Lecture 9&10 Flashcards
What are the 3 types of environments
Modes of environmental effects on growth:
1. unconstrained
- environment is supportive, individual achieves full potential
2 patterned or channelled
- growth is shaped by environmental pressures leading to developmental adaptations in response to challenges
3. constrained
- phenotypic plasticity does not allow for a complete adaptation
- growth is constrained and the full impact of the challenges depends on timing and severity of the insult
The relationship between mothers and unborn offspring is marked by?
(the baby’s first environment is the mother)
- constrains in the quality of the mothers environment, which necessarily translate into the quality of the fetus’s environment
- the conflicts of interests between the players invovled
External Constraints –> 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
- in certain cases (e.g., IUGR: Intrauterine Growth Restriction), survival is possible but it comes at a cost which can be developmental issues or future health problems
The resulting post-natal phenotypes may represent:
1. the unavoidable costs of prenatal constraints
2. the costs of prenatal adaptations to those prenatal challenges
3. predictive adaptive responses
- Unavoidable costs have unavoidable results
No benefits associated - the result of not having enough resources. A small phenotype, for example, could simply be the result of scarce energetic resources
- The costs of prenatal adaptations
Surviving in utero challenges may require changes in developmental trajectories, often trade-offs such as lower quality post-natal phenotype (e.g., prioritising neural development may result in increased risk of metabolic syndrome later in life)
- The adaptations made to survive prenatal challenges often come with trade-offs. For example, if a fetus prioritizes neural development to ensure proper brain function, it may do so at the expense of other areas, such as metabolic health. This can lead to an increased risk of metabolic syndrome later in life.
- predictive adaptive responses
Phenotypic changes that do not provide immediate advantages but may aid with predictable future challenges (e.g., early exposure to elevated maternal cortisol may affect stress axis activity later in life - those changes may be adaptive)
- PARs refer to phenotypic changes that may not provide immediate advantages but are thought to prepare the organism for predictable future challenges.
- early exposure to elevated levels of maternal cortisol can influence the development of the stress axis in the offspring. This suggests that the fetus is capable of “predicting” future stressors based on the maternal environment and adapting accordingly
- While these changes may not seem beneficial in the short term, they can be adaptive in the long run, helping the individual cope with similar stressors later in life
How can developmental plasticity help survive pre or post-natal challenges? (Example: Daphina)
Developmental plasticity refers to the ability of an organism to change its development in response to environmental cues.
Example of developmental adaptation - Daphnia: Daphnia, commonly known as water fleas, can grow protective structures, such as helmets and spikes, when they detect chemical cues (pheromones) indicating the presence of predators. This is a clear illustration of how environmental signals can trigger adaptive changes in morphology.
- the ability to develop these protective features in response to perceived threats enhances the chances of survival for Daphnia in predator-rich environments. This example shows the importance of developmental plasticity as a mechanism that allows organisms to respond dynamically to their surroundings.
conflicts can start in utero
Mother-offspring relationships are marked by conflicts of interests between all people involved (usually: mother, fetus, and father)
There can even be intra-genomic conflicts, suggesting that there can even be conflicts within the genome of an individual. This refers to situations where different genes can have competing interests, possibly inherited from each parent, further complicating the interaction during development.
Intra-genomic conflict hypothesis
Predicts different replication strategies by individual genes within a genome leading to conflicts that affect the phenotype
This phenomenon could be the result of different transmission strategies within parent (e.g., meiotic drive) or competition between genes of different parental origins
Meiotic drive: segregation distortion during meiosis (e.g., some alleles are over-represented in oocytes)
- In meiotic drive, certain alleles (versions of a gene) can manipulate the meiotic process to ensure that they are more likely to be included in the gametes, thus increasing their representation in the offspring.
genotype, phenotype, and environment equation
phenotype = genotype + environment
Some genes are part of other genes environment
The presence of particular alleles on the genome can affect the transmission of other alleles AND affect the expression of other alleles!
