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Reciprocal Altruism What about cooperation among unrelated individuals? What about cooperation among unrelated individuals? Trivers proposed individuals.

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Presentation on theme: "Reciprocal Altruism What about cooperation among unrelated individuals? What about cooperation among unrelated individuals? Trivers proposed individuals."— Presentation transcript:

1 Reciprocal Altruism What about cooperation among unrelated individuals? What about cooperation among unrelated individuals? Trivers proposed individuals will act altruistically if favor is later returned Trivers proposed individuals will act altruistically if favor is later returned Two conditions for reciprocal alturism to evolve: Two conditions for reciprocal alturism to evolve: – Cost to actor must be smaller than or equal to benefit to recipient – Individuals that fail to reciprocate must be punished What about cooperation among unrelated individuals? What about cooperation among unrelated individuals? Trivers proposed individuals will act altruistically if favor is later returned Trivers proposed individuals will act altruistically if favor is later returned Two conditions for reciprocal alturism to evolve: Two conditions for reciprocal alturism to evolve: – Cost to actor must be smaller than or equal to benefit to recipient – Individuals that fail to reciprocate must be punished

2 Reciprocal Altruism Most likely to evolve when: Most likely to evolve when: – Each individual repeatedly interacts with same set of individuals – Many opportunities for altruism in an individual’s lifetime – Individuals have good memories – Potential altruists interact in symmetrical situations Roughly equal benefits and costs Roughly equal benefits and costs Most likely to evolve when: Most likely to evolve when: – Each individual repeatedly interacts with same set of individuals – Many opportunities for altruism in an individual’s lifetime – Individuals have good memories – Potential altruists interact in symmetrical situations Roughly equal benefits and costs Roughly equal benefits and costs

3 Reciprocal Altruism Will evolve in long-lived, intelligent, social species with small group size, low dispersal rates, and mutual dependence in activities Will evolve in long-lived, intelligent, social species with small group size, low dispersal rates, and mutual dependence in activities Less likely to evolve in species with dominance hierarchies Less likely to evolve in species with dominance hierarchies Difficult to observe and quantify in nature Difficult to observe and quantify in nature Will evolve in long-lived, intelligent, social species with small group size, low dispersal rates, and mutual dependence in activities Will evolve in long-lived, intelligent, social species with small group size, low dispersal rates, and mutual dependence in activities Less likely to evolve in species with dominance hierarchies Less likely to evolve in species with dominance hierarchies Difficult to observe and quantify in nature Difficult to observe and quantify in nature

4 Reciprocal Altruism Blood-Sharing in Vampire Bats Blood-Sharing in Vampire Bats – Social group of 8-12 females and their dependent offspring – Roost together and associate with each other daily – Average r between individuals in study group in Costa Rica was 0.11 – Vampire bats share blood meals – Hunting is difficult and individuals are only successful 67-93% of time Prey are wary Prey are wary Blood-Sharing in Vampire Bats Blood-Sharing in Vampire Bats – Social group of 8-12 females and their dependent offspring – Roost together and associate with each other daily – Average r between individuals in study group in Costa Rica was 0.11 – Vampire bats share blood meals – Hunting is difficult and individuals are only successful 67-93% of time Prey are wary Prey are wary

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6 Reciprocal Altruism Blood-Sharing in Vampire Bats Blood-Sharing in Vampire Bats – Without eating for three nights, a bat will starve to death – Both degree of relatedness and degree of association were significantly related to probability of regurgitating blood – Blood-sharing is not random but based on relatedness and hope of future reciprocity Blood-Sharing in Vampire Bats Blood-Sharing in Vampire Bats – Without eating for three nights, a bat will starve to death – Both degree of relatedness and degree of association were significantly related to probability of regurgitating blood – Blood-sharing is not random but based on relatedness and hope of future reciprocity

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8 Interactions Among Species

9 Coevolution 1. Two species that interact affecting the genetic structure of one another. Each one acts as a selective force on the other (lineages change in parallel) 2. Co-speciation – Do 2 lineages speciate in the same pattern? Perhaps like a lichinous fungi and its algae symbiont. 1. Two species that interact affecting the genetic structure of one another. Each one acts as a selective force on the other (lineages change in parallel) 2. Co-speciation – Do 2 lineages speciate in the same pattern? Perhaps like a lichinous fungi and its algae symbiont.

