hsci 216 final

Altricial

Hatched or born helpless and requiring significant parental care

Precocial

hatched or born in an advanced state and able to feed itself and move independently almost immediately

Modes of environmental effects on growth

• Unconstrained ; environment is supportive, individual achieves full potential

• Patterned or channeled ; growth is shaped by environmental pressures leading to developmental adaptations in response to challenges

• Constrained ; phenotypic plasticity does not allow for a compete adaptation. Growth is constrained and full impact of the challenges depends on timing and severity of the insult

Mother and offspring relationship

1. Constrains in the quality of the mother’s environment which necessarily translate into the quality of the fetus environment

2. The conflicts of interests between the players involve (resource sharing)

External constraints to Internal effects

In constrained environments, the fetus may be able to adapt to the pressures of the environment. Adaptation and survival will depend on the nature and intensity of the constraint

Post-natal phenotypes

1. The unavoidable costs of prenatal constraints ; No benefit associated - the result of not having enough resources. A small phenotype, for example, could simply be the result of scarce energetic resources

2. The costs of prenatal adaptations ; Surviving in the utero challenges may require changes in developmental trajectories, often trade offs such as lower quality post nala phenotypes

3. Phenotypic adaptive responses ; Phenotypic changes that do not provide immediate advantages but may aid with predictable future challenges

Intra-genomic conflicts

• Predicts different replication strategies by individual genes within a genome leading to conflicts with affect the phenotype

• This phenomenon could be the result of different transmission strategies within parent or competitive between genes of different parental origin

• Meiotic drive ; segregation distortion during meiosis

Parental origin

• Maternal genes

  • Maximize inclusive fitness of the mother

  • Modulate investment according to offspring quality

  • Sensitive to trade offs between offspring quantity and quality

  • Sensitive to trade offs current between future offspring

• Parental genes

  • Survive at (almost) all costs

  • Take as much from mom as possible

Selective pressure on paternal genes (genomic imprinting conflict)

Promiscuous mating systems would lead to lower genetic relatedness to father in a mother’s brood => selection should favour paternal genes that either favour maternal investment or silence maternal genes that downregulate maternal investment (maternally expressed demand-suppressing genes)

Selective pressure on Maternal genes (genomic imprinting conflict)

• Selection should favour maternal genes that aid in the regulation of maternal investment

• Maternal genes that silence paternally expressed genes that increase demands on the mother

Potential times for conflict

1. Conception

2. Early survival of the embryo

3. Placentation

4. Intrauterine growth

5. Gestational length

6. Early post-partum

7. Post-natal development

Conflict at conception and early survival of the embryo

• Deteriorating environments may lead to mechanisms preventing conception, including, anovulatory cycles, hostile vaginal environment

• Embryos with developmental problems may change the mother’s cost and trigger the suppression of reproduction function by, for example, preventing implantation

• Potential proximate mechanisms ; changing uterine chemical or physical environment

• These mechanisms are not necessarily independent or mutually exclusive. Progesterone promotes local vasodilation and uterine musculature quiescence by inducing nitric oxide synthesis in the decidua (uterine lining during pregnancy)

Conflict at placentation and Consequences for intra uterine growth

• Fetal tissue invades maternal spiral arteries and secrete human placental lactogen (hPL)

• Consequences for the mother

  • Increased blood => increased nutrients to the fetus

  • Moms can’t reduce blood nutrients content without reducing energy supply to their own tissues

• Maternal defense

  • Vasoconstriction (reduction of the diameter of blood vessels) which results in increased blood pressure

Pre-eclampsia

• Leads to decreased blood flow to the placenta causing complications such as premature births and low birth rates

• Also leads to decreased blood flow to the mother’s kidneys, brain, liver and retina

• Can lead to eclampsia which includes seizures, maternal cerebral hemorrhage and deaths

Pre-eclampsia effects

• Appear to be mediated by immunological interactions between male and female tissues

• Role of the male partner ; certain men appear to be linked to higher risks of pre-eclampsia in their partners

Gestational diabetes

• The placenta releases human placental lactogen, affecting maternal receptors, increasing insulin resistance, keeping blood glucose circulating for a longer period of time

• The longer it takes a mother to reduce her blood sugar after each meal, the more glucose a fetus receives

• To counter the effects of hPL, mother’s bodies increase insulin secretion

• Health risks

  • Really large babies are associated with birth difficulties

  • Increased risk of maternal non-gestational diabetes post-parto

  • Newborn’s problems regulating circulating glucose, increased risk of diabetes and obesity