What would benefit genes, according to their parental origin
Maternal genes:
- maximise inclusive fitness of the mother
- modulate investment according to offspring quality
- sensitive to tradeoffs between offspring quantity and quality
- sensitive to tradeoffs between current and future offspring
Paternal genes:
- survive at (almost) all costs
- take as much from mom as possible (despite costs to siblings)
paternal genes prioritize the immediate survival and success of the offspring, often at the expense of the mother’s resources or the well-being of siblings. The paternal strategy is more about extracting as much benefit as possible to ensure the survival and competitiveness of their specific genes. This can lead to conflict between maternal and paternal genetic interests, as the latter may push for greater resource allocation that is not always in line with the mother’s long-term genetic fitness strategy.
Genomic Imprinting Conflict - Selective pressure on paternal genes
In species with promiscuous mating systems, where a mother’s brood might have multiple fathers, there’s a decreased genetic relatedness of offspring to any particular father. This can create a conflict where paternal genes are pressured to ensure their survival and propagation, often by influencing the mother’s resource allocation.
Paternal genes may evolve strategies to either enhance maternal investment in their offspring or inhibit maternal genes that promote resource-sharing amongst all offspring. This often involves silencing maternally expressed genes that suppress such paternal strategies.
Genomic Imprinting Conflict - Selective Pressure on Maternal genes
- Genomic imprinting conflict refers to the evolutionary struggle between maternal and paternal genes within a developing organism, each trying to influence the organism’s traits in their favor.
- The maternal genes are under pressure to regulate maternal investment wisely, favoring those that optimize resource allocation for the mother’s benefit and the survival of all her offspring. They also work to silence paternal genes that might increase resource demands on the mother, which can be detrimental if they require excessive investment.
- This can lead to conflicts during pregnancy because paternal genes may favor maximizing fetal growth even at the expense of the mother’s health, while maternal genes may favor a balance between fetal growth and maternal well-being.
if a species mating system can affect maternal-fetal conflict, does it affect us humans?
Yes, the mating system can shape the evolutionary strategies of both maternal and paternal genes, influencing how they negotiate resource allocation and investment in offspring, which is a critical aspect of reproductive success and evolutionary fitness in humans.
For example, in a more monogamous context, maternal genes might be more inclined to invest heavily in offspring, knowing that the paternal genes are also closely related and invested in the same offspring. Conversely, in more promiscuous contexts, paternal genes might push for greater resource allocation to their specific offspring, potentially leading to increased conflict over resources.
what is our mating system?
The mating system of a species refers to the way in which it pairs for reproduction. In humans, the predominant mating system is often described as monogamous, where one male and one female form a pair bond for mating and raising offspring. However, human mating systems are complex and can include variations such as polygamy (one individual having multiple partners) and serial monogamy (having multiple monogamous relationships over a lifetime).
how monogamous are Homo sapiens?
While many cultures promote monogamous relationships, the actual practice can vary widely. Research indicates that while many people enter into monogamous marriages, infidelity and non-monogamous relationships are also common. This suggests that while monogamy is a social norm, it is not universally adhered to.
- in terms of selective pressures leading to evolution, Homo sapiens is a species with a moderate degree of polygamy
- approx 38% of Canadian marriages end in divorce
Potential Outcomes in any “Tug of War”
“tug of war,” the image uses a metaphor to explore potential outcomes in various situations that involve opposing forces or interests. It highlights three possible outcomes: dynamic equilibrium, where neither side gains dominance; one side winning, which results in a negative outcome for the other; and a situation where both sides lose. This analogy is used to explain how these scenarios can influence developmental trajectories, emphasizing the lasting impact such conflicts can have on growth and progression.
Dynamic equilibrium suggests that a balance is reached where both sides maintain their positions, potentially leading to stability. However, if one side wins, it could mean a disadvantage or setback for the other, illustrating an imbalance that could impede progress. Alternatively, if both sides lose, it indicates mutual failure to achieve desired outcomes. This concept serves as a reminder of how such conflicts impact development, whether in personal growth, relationships, or broader societal issues.
