A genetic analysis of parent-offspring conflict
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Animal ecology
Parent–offspring conflict
Conflicts over parental investment are predicted to be common among family members, especially between parents and their offspring. Parent-offspring conflict has been studied in many brood-caring organisms, but whether its outcome is closer to the parental or offspring optimum is usually unknown, as is whether the presence of a second parent, a caring male partner, can affect the outcome. Here, we manipulated the initial brood size of single and paired female burying beetles to examine how many offspring are necessary to maintain parental care in the current brood. We found that mothers continued to invest in small broods even if their reproductive output would have been higher if they had discontinued their care and produced a second brood instead. Consequently, our data suggests that the offspring have the upper hand in the conflict. However, our results further show that paired females laid a second egg clutch more often and produced more offspring than single females, suggesting that the presence of a male partner shifts the conflict outcome towards the parental optimum. This latter result not only is a novel aspect of parent-offspring theory, but also represents an additional factor that might explain the evolution of biparental care.
Paternal care
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Maternal effects can provide offspring with reliable information about the environment they are likely to experience, but also offer scope for maternal manipulation of young when interests diverge between parents and offspring. To predict the impact of parent–offspring conflict, we model the evolution of maternal effects on local adaptation of young. We find that parent–offspring conflict strongly influences the stability of maternal effects; moreover, the nature of the disagreement between parents and young predicts how conflict is resolved: when mothers favor less extreme mixtures of phenotypes relative to offspring (i.e., when mothers stand to gain by hedging their bets), mothers win the conflict by providing offspring with limited amounts of information. When offspring favor overproduction of one and the same phenotype across all environments compared to mothers (e.g., when offspring favor a larger body size), neither side wins the conflict and signaling breaks down. Only when offspring favor less extreme mixtures relative to their mothers (something no current model predicts), offspring win the conflict and obtain full information about the environment. We conclude that a partial or complete breakdown of informative maternal effects will be the norm rather than the exception in the presence of parent–offspring conflict.
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When parent-offspring relations in sexually reproducing species are viewed from the standpoint of the offspring as well as the parent, conflict is seen to be an expected feature of such relations. In particular, parent and offspring are expected to disagree over how long the period of parental investment should last, over the amount of parental investment that should be given, and over the altruistic and egoistic tendencies of the offspring as these tendencies affect other relatives. In addition, under certain conditions parents and offspring are expected to disagree over the preferred sex of the potential offspring. In general, parent-offspring conflict is expected to increase during the period of parental care, and offspring are expected to employ psychological weapons in order to compete with their parents. Detailed data on mother-offspring relations in mammals are consistent with the arguments presented. Conflict in some species, including the human species, is expected to extend to the adult reproductive role of the offspring: under certain conditions parents are expected to attempt to mold an offspring, against its better interests, into a permanent nonreproductive.
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All expenditures involve an opportunity cost. This is true in economics: Money spent on one activity is unavailable for other activities. But it is also true in evolutionary biology: Time, resources, or energy expended on one fitness-enhancing activity is unavailable for other fitness-enhancing activities. Organisms, like consumers, are faced by trade-offs. Beyond a certain level of reproductive expenditure on any particular offspring, a parent's resources are better allocated to other uses, say to fighting disease or laying down fat to survive the next winter. And these other uses, either directly or indirectly, translate into less investment in other offspring. An organism usually maximizes its expected number of surviving offspring, not by investing everything in a single offspring, but by spreading its reproductive effort across multiple offspring (1).
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Parent–offspring conflict
Coevolution
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The theory of parent–offspring conflict is extended to plants that produce many offspring in one reproductive event. The energetic cost of begging signals and the timing of offspring conflict are explicitly taken into account. We find that if the indirect costs of increased provisioning of selfish offspring are borne by their brood mates, then offspring are selected to solicit in so costly a way that a substantial part of parental investment in a brood goes to solicitation rather than offspring's growth and survival. Consequently, offspring conflict often results in smaller seed size than the parental optimum in the absence of conflict, although each offspring still consumes more resources than the amount its mother is willing to give. While the optimal sex allocation can be shown to be independent of solicitation and sibling conflict, the overall reproductive effort is always lowered by parent–offspring conflict. The timing of offspring conflict during the period of parental investment is demonstrated to be an important factor that influences the outcome of parent–offspring conflict. The more resources are allocated to individual offspring before the occurrence of offspring solicitation, the less offspring should solicit, and hence the closer the offspring size to the parental optimum. Copyright 2000 Annals of Botany Company
Parent–offspring conflict
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Sibling rivalry (animals)
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Parent–offspring conflict theory, formulated by evolutionary biologist Robert Trivers in 1974, maintains that parents and offspring should disagree over the amount of parental resources invested in the offspring so that offspring should always demand more than parents are willing to invest. This disagreement reflects an underlying genetic conflict of interest: while parents are equally related to all of their offspring and predisposed to invest equally in them, each individual offspring is fully related to itself but only half related to its siblings. Parent–offspring conflict has been documented in both animals and humans and is expressed physiologically during gestation and at the behavioral and psychological level after birth.
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Parent–offspring conflict
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The evolution of family life has traditionally been studied in parallel by behavioral ecologists and quantitative geneticists. The former focus on parent-offspring conflict and whether parents or offspring control provisioning, whereas the latter concentrate on the coadaptation of parental supply and offspring demand. Here we show how prenatal effects on offspring begging can link the two different approaches. Using theoretical and experimental analyses, we show that when offspring control provisioning, prenatal effects primarily serve the parent's interests: Selection on parents drives coadaptation of parent and offspring traits. In contrast, when parents control provisioning, prenatal effects primarily serve the offspring's interests: Selection on the offspring drives coadaptation of parent and offspring traits. Parent-offspring conflict may thus be responsible for the selective forces that generate parent-offspring coadaptation.
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Abstract Maternal effects can provide offspring with reliable information about the environment they are likely to experience, but also offer scope for maternal manipulation of young when interests diverge between parents and offspring. To predict the impact and outcome of parent-offspring conflict, we model the evolution of maternal effects on local adaptation of young. We find that parent-offspring conflict strongly influences the stability of maternal effects; moreover, the nature of the disagreement between parents and young predicts how conflict is resolved: when mothers favour less extreme mixtures of phenotypes relative to offspring (i.e., when mothers stand to gain by hedging their bets), mothers win the conflict by providing offspring with only limited amounts of information. When offspring favour overproduction of one and the same phenotype across all environments compared to mothers (e.g., when offspring favour a larger body size), neither side wins the conflict and signaling breaks down. Only when offspring favour less extreme mixtures relative to their mothers (the case we consider least likely), offspring win the conflict and obtain full information about the state of the environment. We conclude that a partial or complete breakdown of informative maternal effects will be the norm rather than the exception in the presence of parent-offspring conflict.
Parent–offspring conflict
Maternal effect
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