10 Concepts of Coevolution Coevolution as a process of reciprocal adaptive response Coevolution as a process of reciprocal adaptive response 1.Specific coevolution: Coevolution of two (or few) species 2.Guild Coevolution (diffuse, or multispecific): Coevolution among sets of ecologically similar species 3.Escape-and-radiate coevolution 4.Cospeciation (introduced by interaction) Coevolution as a pattern, detected by phylogenetic analysis Coevolution as a pattern, detected by phylogenetic analysis 1.Cospecieation (coincident speciation) 2.Parallel cladogenesis Coevolution as a process of reciprocal adaptive response Coevolution as a process of reciprocal adaptive response 1.Specific coevolution: Coevolution of two (or few) species 2.Guild Coevolution (diffuse, or multispecific): Coevolution among sets of ecologically similar species 3.Escape-and-radiate coevolution 4.Cospeciation (introduced by interaction) Coevolution as a pattern, detected by phylogenetic analysis Coevolution as a pattern, detected by phylogenetic analysis 1.Cospecieation (coincident speciation) 2.Parallel cladogenesis

11 Co-evolution VS. Co-adaptation Co-evolution is when genetic composition of both species changes, each affecting the other. Co-evolution is when genetic composition of both species changes, each affecting the other. We assume co-evolution leads to co- adaptation. We assume co-evolution leads to co- adaptation. But you can have co-adaptation without co- evolution (birds on same island with different bill shapes  may have evolved in allopatry before sympatric overlap) But you can have co-adaptation without co- evolution (birds on same island with different bill shapes  may have evolved in allopatry before sympatric overlap) So, co-evolution should lead to co- adaptation but co-adaptation is not necessarily the result of co-evolution So, co-evolution should lead to co- adaptation but co-adaptation is not necessarily the result of co-evolution Co-evolution is when genetic composition of both species changes, each affecting the other. Co-evolution is when genetic composition of both species changes, each affecting the other. We assume co-evolution leads to co- adaptation. We assume co-evolution leads to co- adaptation. But you can have co-adaptation without co- evolution (birds on same island with different bill shapes  may have evolved in allopatry before sympatric overlap) But you can have co-adaptation without co- evolution (birds on same island with different bill shapes  may have evolved in allopatry before sympatric overlap) So, co-evolution should lead to co- adaptation but co-adaptation is not necessarily the result of co-evolution So, co-evolution should lead to co- adaptation but co-adaptation is not necessarily the result of co-evolution

12 Using Phylogenies to Answer Questions Coevolution Coevolution – Leaf-cutting ants and fungi they farm Leaf cutters grow fungus on leaves that they cut for food Leaf cutters grow fungus on leaves that they cut for food 200 ant species of tribe Attini each farm a different fungus species 200 ant species of tribe Attini each farm a different fungus species Did the two groups cospeciate? Did the two groups cospeciate? – Phylogenies should be congruent Hinkle found congruence on all branches but one Hinkle found congruence on all branches but one Fungi were domesticated more than once Fungi were domesticated more than once Coevolution Coevolution – Leaf-cutting ants and fungi they farm Leaf cutters grow fungus on leaves that they cut for food Leaf cutters grow fungus on leaves that they cut for food 200 ant species of tribe Attini each farm a different fungus species 200 ant species of tribe Attini each farm a different fungus species Did the two groups cospeciate? Did the two groups cospeciate? – Phylogenies should be congruent Hinkle found congruence on all branches but one Hinkle found congruence on all branches but one Fungi were domesticated more than once Fungi were domesticated more than once

