theory and some data parent-offspring conflict theory ... · pdf fileattachment early stress...

1

1) Bioassay:Health and nutrition?

Adequate PoorWait and see; maybe

things will get better

2) Socioassay:Security?

AdequatePoor

Reproduce

early

Effects on

fetus

Parental investment

and parent-offspring

conflict theory

Continue G&D; maximise

size, learning, etc

• Theory and Some Data

– Parent-Offspring Conflict Theory

• Research Example

– The Evolutionary Ecology of Low Birth Weight

• How Could this Research be Done?

– Research Project?

Maternal Obligation to Provide Parental Investment Maternal Obligation to Provide Parental Investment

What Are We Really Talking About?Birth weight is often presented as a

textbook example of stabilising selection

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So, now lets find the average birth weight.

Average (3,000 – 3,500 grams) is lower than the best possible outcome for the baby (3,500 – 4,000)

Resolution to the Paradox

Hamilton – Inclusive Fitness

Trivers – Parent-Offspring Conflict Theory

Haig – POC Applied to Pregnancy

Inclusive Fitness: The ability of an individual to get his/her genes into future generations.

WD Hamilton 1936 - 2000

Parent-offspring conflict:

• Parent and offspring are not genetically identical

• They both aim to maximise Inclusive Fitness

• Offspring wants more Parent wants to give less = CONFLICT!

Why Does This Conflict Occur?

• Maximise Mum’s Inclusive Fitness

– Reduce care when influence on survival decrease, start investing in her next offspring

• Maximise Offspring’s Inclusive Fitness

– Maintain its own benefit until it is outweighed by the cost to its siblings


• Mum & Baby – 50%

– But, Mum to all Offspring –50% (same)

• Offspring with itself – 100%

– Offspring with sibling – 50%(or less if diff Father!)

• Therefore, current offspring wants more than mother wants to give = conflict

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Mother’s Optimum

Fetus’ optimum

How Does This Fit Into What YOU Know?

The Evolutionary Ecology of Low Birth Weight

A Theoretical Synthesis

Why Might a Parent “Choose” to Invest Less?

Po

pu

lati

on

Siz

e

Time

K

r-selection: minimax strategy of downside risk protection (minimizes

chance of maximum possible fitness cost – i.e., lineage extinction)

K-selection: maximin strategy of setting stage for the future

(maximizes chance of minimum possible fitness benefit – i.e.,

2 offspring for lineage maintenance; zero population growth)

Carrying capacity

↑↑↑↑ environmental risk and uncertainty Ecological niche (adaptive problem)

↑↑↑↑ early psychosocial stress, insecurity

Maximise current reproduction

• early menarche

• early first sex

• early childbearing

Phenotypic representation (subjectiveexperience) of ecological niche

Optimal reproductive strategy(adaptive solution)

Components of strategy(mechanisms, tactics)

H1

An Evolutionary

Ecological Model

of Low Birth Weight

What Can We Predict From The Trade-off Between Current and Future Reproduction?

11.6

12.6

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13.7

14.214.4

10

10.5

11

11.5

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12.5

13

13.5

14

14.5

India

n girl

s adopte

d

into

Sw

eden

Privile

ged India

n

urban Sw

edish

Urb

an India

n

Rura

l India

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Proos, Hofvander and Tuvemo 1991. Menarcheal age and growth pattern of

Indian girls adopted into Sweden. Acta Paediatr. Scand. 80:852.

Age at

menarche

4

How Does This Relate to Low Birth Weight?

• Quality Quantity Trade-off

• Low quality = LBW

• Prediction: Individuals who have an earlier menarche are more likely to have LBW babies.

0

0.5

1

1.5

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2.5

Ad

juste

d O

dd

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Age at Menarche

Early Average Late

Gestational Age by

Obstetric Estimate Last Menstrual Period

Age at Menarche

Early Average Late

Scholl et al. 1989. Effects of early maturation on fetal growth. Annals of Human Biology, 16(4):335-345.

