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In mammals, birth mass is an important predictor of early growth and survival. Within litters, heavier siblings are usually able to outcompete smaller siblings and gain more resources, thereby often permanently shaping phenotypic development. Early body size and growth are particularly important for later fitness. Only few studies investigated if and how differences within the early family environment contribute to long-term variation in fitness among individuals. We quantified if initial differences in size translate to size differences in adulthood and whether birth mass, relative size within the litter, litter size or the litter sex-ratio affect maturation and reproductive output of female wild cavies (Cavia aperea). Initial differences in mass were maintained until animals reached maximum adult mass at two years of age. Heavier sisters matured earlier and invested more into their first litter than smaller sisters, presumably because smaller sisters invested more into their own growth during the first pregnancy. Growing up in mixed-sexed litters in comparison to female-only litters slowed down maturation in smaller but not the heaviest female within a litter and had no effect on female reproductive effort. Variation in reproduction of multiparous females was to a lesser extent explained by the initial relative size of siblings. Offspring survival to independence was high but slightly lower when mothers had been born as smaller sisters. Our results demonstrate that factors of the early family environment not only affect immediate offspring development but lead to long-term fitness consequences. Significance: Environmental conditions during an individuals' early life can have profound long-term consequences. For many animals, siblings represent one of the most important components of the early social environment during development, with larger siblings typically being competitively superior. We here show for the cavy (Cavia aperea) that such early sibling differences affect the timing and investment into first reproduction and potential life-long fitness in a precocial mammal. Initial size differences between siblings persist long into adulthood. Heavier sisters matured earlier than their smaller sisters and invested more into the first litter. Initial size differences among siblings even explained variation in later reproduction. In conclusion, the slight advantage gained by larger relative size within a litter explains a substantial part of individual differences in lifetime fitness. [ABSTRACT FROM AUTHOR]

Siblings compete for limited parental resources, which can result in a trade-off between family size and child growth outcomes. Welfare incentives may improve parental circumstances in large families by compensating for the additional costs of an extra child and increasing the resources available to a family. The improvements in conditions may influence parents to increase their investment, expecting greater returns from the investment in child survival and development, while in turn increase sibling competition for the investment. This study assessed whether welfare benefits have influenced parental investment trade-offs and competition between siblings among Serbian Roma, a population largely dependent on welfare. Using data from the UNICEF Multiple Indicator Cluster Survey 6, this study assessed the associations between maternal investment, child cash benefits, sibship size, and child anthropometry, as an indicator of health, among 1096 Serbian Roma children aged 0 to 59 months. Living in a small family benefited Roma children, while the incentives increased competition between siblings. Maternal investment was negatively associated with incentives, as the improvements brought about were insufficient to influence a change in maternal perceptions about the local setting uncertainty and thus promote an increase in investment. [ABSTRACT FROM AUTHOR]

Family life often involves interactions between individuals who have different fitness goals, leading to conflict. Resolution of this conflict is key for the stabilisation of family life. Here, we used a lizard, Liopholis whitii, that lives in facultative family groups to characterise the nature and extent of sibling conflict and test the role that individual and litter characteristics play in shaping conflict between family members. We found significant variation in conflict between family groups, specifically in relation to siblings. In approximately half of the litters, siblings were aggressive towards one another, while in the other half of litters, there was no aggression observed between siblings. There were no differences between aggressive and non-aggressive litters in the key factors predicted to mediate conflict, including sex, offspring size, or litter size. However, in aggressive litters, the maximum amount of within-litter conflict decreased with an increase in the spread between births of siblings. First-born offspring were significantly more likely to be aggressive towards their siblings compared to second and third born offspring. While one offspring was usually the target of that aggression, we found no evidence that any individual-level factor predicted who received aggression. In aggressive litters, aggressive offspring spent a greater amount of time with their mother compared to non-aggressive offspring. Similar asymmetries in the amount of time offspring spent with their mother between siblings were also observed in non-aggressive litters. Combined, our results suggest that birth order is the main driver of sibling conflict in aggressive litters in this facultatively social lizard species, suggesting that birthing asynchrony may provide females with a mechanism to manage conflict. Significance statement: Conflict is a ubiquitous aspect of family life; it occurs between adults, between parents and offspring as well as between siblings. We show that the extent of conflict between siblings varies considerably within and between families in a lizard that exhibits prolonged associations between parents and offspring. We found no effects of offspring sex or size on within or between litter conflict. Instead, the number of days that passed between the birth of offspring appears to be the main factor that influences how much conflict there is between siblings. Furthermore, birth order was the main factor predicting which offspring was dominant. Combined this suggests that birthing asynchrony, the ability of females to spread out births across multiple days, may play a crucial role in the management of conflict in this system. As the moderation of conflict is crucial for the stabilisation of family life, these results provide important insights into the early evolution of social life. [ABSTRACT FROM AUTHOR]

Because of ongoing rapid climate change, many ecosystems are becoming both warmer and more variable, and these changes are likely to alter the magnitude and variability of natural selection acting on wild populations. Critically, changes and fluctuations in selection can impact both population demography and evolutionary change. Therefore, predicting the impacts of climate change depends on understanding the magnitude and variation in selection on traits across different life stages and environments. Long-term experiments in wild settings are a great opportunity to determine the impact of environmental conditions on selection. Here we examined variability in the strength of selection on size traits of nestling black-legged kittiwakes (Rissa tridactyla) in a 25-year study including a food supplementation experiment on Middleton Island in the Gulf of Alaska. Using mixed effect models, we examined the annual variability of stage-specific and resource-specific selection gradients across 25 years. We found that (a) larger and heavier hatchlings were the most likely to survive during early ontogeny, (b) non-food supplemented younger nestlings in a brood experienced the strongest selection, and (c) warmer conditions increased the magnitude of selection on nestling mass and affected non-food supplemented and second-hatched nestlings the most. Our results suggested that variable resource dynamics likely caused some of the changes in selection from year to year and that warming conditions increased the strength of selection on subarctic seabird growth. However, our experimental manipulation revealed that local environmental heterogeneity could buffer the selection expected from broader climatic changes. Consequently, understanding the interactive effects of local conditions and general changes in climate seems likely to improve our ability to predict future selection gradients. [ABSTRACT FROM AUTHOR]

