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: Handedness30% Diastolic blood pressure45% Twinning50% Systolic blood pressure55% Body weight65% Stature and tooth size85% Fertility10-20% IQ60-80%

(2) There is a struggle for existence Resources are limiting There is competition for resources, including mates

(3) Variation influences the struggle dicots monocots vs.. Columbian ground squirrel

min energy constraint time constraint Digestive constraint Optimal diet Dicots consumed Monocots consumed 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 Dicots consumed Monocots consumed r 2 = 0.94 (a)variation in the ability to forage optimally

Mark Ritchie compare the predicted “ optimal ” diet and the actual diet for 109 individuals squirrels Dicots consumed Monocots consumed r 2 = 0.94 (a)variation in the ability to forage optimally Deviators Optimal

Mother ’ s deviation Offspring ’ s deviation (b) optimal foraging is a heritable trait Mothers raise offspring Offspring on their own

(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

Life history traits

Schooling behavior - dilutes individual risk - greater vigilance - group confusion Predator-inspection behavior - method to ascertain the identity and intentions of the assailant low risk low risk (Magurran et al. 1996)

Male coloration and female choice Predation risk (cichlids) Predation risk (prawns) Low risk mean # spots mean size (Endler 1980)

Correlations vs. experimental tests Haskin ’ s 1957 transplant experiment

black = % females schooling 10mm (Magurran et al. 1996) Transplant experiment results:

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

C S C C C C C C C C S S S S S SS S S C X X C S C C C C C C S C C C C C Group Selection – differential survival/reproduction of groups 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 Aka. Trajedy of the Commons The “ selfish ” individual reaps the rewards in a world of self-restraint It receives a private benefit while everyone shares the public cost

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...