Proportion of SGA by Age at Menarche

How Does this Relate to Low Birth Weight?




• early menarche

• early first sex





H1

An Evolutionary

Ecological Model

of Low Birth WeightFoetal trade-offs

• LBW (foetal side of IUGR)

HH22

Parent-offspring conflict

• large placenta for birthweightH

Parent-Offspring Conflict

• Haig’s application of parent-offspring conflict to pregnancy

• Maternal restriction to fetal growth (e.g. nutrition)

• What would we expect the fetus to “do”?

• How could this be achieved?

Earlier Menarche, LBW and Larger Placenta




• early menarche

• early first sex





H1

Foetal trade-offs


H2

An Evolutionary

Ecological Model

of Low Birth Weight


• large placenta for birthweightH3

How Would You Actually Test These Predictions??

The Evolutionary Ecology of Low Birth Weight

Evolutionary Theory: A Tool for Making Testable Predictions

5




• early menarche

• early first sex





Maternal trade-offs

• ↑↑↑↑BMI• ↓↓↓↓throughput to foetus

(maternal side of IUGR)


• large placenta for birthweight

Foetal trade-offs


Costs of reproduction(trade-offs)

HH11

HH22

HH33An Evolutionary

Ecological Model

of Low Birth Weight

Assessment of Early Psychosocial Stress and Attachment

Early Stress

• A Life Events Inventory (LEI)

– Adapted for Australian populations

– New: Adverse Childhood Experiences (ACE)

questionnaire

Attachment

• The Parental Bonding Instrument

– Attachment secure/insecure

Maximising Current Reproduction

• Cannot be measured directly

• Inferred from reproductive events

• Standard demographics questionnaire

– age at menarche

– age at first sex

– age at first childbearing

Birth Weight and Placental Weight

• Hospital records

• Confounding variables

• Standardisation of placental weight

– weighing to the gram

– strip amnion to the cord

– cut chorion at the edge of placenta

– cord removed flush with the placenta

Some gross placenta (human) photos to follow

WARNING!Membranes (intact, colour)

6

Parenchyma (dimensions, colour and shape) Cord Insertion

Is a larger placenta adaptive or beneficial?

Evers, I.M., et al (2003). Placental pathology in women with type 1 diabetes and in a

control group with normal and large-for-gestational age infants. Placenta 24, 819-825.

DM

(aga)

DM

(lga)

CON

(aga)

CON

(lga)

What is the Significance of a Large Placenta?

• The Barker Hypothesis

– Fetal origins of adult disease

• Individuals who were small babies with large placentas had highest blood pressure

• Risk for hypertension in adulthood

Barker, D.J.P., Bull, A.R. et al (1990). Fetal and placental size and risk of

hypertension in adult life. British Medical Journal, 301, 259-262.

What is the Significance of Placental Weight?

• The Fetal Origins of Adult Disease

• Recent review (2002): 19/25 studies that looked at placental weight and adult disease or indicators of adult disease found associations

• Useful as guide for preliminary investigations

Godfrey, K.M. (2002). The role of the placenta in fetal programming – A review.

Placenta, 23(Suppl. A, Trophoblast Research 16), S20-S27.

Important Note

Placental weight is not the causal factor in e.g. fetal origins of adult disease, it is an indication of the many important factors that are the maternal environment

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50%40%30%20%10%0%

1.0

.9

.8

.7

.6

.5

.4

.3

Percent of women

Hu

man

Dev

elo

pm

en

t In

dex

(r = -.87; p <.001)

Relationship between UN Human Development Index and percent of

total births to women aged 20-24 who gave birth before they were 18.HDI = mean years of education

standardised per capita incomelife expectancy at birth

(Source: Alan (Source: Alan Guttmacher Guttmacher Institute 1998)Institute 1998)

theory and some data parent-offspring conflict theory ... · pdf fileattachment early stress...

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