Familial conflict, including parent–offspring conflict (POC) and sibling competition (SC), occurs when an individual maximizes its access to a limiting resource at the expense of a related individual. The role of familial conflict for competition over space as a limited resource remains relatively unexplored. In this study, we examined how familial conflict affects natal dispersal and settlement decisions of a solitary mammal, the brown bear, Ursus arctos , and tested whether these settlement patterns covary with fitness. First, we tested whether the distance settled from the natal range was affected by aspects of POC (litter type: single versus multiple; mother's age; mother's living status) and SC (settled near versus far from the natal home range, body size). We then modelled how distance settled from the natal range influenced three measures of fitness: survival to reproduction, lifetime reproductive success and lifetime survival. In line with POC, we found that daughters settled twice as far from the natal range when their mother was alive than when she was dead. We found strong evidence for SC where in sibling pairs, the 'near' sister settled nearly three times closer to the natal range than her sibling. We found contradictory patterns in fitness outcomes based on settlement distance, such that females settling closer to the natal range had higher lifetime survival but were less likely to successfully wean at least one offspring. Despite survival advantages gained by settling closer to the natal range, there was no evidence that settlement distance influenced lifetime reproductive success. Fitness outcomes in this population may be influenced more by factors related to annual hunting than by familial conflict or proximity to the natal range. • Differences in settlement patterns of female bears suggest parent-offspring conflict. • Larger siblings settle closer to the natal range, a sign of sibling competition. • Female brown bears settling closer to the natal range have higher lifetime survival. • Annual harvest may disrupt fitness patterns in brown bears. [ABSTRACT FROM AUTHOR]

Brood parasites have demanding needs of host resources. Brood parasitic offspring are highly competitive and frequently cause the failure of host broods and the survival of a single parasitic offspring. Accordingly, virulent brood parasites lay a single egg in the same host nest to avoid sibling competition. In the cuckoo catfish (Synodontis multipunctatus), which parasitize mouthbrooding cichlid fishes in Lake Tanganyika, the modes of host and parasite oviposition lead to frequent cases of multiple parasitism. We experimentally tested the prediction that multiple parasitism leads to frequent cannibalism among offspring. Cuckoo catfish embryos prey upon host offspring to obtain nourishment during their 3-week development in the host buccal cavity and may also consume conspecific embryos. The potential benefits of cannibalism in the system are, therefore, twofold; to decrease competition for limited resources (i.e. host brood with rich yolk sacs) and to directly obtain nourishment by consuming rivals. We found that cannibalism indeed provided measurable benefits in terms of increased growth of the cannibals, but cannibalism was rare and typically occurred once all host offspring had been consumed. This implies that cannibalism among cuckoo catfish embryos emerges to mitigate starvation rather than eliminate competition. [ABSTRACT FROM AUTHOR]

Early life for animals is often a time of rapid growth and development. In a resource-limited environment, life history theory predicts that there must be trade-offs between resource sinks in ways that optimize future survival and reproductive success. Telomeres have emerged as putative indicators of these early life trade-offs, but there are conflicting accounts as to how developmental traits and conditions impact telomere length and dynamics. For 2 years, we studied the nestlings of a breeding population of barn swallows from day 6 to day 12 of life, measuring various ontogenetic factors to understand to what extent they explain variation in telomere length and dynamics. We unexpectedly found that telomeres lengthened between the two sampling points. Nestlings in large broods had shorter telomeres, but surprisingly, individuals that grew faster from day 6 to day 12 had longer telomeres and more telomere lengthening. Nestlings with higher mass relative to their nestmates on d6 had shorter telomeres, suggesting that the relatively fast growth barn swallows experience early in development is more costly than the relatively slower growth later in development. These effects were only found in the first year of study. Telomere lengthening may be due to the initiation of new hematopoietic cell lines during development or the expression of telomerase early in life. Favorable early life conditions and high parental investment could allow for more growth with little to no cost to telomere length or dynamics. [ABSTRACT FROM AUTHOR]

While delaying natal dispersal can provide short-term benefits for juveniles, lifetime fitness consequences are rarely assessed. Furthermore, competition for limited positions on a natal territory could impose an indirect fitness cost on the winner if the outcome has negative effects on its siblings. We use radio-tracking and 58 years of nesting data in Ontario, Canada to examine the lifetime fitness consequences of sibling expulsion in the Canada jay (Perisoreus canadensis). Six weeks after fledging, intra-brood dominance struggles result in one 'dominant juvenile' (DJ) remaining on the natal territory after expelling its subordinate siblings, the 'ejectees' (EJs). Despite an older age-at-first-reproduction, DJs produced more recruits over their lifetime and had higher first-year survival than EJs, leading to substantially higher direct fitness. Even though DJs incurred an indirect fitness cost by expelling their siblings and there was no evidence that their presence on the natal territory increased their parents' reproductive output the following year, they still had substantially higher inclusive fitness than EJs. Our results demonstrate how early-life sibling conflict can have lifetime consequences and that such fitness differences in Canada jays are driven by the enhanced first-year survival of DJs pursuant to the early-summer expulsion of their sibling competitors. [ABSTRACT FROM AUTHOR]

Aggression represents the backbone of dominance acquisition in several animal societies, where the decision to interact is dictated by its relative cost. Among siblings, such costs are weighted in the light of inclusive fitness, but how this translates to aggression patterns in response to changing external and internal conditions remains unclear. Using a null-model-based approach, we investigate how day-to-day changes in food provisioning affect aggression networks and food allocation in growing red kite (Milvus milvus) nestlings, whose dominance rank is largely dictated by age. We show that older siblings, irrespective of age, change from targeting only close-aged peers (close-competitor pattern) when food provisioning is low, to uniformly attacking all other peers (downward heuristic pattern) as food conditions improve. While food allocation was generally skewed towards the older siblings, the youngest sibling in the nest increased its probability of accessing food as more was provisioned and as downward heuristic patterns became more prominent, suggesting that different aggression patterns allow for catch-up growth after periods of low food. Our results indicate that dynamic aggression patterns within the nest modulate environmental effects on juvenile development by influencing the process of dominance acquisition and potentially impacting the fledging body condition, with far-reaching fitness consequences.

