Theory and Some Data Parent-Offspring Conflict Theory. Research Example The Evolutionary Ecology of Low Birth Weight

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1 1) Bioassay: Health and nutrition? Adequate 2) Socioassay: Security? Poor Wait and see; maybe things will get better Theory and Some Data Parent-Offspring Conflict Theory Research Example The Evolutionary Ecology How Could this Research be Done? Research Project? Poor Adequate Continue G&D; maximise size, learning, etc Reproduce early Parental investment and parent-offspring conflict theory Effects on fetus 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 1

2 So, now lets find the average birth weight. Resolution to the Paradox Hamilton Inclusive Fitness Trivers Parent-Offspring Conflict Theory Haig POC Applied to Pregnancy Average (3,000 3,500 grams) is lower than the best possible outcome for the baby (3,500 4,000) Inclusive Fitness: The ability of an individual to get his/her genes into future generations. 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! WD Hamilton 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 Why Does This Conflict Occur? 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 2

3 Why Does This Conflict Occur? How Does This Fit Into What YOU Know? Mother s Optimum Fetus optimum The Evolutionary Ecology A Theoretical Synthesis Why Might a Parent Choose to Invest Less? r-selection: minimax strategy of downside risk protection (minimizes chance of maximum possible fitness cost i.e., lineage extinction) Population Size K Carrying capacity 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) Time What Can We Predict From The Trade-off Between Current and Future Reproduction? Ecological niche (adaptive problem) Age at menarche Indian girls adopted into Sweden Privileged Indian urban 13 Swedish 13.7 Urban Indian 14.2 Rural Indian 14.4 Rural Indian Proos, Hofvander and Tuvemo Menarcheal age and growth pattern of Indian girls adopted into Sweden. Acta Paediatr. Scand. 80:852. 3

4 How Does This Relate to Low Birth Weight? Proportion of SGA by Age at Menarche Quality Quantity Trade-off Low quality = LBW Prediction: Individuals who have an earlier menarche are more likely to have LBW babies. Adjusted Odds Ratio Age at Menarche Early Average Late Age at Menarche Early Average Late Gestational Age by Obstetric Estimate Last Menstrual Period Scholl et al Effects of early maturation on fetal growth. Annals of Human Biology, 16(4): How Does this Relate to Low Birth Weight? Parent-Offspring Conflict Ecological niche (adaptive problem) 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? Parent-offspring conflict large placenta for birthweight Foetal trade-offs LBW (foetal side of IUGR) H H 2 Earlier Menarche, LBW and Larger Placenta How Would You Actually Test These Predictions?? Ecological niche (adaptive problem) The Evolutionary Ecology Evolutionary Theory: A Tool for Making Testable Predictions Parent-offspring conflict large placenta for birthweight Foetal trade-offs LBW (foetal side of IUGR) H 3 H 2 4

5 Ecological niche (adaptive problem) Costs of reproduction (trade-offs) Maternal trade-offs BMI throughput to foetus (maternal side of IUGR) Parent-offspring conflict large placenta for birthweight Foetal trade-offs LBW (foetal side of IUGR) H 3 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 H 2 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 WARNING! Membranes (intact, colour) Some gross placenta (human) photos to follow 5

6 Parenchyma (dimensions, colour and shape) Cord Insertion Is a larger placenta adaptive or beneficial? 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 DM (aga) DM (lga) CON (aga) CON (lga) 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, 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, 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 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 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. 6

7 Human Development Index (r = -.87; p <.001).3 0% 10% Percent 20% of women 30% Relationship between UN Human Development Index and percent of total births to women aged who gave birth before they were 18. HDI = mean years of education standardised per capita income life expectancy at birth (Source: Alan Guttmacher Institute 1998) 40% 50% 7