10.3 Parent-offspring conflict

Parent-offspring conflict arises from divergent evolutionary interests between parents and offspring. Parents aim to distribute resources equally among all offspring, while offspring demand more for themselves. This conflict shapes parental investment strategies and offspring behavior across animal species.

The intensity of conflict varies based on factors like parental ability to invest, offspring need, and family size. Resolution strategies involve an evolutionary arms race between parental control mechanisms and offspring counterstrategies, influencing growth, survival, and future reproductive success for both parties.

Evolutionary basis of conflict

• Parent-offspring conflict arises from differences in the optimal level of parental investment for parents and offspring due to their divergent evolutionary interests
• Genetic relatedness between parents and offspring is a key factor influencing the intensity and resolution of parent-offspring conflict

Genetic relatedness between parents and offspring

Top images from around the web for Genetic relatedness between parents and offspring

• 

  Genetics and the Environment | Biology for Majors I View original

  Is this image relevant?

• 

  Characteristics and Traits | OpenStax Biology 2e View original

  Is this image relevant?

• 

  Genetic variation in offspring indirectly influences the quality of maternal behaviour in mice ... View original

  Is this image relevant?

• 

  Genetics and the Environment | Biology for Majors I View original

  Is this image relevant?

• 

  Characteristics and Traits | OpenStax Biology 2e View original

  Is this image relevant?

1 of 3

Top images from around the web for Genetic relatedness between parents and offspring

• 

  Genetics and the Environment | Biology for Majors I View original

  Is this image relevant?

• 

  Characteristics and Traits | OpenStax Biology 2e View original

  Is this image relevant?

• 

  Genetic variation in offspring indirectly influences the quality of maternal behaviour in mice ... View original

  Is this image relevant?

• 

  Genetics and the Environment | Biology for Majors I View original

  Is this image relevant?

• 

  Characteristics and Traits | OpenStax Biology 2e View original

  Is this image relevant?

1 of 3

• Parents are equally related to all their offspring (coefficient of relatedness = 0.5) while offspring are more related to themselves (r = 1.0) than to their siblings (r = 0.5 for full siblings, r = 0.25 for half-siblings)
• This asymmetry in relatedness creates different optimal levels of parental investment for parents and offspring
• Parents are selected to distribute resources equally among all offspring to maximize their total reproductive success (inclusive fitness)
• Offspring are selected to demand more resources for themselves at the expense of their siblings to maximize their own individual fitness

Divergent evolutionary interests

• Parents and offspring have conflicting interests over the allocation of parental resources (time, energy, food, protection) among offspring
• Offspring favor higher levels of investment in themselves than parents are selected to provide based on the costs and benefits for their inclusive fitness
• This divergence in evolutionary interests leads to parent-offspring conflict over the level and duration of parental care
• Examples of conflict manifestation include offspring begging for more food than optimal for parents to provide and weaning conflict in mammals

Manifestations in animals

• Parent-offspring conflict can manifest in various forms across different animal taxa depending on the specific life history, ecology, and social system
• Common manifestations include sibling competition, offspring demanding more parental investment, parent-offspring communication and signaling, and weaning conflict

Sibling competition for resources

• Offspring compete with their siblings over limited parental resources (food, attention, protection) to maximize their own share of investment
• Sibling rivalry can involve physical aggression (fighting, pushing siblings away from parents), vocal disputes (begging calls, crying), or scramble competition (racing to parents first)
• Examples include siblicide in birds (blue-footed boobies) where dominant chicks attack and kill their younger siblings and competitive begging in passerine birds (house sparrows) where nestlings vocally compete for food from parents

Offspring demanding more parental investment

• Offspring employ various behavioral strategies to extract more resources from parents than parents are selected to provide based on the costs to their residual reproductive value
• Begging behavior is a common manifestation where offspring use vocal, postural, or chemical signals to solicit food and attention from parents beyond their actual need
• Examples include exaggerated begging calls in bird nestlings (American robins) that manipulate parental food provisioning and pup vocalizations in mammals (domestic cats) that elicit parental care and protection

Parent-offspring communication and begging

• Parent-offspring conflict is often mediated through communication signals, particularly begging behavior by offspring to solicit resources from parents
• Begging can be an honest signal of offspring need (hunger, condition) that parents use to make investment decisions or a manipulative signal that offspring use to extract more resources than optimal for parents
• The evolution of begging signals is shaped by the balance between the benefits of increased investment for offspring and the costs of excessive investment for parents
• Examples include begging calls in altricial bird nestlings (barn swallows) that honestly signal hunger and need and exaggerated mouth coloration in canary nestlings that manipulates parental food allocation