Kin selection theory predicts that individual progeny members, in species where offspring share depreciable parental care, should increasingly attempt to monopolize resources provided by the parents as their relatedness to brood competitors declines. Although the level of relatedness among broodmates is often variable in vertebrates, whether it affects within-brood competition dynamics has seldom been studied. We tested this prediction in nestlings of the lesser kestrel, Falco naumanni , a cavity-nesting colonial raptor that can breed in high-density colonies, where nestlings often move between nearby nests, generating mixed parentage among broodmates. Pairs of nestlings composed of either unrelated, unfamiliar individuals or siblings were experimentally forced to compete for food. Nestlings stole prey more frequently when competing with an unrelated, unfamiliar competitor than when competing with a sibling. This finding adds to the limited evidence that rivalry among broodmates is affected by their relatedness, suggesting that kin recognition and kin selection may play an important role in determining individual competitive strategies and care allocation in multiparous species. • Coloniality favours the occurrence of mixed kinship broods. • Competition for food should differ between siblings and unrelated offspring. • We tested this prediction in mixed kinship lesser kestrel broods. • Prey thefts were more frequent when competitors were unrelated. • Kin selection affects competitive behaviour in altricial avian offspring. [ABSTRACT FROM AUTHOR]

Light is a salient and variable ecological factor that can impact developmental trajectories of vertebrate embryos, yet whether prenatal light environment can act as an anticipatory cue preparing organisms to cope with postnatal conditions is still unclear. In asynchronous birds, last-laid eggs are particularly exposed to sunlight as parental incubation behavior becomes intermittent after the hatching of senior chicks. Here, we explore whether natural variations in prenatal light exposure shape the distinctive phenotype showed by last-hatched chicks of a semi-precocial seabird, the yellow-legged gull (Larus michahellis), potentially preparing them to cope with the postnatal competitive context. To do this, we manipulated the amount of light received by last-laid eggs (within a natural range) during last stages of embryonic development. Prenatal exposure to light cues promoted the development of the resilient "junior phenotype" exhibited by last-hatched gull chicks, characterized by accelerated hatching, increased begging behavior and a slower growth rate. These developmental and behavioral adjustments were accompanied by down-regulation of genes involved in metabolism and development regulation (SOD2 and TRalpha), as well as changes in the HPA-axis functioning (lower baseline corticosterone and robust adrenocortical response). Junior chicks exposed to light cues during the embryonic development showed longer telomeres during the early postnatal period, suggesting that light-induced adjustments could allow them to buffer the competitive disadvantages associated with hatching asynchrony. Our study provides evidence that postnatal junior phenotypes are, at least in part, prenatally shaped by light cues that act during a critical temporal window of developmental sensitivity. [ABSTRACT FROM AUTHOR]

The benefits of parental care are often seen as a cornerstone of family life evolution. However, recent studies show that sibling interactions can also confer substantial benefits to juveniles. Here, we tested a new hypothesis suggesting that the need for juveniles to access sibling interactions may encourage juveniles to remain in a family group, thereby consolidating the early stages of family life evolution when parental care is facultative. We set up juveniles of the European earwig, Forficula auricularia (a family-living insect in which maternal care is facultative and juveniles can forage for themselves and cooperate with siblings) either alone, with siblings, or with siblings and their mother, and then quantified effects on the development, morphology and four fitness-related behaviours of the resulting adults. We found that isolated juveniles reached adulthood more quickly and that these adults were overall larger but showed impaired aggregation behaviour when compared with juveniles raised together with siblings or with siblings and their mother. By contrast, sibling deprivation did not affect offspring survival, male forceps length (an ornament involved in reproductive success) and three other behaviours in adults (boldness, general activity and exploration). All these results were independent of adult sex, although females overall reached adulthood earlier and were larger than males. Altogether, our findings suggest that the potential benefits of sibling interactions measured in this study play a minor role in the maintenance of earwig family life. They also emphasize the need to study the evolutionary drivers of family life in species where all members can switch from family to solitary life, a scenario that probably prevailed in the early evolution of sociality. • Do the benefits of sibling interactions support the maintenance of family life? • We addressed this question by testing the effects of sibling deprivation in earwigs. • We found that it produces adults with impaired aggregation and faster development. • But it has no effect on survival and three other fitness-related behaviours. • This questions the role of sibling interactions in the emergence of family life. [ABSTRACT FROM AUTHOR]

Being one of Freud's most famous contributions to psychoanalysis, the Oedipus complex is still a topic of heated interest. It has been disputed in many different disciplines ranging from anthropology to biology. This theoretical paper aimed to explain the phenomena that are represented by children's affectionate and assertive attitudes towards their parents, named as the Oedipus complex by some, in terms of parent–offspring conflict, sibling competition, and infanticide. All of these evolutionary biological concepts or their combination could conceive specific relational settings similar to those emerging in the Oedipus complex. Psychoanalysis surely acknowledges the effects of parent–offspring conflict or sibling dynamics on familial relations and character formation. Nevertheless, they have been generally overshadowed by other primary theoretical concepts. Considering the findings from evolutionary biology and developmental psychology, it was asserted that parent–offspring conflict and sibling dynamics must be included in the conceptualization of oedipal-like behaviors. In light of these hypotheses, related literature and suggestions for further studies were discussed. [ABSTRACT FROM AUTHOR]

The influence of inclusive fitness interests on the evolution of human institutions remains unclear. Religious celibacy constitutes an especially puzzling institution, often deemed maladaptive. Here, we present sociodemographic data from an agropastoralist Buddhist population in western China, where parents sometimes sent a son to the monastery. We find that men with a monk brother father more children, and grandparents with a monk son have more grandchildren, suggesting that the practice is adaptive. We develop a model of celibacy to elucidate the inclusive fitness costs and benefits associated with this behaviour. We show that a minority of sons being celibate can be favoured if this increases their brothers' reproductive success, but only if the decision is under parental, rather than individual, control. These conditions apply to monks in our study site. Inclusive fitness considerations appear to play a key role in shaping parental preferences to adopt this cultural practice. [ABSTRACT FROM AUTHOR]

Post-natal growth has long-term consequences for survival and fitness in birds and is subject to strong directional selection. Highly variable patterns of nestling development are influenced by an array of extrinsic and intrinsic factors. This study analysed the impacts of hatching order, nestling subperiod, brood size and weather conditions, all of which could influence the growth rate of Marsh Harrier Circus aeruginosus nestlings. It was conducted over a period of 6 years, during which measurements of 173 nestlings from 66 nests were made at fishpond complexes in eastern Poland. Relative growth rates (RGR) were calculated on the basis of tarsus and wing lengths during two subperiods of nestling development. Linear mixed models showed that the hatching order and nestling subperiod influenced nestling growth, whereas brood size did not affect wing or tarsus relative growth rates. The effect of hatching order differed between the two traits and between subperiods. Marginal nestlings in broods of five exhibited poor wing growth and perished before fledging. In contrast to wing growth, tarsus growth rates were similar in all the siblings in the first subperiod. During the second developmental subperiod, the growth rates of both locomotor traits exhibited the same pattern, i.e., higher values in the later-hatched chicks than in the earlier ones. Precipitation, but not temperature, had a negative impact on growth in the second subperiod. Our results show a variation in growth patterns between nestmates, which was the most evident in the rate of wing growth. The study enhances our understanding of brood reduction and cainism in birds of prey. [ABSTRACT FROM AUTHOR]