13 Leaf Cutting Ants

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15 Evolution of Mimicry Complex interaction among multiple species believed to arise from co- evolution, though it has not been proven so. For sure, at least, this is co- adaptation. Complex interaction among multiple species believed to arise from co- evolution, though it has not been proven so. For sure, at least, this is co- adaptation. Major Types of Mimicry: Major Types of Mimicry: – Mullerian Mimicry – Batesian Mimicry – Mertensian Mimicry Complex interaction among multiple species believed to arise from co- evolution, though it has not been proven so. For sure, at least, this is co- adaptation. Complex interaction among multiple species believed to arise from co- evolution, though it has not been proven so. For sure, at least, this is co- adaptation. Major Types of Mimicry: Major Types of Mimicry: – Mullerian Mimicry – Batesian Mimicry – Mertensian Mimicry

16 Mullerian Mimicry When a group of species that are distasteful, poisonous, or otherwise noxious, resemble each other in morphology or behavior When a group of species that are distasteful, poisonous, or otherwise noxious, resemble each other in morphology or behavior Often brightly colored and have some kind of warning system  Aposematic Trait Often brightly colored and have some kind of warning system  Aposematic Trait They call attention to themselves and warn of danger. This warning is assumed to ward off potential predators or increase fitness in some way. They call attention to themselves and warn of danger. This warning is assumed to ward off potential predators or increase fitness in some way. The more these species look alike, the easier it is for a predator to remember that one warning pattern (eg. coral snakes bands) The more these species look alike, the easier it is for a predator to remember that one warning pattern (eg. coral snakes bands) When a group of species that are distasteful, poisonous, or otherwise noxious, resemble each other in morphology or behavior When a group of species that are distasteful, poisonous, or otherwise noxious, resemble each other in morphology or behavior Often brightly colored and have some kind of warning system  Aposematic Trait Often brightly colored and have some kind of warning system  Aposematic Trait They call attention to themselves and warn of danger. This warning is assumed to ward off potential predators or increase fitness in some way. They call attention to themselves and warn of danger. This warning is assumed to ward off potential predators or increase fitness in some way. The more these species look alike, the easier it is for a predator to remember that one warning pattern (eg. coral snakes bands) The more these species look alike, the easier it is for a predator to remember that one warning pattern (eg. coral snakes bands)

17 Coral snakes  all coral snakes are venomous. There are around 70 species in the new world. Over 90% of them look extremely similar, especially with respect to color and pattern Coral snakes  all coral snakes are venomous. There are around 70 species in the new world. Over 90% of them look extremely similar, especially with respect to color and pattern We assume that their similarity in appearance allows predators to evolve the ability to identify them as poisonous and leave them along We assume that their similarity in appearance allows predators to evolve the ability to identify them as poisonous and leave them along Thus, there is an advantage that all share from looking similar Thus, there is an advantage that all share from looking similar Coral snakes  all coral snakes are venomous. There are around 70 species in the new world. Over 90% of them look extremely similar, especially with respect to color and pattern Coral snakes  all coral snakes are venomous. There are around 70 species in the new world. Over 90% of them look extremely similar, especially with respect to color and pattern We assume that their similarity in appearance allows predators to evolve the ability to identify them as poisonous and leave them along We assume that their similarity in appearance allows predators to evolve the ability to identify them as poisonous and leave them along Thus, there is an advantage that all share from looking similar Thus, there is an advantage that all share from looking similar Examples of Mullerian Mimicry

18 Batesian Mimicry A non-noxious or non-poisonous mimic looks like a noxious model A non-noxious or non-poisonous mimic looks like a noxious model For our coral snake example, the venomous coral snakes would be the model and non-venomous snakes looking like coral snakes are the mimics For our coral snake example, the venomous coral snakes would be the model and non-venomous snakes looking like coral snakes are the mimics A non-noxious or non-poisonous mimic looks like a noxious model A non-noxious or non-poisonous mimic looks like a noxious model For our coral snake example, the venomous coral snakes would be the model and non-venomous snakes looking like coral snakes are the mimics For our coral snake example, the venomous coral snakes would be the model and non-venomous snakes looking like coral snakes are the mimics

