental care.
... This is because any increase in the chance of resource consumption by males may reduce the amounts of resources for females and larvae. This assumption is supported by the fact that females benefit from male desertion by feeding more from the carcass (Boncoraglio and Kilner 2012), and the sexual conflict over parental care is more pronounced as carcass size is decreased (Ratz et al. 2021). Carcass preparation influenced the investment in current reproduction, with parents that breed on non-prepared carcasses providing more parental care and caring for longer than parents that breed on prepared carcasses. ...
... Our results are consistent with previous studies that parents produce more and heavier larvae when breeding on larger carcasses (Smiseth et al. 2014;Richardson and Smiseth 2019;Ratz et al. 2021). In addition, consistent with prior work on other species, there was a trade-off between larvae number and average larval mass when parents were breeding on prepared carcasses (Trumbo 2017). ...
Life-history theory predicts trade-offs between investment in current versus future reproduction. However, many studies find no or even positive correlations among these traits. The absence of the trade-off may result from resource availability, as it influences resource allocation to different traits. In addition, since large amounts of resources require additional effort in processing, resource maintenance may affect the detection of reproductive trade-offs. Here, we carried out two breeding attempts to assess the effects of resource availability and maintenance on reproductive trade-offs for both sexes in the burying beetle ( Nicrophorus vespilloides ). In the first breeding attempt, we simultaneously manipulated carcass size (small versus large) and carcass preparation (non-prepared versus prepared). In the second breeding attempt, we provided parents with same-sized, non-prepared carcasses. For both breeding attempts, we monitored the main and interactive effects of carcass size and carcass preparation on parental effort and reproductive outcome. In the first breeding attempt, males gained more weight and provided more care as carcass size increased, whereas females gained more weight but did not change their care. In addition, when breeding on non-prepared versus prepared carcasses, both parents provided more care and gained more weight. In the second breeding attempt, with increased investment for the first breeding, parents did not show decreased investment for the second brood, vice versa. In contrast, males breeding on large or non-prepared carcasses gained more weight during the first breeding attempt, then provided more care in subsequent reproduction. There were no differences in subsequent female care among different treatments.
Significance statement
Resource availability and resource maintenance may affect the detection of reproductive trade-offs. Here, we simultaneously manipulated carcass size and carcass preparation to assess these effects. This is the first time that the effects of resource availability and resource maintenance on reproductive trade-offs have been separated in burying beetles. Our findings suggest that despite the increased costs of parental care and resource maintenance, parents breeding on large or non-prepared carcasses gained more benefits in terms of increased body weight by staying longer and feeding more from the carcasses. Such benefits gained during the first breeding attempt offset the costs of current reproduction to some degree and masked the reproductive trade-off between current and future reproduction in terms of parental care. These findings enhance the understanding of the effects of resource availability and maintenance on reproductive trade-offs.
