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組員 : 李誠裕 , 胡家怡 , 陳昱儒 , 陳彥旭 , 黃郁雲 , 鄭元誠

The rarity of twins: a result of an evolutionary battle between mothers and daughters- or do they agree?. From: Gine et al. 2009. Behav. Ecol. Sociobiol . 63: 1133-1140. 組員 : 李誠裕 , 胡家怡 , 陳昱儒 , 陳彥旭 , 黃郁雲 , 鄭元誠. Introduction. Parent-offspring theory (POC)

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組員 : 李誠裕 , 胡家怡 , 陳昱儒 , 陳彥旭 , 黃郁雲 , 鄭元誠

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  1. The rarity of twins: a result of an evolutionary battle between mothers and daughters- or do they agree? From: Gine et al. 2009. Behav. Ecol. Sociobiol. 63: 1133-1140 組員: 李誠裕,胡家怡,陳昱儒, 陳彥旭,黃郁雲,鄭元誠

  2. Introduction • Parent-offspring theory (POC) • the optimal levels of PI is often different between parent and their offsprings. (Trivers, 1974) • Siblicide • The extreme situation caused by POC • In birds & mammals (Mock & Parker 1997; Frank et al., 1991) • In humans?

  3. Twins of humans • Abortion rate: • Generally, only about 15% of abortion cases were spontaneous abortions • In twins, 30-78% of abortion cases were spontaneous abortions (Forbes, 1997) • Why? Hormone secretion by selfish twins! (Mock & Parker 1997)

  4. Human twinning rate • The frequency of twins in humans : 0.2-2% • Parent-offspring Conflict Hypothesis (POCH)? • The Insurance Egg Hypothesis (IEH) (Anderson, 1990) • The Natural Selection Hypothesis (NSH) (Lummaa, 1998)

  5. Aim • To test if the rarity of twins is due to POC • Prediction • offspring win: twins have higher fitness than mothers in family where one twin survived • parent win: mother have higher fitness than twins in families were both twin survived

  6. Methods • Demographic Data • Population of Smola & Soknedal in Norway • From 1700-1900 AD • Record life history traits for woman • Number of children • Number of adult children • Number of children married • Reproductive period • Birth interval

  7. Demographic Data Mother M-So M-STw M-MT singletons from no-twin families singletons from twin families twins P1(M-Tw) Offspring M-Tw P2 (M-Tw) mothers are twins

  8. Correlation of LRS and other life history traits *: compared with (M-So) †: compared with P2(M-Tw)

  9. Correlation of LRS and other life history traits • Mothers of twins have high quality (Sear et al. 2001; Helle et al. 2004)

  10. Is there any conflict between the mothers of twins and the twins? • Inclusive fitness: • twin growing up as a singleton: NAC + 0.5×0.0NAC • twin growing up with a co-twin: NAC + 0.5×2.5 (because mean NAC=2.5)

  11. P1(Mother) P1(Daughter) P2(Mother) P2(Daughter) • Post hoc (Tukey's HSD test) analysis 5.5 3.8 * P2(Mother) P2(Daughter) V.S. (P=0.048) P1(Mother) V.S. P1(Daughter) (P=0.40) 4.5 6.3 Is there any conflict between the mothers of twins and the twins? • There’s significant different among the four groups’ inclusive fitness (F3, 114=3.7, P=0.014) 4.5 6.3 5.5 3.8

  12. Post hoc (Tukey's HSD test) analysis 5.5 3.8 * P2(Mother) P2(Daughter) V.S. (P=0.048) P1(Mother) V.S. P1(Daughter) (P=0.40) 4.5 6.3 However… • Selfish twins maximized their inclusive fitness by the • death of their co-twins • Mothers of twins increased their inclusive fitness by • rearing both twins to adulthood.

  13. However… In mother view: P1: (1×6.3=6.3 grandchildren) P2: (2×2.5=5.0 grandchildren)

  14. Conclusion • This findings do not provide support for the idea that POC is responsible for the rarity of twins in humans. • twins maximize their inclusive fitness by growing up as singletons • mothers of twins seem to gain by raising both twins to independence • but it is only short-term benefit

  15. Thanks for your attention~

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