*“Tug of Wars” do affect developmental trajectories
Potential times for conflict during reproductive and developmental processes.
- Conception
- Early survival of the embryo
- Placentation
- Intrauterine growth
- Gestational length
- Early post-partum
- Post-natal development
- Conflict at conception and early survival of the embryo
- deteriorating environments may lead to mechanisms preventing conception, including anovulatory cycles (ovulation does not occur), hostile vaginal environment
- embryos with developmental problems may change the mother’s cost-benefit balance with respect to a reproductive event and trigger the suppression of reproductive function by, for example, preventing implantation
Embryonic Viability: If an embryo exhibits developmental problems—such as genetic abnormalities or poor growth—its chances of surviving to birth and thriving after birth may be compromised. This can lead the mother to reassess the potential benefits of continuing the pregnancy. - This adaptive response suggests that the reproductive system is not a passive process but actively responds to the conditions and quality of the developing embryo. This mechanism can be seen as a way for mothers to optimize their reproductive success by ensuring that they invest in embryos that have the best chance of survival and future reproductive success.
Preventing implantation
Preventing Implantation: This refers to the body’s ability to stop an embryo from attaching to the uterine lining.
Potential Proximate Mechanisms: Changing uterine chemical (e.g. luteal deficiencies, failure to activate the IL-1 system [a regulator of uterine receptivity]) or physical environment (excessive uterine contractility: The uterus is a muscular organ, and its contractions can influence implantation. If the uterus is overly contractile, it may physically expel the embryo or create an environment that is not conducive to implantation)
These mechanisms are not necessary independent or mutually exclusive (For example, hormonal changes can influence both the chemical and physical conditions of the uterus simultaneously). Progesterone promotes local vasodilatation and uterine musculature quiescence by inducing nitric oxide synthesis in the decidua (uterine lining during pregnancy)
Local Vasodilatation: Progesterone promotes vasodilatation, which is the widening of blood vessels. This process increases blood flow to the uterine lining (decidua), providing it with the necessary nutrients and oxygen to support a developing embryo.
Uterine Musculature Quiescence:
- Muscle Relaxation: Progesterone also induces quiescence in the uterine musculature, meaning it helps relax the uterine muscles. This relaxation is important because excessive uterine contractions can hinder implantation and disrupt the early stages of pregnancy.
- Nitric Oxide Synthesis: Progesterone promotes the synthesis of nitric oxide (NO) in the decidua. Nitric oxide is a signaling molecule that plays a significant role in vasodilatation and muscle relaxation. By increasing nitric oxide levels, progesterone helps ensure that the uterine environment is both well-perfused (with blood) and calm (with relaxed muscles), which is conducive to implantation.
- Pregnancy loss as a consequence of poor periconceptional conditions
Periconceptional refers to the period surrounding conception, specifically the time frame just before and immediately after fertilization occurs.
Possible correlation between high cortisol levels and early pregnancy loss, suggesting that stress management may be crucial for improving periconceptional conditions and pregnancy outcomes.
can mothers bodies assess the ability of an embryo to develop?
Potential mechanisms: By the levels of cytokines or human chorionic gonadonthropin (hCG) the embryos produce
- Cytokines are small proteins that play a crucial role in cell signaling, potentially influencing immune responses and communication between cells, while hCG is a hormone produced by the placenta after implantation, crucial for maintaining pregnancy.
- The mother’s body may use the levels of these substances to gauge the embryo’s viability. If an embryo produces optimal levels of cytokines or hCG, it might signal to the mother’s system that it is developing properly, leading to supportive physiological adaptations. Conversely, abnormal levels could indicate developmental issues, potentially leading to early pregnancy loss
This process is part of the broader field of maternal-fetal communication, which is essential for understanding how pregnancies are maintained and why some fail.