Although cranial morphology of modern birds has been an important subject of evolutionary studies, detailed information on postnatal ontogeny of the avian skull remains very scarce. Herein, a wild population of the black‐tailed gull (Larus crassirostris) breeding on Kabu Island was examined to explore relationships between their growth strategies and ontogenetic changes in the cranial shape. By examining growth series covering a major part of the postnatal ontogenetic period, it was clarified that the typical form of the adult larid skull was produced through dynamic proportional changes among cranial structures after hatching. Cranial structures related to the oral capacity and deglutition (e.g., some elements of hyoid bones) attained the adult sizes before fledging, whereas other structures apparently reached the adult sizes well after leaving the nest. The palatal width exhibited positively allometric growth against the skull volume in chicks in the early nestling stage, followed by a period of negative allometry in the later growth stage. A nestling gull has to acquire swallowing ability by the time of fledging at the latest because this ability is apparently essential for a food intake without parental aid. In addition, because nestlings mainly feed on foodstuffs supplied by their parents, previous studies suggested the possibility that siblings within a nest compete for food resources. Under this scenario, early acquisition of swallowing abilities, as indicated by the allometric patterns of relevant cranial structures, may be an adaptive trait that enhances survival of nestlings. [ABSTRACT FROM AUTHOR]

The growth pattern of an organism is influenced by multiple factors, such as its sex, parental investment, food abundance and sibling competition. For species showing sexual size dimorphism, the sex of siblings is expected to affect the growth of nestlings through differences in competitive hierarchies mediated by an asymmetry in body size. This study describes growth curves of Ryukyu Scops Owl Otus elegans nestlings, based on the analysis of body mass, wing length and tarsus length in 99 individuals. We subsequently tested for effects of sex of the nestlings, having an older male sibling, hatching order and brood size on the growth curves. Overall, we detected significant effects of several predictor variables, although differences between groups were often small. Males and later hatched chicks had lower body mass throughout their growth. The smaller the brood, the heavier the chicks were on days 0–1 and 30–32, although this relationship was reversed on days 8–13. Males and later hatched chicks also had shorter wings. Males had shorter tarsi than females from day 0 to day 4, however, dimorphism in this trait was reversed afterwards. Chicks in a large brood had longer tarsi. Earlier hatched chicks had longer tarsi in the first half of the growth period, but some of this difference had disappeared by the second half. From day 0 to day 3, individuals with an older brother had longer tarsi than those with an older sister. However, halfway through the growth period and thereafter, individuals with an older brother had shorter tarsi than those with an older sister. The fact that older brothers had an effect on the tarsus growth of their siblings was not due to sexual body size asymmetry, as in fact males were smaller than females in wing length and body size. We suggest that sexual differences in aggression mediated by androgens may have played a role. [ABSTRACT FROM AUTHOR]

Widespread recognition of the contribution of individual differences in behavioral phenotype to evolutionary processes raises questions as to their developmental origin: when and in what contexts such differences emerge and what aspects of the developmental environment contribute to these? We studied individual differences among littermates of the domestic cat Felis silvestris catus when competing for meat at weaning, a challenging period in mammalian development. During postnatal weeks six, seven, and eight, we tested 67 weanling kittens (40 males, 27 females) from 16 litters of mixed breed cats maintained as part of a free-ranging breeding colony. Twice a week, we tested the kittens' behavior after they were food deprived and presented together with their siblings for 2 min with a highly palatable food, a piece of raw beef. We found stable individual differences among littermates across 3 weeks of testing in latency to reach the meat, time spent eating from it, time spent monopolizing it, and number of aggressive behaviors directed toward littermates. There was no effect of sex on any of the behavioral measures. However, kittens with lower body mass at birth (and then also lower body mass at the age of testing) relative to their littermates competed more vigorously and successfully for the meat than their heavier siblings. This suggests the importance of motivational factors arising during early development in shaping individual differences in behavior such as among littermates in the present study, when competing for a biologically relevant resource. Significance statement: In polytocous mammals, body mass at birth is a good predictor of growth and survival, with heavier young relative to their littermates usually obtaining a greater share of resources such as the mother's milk. It is therefore often assumed that this advantage will translate into differences in behavior in other contexts, such that heavier littermates will gain more resources at later life stages by showing a more aggressive, "dominant" behavioral style. The findings of the present study challenge this view by demonstrating that in the domestic cat, lighter littermates were more competitive in obtaining meat at weaning. We suggest that differences in the motivational state of individuals should also be considered when accounting for the early development of individual differences in behavior, including among littermates, and may contribute to what might be broadly considered an individual's personality or behavioral style. [ABSTRACT FROM AUTHOR]

Evolutionary theory suggests that individuals can benefit from deferring the fitness cost of developing under poor conditions to later in life. Although empirical evidence for delayed fitness costs of poor developmental conditions is abundant, individuals that die prematurely have not often been incorporated when estimating fitness, such that age‐specific fitness costs, and therefore the relative importance of delayed fitness costs are actually unknown.We developed a Bayesian statistical framework to estimate age‐specific reproductive values in relation to developmental conditions. We applied it to data obtained from a long‐term longitudinal study of common terns Sterna hirundo, using sibling rank to describe variation in developmental conditions. Common terns have a maximum of three chicks, and later hatching chicks acquire less food, grow more slowly and have a lower fledging probability than their earlier hatched siblings.We estimated fitness costs in adulthood to constitute c. 45% and 70% of the total fitness costs of hatching third and second, respectively, compared to hatching first. This was due to third‐ranked hatchlings experiencing especially high pre‐fledging mortality, while second‐ranked hatchlings had lower reproductive success in adulthood. Both groups had slightly lower adult survival. There was, however, no evidence for sibling rank‐specific rates of senescence.We additionally found years with low fledgling production to be associated with particularly strong pre‐fledging selection on sibling rank, and with increased adult survival to the next breeding season. This suggests that adults reduce parental allocation to reproduction in poor years, which disproportionately impacts low‐ranked offspring.Interpreting these results, we suggest that selection at the level of the individual offspring for delaying fitness costs is counteracted by selection for parental reduction in brood size when resources are limiting. [ABSTRACT FROM AUTHOR]

I present a model for the evolution of a seed bank in the absence of externally driven environmental variation. I use Evolutionarily Stable Strategy (ESS) analyses of both analytic and simulation models to assess the conditions under which a dormant genotype can invade and resist invasion. In my models, plant seeds compete through lottery for discrete safe sites holding one individual each. Analyzing the conditions under which a dormant genotype can invade when rare and resist invasion once established, I conclude that dormancy can be an ESS when some fraction of seeds is retained locally, seed bank survival is high, and mortality in the seed bank is low. The advantage of dormancy stems from the ability of dormant seeds to recapture a lost site and the fact that a plant’s offspring are more likely to win the lottery in its own site than in any new site. The advantage of dormancy does not depend on individual fecundity or on low relatedness with the offspring of kin, making this mechanism distinct from earlier models of sib competition.