Conflict over gestational length

• The fetus gains substantial endocrine control over its own gestation quite early

• Parturition is triggered by the adrenal glands leading to the maturation of the lungs

• A deteriorating environment can affect the maturation of the adrenals leading to premature births

• Cost-benefit analysis of staying in utero versus being born early may play a role

Intrauterine growth in retardation (IUGR)

• Fetal weight < 10th percentile = smaller than expected for gestational age

• Babies tend to appear thin, pale, and have loose, dry skin. Thin and dull-looking umbilical cords, rather than shiny and fat

• Maternal factors

  • High BP, chronic kidney disease, diabetes and CVD, malnutrition, anemia, and infections and substance abuse

• Factors involving the uterus and placenta

  • Placental abruption

  • Placenta previa

  • Decreased blood flow

• Factors related to the fetus

  • Multiple gestation (twins, triplets, etc.)

  • Chromosomal and developmental anomalies

Post natal conflict : Early post-partum

• Post-partum depression

• Low social and emotional support ; low sense of self-esteem; feelings of maternal inadequacy and isolation; financial problems ; and major life changes

• Mechanisms of behavioural adaptations

  • Increased risk of developing depression, under challenging conditions, linked to an increase risk of maternal neglect

  • The extreme expression of the trait being post-partum psychosis which increases the risk of infanticide

From the womb to the world

• Growth problems in utero; long lasting consequences including fetal programing and chronic diseases in adulthood

• Growth problems in childhood ; great impact on psychosocial adjustment

Factors affecting growth trajectories

• Perinatal problems

• Nutrition

• High altitude hypoxia

• Pollutants

• Maternal health conditions

• Psychosocial environment

• Social and economic status

Post natal development

1. Nutrition

2. Pollutants

3. Psychosocial environment

4. Social and economic status

Growth and nutrition

• Early nutrition is crucial for healthy growth

• Breast fed infants grow differently from formula fed infants

• Breast milk usually starts to be supplemented at 4-6 months. Timing and supplementary food items vary across populations

Growth and socioeconomic status (SES)

• Possible causes of this associations

  • Nutritional status

  • Disease load

  • Access to medical care

  • Psychosocial stress

• Stunting/delayed developmental observed in association with emotional deprivation/pathologic psychosocial environment resulting from a disturbed relationship between child and caregivers

Puberty

Onset of reproductive, physical and behavioural changes leading to adulthood

Ovarian cycle

• Follicular phase (1-14):

  • Follicle egg grows and matures

  • FSH from the anterior pituitary stimulates follicle growth

  • Growing follicle releases estrogen, which promotes further follicle development and signals the uterine lining to proliferate

• Ovulation (14):

  • Mature follicle bursts and releases an oocyte

  • Surge in LH triggers ovulation

• Luteal phase (15-28):

  • Ruptured follicle transforms into the corpus luteum which secretes progesterone

  • Progesterone maintains the uterine lining for potential implantation

Uterine cycle

• Menstrual (1-5):

  • Shedding of the uterine lining due to low estrogen and progesterone

  • Low levels of both hormones trigger menstruation

• Proliferative (6-14):

  • Endometrium regenerates and thickens

  • Rising estrogen stimulates rebuilding

• Secretory phase (15-28):

  • Endometrium becomes more glandular and vascular to support implantation

  • Progesterone makes the lining receptive to an embryo

  • If no fertilization occurs, progesterone falls => lining breaks down => next menstrual phase

Male hormone cycle

• GnRH from the hypothalamus triggers the pituitary

• The pituitary releases FSH and LH

  • FSH => sertoli cells => sperm production + inhibin

  • LH => leydig cells => testosterone production

• Inhibin controls FSH levels

• Testosterone controls GnRH and LH levels by negative feedback

HPGA during puberty

• Changes in hypothalamic function => attainment of a mature pattern of circhoral GnRH

• Gonadostat hypothesis ; decrease in response to the negative feedback of gonadal steroids during puberty

• Hypophysiotropic hypothesis ; Puberty is associated with an increase in positive feedback by stimulatory factors

Correlates of HPGA maturation

• Somatotropic axis

• Adrenarche

• Insulin sensitivity

• Leptin levels

• Body composition

• Skeletal maturation

Somatotropic axis

• Regulated by the hypothalamus via release of growth hormone releasing hormone

• Act on the pituitary to regulate ethe release of growth hormone

• GH stimulates the release of insulin like growth factors form the liver and other tissues

• GH and IGF-1 stimulate skeletal growth and protein anabolism

• The increase in ….. somatotropic activity appears to be a consequence of gonadal steroid production