- Conflict at placentation
The fetal tissue invades the maternal spiral arteries, which play a key role in regulating blood flow to the placenta. These changes are critical for ensuring that the developing fetus receives adequate nutrients and oxygen. The process is complex and carefully regulated, involving the secretion of human placental lactogen (hPL) among other hormones and factors. This secretion can affect the diameter of the maternal spiral arteries, thereby increasing the blood volume reaching the placenta.
The interplay between the maternal and fetal tissues at the placenta can create a biological “conflict” because while the fetus benefits from increased blood flow, this can sometimes challenge maternal hemodynamics and nutrient reserves. Human placental lactogen, in particular, serves to modify maternal physiology to better support fetal demands, often influencing maternal metabolism and circulation.
- Conflict at placentation & 4. Consequences for intra uterine growth
Consequences for the mother
- increased blood to placenta results in increased nutrients to the fetus
- Moms can’t reduce bloods nutrient content without reducing energy supply to their own tissue
- the maternal defence is vasoconstrictions (reduction of the diameter of blood vessels), which results in increased blood pressure
Pre-eclampsia & eclampsia
Pre-eclampsia is a condition that typically occurs after the 20th week of pregnancy and is characterized by high blood pressure (hypertension) and signs of damage to other organ systems, most commonly the kidneys and liver.
- leads to decreased blood flow to the placenta causing complications such as premature births and low birth weight (LBW)
- also leads to decreased blood flow to the mothers kidneys, brain, liver and retina
Pre-eclampsia can leed rapidly to eclampsia, with dire consequences for mother and child, including maternal cerebral haemorrhage, seizures, and death, as well as fetal stillbirths
- preeclampsia can be treated (anti-hypertensives and magnesium sulphate) but that only definite “cure” is delivering the fetus
Eclampsia is a severe progression of pre-eclampsia that involves the onset of seizures in a woman with pre-eclampsia. It is a life-threatening condition.
The risk of pre-eclampsia increases with changes in sexual partner
- only 4.7% of women who conceive with the same partner develop pre-eclampsia vs 24% of those who conceived pregnancies with different partners (donor-insemination, donor-embryo pregnancies show higher risks)
- sexual cohabitation, frequent intercourse and oral sex with the same partner have been reported to reduce the risk of preeclampsia
How are the effects of pre-eclampsia mediated? What is the role of the male partner(s)?
- some pre-eclampsia effects appear to be mediated by immunological interactions between male (e.g. semen, fetal tissues) and female tissues
The role of the male partner: certain men appear to be linked to higher risks (double the risk of pre-eclampsia in their partners)
could pre-eclampsia have an effect on sexual selection in humans?
given the selective pressures this condition exerts (estimated to affect a ~10% of pregnancies) - pre-eclampsia may have had some effect in the evolution of human mating systems
Health implications of viewing pre-eclampsia as a paternal/fetal strategy
More needs to be learned, but the following approaches may help:
- strengthen maternal counter-adaptations to limit fetal manipulation (improving mothers immune response, hormonal regulation, and improving vascular health)
- preventing nutritional conditions that trigger it
Develop preventive tests for:
- men who had partners who experienced pre-eclampsia
- women who change partners between pregnancies
- More on intrauterine growth: gestational diabetes or “the fight for sugar” between mother and fetus
- the placenta releases human placental lactose (hPL), affecting maternal receptors, increasing insulin resistance, keeping blood glucose (sugar) circulating for a longer period of time after each meal
- 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
- this conflict can result in gestational diabetes (3-5% incidence)
Health risks:
- really large babies are associated with birth difficulties
- increased risk of maternal non-gestational diabetes
- newborns 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
