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Proximate and Ultimate Roles of Food Amount in Regulating Egret Sibling Aggression
Ecology
Abstract
Sibling agression in unmanipulated broods of great egrets Casmerodius albus and great blue herons Ardea herodias did not decline with increasing amounts of food; indeed, this relationship may be weakly positive. In egret broods, the strongest predictors of total brood success were competitive vigor of the youngest sib and fighting rate. Wild egret bonds whose food amount was experimentally doubled did not reduce fighting rates, but experienced significantly lower brood reduction than control broods. Captive egret broods whose food amount was decreased did not increase fighting rates, but suffered significantly more brood reduction than control broods. In the wild, food amount appears not to be a sufficiently stable parameter on which to base prudent sib-aggression stratgies. Food amount thus has little direct influence on fighting behavior in these birds, though it consistently influences chick survival. Thus the proximate effects of this ecological variable must be divorced from its ultimate role, at least in species such as these ardeids and in obligate-siblicidal species. It is predicted that sibling aggression will be food-amount dependent in species whose food fluctuations are relatively slow.-from Authors
... In most siblicidal birds (e.g. egyptian heron (Bubulcus ibis), blue-footed booby (Sula nebouxii), gray heron (Ardea cinerea), laughing kookaburra (Dacelo gigas)) however, the consequences of intrabrood aggression are highly variable, and dependent on environmental conditions [47]. In these species siblicide is said to be 'facultative'. ...
... In these species siblicide is said to be 'facultative'. Variables known to influence the probability of avian siblicide include food availability [48], brood size [49], prey size [47] and the degree of competitive asymmetry between nestmates [50,51]. Although sibling rivalry has been a relatively neglected topic in the study of mammalian social development, it has been documented among juvenile pigs, goats, primates, marsupials and carnivores (reviewed in [46]). ...
The paper considers evolutionary dynamics of a structured population with density-dependent regulation of juvenile survival. Such a type of density limitation is not unusual for natural populations. It occurs as either competition for food resources or sibling aggression, and, moreover, cannibalism or infanticide. Birth rate is assumed to change during the process of microevolution. The stability loss of non-trivial fixed points was shown to realize according to both the Neimark-Sacker scenario and the Feigenbaum one. The stability loss scenario is shown to be determined by both the mature individuals’ contribution to limiting juvenile survival and birth rate level. The bifurcations, dynamic modes and a possibility of their shifting are studied for the model proposed. The model reveals bistability and multistability both the population number and gene frequencies dynamics. There are bifurcations leading to fluctuations of gene frequencies in the proposed model. Thus, both monomorphic equilibriums and oscillation modes of the population genetic composition are simultaneously possible in the system. With the same values of population parameters in the case of variations in its current stage and/ or genetic composition, such multistability can lead not only to a change in the dynamic mode due to an evolutionary growth of individual fitness, but also to a change in the evolution direction. As a result, different mechanisms of fluctuation emergence can be realized in a population at the same values of demographic parameters.
... At the extreme, parents condemn last-hatched chicks to near certain execution. Fatal sibling aggression including pecking, exclusion during feeding bouts, or eviction from the nest has been documented in a range of avian species (Miller 1973;Gargett 1978;Stinson 1979;Bechard 1983;Braun & Hunt 1983;Cash & Evans 1986;Mock et al. 1987;Anderson 1989;Drummond 1989;Drummond & Garcia Chavelas 1989, Bryant & Tatner 1990Lamey 1990;Bortolotti et al. 1991;Boal & Bacorn 1994;Heinsohn 1995;Creighton & Schnell 1996;Reynolds 1996;Gerhardt et al. 1997;Estes et al. 1999). Brood enlargement experiments indicate that parents of such species are sometimes capable of provisioning both chicks, which suggests that the parent's optimal brood size is larger than the offspring allow; that is, the offspring are winning parent-offspring conflicts over brood size (Anderson 1990b). ...
... A lthough for facultatively lethal aggression there are several hypotheses explaining how siblicide could evolve, always considering the strong benefi ts of fi ghting for sibling competition. Food amount hypothesis (Mock et al., 1987), Prey Size Hypothesis (Mock, 1985), Brood Reduction Hypothesis, and Bet-hedging Hypothesis (Forbes, 1991;Mock & Lamey, 1991) explain different pathways of regulation of aggression. Mostly, they suggest that siblicide evolved to adjust the number of offspring to the available resources at the stage when parental investment is not big to prevent bigger losses. ...
... The importance of size differences in predicting aggression was expected: Rojas (2014) established that cannibalism between D. tinctorius tadpoles occurs faster with increasingly size-mismatched pairs. In fact, across the animal kingdom, the aggressor in a pair/group is most often the larger individual, which typically faces a smaller risk of injury (Mock et al. 1987;Mayntz and Toft 2006;Ibáñez and Keyl 2010). However, our findings highlight that in this system aggression is not solely mediated by size differences, but that some form of kin discrimination is also at play. ...