Weaning conflict in mammals

• Weaning conflict is a specific manifestation of parent-offspring conflict in mammals where offspring resist the termination of nursing and demand continued lactation beyond the optimal time for mothers
• Mothers are selected to wean offspring when the costs of continued nursing (energetic, opportunity costs) exceed the benefits for their lifetime reproductive success
• Offspring are selected to prolong nursing to maximize their own growth, survival, and future reproduction, leading to behavioral conflict and weaning tantrums
• Examples include mother-infant struggles during weaning in primates (rhesus macaques) and vocal protests by offspring during forced weaning in ungulates (sheep)

Conflict resolution strategies

• Parent-offspring conflict is resolved through a coevolutionary arms race between parental control mechanisms and offspring counterstrategies
• The resolution of conflict depends on the costs and benefits of different strategies for parents and offspring in a given ecological and social context

Parental control mechanisms

• Parents evolve strategies to control the level and duration of investment in offspring and limit the costs of excessive demand
• Physical control mechanisms include limiting access to resources (concealing food, restricting nursing), actively rejecting offspring (pushing away, aggression), or abandoning offspring (reducing visit rates, leaving territory)
• Physiological control mechanisms involve hormonal changes that reduce milk production (prolactin reduction) or alter offspring behavior (cortisol increase)
• Examples include reduced nursing frequency by mother pinnipeds (elephant seals) to limit milk transfer and increased glucocorticoid levels in bird parents (great tits) to reduce offspring begging intensity

Offspring counterstrategies

• Offspring evolve counterstrategies to manipulate parents into providing more resources than optimal for parental fitness
• Behavioral counterstrategies include escalated begging (louder, more persistent), physical manipulation (wing-flapping, pushing), or deception (false alarm calls, exaggerated need)
• Physiological counterstrategies involve hormonal tactics that increase resource demand (elevated growth hormone) or reduce the effectiveness of parental control (decreased sensitivity to cortisol)
• Examples include exaggerated begging displays by bird nestlings (house sparrows) to attract more parental feeding visits and reduced glucocorticoid receptors in mammal infants (mice) to resist stress-induced suppression of demand

Evolutionary arms race

• Parent-offspring conflict resolution involves a dynamic coevolutionary process where parental strategies and offspring counterstrategies evolve in response to each other over evolutionary time
• The arms race between parents and offspring leads to an escalation of tactics and an eventual equilibrium where the costs and benefits of further escalation are balanced for both parties
• The outcome of the arms race depends on the relative power of parents and offspring to control investment and the costs of escalated conflict for each party
• Examples include the coevolution of larger offspring size and reduced litter size in mammals (domestic dogs) as a result of sustained parent-offspring conflict over resource allocation

Factors influencing conflict intensity

• The intensity and resolution of parent-offspring conflict are influenced by various ecological, social, and life-history factors that shape the costs and benefits of parental investment for parents and offspring
• Key factors include parental ability to invest, offspring need and condition, number of offspring and relatedness, and life history and mating system

Parental ability to invest

• Parental ability to invest resources in offspring depends on their own condition, resource availability, and competing demands (self-maintenance, future reproduction)
• Parents in good condition with abundant resources are expected to invest more in current offspring and experience less intense conflict
• Parents in poor condition or resource-limited environments face higher costs of investment and are expected to experience more intense conflict with offspring
• Examples include reduced conflict intensity in bird parents (pied flycatchers) supplemented with extra food and increased conflict intensity in mammal mothers (rhesus macaques) under nutritional stress

Offspring need and condition

• Offspring need for parental investment depends on their developmental stage, body condition, and environmental challenges (food availability, predation risk)
• Offspring in greater need (younger, poorer condition, harsher environment) are expected to demand more resources from parents and escalate conflict
• Offspring in better condition or more favorable environments are expected to demand less from parents and experience less intense conflict
• Examples include increased begging intensity by bird nestlings (barn swallows) in poorer body condition and reduced conflict intensity in primate infants (baboons) in resource-rich habitats

Number of offspring and relatedness

• The number of offspring and their relatedness to each other influence the intensity of sibling competition and parent-offspring conflict
• Parents with larger broods or litters face higher costs of investment per offspring and are expected to experience more intense conflict over resource allocation
• Offspring with more siblings or lower relatedness (half-siblings) face greater competition for limited parental resources and are expected to escalate conflict
• Examples include increased sibling aggression in bird broods (blue-footed boobies) with more chicks and higher begging intensity in passerine nests (house sparrows) with mixed paternity