- As the pregnancy progresses, the fetus produces hormones that influence its own development and the timing of birth. Meaning the fetus is not entirely passive; it can actively participate in signaling when it is ready to be born. - Parturition is triggered by the adrenal glands leading to the maturation of the lungs
- The process of labor (parturition) is initiated by hormonal signals from the adrenal glands. These glands produce hormones such as cortisol, which play a key role in preparing the fetus for birth. One of the critical functions of these hormones is to stimulate the maturation of the fetal lungs, making them ready for breathing air after delivery. - A deteriorating environment can affect the maturation of the adrenals leading to premature births
- If the intrauterine environment becomes unfavorable—due to factors like maternal illness, poor nutrition, or stress—it can negatively impact the development and function of the fetal adrenal glands. This impairment may lead to premature birth, as the fetus may not be able to produce the necessary hormones to signal that it is ready to be born. - Cost-benefit analysis of staying in utero vs being born early may play a role (e.g.: in case of infection better be born, even when small-for-gestational-age deliver early)
- The fetus may engage in a sort of “cost-benefit analysis” regarding the timing of birth. If the intrauterine conditions are poor (e.g., due to infection or other stressors), the fetus might be better off being born early, even if it means being smaller than expected for its gestational age. This decision-making process is thought to be influenced by the fetus’s ability to assess its environment and the potential risks of remaining in the womb versus the risks of premature birth
Growth in utero: birth weight (BW)
BW: a proxy for growth in utero
Median BW = 7.4lb
LBW = < 5.5lb
- heavily influenced by maternal nutrition and disease
- low correlation with paternal size (r <0.3)
- babies size tend to be more strongly associated with maternal than paternal size
Growth in utero: maternal nutrition and BW
- The “hunger winter” during WW2, a classic example of the relationship between maternal nutrition and BW
- women were consuming<800 calories/day
- BW decreased by 1lb
- almost 50% of babies were born w LBW
Growth in utero: intrauterine growth retardation (IUGR)
IUGR is when a fetus is smaller than expected for its gestational age, often weighing below the 10th percentile for its age. This condition is also referred to as being “small for gestational age” (SGA)
- IUGR babies appear thin, pale, have loose, dry skin and thin and dull-looking umbilical cords
Proximate factors associated with IUGR
Maternal factors:
- High BP, chronic kidney disease, diabetes and CVD, malnutrition, anaemia, infections, substance use (alcohol, drugs, smoking)
Factors involving the uterus and placenta:
- decreased blood flow
- placental abruption (detachment from the uterus)
- placenta previa (attaches low in the uterus)
Factors related to the fetus:
- multiple gestation (twins, triplets)
- chromosomal and birth anomalies (chromosomal anomalies can occur when there are extra chromosomes, missing chromosomes, or structural changes in the chromosomes) (birth anomalies are birth defects, are structural or functional abnormalities that occur during fetal development. These can affect various parts of the body, including the heart, brain, limbs, and other organs)
IUGR Consequences
- organ growth limitations
- low fetal heart rate (due to blood flow restrictions)
Higher risk for:
- stillbirth
- low Apgar scores
- meconium aspiration
- hypoglycemia
- body temperature regulation problems
- polycythemia (too many red blood cells)
All of which has long-term postnatal developmental & health consequences
Treatment for IUGR
Effects can be minimised, but not reversed, with interventions that include:
Maternal nutrition: may increase gestational weight gain and fetal growth
Maternal bedrest: may help improve circulation to the fetus
Delivery: if IUGR endangers the health of the fetus then an early, induced, delivery may be necessary
- Post-natal conflict: Early post-partum
Mothers regain control, postpartum depression (15% of women) can lead to neglect and in extreme cases, postpartum psychosis (1 per 1000) may lead to infanticide
Evolved mechanisms for maternal investment avoidance?