The number of conspecifics present during the juvenile stages can have profound consequences on development rates and adult body size, traits often closely related to fitness. Conspecifics can have direct negative effects on each other due to resource competition, and also direct positive effects due to benefits like improved thermoregulation. We investigated morphological and developmental consequences of juvenile group size in the leaf-footed cactus bug Narnia femorata (Hemiptera: Coreidae). These insects are ideal to test the consequences of social environment during development because nymphs naturally aggregate in groups of varying size. Furthermore, the sexual dimorphism of this species allowed us to test for sex-specific effects of developmental density. Males possess enlarged hind legs used as weapons in male-male contests, yet females are physically larger. We found insects from smaller groups had 43% higher mortality than those from the larger groups. On average, adult body and hind leg sizes did not differ across densities for either sex. Interestingly, we found that those first to mature into adults within a sibling group became the largest adults. The largest, fastest males to adulthood also wielded the biggest weapons due to the positive allometry of this trait. [ABSTRACT FROM AUTHOR]

When eggs hatch asynchronously, offspring arising from last-hatched eggs often exhibit a competitive disadvantage compared with their older, larger nestmates. Strong sibling competition might result in a pattern of resource allocation favoring larger nestlings, but active food allocation towards smaller offspring may compensate for the negative effects of asynchronous hatching. We examined patterns of resource allocation by green-rumped parrotlet parents to small and large broods under control and food-supplemented conditions. There was no difference between parents and among brood sizes in visit rate or number of feeds delivered, although females spent marginally more time in the nest than males. Both male and female parents preferentially fed offspring that had a higher begging effort than the remainder of the brood. Mean begging levels did not differ between small and large broods, but smaller offspring begged more than their older nestmates in large broods. Male parents fed small offspring less often in both brood sizes. Female parents fed offspring evenly in small broods, while in large broods they fed smaller offspring more frequently, with the exception of the very last hatched individual. These data suggest male parrotlets exhibit a feeding preference for larger offspring—possibly arising from the outcome of sibling competition—but that females practice active food allocation, particularly in larger brood sizes. These differential patterns of resource allocation between the sexes are consistent with other studies of parrots and may reflect some level of female compensation for the limitations imposed on smaller offspring by hatching asynchrony.

To resolve conflicts over limited resources, animals often communicate about their motivation to compete. When signals are transient, the resolution of conflicts may be achieved after an interactive process, with each contestant adjusting its signaling level according to the rival's behavior. Unfortunately, the importance of the real-time signal adjustment in conflict resolution remains understudied, especially using experimental approaches. Here we developed a novel “automatic interactive playback” that interacts real-time with a live individual. It allowed us to experimentally test the efficacy of different behavioral strategies to dominate conflicts in nestling barn owls (Tyto alba). In this species, nestlings vocally negotiate for priority access to the impending food item in the absence of parents. Two opposite vocal strategies were tested for their prospects of success: under the “matching” vs. “mismatching” strategy, the playback behaves in the same vs. opposed way as the nestling, respectively. We evaluated how these two strategies affected the two main negotiation parameters: call duration and call rate. We found that the best strategies to reduce the nestling's vocalizations and hence dominate the negotiation are to match the call duration of the opponent and to mismatch its call rate. However, the latter strategy is the only one that allowed the playback to dominate the vocal interaction by inducing the opponent to become totally silent. Therefore, to prevail in a negotiation session, barn owl nestlings should delay the transmission of signals rather than simultaneously escalate vocalizations as commonly observed in animal competitive interactions. In addition, we showed that matching call duration and mismatching call rate require a larger investment by the playback, in terms of number and duration of calls, than the less effective strategies. Assuming that vocalizations are costly, this suggests that such behavioral strategies are honest. Our results highlight the importance of real-time signaling adjustment in communication processes over resource competition and emphasize the power of using interactive playback settings to investigate conflict resolution in animals.

Maternal and environmental effects can have profound effects on offspring performance by generating variation in offspring phenotypes, independent of genetic effects. Within avian broods, differential maternal investment of resources across the laying sequence is thought to be an adaptive strategy to modulate competitive hierarchies induced by hatching asynchrony. In this study, we evaluated the relative importance of maternally derived within-clutch variation and the asymmetric post-hatching environment for growth and survival of common tern (Sterna hirundo) siblings. We experimentally manipulated hatching order, resulting in chicks from last-laid eggs hatching first and vice versa. Although both initial age and size asymmetries were larger within experimental than control broods, the early survival of last-hatched chicks was similar between groups. Initial positive effects of egg size disappeared as siblings approached fledging. Ultimately at fledging, both within-brood growth and cumulative survival patterns were similar between experimental and control broods, suggesting that the effects of systematic variation of egg constituents (e.g., maternally derived yolk hormones) and egg size are too subtle and largely overwhelmed by the effects of hatching asynchrony. Therefore, we conclude that variation in offspring phenotypes is pre-dominantly determined by the social environment experienced post-hatching. Maternal effects may further fine-tune phenotypic variation in response to varying environmental conditions, but this needs to be tested through empirical studies in which multiple maternal effects are measured simultaneously under different environmental conditions. [ABSTRACT FROM AUTHOR]

Earlier offspring mortality before independence saves resources for kin, which should be more beneficial when food is short. Using 24 years of data on age-specific common tern (Sterna hirundo) chick mortality, best described by the Gompertz function, and estimates of energy consumption per age of mortality, we investigated how energy wasted on nonfledged chicks depends on brood size, hatching order, and annual abundance of herring (Clupea harengus), the main food source. We found mortality directly after hatching (Gompertz baseline mortality) to be high and to increase with decreasing herring abundance. Mortality declined with age at a rate relatively insensitive to herring abundance. The sensitivity of baseline mortality to herring abundance reduced energy wasted on nonfledged chicks when herring was in short supply. Among chicks that did not fledge, last-hatched chicks were less costly than earlier-hatched chicks because of their earlier mortality. However, per hatchling produced, the least energy was wasted on chicks without siblings because their baseline mortality was most sensitive to herring abundance. We suggest that earlier mortality of offspring when food is short facilitates economic adjustment of posthatching parental investment to food abundance but that such economic brood reduction may be constrained by sibling competition. [ABSTRACT FROM AUTHOR]