Life history and mating system

• Life history traits (lifespan, reproductive rate) and mating systems (monogamy, polygyny) shape the costs and benefits of parental investment and influence conflict intensity
• Species with fast life histories (short lifespan, high reproductive rate) are expected to invest more in current offspring and experience less intense conflict due to lower costs of investment
• Species with slow life histories (long lifespan, low reproductive rate) are expected to invest less in current offspring and experience more intense conflict due to higher costs of investment
• Monogamous species with biparental care are expected to have less intense conflict than polygynous species with uniparental care due to shared costs of investment
• Examples include reduced conflict intensity in fast-lived rodents (mice) compared to slow-lived primates (gorillas) and lower offspring demand in monogamous birds (great tits) compared to polygynous mammals (red deer)

Consequences for fitness

• Parent-offspring conflict has important consequences for the fitness of both parents and offspring, shaping the evolution of optimal investment levels and life-history strategies
• The resolution of conflict influences offspring growth, survival, and future reproductive success, as well as parental residual reproductive value and lifetime fitness

Optimal investment levels for parents

• Parents are selected to optimize their level of investment in current offspring based on the costs and benefits for their residual reproductive value and lifetime fitness
• Optimal investment levels depend on the trade-off between current and future reproduction, as well as the diminishing returns of additional investment on offspring fitness
• Parents that invest too little in current offspring risk reduced offspring survival and reproductive success, while parents that invest too much risk reduced future reproductive opportunities and survival
• Examples include the evolution of optimal clutch size in birds (great tits) that maximizes parental fitness based on the trade-off between offspring number and quality

Effects on offspring growth and survival

• The level of parental investment and the resolution of parent-offspring conflict have direct effects on offspring growth, development, and survival
• Offspring that receive more parental resources (food, protection) are expected to grow faster, reach larger sizes, and have higher survival rates
• Offspring that receive insufficient parental investment due to intense conflict or parental restriction are expected to have reduced growth, smaller sizes, and lower survival
• Examples include positive effects of increased parental feeding on nestling growth rates in birds (pied flycatchers) and negative effects of maternal restriction on infant growth in mammals (rhesus macaques)

Influence on future reproductive success

• The consequences of parent-offspring conflict extend beyond the current reproductive event and influence the future reproductive success of both parents and offspring
• Offspring that receive adequate parental investment and resolve conflict favorably are expected to have higher reproductive success as adults due to better condition and competitive ability
• Parents that optimize their investment levels and minimize the costs of conflict are expected to have higher lifetime reproductive success through increased survival and future reproductive opportunities
• Examples include positive effects of favorable conflict resolution on offspring mating success in birds (barn swallows) and negative effects of intense conflict on maternal reproductive lifespan in mammals (red deer)

Empirical evidence across taxa

• Parent-offspring conflict has been studied empirically in a wide range of animal taxa, revealing the diversity of conflict manifestations and resolution strategies
• Empirical evidence comes from observational studies, experimental manipulations, and comparative analyses across species with different life histories and ecologies

Birds

• Birds have been a model system for studying parent-offspring conflict due to their altricial development, parental care, and observable begging behavior
• Empirical studies have demonstrated the role of begging as an honest signal of need (barn swallows) or a manipulative signal of demand (canaries)
• Experimental manipulations of brood size (house sparrows), food availability (pied flycatchers), and parental condition (great tits) have revealed the factors influencing conflict intensity and resolution
• Comparative analyses across bird species have shown the influence of life history (clutch size, lifespan) and ecology (food abundance, predation risk) on parent-offspring conflict

Mammals

• Mammals exhibit diverse forms of parent-offspring conflict, particularly in the context of lactation and weaning in species with extended parental care
• Empirical studies have investigated the behavioral and physiological mechanisms of conflict, such as weaning tantrums in primates (rhesus macaques) and vocal protests in ungulates (sheep)
• Experimental manipulations of litter size (mice), maternal condition (rats), and resource availability (meerkats) have demonstrated the factors shaping conflict intensity and resolution
• Comparative analyses across mammalian taxa have revealed the influence of life history (lifespan, reproductive rate) and mating system (monogamy, polygyny) on parent-offspring conflict

