Parental Investment and Reproductive Strategies

• Parental investment compromises the ability to produce additional offspring to assist current offspring
• The extent to which varies across species and is shaped by evolutionary pressures to maximize fitness

Parental Care Strategies

• Strategies exist on a continuum No Parental Care:
• Many fish and reptile species simply lay eggs and provide no further assistance
• Example: Brown trout, most reptiles Minimal Parental Care:
• Some species offer basic protection
• Example: Nile crocodiles carrying hatchlings to water Extensive Parental Care:
• Some mammals, including humans, invest heavily in offspring care, providing food, protection, and socialization

Reproductive Investment

• The sex that invests more in offspring typically females in mammals is more selective in mate choice
• Males in many species prioritize increasing reproductive opportunities unless paternal care improves offspring survival and their fitness

Key terms

• Parental Investment: The resources (time, energy) a parent provides to offspring at the cost of future reproductive opportunities
• Fitness: An organism's ability to survive and reproduce, passing genes to the next generation

The Importance of Parental Care

• Crucial for the survival of offspring in many species, including humans
• Increases offspring survival rates
• Shapes competition for mates by influencing mate selection
• Affects the physical and psychological development of offspring
• Plays a role in the socialization of young in many species
• Varies greatly
• Some parents engage in extensive interaction and nurturing
• Others show neglect or minimal interaction, with consequences for child development

The Role of Hormones

• Endocrine factors influence parenting abilities
• Poor parenting may be linked to specific hormonal and neural mechanisms.

Key terms

• Endocrine Correlates: Hormonal factors associated with behaviors such as parenting
• Socialization: The process by which individuals learn behaviors, norms, and skills for functioning in society

Altricial vs Precocial

• Two major reproductive strategies exist among vertebrates:

Altricial Offspring

• Born immature, requiring extensive parental care
• Example: Rats, humans

Precocial Offspring

• Born relatively mature, needing less parental investment
• Example: Guinea pigs

Trade-offs

• Altricial species invest less before birth but require more parental care post-birth
• Precocial species invest more in gestation but require less care after birth

Maternal behavior

• Often emerges instinctively but improves with experience
• Example: Primates and rodents show improved maternal care after the first litter
• Hormones play a key role in the onset and maintenance of maternal behavior
• Examples: Nest building, nursing, protection, and retrieval of young
• Example: Dogs retrieving puppies, mother rats grooming pups

Key Terms

• Altricial: Offspring born in an underdeveloped state, requiring significant parental care
• Precocial: Offspring born well-developed, capable of some independence soon after birth
• Maternal Behavior: Parental behaviors performed by mothers to ensure offspring survival

Sex Differences in Parental Behavior

• In most species, maternal care is far more common than paternal care

Biological investment

• Females produce fewer, resource-rich gametes (eggs), leading to greater investment in each offspring
• Males produce numerous, small, mobile gametes (sperm) and can fertilize many females

Reproductive Effort

• Divided into: Mating effort:
• Males maximize reproductive success by fertilizing multiple females

Parental effort:

• Females invest heavily in each offspring, as reproductive opportunities are limited
• A human male can theoretically fertilize hundreds of women in the time a single woman can complete a pregnancy

Key Terms

• Parental Investment: The resources allocated to offspring at the cost of future reproduction
• Reproductive Success: The passing of genes to the next generation by producing surviving offspring

Evolutionary Explanations for Parental Differences

• Research by Bateman in 1948 on fruit flies demonstrated sex differences in reproductive success
• Some males fertilized many females, while others had no offspring
• All females had relatively equal reproductive success

Male Strategy

• Compete for access to multiple females to maximize reproductive success

Female Strategy

• Prioritize offspring survival since reproductive opportunities are limited

In species where offspring survival depends on both parents

• Example - Many birds, paternal care is more common

Trade-offs in paternal investment

• Males that provide care lose opportunities to mate
• Paternal care evolves when it significantly improves offspring survival

Key Terms

• Bateman's Principle: Male reproductive success varies with the number of mates, while female success is constrained by gamete production and offspring viability
• Paternal Care: Male investment in offspring beyond fertilization

Parental Behavior Across Species

• Birds: More likely to exhibit paternal care because both parents are needed for feeding and protection
• Mammals: Paternal care is rare; females typically handle parental duties due to lactation and gestation constraints