Siblings often compete for limited resources, particularly food provided by their parents. Such competition is usually nonviolent, but direct aggression has evolved in some species. However, there is little knowledge about sibling aggression in species without parental provisioning. Here, we investigated sibling aggression in the cichlid Neolamprologus furcifer in Lake Tanganyika, Zambia. In this species, females guard their broods in the nest but do not provide any food. Early-stage fry did not show any sibling aggression while foraging on plankton, but began to show nonlethal aggression once they started to forage on small benthic shrimp at 2 weeks of age. The frequency of sibling aggression decreased at week 7, when the density of fry decreased remarkably. Sibling aggression also decreased following a short-term increase in food through supplemental feeding. The aggression was higher in the morning than in the afternoon despite higher abundance of shrimp at that time, and decreased when the number of shrimp in the nest was experimentally reduced. These results indicate that food availability affects sibling aggression of animals that do not exhibit parental provisioning. [ABSTRACT FROM AUTHOR]

In a food-limited system, parents may have to allocate resources in ways that do not benefit all their offspring equally. We investigated food allocation and parent and chick behaviours in Magellanic penguins at their colony in Punta Tombo, Argentina, by observing feedings in one- and two-chick broods after the chicks were more than 20 days of age. Feeds lasted 21 min on average, and the length of a feed was not correlated either with the number of chicks in a brood, or with the amount of food the parents gave. Parents with two-chick broods distributed food evenly to both chicks. Although single chicks were fed more than chicks with siblings, as a proportion of a chick's start weight, both single chicks and lighter chicks in two-chick broods received significantly more food than heavier chicks. Chicks continued begging after the last feed in nearly half of the two-chick broods, suggesting they were not sated and so are food-limited. In linear mixed-effects models that considered, respectively, the absolute amount of food a chick received and the amount of food it received as a proportion of its start weight, chick begging was the most significant predictor of how much it was fed. Jostling behaviours between the chicks did not correlate with the amount of food either one received. Parental nonfeeding behaviours in two-chick broods (e.g. bending towards a chick and opening the bill but not regurgitating food) were more frequently directed at the lighter chick, but did not correlate with the amount of food a chick received. These results suggest (1) parents are motived to feed their chicks quickly, (2) parents try to allocate food equally to chicks of this age and (3) chicks devote most of their energy trying to get fed by the parent, rather than competing antagonistically with one another. Highlights • We observed parental and chick behaviour of Magellanic penguins during feeds. • Parents distributed food equally between heavier and lighter chicks >20 days old. • As a proportion of a chick's start weight, lighter chicks received more food. • A chick's begging was the most significant predictor of how much it was fed. • Chicks begged energetically for food but did not generally antagonize each other. [ABSTRACT FROM AUTHOR]

Interactions among siblings fall on a continuum with competition and cooperation at opposite ends of the spectrum. Prior work on the burying beetle Nicrophorus vespilloides suggests that parental care shifts the balance between competition and cooperation by masking a density‐dependent shift from cooperation to competition. However, these results should be interpreted with caution because they were based on correlational evidence for an association between larval density at dispersal and mean larval mass at dispersal. Here, we test for a causal effect of the initial density of larvae in a brood on the larvae's subsequent performance in the absence of care. We find no effect of the initial larval density on mean larval mass. Thus, our results provide no evidence for sibling cooperation in the absence of care in this species. However, using larval density at dispersal as a predictor of mean larval mass at dispersal, there was a significant correlation between larval density and mean larval mass. Our study highlights the importance of using experimental designs that exclude confounding effects due to shared environmental conditions that otherwise could be misinterpreted as evidence for sibling cooperation. [ABSTRACT FROM AUTHOR]

It is commonly observed in many bird species that dependent offspring vigorously solicit for food transfers provided by their parents. However, the likelihood of receiving food does not only depend on the parental response, but also on the degree of sibling competition, at least in species where parents raise several offspring simultaneously. To date, little is known about whether and how individual offspring adjusts its begging strategy according to the entwined effects of need, state and competitive ability of itself and its siblings. We here manipulated the hunger levels of either the two heaviest or the two lightest blue tit (Cyanistes caeruleus) nestlings in a short-term food deprivation experiment. Our results showed that the lightest nestlings consistently begged more than the heaviest nestlings, an effect that was overruled by the tremendous increase in begging behaviour after food deprivation. Meanwhile, the amplified begging signals after food deprivation were the only cue for providing parents in their decision process. Furthermore, we observed flexible but state-independent begging behaviour in response to changes in sibling need. As opposed to our expectations, nestlings consistently increased their begging behaviour when confronted with food deprived siblings. Overall, our study highlights that individual begging primarily aims at increasing direct benefits, but nevertheless reflects the complexity of a young birds' family life, in addition to aspects of intrinsic need and state. [ABSTRACT FROM AUTHOR]

Understanding the impressive interspecific variation in avian eggshell colouration has attracted the attention of evolutionary ecologists for more than a century. Several functional explanations predict positive covariation between eggshell pigmentation and phenotypic quality of nestlings. We test this prediction in spotless starlings Sturnus unicolor by using biometric measurements and telomere length of hatchlings and fledglings as proxies of phenotypic quality. Female spotless starlings lay immaculate blue‐green eggs, a sexually selected signal directed to males. Pigmentation predicts positive associations with concentration of antioxidants and testosterone in the yolk and with paternal provisioning effort during nestling growth. Eggshell pigmentation (blue‐green chroma) is not associated with telomere length of hatchlings, which suggests weak maternal effects on this trait. However, we find negative associations of eggshell colouration with both body condition and telomere length of fledglings. Moreover, we find positive associations between eggshell colouration and clutch size, which suggests that sibling competition is higher in nests with more coloured eggshells. Previous works demonstrated that level of sibling competition is positively related to telomere erosion and, thus, the detected negative associations between eggshell colouration, body condition and telomere length of fledglings would reflect higher level of competition in nests with more coloured eggshells. We therefore speculate with the possibility that females that lay larger clutches also lay more coloured eggshells that elicit increased paternal provisioning effort and, thus, raise larger broods at the expense of telomere erosion of their offspring. [ABSTRACT FROM AUTHOR]