• Both estradiol and testosterone affect GH production by augmenting the amplitude of GHRN pulses

Adrenarche

• Adrenal glands

• Adrenal cortex

• Adrenal medulla

• During …… the adrenal cortex develops a third layer called the zona reticularis and begins producing large amounts of adrenal androgens

• Can be triggered by a change in insulin sensitivity in late childhood

Insulin

• One of the major hormones controlling energy metabolism

• Produced by islet cells in the pancreas

• Stimulates the cellular uptake of glucose

• Insulin and growth hormone up regulate each other

• Elevated insulin leads to increased levels of IGF-1 and gonadal steroid hormone levels

• During puberty there is a transient decrease in insulin sensitivity

• Increase in insulin levels => increases in gonadal steroid => pubertal development

Leptin levels

• Adipocytes in subcutaneous fat tissue

• The epithelium of the stomach

• Regulate the amount of fat stored in the body

• In rodents, leptin receptors are highly expressed in areas of the hypothalamus known to be important in regulating food intake, energy expenditure and body weight

• Increases with increased fat mass during puberty, but whether it promotes or it is a consequences of HPGA maturation is still unclear

• Women have 3x more leptin per fat mass than men

• Estrogen stimulates leptin production. Testosterone suppresses leptin production

• Stronger relationship between energy balance and leptin in women than in men

Skeletal maturation

• Striking synchronization of reproductive and skeletal maturation in humans

• High correlation between menarche and attainment adult of pelvic size

• Skeletal maturation hypothesis; timing of puberty is coordinated with the attainment of appropriate physical size for reproduction

Why are reproductive health studies biases towards women

Pregnancy, childbirth and most contraceptive methods directly involve the female body, making women the primary focus of research and intervention. This focus often neglects male reproductive health and reinforces an unequal responsibility for fertility and family planning

What limitations have been there been in terms of women’s reproductive studies in the past

• Women are the limiting reactant (egg)

• Medical research historically relied heavily on male subjects

What aspects of women reproductive ecology are different from that of other mammalian female

• Concealed ovulation

• Long lifespans with menopause

• Lack of estrus

• Continuous cycle

What hypothesis have been proposed to explain women’s ‘cryptic’ evolution

• Daddy at home

  • Mate guarding, increased bonding, increased male derived benefits, increased paternity certainty, increased paternal investment

• Many fathers

  • Multiple partners, unclear paternity, multiple “male benefits”, lower paternal investment

• Female rivalry

  • Computational model suggests that females who concealed ovulation avoided female to female aggression parenting relationships with males and had more children

What are the benefits and costs of continuous ovulation

• Religious beliefs

• Family and social mandates

• Or life goals such as academics

• Or financial difficulty

• Maternal depletion

• Increased offspring mortality

Can women orgasms be seen as adaptive

• Promotes pair bonding ; Release oxytocin and other bonding hormones, strengthening emotional intimacy between partners, which can encourage long term pair bonds and increase paternal investment in offspring

• Sperm retention hypothesis ; Some studies suggest that orgasms during intercourse may help with sperm transport or retention, possibly increasing the chance of conception when a woman is most fertile

• May simply be a byproduct of male orgasm because male and female genital structures develop from the same embryonic tissues

• Not all women regularly experience orgasm during intercourse suggesting it is not strictly necessary for reproduction

Why would energy balance be associated with reproductive function

When energy intake is too low the body conserves resources by suppressing reproductive hormones, which can delay ovulation or stop menstrual cycles to avoid the risks of pregnancy when is energy insufficient

Why would birth size be related to adult gonadal steroid levels

• Birth size can be related to adult gonadal steroid levels because it reflects early nutritional and developmental conditions that program the body’s growth and endocrine system

• Smaller birth size often indicated poor fetal nutrition

Why does testosterone in human males vary across the life span

• Early life : Levels are low during childhood but spike briefly in infancy to help develop male reproductive organs

• Puberty : Levels rise sharply to trigger sexual maturation, muscle growth, voice deepening, and fertility

• Adulthood : Testosterone stays high to maintain reproductive function, muscle mass, and libido but gradually declines with age due to natural aging of the testes and changes in hormone regulation

How can menarche and post-partum amenorrhea be compared

• Menarche : Is the first menstrual period, signaling the start of a womens reproductive capacity

• Postpartum amenorrhea : temporary absence of menstruation after childbirth, which naturally spaces births by delaying the return of fertility while the mother recovers and often breastfeeds