In juveniles extreme intraspecies aggression can seem counter-intuitive, as it might endanger their developmental goal of surviving until reproductive stage. Ultimately, aggression can be vital for survival, although the factors (e.g., genetic or environmental) leading to the expression and intensity of this behavior vary across taxa. Attacking (and sometimes killing) related individuals may reduce inclusive fitness; as a solution to this problem, some species exhibit kin discrimination and preferentially attack unrelated individuals. Here, we used both experimental and modeling approaches to consider how physical traits (e.g., size in relation to opponent) and genetic relatedness mediate aggression in dyads of cannibalistic Dendrobates tinctorius tadpoles. We paired full-sibling, half-sibling, and non-sibling tadpoles of different sizes together in an arena and recorded their aggression and activity. We found that the interaction between relative size and relatedness predicts aggressive behavior: large individuals in non-sibling dyads are significantly more aggressive than large individuals in sibling dyads. Unexpectedly, although siblings tended to attack less overall, in size-mismatched pairs they attacked faster than in non-sibling treatments. Using a theoretical model to complement these empirical findings, we propose that larval aggression reflects a balance between relatedness and size where individuals trade-off their own fitness with that of their relatives. Lay Summary Before you eat someone, you have to attack them first. Here, we investigated the factors that shape aggression in the cannibalistic tadpoles of the dyeing poison frog. We find that aggression depends on both size and relatedness: when set in pairs, large tadpoles are half as aggressive towards their smaller siblings than to nonsibs. It looks like belonging to the same family provides some protection against aggression, though no one is ever truly safe.
... We observed higher nutrition associated with more aggressive interactions. This is in contrast to classical competition theories, which predict that a decrease in resources will lead to increased aggression between conspecifics (Maynard Smith & Harper, 1988) and siblings (Hodge et al., 2009;Mock et al., 1987). ...
Nourishment can have profound effects on social behaviour, including aggressive interactions between individuals. The prevailing theoretical and empirical understanding is that when nutritional resources are limited, inter‐individual competition and aggression will increase. Alternatively, studies from some group‐living species suggest limited nutrition can lead to increased cooperation, including by a reduction in inter‐individual aggression. Thus, a general model for understanding how and why nutritional resource limitation affects aggressive behaviour remains elusive.
We suggest that the link between nourishment and future reproductive potential may be a key missing element of models that predict how nutritional resource availability affects inter‐individual aggression in social animals.
We investigated how nourishment influenced intra‐colony aggression and its molecular correlates in colonies of the social paper wasp Polistes fuscatus, which contain workers that maintain flexible reproductive potential as adults. We subjected colonies to either a high or low feeding treatment, and examined subsequent effects on behaviour, nutritional/reproductive physiology and brain gene expression.
We found that nutritional restriction reduced aggressive interactions. Thus, resource limitation was linked to reduced intra‐group conflict. Thus, individual worker paper wasps appear to have the capacity to adjust their behaviour (e.g. reduced aggression) in response to nutritional stress; this suggests they may invest nutritional resources in the colony when resources are limiting, and in the self (and possible future reproduction) when resources are abundant.
Differential brain gene expression results implicate two well‐known neuropeptides associated with aggression and/or nutrient signalling across taxa, Tachykinin and Neuropeptide F, as possible mediators of nutritionally dependent intra‐colony aggression. This adds to a growing understanding that deeply conserved genes associated with core, conserved behaviours such as feeding and aggression in solitary insects can play a role in the regulation of social plasticity in more highly social species.
A free Plain Language Summary can be found within the Supporting Information of this article.
... For example, in great egrets, dominant chicks will peck at a subordinate chick until it stops competing for food when a parent arrives. In such instances, subordinates often succumb to starvation or fall out of nests in an attempt to evade the aggressive behavior by dominant chicks (Mock et al. 1987). However, although prevalent, sibling aggression does not invariably result in siblicide (Leonard et al. 1988;Hodge et al. 2007;Satoh et al. 2019), and more detailed studies of such cases are necessary to gain a more complete understanding of the diverse functions of nonlethal sibling aggression in animals. ...
Siblings often compete for limited resources, such as food provided by their parents. However, although several functions of nonlethal sibling (nonsiblicidal) aggression have been proposed, there is currently little empirical evidence for these, apart from food monop-olization. Here, we investigated the functions of nonlethal sibling aggression in the biparental-caring territorial herbivorous cichlid Varibilichromis moorii. We found that the juveniles of this species are highly aggressive and that larger juveniles are more aggressive toward their smaller siblings. Larger juveniles feed on algae more frequently than smaller siblings, thereby indicating a dominance hierarchy. Sibling aggression decreased when algae in the nest was experimentally removed. Furthermore, the removal of smaller juveniles decreased sibling aggression among the remaining larger juveniles, whereas the removal of larger juveniles increased aggression among smaller juveniles. The algal feeding rate of juveniles only increased when larger individuals were removed from the nest. Moreover, larger juveniles attained higher growth rates and remained in natal nests longer than smaller individuals. Our results indicate that sibling aggression may facilitate the monopolization of resources by larger juveniles and extend the parental care period. Interestingly, a small subset of juveniles was observed to migrate to other nests. These juveniles were larger than those of the host brood, and their growth rate increased within the new nests. We suggest that subordinate juveniles may disperse from natal nests and sneak into new nests to enhance their rank, which may represent a novel example of a "best of a bad job" strategy associated with sibling competition.