The choice of stimuli used in tests of animal behaviour can have a critical effect on the outcome. Here we report two experiments showing how different foods influenced aggressive behaviour in competition tests at weaning among littermates of the domestic cat. Whereas in Experiment 1 canned food elicited almost no overt competition, a piece of raw beef rib elicited clearly aggressive behaviour among littermates. In Experiment 2 the food stimuli were chosen to differ from raw beef rib in various combinations of taste/smell, texture and monopolizability. Kittens showed different levels of aggression in response to the five stimuli tested, which suggests that the strong effect of beef rib in eliciting aggressive behaviour was due to a complex combination of features. We suggest that using stimuli approximating the evolved, functional significance to the species concerned is more likely to result in robust, biologically relevant behaviours than more artificial stimuli. [ABSTRACT FROM AUTHOR]

Altricial young are dependent on adults for protection and food, and they display nutritional need by begging to elicit feeding from parents. Begging at high levels can be energetically expensive and attract predators; thus, an individual must balance its nutritional needs with these potential costs. Further, because a parent is limited in the amount of food it can provide, begging can contribute to both parent-offspring conflict and sibling-sibling competition. Many extrinsic and intrinsic factors may contribute to begging behavior. One intrinsic factor of interest is corticosterone (CORT), a metabolic hormone hypothesized to play a role in regulating a nestling’s begging behavior. We investigated the hypothesis that increased exposure to CORT influences nestling begging behavior in an altricial species, the Florida scrub-jay ( Aphelocoma coerulescens ). We treated one nestling per treatment nest with a twice-daily dose of exogenous hormone via a CORT-injected waxworm, whereas a second individual received a vehicle-injected waxworm. We monitored individual nestling and adult behavior at all nests with the use of high-definition video cameras on several days during treatment. We found no difference in begging rate between CORT fed and vehicle fed nestlings within a treatment nest. Further, to determine whether CORT treatment had indirect effects on the entire brood, we monitored additional nests, in which nestlings were not manipulated. When treatment and controls were compared, overall begging rates of nestlings in treatment nests were greater than those in control nests. This result suggests that CORT treatment of an individual altered its behavior, as well as that of its siblings. [ABSTRACT FROM AUTHOR]

Mammals have developed a variety of suckling behaviours ranging from tenacious nipple attachment in some rodents and marsupials to once-a-day suckling in rabbit. However, a common feature of suckling that was found in many mammals is the suckling order, or a partial preference to suckle a particular teat (teat fidelity) or part of the udder (suckling preference). A lack of suckling order is observed only in a few mammals. In this article, the possible background of the presence or absence of suckling order in eutherian polytocous mammals is discussed either from the maternal investment or sibling competition point of view. Characteristics related to maternal investment in species in which the suckling order has already been studied at least partially, were classified using C4.5 algorithm (J48 classifier in Weka 3.8.1), and decision tree was built. In the context of sibling competition, an extensive form game (game theory) was predicted to show the optimal suckling strategy considering the basic relations among littermates in two situations (littermates of equal strength/dominance and littermates with different strength/dominance). Although no ultimate conclusion can be drawn, it appears that the suckling order is typical for species whose reproductive system requires a lower maternal investment (up to one litter/year, monogamy, biparental care, lower litter birth weight); and, it appears that the suckling order is inherent to the weaker (inferior) siblings. [ABSTRACT FROM AUTHOR]

Sex allocation models still fail to predict the complex sex ratio patterns in broods of vertebrates. A major problem when studying mother–brood interactions is the difficulty in disentangling hypotheses involving maternal preferences from processes that do not imply maternal manipulation. We studied maternal resource allocation in mixed-sex, same-sex and single-chick broods in the great bustard, Otis tarda . Females normally rear a single chick, and previous work has shown that maternal investment influences male more than female breeding success. Therefore, mothers of two-chick broods were assumed to be in good condition and candidates to show a preference for sons. Results showed that male chicks of mixed-sex broods remained close to the mother for twice as long as their sisters, and received double the number of maternal feedings. However, sex differences in maternal feeding rate disappeared when considering only simultaneous begging approaches from both siblings. Proximity to the mother and its interaction with begging approach intensity were the factors determining the higher begging success of male chicks. In single-chick broods, females did not receive fewer maternal feedings than males. Overall, our results suggest that female chicks of mixed-sex broods become outcompeted by their larger brothers, which remain close to the mother much longer, preventing their sisters from taking a larger share of maternal feedings. We conclude that mothers do not show a preference for feeding male over female chicks, and that the sex differences in feeding rate are determined by the higher food requirements of male chicks due to their sexually selected, much faster growth rates. The higher mortality of females in mixed-sex broods contrasts with the pattern of male-biased mortality typical in this species, and supports our interpretation of an asymmetric competitive ability of male offspring as the mechanism responsible for the sex bias in maternal expenditure. [ABSTRACT FROM AUTHOR]

Parental care is a limited resource which in many species is acquired by the offspring through begging behaviours and often causes competition between siblings. The Neotropical poison frog Ranitomeya variabilis provides a very specific form of parental care: because its tadpoles are cannibalistic males usually separate them from their siblings after hatching by transporting them singly to small water bodies. However, in some cases parents do not transport their tadpoles but let them all hatch into the same pool. Here, we investigate if abandoned tadpoles of R. variabilis actively seek parental care in form of transportation. We conducted experiments where tadpoles of the same clutch were presented with con- and heterospecific frogs, and both moving and non-moving frog models. Our results revealed that abandoned tadpoles actively approached all frogs and sometimes even climbed onto their backs. We suggest that this tadpole behaviour may function to allow tadpoles to escape sibling competition and cannibalism. Being the first (and possibly the only one) to leave the shared pool should give a tadpole a high survival advantage over its brood-mates. We further found that tadpoles did not approach artificial models, suggesting that these where either not natural enough or that tadpoles do not recognize frogs by visual or tactile cues but might use chemical or multiple stimuli. The latter is also the case in related egg-feeding species where tadpoles beg for food. We therefore discuss our results in relation to potential begging behaviours, as well as fixed action patterns and parent-offspring conflict, being potential questions opening up for future examinations regarding our findings. [ABSTRACT FROM AUTHOR]