What could the role of maternal fetal conflict be in the temporal distribution of pregnancy losses

• Early in pregnancy; Embryo is not viable or imposes too high an energetic cost, the mothers body may favour early loss to conserve resources for future, healthier pregnancies

• Later in pregnancy; Fetus grows, may demand more resources increasing risks like pre eclampsia

Why did John M. Thoday, 1973 stated that “No Characteristic is inherited, and none is acquired. All are developed”

Genes don’t give you traits but can influence how much you get of the traits such as hair or eye colour. Genes wont give the colour but influence it to be that colour

How can plasticity evolve

• Environmental variation exists : Environment changes in ways that affect survival and reproduction, individuals that can adjust their traits have an advantage

• Costs and benefits favour flexibility : When the benefits of being flexible outweigh the energetic or development costs, natural selection favours genes that enable plastic responses

How is it possible for genes within a genome to be in conflict with each other

• Selfish genetic elements ; some genes can spread themselves in the genome even if they harm the organisms overall fitness

• Parent-offspring conflict ; Genes inherited from the mother and father may favour different resource demands; for example paternally derived genes may limit this to protect the mother health and reproduction

• Sexual conflict : Genes that benefit on sex can harm the other (genes that increase male mating success but lower female fertility)

Why would the mating system of a species affect maternal conflct

• In species with multiple mates; Fetus may carry genes from father unrelated to the mother future offspring, so paternal genes favour extracting as many resources as possible now, increasing conflict with mothers interest to conserve resources to herself

• In monogamous species; Paternity is more certain, so both maternal and parental genes have more aligned interests in balancing current fetal demands with the mothers long term reproductive health, reducing conflict

Expect mothers, fathers and children to always be in ‘biological conflict’ in other words should we expect them to collaborate on some tasks or always compete

• Collaboration ; Parents and children share genes, so helping each other often maximize everyone’s genetic fitness. For example parents invest care and protection, while children cooperate by signaling needs honestly and bonding socially

• Conflict ; At the same time, there are built in conflicts over how much care or resources should go to this child versus future siblings or the mother s and father competing genetic interests in a childs development

Why do tissues grow and mature following different patterns

• Vital organ (brain); develop early and rapidly to ensure survival and learning

• Reproductive tissues; mature later, timed with puberty when the body is big and healthy enough

• Muscle and bone ; often grow quickly during adolescence to support increased activity and reproductive success

What is the trajectory of human growth

• Rapid growth in womb

• Rapid growth in infancy

• Pubertal growth spurt

What is the difference between growth and development

• Growth; refers to the increase in size or mass

• Development; means the progression of functional and structural changes

Growth canailzation

Tendency for an organisms growth to stay on a typical, stable path despite minor environmental or genetic disturbances

Breast feeding is the best why

• Provides perfect balance of nutrients, antibodies and enzymes tailored for the babys growth and immune system

• Contains antibodies that help protect infants from infections and disease

• Strengthens emotional bonding between mother to baby

• Minimizes the exposure of pathogens for the infant

Why is weaning consider a critical developmental bottleneck

• Transition from same, nutrient rich breast milk to other foods that may be less nutritious or expose the child to infections

• During this time, the childs immune system and digestive system are still developing, making them more vulnerable to malnutrition and disease

Why do humans grow slowly compared to other mammals

• Prolonged growth period supports the development for large brains, complex learning, and social skills needed for survival in complex societies

• Slow growth allows more time for children to acquire knowledge, build social relationships, develop skills before becoming independent

Describe sex differences in the timing and intensity of the adolescent growth spurt

• Timing; Girls usually start growth spurt two years earlier than boys. 9-11 for female and 11-13 for boys

• Intensity; Boys generally have a more intense and longer lasting spurt

Why is puberty considered a critical life history transition

• Shift from childhood to reproductive maturity, enabling an individual to produce offspring and pass on genes

• It triggers major biological, physical and social changes like rapid growth, sexual development and new social roles

What is the role of hypothalamus in that transition

Releases GnRH which signals the pituitary gland to produce LH and FSH

Could the role of the hypothalamus be seen as an adaptation

Yes its regulating puberty can be seen an an adaptation because it allows humans to time sexual maturation in response to internal and external conditions

What are the correlates of the HPG maturation

Why and how are reproductive and skeletal maturation related for women

Reproductive and skeletal maturation are linked in women because estrogen from the ovaries drives both puberty and bone growth, ensuring the body is strong and developed enough for pregnancy and childbirth. Estrogen causes the growth spurt and later fuses growth plates, aligning bone maturity with reproductive readiness.