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Evolution and Adaptation - mutation - migration - genetic drift - Natural Selection Darwin’s Postulates: (1) There is heritable variation (2) There is a struggle for existence (3) Variation influences the struggle and Natural Selection follows ... (1) There is heritable variation Heritability in selected human traits: Handedness Diastolic blood pressure Twinning Systolic blood pressure Body weight Stature and tooth size 30% 45% 50% 55% 65% 85% Fertility IQ 10-20% 60-80% (2) There is a struggle for existence Resources are limiting There is competition for resources, including mates (3) Variation influences the struggle Columbian ground squirrel dicots vs.. monocots Monocots consumed Digestive constraint Optimal diet time constraint Dicots consumed min energy constraint Mixture of monocots and dicots - Monocots limited by handling time - Dicots limited by digestion Mark Ritchie compare the predicted “optimal” diet and the actual diet for 109 individuals squirrels Monocots consumed (a) variation in the ability to forage optimally r2 = 0.94 Dicots consumed Mark Ritchie compare the predicted “optimal” diet and the actual diet for 109 individuals squirrels Monocots consumed (a) variation in the ability to forage optimally r2 = 0.94 Optimal Deviators Dicots consumed Offspring’s deviation (b) optimal foraging is a heritable trait Mothers raise offspring Offspring on their own Mother’s deviation (c) There is a struggle for existence Relative to optimal foragers, deviators have lower surplus energy intake and .... (c) Variation influences the struggle ... as a consequence, deviators have i) lower somatic growth ii) lower survival iii) smaller litter sizes Mark Ritchie’s study beautifully illustrates Darwin's Postulates in action: Heritable Variation Struggle for Existence Variation influences the Struggle but...falls short of documenting Natural Selection Evolution by Natural Selection – Guppies on the island of Trinidad Evolution by Natural Selection – Guppies on the island of Trinidad Life history traits Schooling behavior - dilutes individual risk - greater vigilance - group confusion low risk Predator-inspection behavior - method to ascertain the identity and intentions of the assailant low risk (Magurran et al. 1996) (Endler 1980) Male coloration and female choice mean # spots mean size Predation risk (cichlids) Low risk Predation risk (prawns) Correlations vs. experimental tests Haskin’s 1957 transplant experiment Transplant experiment results: black = % females schooling 10mm (Magurran et al. 1996) Summary: 1) “Natural experiment” – Guppy populations that have experienced different regimes of predation risk show different levels of anti-predator behavior 2) Transplanted (1957) high-risk guppies behave like native low-risk guppies (evolution in 34 years or ~100 generation) 3) Changes in color-patterns that function in mate choice were apparent after 13 months!! At what level does Natural Selection operate? The Individual or the Group? “lions rarely fight to the death because if they did it would endanger the survival of the species” “salmon migrate thousands of miles from the ocean to their inland spawning grounds killing themselves in the process with exhaustion to ensure the survival of the species” Wynne-Edwards proposed that organisms have adaptations to ensure its population or species controls its rate of consumption Likewise, individuals should restrict their birth rate to prevent over-population Are these accurate statements?? “lions rarely fight to the death because if they did it would endanger the survival of the species” “salmon migrate thousands of miles from the ocean to their inland spawning grounds killing themselves in the process with exhaustion to ensure the survival of the species” Wynne-Edwards proposed that organisms have adaptations to ensure its population or species controls its rate of consumption Likewise, individuals should restrict their birth rate to prevent over-population Are these accurate statements?? NO! Natural selection acts at the level of the individual, not the group Group Selection – differential survival/reproduction of groups C C C S C C S C S C CC C S C C C X C S S S C S C CC C S C C C S X S S But why won’t this work? 1) Groups would have to die out faster than individuals, which rarely happens 2) Groups would have to be isolated 3) “Cooperative” groups are always vulnerable to invasion of selfish individuals This does not mean cooperation or behaviors that serve the “good of the group” cannot evolve (reality tells us differently), but rather that most of these behaviors are inherently selfish The “selfish” individual reaps the rewards in a world of self-restraint It receives a private benefit while everyone shares the public cost Aka. Trajedy of the Commons Introduction to: alternative mating strategies sexual selection and mate choice reproductive behavior and the roles of males and females foraging behavior anti-predator behavior living in groups cooperation social contracts Formulating and testing hypotheses about the evolution of behavior: (1) Experimental approaches – particularly those that make quantitative rather than qualitative predictions (2) The comparative approach – when experiments fail...