Offspring often solicit, and compete for, limited parental care by elaborate begging behaviour. Kin selection theory predicts that competing offspring should modify the intensity of their begging depending on the degree of relatedness to their nest- or litter-mates., Empirical evidence in birds, which are a key model in the study of parent-offspring interactions, indeed indicates that a lower level of relatedness between offspring in the nest correlates with more intense begging (i.e. more 'selfish' behaviour). This implies that competing nestlings can recognize kin, but the mechanism underlying such discrimination is unclear. Birds have long been thought to mainly rely on visual and auditory cues in their social communication, but there is now growing evidence for the importance of olfactory cues too., To assess the potential importance of olfactory cues in modulating nestling begging behaviour, we experimentally tested in a free-living bird, the blue tit Cyanistes caeruleus, if nestlings discriminate and adjust their begging behaviour depending on their familiarity with a conspecific nestling odour stimulus., We found that individuals responded with longer and more intense begging bouts to an unfamiliar compared with a familiar odour stimulus., Our findings provide first evidence for a role of olfaction in modulating offspring begging behaviour in a wild bird population. Although our experiment cannot differentiate between the effects of familiarity and relatedness, it raises the interesting possibility that blue tit nestlings may also discriminate between odours of close kin and less related individuals, and adjust their begging behaviour accordingly. This hypothesis requires further testing., A is available for this article. [ABSTRACT FROM AUTHOR]

In this comparative article of European and American contexts, we investigate how siblings influence individuals’ access to marriage. We use a comparative and quantitative event history analysis approach to identify similarities and differences between the contexts studied. We find evidence in both contexts of customs that stipulated that siblings should marry in order of birth and also positive stimulative effects from married siblings on their unmarried counterparts, particularly in opposite-sex pairs. At the same time, we find evidence for negative effects as a consequence of recent marriages of siblings, demonstrating that sibling competition for access to marriage went on simultaneously. [ABSTRACT FROM AUTHOR]

Parents may feed nestlings based on positional cues resulting from sibling competition for favored positions at the front of a nest cavity, or they may assess begging intensity regardless of location within the nest. We independently manipulated proximity to the nest entrance and hunger level to determine whether western bluebird ( Sialia mexicana) parents favor hungrier nestlings or instead feed nestlings closest to the nest entrance. We used a balanced design to vary hungry and fed nestlings between the back and front of the nest box. We deprived half of the nestlings in each brood of food for an hour, and then, each nestling was constrained using Plexiglas dividers to a quadrant in the nest box. We videotaped inside the box to assess begging intensity and food delivery to individual nestlings. Hungry nestlings begged more intensely and received more food than fed nestlings, regardless of their proximity to the nest entrance. However, when delivering the first feed to nestlings, parents favored front nestlings over hungry nestlings, possibly due to a bias resulting from the manipulation, which involved replacing and rearranging nestlings after a 1-h period. Overall, parents did not favor nestlings in the front of the nest over those in the back. Parents therefore are able to distinguish hungrier nestlings and preferentially feed them under favorable environmental conditions, when brood reduction is uncommon. Significance statement: When parents choose which offspring to feed, they may assess begging signals, which can include movements and vocalizations that vary in intensity. Alternatively, cavity-nesting species may use simple rules such as favoring offspring that have pushed to the front of the nest. We conducted an experiment to determine whether western bluebird ( Sialia mexicana) parents would preferentially feed hungry nestlings over fed nestlings when Plexiglas dividers prevented competition and equalized the frequency with which hungry and fed nestlings were in the front versus back of the nest. After depriving half of each brood of food for an hour, we measured begging intensity and food delivery. Parents preferentially fed hungrier nestlings, which begged more intensely, regardless of their position in the nest, indicating that parents are able to distinguish between hungry and fed nestlings. [ABSTRACT FROM AUTHOR]

Aggression represents the backbone of dominance acquisition in several animal societies, where the decision to interact is dictated by its relative cost. Among siblings, such costs are weighted in the light of inclusive fitness, but how this translates to aggression patterns in response to changing external and internal conditions remains unclear. Using a null-model-based approach, we investigate how day-to-day changes in food provisioning affect aggression networks and food allocation in growing red kite ( Milvus milvus ) nestlings, whose dominance rank is largely dictated by age. We show that older siblings, irrespective of age, change from targeting only close-aged peers (close-competitor pattern) when food provisioning is low, to uniformly attacking all other peers (downward heuristic pattern) as food conditions improve. While food allocation was generally skewed towards the older siblings, the youngest sibling in the nest increased its probability of accessing food as more was provisioned and as downward heuristic patterns became more prominent, suggesting that different aggression patterns allow for catch-up growth after periods of low food. Our results indicate that dynamic aggression patterns within the nest modulate environmental effects on juvenile development by influencing the process of dominance acquisition and potentially impacting the fledging body condition, with far-reaching fitness consequences., Competing Interests: We declare we have no competing interests., (© 2023 The Authors.)

Across a wide range of taxa, larger mothers produce larger offspring. Theory assumes that larger, more fecund mothers create higher local densities of siblings, and so larger mothers produce larger offspring to offset sibling competition. This assumption has been debated for over 30 yr, but direct empirical tests are surprisingly rare. Here, we test two key assumptions of classic theories that predict sibling competition drives maternal-size-offspring-size ( MSOS) correlations: (1) independent effects of offspring size and sibling density on offspring performance or (2) as a product of an interaction between these two factors. To simultaneously test these alternative assumptions, we manipulate offspring size and sibling density in the marine invertebrate, Bugula neritina, and monitor offspring performance in the field. We found that, depending on the fitness metric being considered, offspring size and sibling density can either independently or interactively affect offspring performance. Yet sibling density did not affect offspring performance in the ways that classic theories assume. Given our results, it is unlikely that sibling competition drives the positive MSOS correlation observed in this species. Empirical support for these classic theories remains lacking, suggesting alternative explanations are necessary. [ABSTRACT FROM AUTHOR]

Strong interconnections between family and business which are innate to family firms can prove to be the source of conflict. Of all conflicts, those between family members and especially between siblings erode the family’s harmony and can risk the firm’s continuity. The passing of the family firm’s control from the founders to the next generation is a critical stage for the family firm and can be a catalyst for conflict. This article extends the use of game theory in family firm succession to explicitly include the noneconomic factors related to the family dimension, focusing on the emotional cost of conflict resulting from sibling competition. The results show that this cost is fundamental in terms of successor selection. The article shows that the collaborative family outcome , which results from family members cooperating and acting as a unit, is better in promoting firm intergenerational succession and ensuring that the founder’s preferred child is appointed successor. [ABSTRACT FROM AUTHOR]