Insects

• Insects provide valuable insights into parent-offspring conflict in species with parental care, such as subsocial bugs (Adomerus triguttulus) and burying beetles (Nicrophorus vespilloides)
• Empirical studies have investigated the role of chemical communication (pheromones) and behavioral interactions (begging, aggression) in mediating conflict between parents and offspring
• Experimental manipulations of brood size (burying beetles), resource availability (subsocial bugs), and parental condition (dung beetles) have revealed the factors influencing conflict intensity and resolution
• Comparative analyses across insect taxa have shown the influence of life history (brood size, development time) and ecology (resource competition, predation risk) on parent-offspring conflict

Fish

• Fish exhibit diverse forms of parental care and parent-offspring conflict, particularly in species with male-only care (sticklebacks) or biparental care (cichlids)
• Empirical studies have investigated the role of offspring signals (visual, chemical) and parental responses (aggression, abandonment) in mediating conflict
• Experimental manipulations of brood size (sticklebacks), resource availability (cichlids), and parental condition (gobies) have demonstrated the factors shaping conflict intensity and resolution
• Comparative analyses across fish species have revealed the influence of mating system (polygyny, monogamy) and ecology (resource distribution, predation risk) on parent-offspring conflict

Theoretical models and predictions

• Theoretical models have been developed to understand the evolutionary dynamics and adaptive significance of parent-offspring conflict
• These models make predictions about the optimal level of parental investment, the honesty of offspring signals, and the resolution of conflict under different ecological and social conditions

Parent-offspring conflict theory

• Parent-offspring conflict theory, developed by Robert Trivers, provides a framework for understanding the evolutionary basis and consequences of conflict between parents and offspring
• The theory predicts that parents and offspring will disagree over the optimal level of parental investment due to their divergent interests in maximizing their own inclusive fitness
• Parents are predicted to invest in offspring up to the point where the marginal costs equal the marginal benefits for their lifetime reproductive success, while offspring are predicted to demand more investment than optimal for parents
• The theory generates predictions about the factors influencing conflict intensity (relatedness, resource availability) and the coevolutionary arms race between parental control and offspring demand

Honest signaling models

• Honest signaling models investigate the evolution and stability of offspring begging signals as reliable indicators of need or condition
• These models predict that begging signals will be honest and informative to parents when the costs of signaling (energy expenditure, predation risk) are higher for offspring in better condition
• Dishonest or exaggerated begging is predicted to be unstable and selected against when the costs of signaling are condition-dependent and maintain the reliability of the signal
• Empirical tests of honest signaling models have supported the predictions in various taxa, such as the condition-dependence of begging intensity in bird nestlings (barn swallows) and the costs of exaggerated begging in insect larvae (burying beetles)

Evolutionary stable strategies

• Evolutionary stable strategy (ESS) models explore the conditions under which different conflict resolution strategies (parental control, offspring demand) are evolutionarily stable and resistant to invasion by alternative strategies
• These models predict that the resolution of conflict will depend on the relative costs and benefits of different strategies for parents and offspring in a given ecological and social context
• Parental control strategies (e.g., aggression, abandonment) are predicted to be stable when the costs of control are low relative to the benefits of limiting offspring demand, while offspring demand strategies (e.g., begging, manipulation) are predicted to be stable when the costs of demand are low relative to the benefits of increased investment
• ESS models have been applied to various conflict scenarios, such as the stability of honest begging in birds (canaries) and the coevolution of weaning strategies in mammals (mice)

Implications beyond parent-offspring dyads

• The principles and consequences of parent-offspring conflict extend beyond the dyadic interaction between a single parent and offspring to shape the evolution of social systems and reproductive strategies
• Parent-offspring conflict has important implications for the dynamics of cooperative breeding, reproductive skew, and intergenerational effects

Cooperative breeding systems

• Cooperative breeding systems, where non-breeding helpers assist in raising offspring, are influenced by the resolution of conflict between breeders and helpers over the allocation of resources and reproduction
• Parent-offspring conflict theory predicts that helpers will face a trade-off between the inclusive fitness benefits of helping and the direct fitness costs of forgoing their own reproduction, leading to conflict over the level of help provided
• Empirical studies have demonstrated the role of relatedness (meerkats), ecological constraints (acorn woodpeckers), and reproductive skew (Seychelles warblers) in shaping the intensity and resolution of conflict between breeders and helpers
• Comparative analyses across cooperative breeding species have revealed the influence of life history (lifespan, reproductive rate) and social structure (group size, dominance hierarch