19 Examples of Batesian Mimicry In each picture, the snake to the right is the Venomous Coral Snake, while those to the left are the mimics (harmless) In each picture, the snake to the right is the Venomous Coral Snake, while those to the left are the mimics (harmless)

20 Mertensian Mimicry We have seen some examples of deadly poisonous snakes such as Micrurus (Elapidae) and non-poisonous snakes such as Lampropeltus and Pliocercus (Colubridae). We have seen some examples of deadly poisonous snakes such as Micrurus (Elapidae) and non-poisonous snakes such as Lampropeltus and Pliocercus (Colubridae). But there are other snakes that are moderately poisonous, such as members of the genera Rhinobothryum, Erthrolammprus and Pseudoboa. But there are other snakes that are moderately poisonous, such as members of the genera Rhinobothryum, Erthrolammprus and Pseudoboa. Mertens suggests that the moderately poisonous snakes could be the model, not the poisonous snakes. Mertens suggests that the moderately poisonous snakes could be the model, not the poisonous snakes. We have seen some examples of deadly poisonous snakes such as Micrurus (Elapidae) and non-poisonous snakes such as Lampropeltus and Pliocercus (Colubridae). We have seen some examples of deadly poisonous snakes such as Micrurus (Elapidae) and non-poisonous snakes such as Lampropeltus and Pliocercus (Colubridae). But there are other snakes that are moderately poisonous, such as members of the genera Rhinobothryum, Erthrolammprus and Pseudoboa. But there are other snakes that are moderately poisonous, such as members of the genera Rhinobothryum, Erthrolammprus and Pseudoboa. Mertens suggests that the moderately poisonous snakes could be the model, not the poisonous snakes. Mertens suggests that the moderately poisonous snakes could be the model, not the poisonous snakes.

21 Mertensian Mimicry If the moderately poisonous snakes bite a predator, it would get sick and therefore would learn to avoid those and similar snakes in the future. If the moderately poisonous snakes bite a predator, it would get sick and therefore would learn to avoid those and similar snakes in the future. But, if a deadly poisonous snake bites a predator, it would die and never have a chance to learn. But, if a deadly poisonous snake bites a predator, it would die and never have a chance to learn. So, Mertens proposes that the moderately poisonous snakes are the model and both the poisonous and non-poisonous snakes are the mimics. This situation is termed Mertensian mimicry So, Mertens proposes that the moderately poisonous snakes are the model and both the poisonous and non-poisonous snakes are the mimics. This situation is termed Mertensian mimicry If the moderately poisonous snakes bite a predator, it would get sick and therefore would learn to avoid those and similar snakes in the future. If the moderately poisonous snakes bite a predator, it would get sick and therefore would learn to avoid those and similar snakes in the future. But, if a deadly poisonous snake bites a predator, it would die and never have a chance to learn. But, if a deadly poisonous snake bites a predator, it would die and never have a chance to learn. So, Mertens proposes that the moderately poisonous snakes are the model and both the poisonous and non-poisonous snakes are the mimics. This situation is termed Mertensian mimicry So, Mertens proposes that the moderately poisonous snakes are the model and both the poisonous and non-poisonous snakes are the mimics. This situation is termed Mertensian mimicry

22 CHAPTER 12 Evolution of Life History Characters

23 Reproduction Strategies Mice mature early and reproduce quickly whereas bears mature late and reproduce late Mice mature early and reproduce quickly whereas bears mature late and reproduce late Some plants live and flower for only one season, others live and flower for centuries Some plants live and flower for only one season, others live and flower for centuries Some bivalves produce millions of tiny eggs at once, others less than 100 large eggs at a time Some bivalves produce millions of tiny eggs at once, others less than 100 large eggs at a time Mice mature early and reproduce quickly whereas bears mature late and reproduce late Mice mature early and reproduce quickly whereas bears mature late and reproduce late Some plants live and flower for only one season, others live and flower for centuries Some plants live and flower for only one season, others live and flower for centuries Some bivalves produce millions of tiny eggs at once, others less than 100 large eggs at a time Some bivalves produce millions of tiny eggs at once, others less than 100 large eggs at a time