... However, if food resources are plentiful, the parents will be able to provision all their young with adequate food so that all young survive, regardless of hatch rank (Lack 1954). This idea has become known as the ''facultative brood reduction hypothesis'' and more specifically, the ''food amount hypothesis'' (Mock et al. 1987). A brood may be reduced as a direct result of starvation, or by siblicide as a proximate result of an insufficient amount of food. ...
Like many raptors, Red-shouldered Hawks (Buteo lineatus) exhibit asynchronous hatching, which is thought to be a parental strategy for rearing the maximum number of offspring under conditions of unpredictable prey availability. Current knowledge of incubation patterns and the associated behavioral mechanisms by which asynchronous hatching occurs in raptors is limited, and few detailed quantitative studies are available for any species of Accipitriformes. We investigated the effects of egg-laying intervals and parental behavioral incubation patterns during egg-laying on hatching asynchrony in the Red-shouldered Hawk. We used 24-hr/d digital color/infrared video cameras at 15 Red-shouldered Hawk nests to record egg-laying and hatching, and to quantify the proportion of time parents spent incubating, standing, or absent from the nest. The mean egg-laying interval was 2.9 ± 0.1 d or 69.8 ± 2.2 hr (range = 65.8 – 74.2 hr), and the mean duration of incubation (from the onset of full incubation to hatch) for last-laid eggs was 33 d (32–34 d, n = 15). Red-shouldered Hawks exhibited partial incubation behavior, with the delay in the onset of full incubation varying by clutch size and among individuals; full incubation generally began with or just after the laying of the penultimate egg of the clutch. The mean interval between the hatching of the first and second egg was 0.56 ± 0.49 d; between the second and third eggs, 1.24 ± 0.71 d (P = 0.0215); and between the third and fourth eggs, 2.42 ± 0.38 d (P <0.0004). The total amount of time parents at each nest spent incubating during the egg-laying period explained most of the variation in the amount of time between the hatching of their first and last egg (the hatching span; r2 = 0.83, P <0.0001). Hatching patterns were the result of both the egg-laying intervals and the pattern of partial incubation, which may represent an adaptive mechanism to reduce the hatching interval while maintaining the hatching asynchrony.
The diversity of micro-habitats in tropical wetlands allows the coexistence of several species. These sympatric species interact with each other, either directly or indirectly, to optimally use the available resources. They achieve this through niche separation or minimal overlap to avoid competition. India’s wetland ecosystems are home to various sympatric species, such as the Great Egret Ardea alba (GE), Median Egret Ardea intermedia (IE), Little Egret Egretta garzetta (LE) and Cattle Egret Bubulcus ibis (CE). These egret species are closely related, and as a result, have similar niche requirements, which could lead to high intra-specific competition. However, there have been few studies on how these species utilize resources. This study aims to understand the possible mechanisms that enable the coexistence of these species in a tropical wetland. We have examined habitat characteristics, feeding behaviour, timings of seasonal and daily activities, and spacing patterns to evaluate possible models of species coexistence. We discovered that these four sympatric egret species have differences in microhabitat selection, activity patterns, both daily and seasonally, and feeding preferences. The study further indicates that there is a relationship between the niche dimensions, but it is only partially dependent on each other.
In some species, siblings aggressively compete for limited resources. Such aggressive competition can affect siblings’ survival probabilities and hence the reproductive success of their parents. Therefore, parents should have an incentive to reduce such aggressive interactions. Here, I report for the first time mother interference towards aggressive sibling competition in the shell-brooding cichlid Lamprologus ornatipinnis. The mother approached the fighting juveniles vigorously and chased them around. Consequently, severe fighting between the two juveniles was halted. I discuss the function of this maternal interference behaviour towards sibling aggression in comparison to mammal and bird species. This first observation bears the potential to inspire future research on parental interference toward sibling aggression in a hitherto overlooked group of brood-caring vertebrates.
Food represents a limiting resource for the growth and developmental progression of many animal species. As a consequence, competition over food, space, or other resources can trigger territoriality and aggressive behavior. In the monarch butterfly, Danaus plexippus, caterpillars feed predominantly on milkweed, raising the possibility that access to milkweed is critical for growth and survival. Here, we characterize the role of food availability on aggression in monarch caterpillars and find that monarch caterpillars display stereotyped aggressive lunges that increase during development, peaking during the fourth and fifth instar stages. The number of lunges toward a conspecific caterpillar was significantly increased under conditions of low food availability, suggesting resource defense may trigger aggression. These findings establish monarch caterpillars as a model for investigating interactions between resource availability and aggressive behavior under ecologically relevant conditions and set the stage for future investigations into the neuroethology of aggression in this system.
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