Contributing factors include
- lack of social and emotional support
- low sense of self-esteem (postpartum appearance)
- feelings of inadequacy and isolation
- financial problems
- major life challenges such as moving or starting a new job
- Post-natal development: Factors affecting growth trajectories
- pre and perinatal problems
- nutrition
- high altitude hypoxia
- pollutants (drugs, DDT, lead, etc)
- maternal health conditions
- psychosocial environment
- social and economic status
Growth problems in utero
- long-lasting consequences including fetal programming (refers to the concept that environmental factors during pregnancy can influence the development and long-term health of the fetus) and chronic diseases in adulthood
- growth problems in childhood can also have psychosocial consequences
Growth Canalizaiton
Growth Canalization describes the tendency of individuals to maintain a consistent and predictable pattern of growth despite environmental variations or challenges
- A tendency to keep a narrow and predictable track of growth, usually along a centile line
- Growth canalization suggests that individuals tend to follow a specific growth trajectory that is relatively stable over time. This trajectory is often represented on growth charts as centile lines, which indicate the expected range of growth for a population based on age and sex.
- Growth canalization is important for assessing child development and health. It helps healthcare providers identify children who may be experiencing growth issues or deviations from expected growth patterns.
Thrifty Phenotype Hypothesis (aka Barker hypothesis)
Suggests that poor prenatal nutrition can lead to the development of smaller body sizes and lower basal metabolic rates after birth. This adaptation aims to conserve energy by promoting efficient fat metabolism. Such changes can increase the risk of developing metabolic syndrome later in life, which includes conditions like obesity, diabetes, and cardiovascular disease.
On the positive side, this adaptation may help individuals survive in environments with scarce resources by conserving energy efficiently. However, when there’s a mismatch between prenatal and postnatal nutritional environments (for example, poor nutrition in the womb followed by abundant food in adulthood), these adaptations may become disadvantageous and lead to health complications
Infant 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
- weaning period is one of the most vulnerable for growth and development
Extremely inadequately nutrition: protein deficiencies
Protein-energy malnutrition (PEM) affects 50% of children worldwide
- Kwashiorkor tends to develop after 18 months of age as a mother weans a child and replaces breast milk with a diet low in proteins and rich in starches and carbohydrates (characterised by edema)
- thin limbs, enlarged belly
- severe growth faltering
- overall health and mental impairment
Protein and Caloric deficiencies
- when severe PEM is combined with caloric deficient, dehydration, etc, there is an increase risk of infections and circulatory disorders leading to marasmus (can be lethal)
- low breast milk production/intake or low quality “bottle feeding” can result in early (<18 months) onset marasmus
Overnutrition - modern mismatch
- “efficient metabolism,” which was advantageous in historical contexts of food scarcity, becomes problematic in environments abundant with high-calorie foods like those from fast-food chains and readily accessible through the internet.
- major problem in affluent countries, but also in less privileged populations
- low levels of physcial activity
- hyper caloric diet
Growth and SES: Possible causes of this association
- nutritional status
- disease load (refers to the prevalence of illnesses and health conditions)
- access to medical care
- psychosocial stress
Psychosocial short stature (aka psychosocial dwarfism or the Kaspar-Houser syndrome)
A disorder of growth failure and/or delayed development (infancy, childhood, puberty and adolescence) observed in association with emotional deprivation and/or a pathologic psychosocial environment resulting from a disturbed relationship between child and caregivers
Catch-up Growth
Children born in restricted environments placed in a more advantageous environment, grow fast and catch up with those who enjoyed a more nourishing environment
Catch-up growth: An unusually rapid height increase, considering age and/or maturity of an individual, following a transient period of growth inhibition
- children can “lag” then accelerate achieving the same height as their peers
- when children grow without problems, the pattern of growth is more or less parallel to some imaginary “pathway or canal” (centile line)
- canalisation makes it possible to identify a period of catch-up growth
Growth issues of genetic origin can be solved by early interventions - Case study
Case study: 3 year old
Diagnosis: Growth hormone insufficiency (low GH peaks)
Treatment: daily GH injections
A critical life history transition
Childhood (growth and maintenance) –> PUBERTY (critical transition) –> adulthood (reproduction)
There is a strong genetic component determining the timing and pace of the puberty transition
- yet, as w all traits, the environment can affect the expression of the genotype and thus the phenotype
- thus, the timing and pace of this transition are sensitive to internal (developmental) and external (ecological) factors
- Precise proximate determinants and mechanisms are still being studied