Hormonal Influences

• Hormones such as oxytocin, prolactin, and testosterone play key roles in parenting behaviors

Neural Mechanisms

• Research on rats, sheep, and birds reveals that specific brain circuits regulate parental care

Human Parental Behavior

• Varies widely but follows general evolutionary patterns
• Social and cultural factors shape paternal involvement beyond biological constraints

Key Terms

• Hormonal Correlates: Endocrine factors influencing parenting behavior
• Neural Foundations: Brain mechanisms underlying parental instincts

Parental Behavior in Mammals

• Mammals are unique among vertebrates due to mammary glands
• Mammary glands produce milk, allowing mothers to nourish offspring after birth
• This adaptation enables mammals to invest heavily in postnatal care
• Parental care, especially maternal care, is a key characteristic of mammals
• Maternal care includes feeding, protection, and teaching survival skills
• Examples: Human mothers breastfeeding, lionesses guarding cubs
• Exhibit diverse strategies for caring for young
• These strategies depend on offspring development (altricial vs. precocial) and habitat (stable vs. unpredictable)

Mammalian maternal behavior overview

• Produce offspring at different developmental stages: Altricial young:
  • Born undeveloped, requiring extensive care
  • Examples: Rats, dogs, and most rodents
  • These young are blind, hairless, and unable to regulate body temperature

Precocial young:

• Born developed, capable of independent activity
• Examples: Deer, sheep, and horses
• These young can walk, see, and feed shortly after birth
• Marsupials and monotremes have unique adaptations for maternal care
• Marsupials have pouches for carrying and nursing young
• Example: Kangaroos
• Monotremes lay eggs but provide milk for hatched young
• Example: Platypus
• Eutherian mammals show the greatest diversity in parental behavior
• Examples of humans, elephants, and whales exhibit complex care strategies

Marsupials give birth to highly altricial young

• Young resemble embryos and are undeveloped at birth
• Example: A newborn kangaroo is the size of a jellybean
• Mothers have pouches containing mammary glands
• Pouches provide a safe environment for nursing and development
• Example: Kangaroo joeys stay in the pouch for 6–8 months

Examples of marsupial maternal care

• Kangaroos and wallabies: Young stay in the pouch for months
• Opossums and koalas: Young cling to the mother's fur after leaving the pouch Monotremes lay eggs, representing a transitional stage between reptiles and mammals
• Example: Duck-billed platypus and echidnas

Maternal care includes

• Platypus: Builds a burrow, incubates eggs, and provides milk
• Example: A platypus mother seals herself in a burrow to care for her young
• Echidnas: Carry eggs and young in a temporary pouch
• Example: Echidna mothers develop a pouch only during the breeding season

Eutherian mammals have placentas and longer gestation periods:

• Example: Humans, dogs, and rats

The mothers provide food, care & shelter

• Rat mothers build nests and nurse their pups

Key maternal behaviors

Nest building before birth

• Example: Dogs choose a safe, secluded spot to give birth
• Licking young to clean and stimulate them:
• Example: Rat mothers lick pups to remove amniotic fluid and stimulate waste elimination
• Nursing and retrieving young to the nest
• Example: Mother dogs retrieve puppies that wander from the nest

Precocial young are born developed and capable of independent activity:

• Example: Deer, sheep, and horses.
• These young can walk, see, and feed shortly after birth

Two patterns of maternal care

• Hider-type: Young remain hidden at the nest initially
• Example: White-tailed deer fawns stay hidden for 7-10 days
• Mothers forage for food but return to nurse their young
• Once mature enough, young leave the nest and follow their mothers
• Follower-type: Young follow mothers from birth

Semiprecocial young

• Neither fully altricial nor precocial
• Example: Humans, primates, and galagos
• These young are helpless at birth but can cling to their mothers for mobility

Maternal care patterns

• Mothers alternate between carrying young and placing them in nests -Example: Orangutan mothers carry infants while foraging
• Some species deposit young in tree nests during early development
• Example: Galagos hide their young while foraging during the day and carry them at night

Human and primate offspring

• Human infants are helpless but can grasp objects and cling to caregivers
• Primate mothers provide constant care, including nursing, grooming, and protection

Maternal behavior involves

• Pup-directed behaviors: Nursing, retrieving, and licking young
• Example: Rat mothers lick pups to stimulate waste elimination
• Non-pup-directed behaviors: Nest building and defending the nest
• Example: Mother dogs aggressively protect their puppies Hormones and environmental factors influence maternal behavior
• Example: Oxytocin promotes bonding and caregiving in mammals
• First-time mothers may exhibit trial-and-error learning:
• Example: Inexperienced rat mothers may mishandle pups initially

Mammalian paternal behavior

• Rare among mammals, observed in only 3% of species
• Example: Certain carnivores, rodents, and primates
• Paternal behavior is most likely to occur when it increases male reproductive success

Factors influencing paternal care:

Female dependency:

• Males may provide care if females cannot rear offspring alone
• Example: In some primates, males help carry and protect infants

Certainty of paternity:

• Males are more likely to care for offspring if they are certain of their paternity
• Example: Monogamous species like California mice exhibit high paternal investment Mating exclusivity:
• Continued proximity to the female after mating may foster paternal care
• Example: Pair-bonded species like voles show high levels of paternal involvement

Paternal Care

• Behaviors by fathers to ensure offspring survival

Certainty of Paternity

• A male's confidence that he is the biological father of offspring

Biparental Care:

• Both parents contribute to raising offspring

Paternal Care in Rodents

• Documented in several rodent species

California mice

• Males and females form long-term monogamous bonds
• Males spend as much time in the nest as females and perform similar caregiving tasks
• Removal of the father may not lead to offspring mortality but can affect growth and stress responses

Hormonal regulation

• Best understood in rats
• Maternal behavior coincides with birth, linking it to pregnancy and lactation hormones
• Key hormones include prolactin, progesterone, estrogens, oxytocin, and others

Prolactin and lactation

• Prolactin is essential for milk production but is not the sole driver of maternal behavior
• Example: Rats with suppressed prolactin still exhibit maternal care if other hormones are present

Estrogens and maternal behavior

• Estrogen levels rise sharply before birth, priming mothers for caregiving
• Example: Administering estrogen to non-pregnant rats can induce maternal behavior

Sensitization

• Non-pregnant female rats exposed to pups begin to exhibit maternal behavior after 5–6 days
• Example: Nulliparous females groom, nurse, and retrieve pups after repeated exposure Hormonal independence of sensitization Sensitization occurs even in the absence of gonads, pituitary, or adrenal glands
• Example: Male rats also show maternal behavior after prolonged exposure to pups Neurochemical pathways
• Dopamine and other neurotransmitters mediate sensitization
• Example: Fos activation patterns in sensitized females resemble those in postpartum mothers

Hormonal priming:

• For first-time mothers:
• Hormones like estrogen and oxytocin are critical for initiating maternal behavior in first-time mothers
• Example: Rats undergoing their first pregnancy require hormonal priming to care for pups

Experiential influences

• Experienced mothers exhibit maternal behavior faster, even without hormonal priming
• Example: Second-time mothers respond to pups within one day, regardless of hormonal status
• Maternal memory:
• Early postpartum experiences create a “maternal memory” that enhances future caregiving
• Example: Protein synthesis inhibitors block maternal memory formation in rats

Motivation and Performance

• Motivation and performance in maternal behavior
• Motivation refers to the desire to care for offspring, while performance refers to the specific actions taken
• Example: Rats with lesions in the medial preoptic area MPOA show reduced motivation to care for pups

Early Exposure

• Juveniles exposed to neonates develop stronger maternal behaviors later in life
• Rats raised with younger siblings show less fear of pups as adults

Alloparenting Experience

• Helping care for siblings or unrelated young enhances future parenting skills
• Example: Prairie voles and cooperatively breeding species exhibit strong alloparenting behaviors

Neophobia reduction

• Early exposure reduces fear of neonates, making adults more responsive to offspring
• Example: Laboratory rats without early exposure show fear of pups, while wild rats do not

Maternal motivation

• Hormones and brain regions involved: Group, Condition, Brain lesion:
• Postpartum females with access to pups - tested for bar pressing and maternal behavior with a MPOA lesion:
  • Findings:↓ Bar pressing, ↓ maternal behavior
• CYcling females with access to pups - tested for bar pressing and maternal behavior with a MPOA lesion:
• Findings:↓ Bar pressing, ↓ maternal behavior
• Interpretation: MPOA is critical for both motivation and execution of maternal behavior
• Amygdala plays a role in maternal motivation postpartum
• Nucleus Accumbens is involved in reward processing of maternal care
• Different brain regions contribute to maternal motivation and performance