24 Life History Analysis The branch of evolutionary biology that tries to sort our reproductive strategies The branch of evolutionary biology that tries to sort our reproductive strategies A “perfect” organism would mature at birth and produce many high quality offspring throughout life A “perfect” organism would mature at birth and produce many high quality offspring throughout life No organism can do this because there are tradeoffs in time, size of offspring, and parental investment No organism can do this because there are tradeoffs in time, size of offspring, and parental investment The branch of evolutionary biology that tries to sort our reproductive strategies The branch of evolutionary biology that tries to sort our reproductive strategies A “perfect” organism would mature at birth and produce many high quality offspring throughout life A “perfect” organism would mature at birth and produce many high quality offspring throughout life No organism can do this because there are tradeoffs in time, size of offspring, and parental investment No organism can do this because there are tradeoffs in time, size of offspring, and parental investment

25 Life History Analysis Life history extremes Life history extremes – Thrip egg mites are born already inseminated by mating with brothers inside mother’s body Adults have short lives Adults have short lives The offspring eat there way out of their mother when she is four days old The offspring eat there way out of their mother when she is four days old – Brown kiwis lay eggs 1/6 of their body weight Chicks are self-reliant within a week Chicks are self-reliant within a week Takes one month for female to produce each egg Takes one month for female to produce each egg Life history extremes Life history extremes – Thrip egg mites are born already inseminated by mating with brothers inside mother’s body Adults have short lives Adults have short lives The offspring eat there way out of their mother when she is four days old The offspring eat there way out of their mother when she is four days old – Brown kiwis lay eggs 1/6 of their body weight Chicks are self-reliant within a week Chicks are self-reliant within a week Takes one month for female to produce each egg Takes one month for female to produce each egg

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27 Life History Analysis Organisms may grow to a large size to make large offspring or reproduce earlier at a smaller size to make smaller offspring Organisms may grow to a large size to make large offspring or reproduce earlier at a smaller size to make smaller offspring For organisms that wait, chance of dying before reproducing is high For organisms that wait, chance of dying before reproducing is high Environmental variation creates life history variation Environmental variation creates life history variation Organisms may grow to a large size to make large offspring or reproduce earlier at a smaller size to make smaller offspring Organisms may grow to a large size to make large offspring or reproduce earlier at a smaller size to make smaller offspring For organisms that wait, chance of dying before reproducing is high For organisms that wait, chance of dying before reproducing is high Environmental variation creates life history variation Environmental variation creates life history variation

28 Life History Analysis Questions to Consider Questions to Consider – Why do organisms age and die? – How many offspring should an individual produce in a year? – How big should each offspring be? Must balance among fitness aspects Must balance among fitness aspects Conflicts arise between male and female parents Conflicts arise between male and female parents Questions to Consider Questions to Consider – Why do organisms age and die? – How many offspring should an individual produce in a year? – How big should each offspring be? Must balance among fitness aspects Must balance among fitness aspects Conflicts arise between male and female parents Conflicts arise between male and female parents

29 Life History Analysis Female Virginia opossum Female Virginia opossum – Nursed for three months and then weaned – Continued to grow for several months until reaching sexual maturity – Had first litter of 8 offspring – Months later had second litter of 7 offspring – At 20 months was killed by a predator – Energy allocation changed through life Female Virginia opossum Female Virginia opossum – Nursed for three months and then weaned – Continued to grow for several months until reaching sexual maturity – Had first litter of 8 offspring – Months later had second litter of 7 offspring – At 20 months was killed by a predator – Energy allocation changed through life

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31 Life History Analysis Differences among life history concern differences in energy allocation Differences among life history concern differences in energy allocation Other female opossums could mature earlier and reproduce earlier Other female opossums could mature earlier and reproduce earlier – Or devote less energy to reproduction and more to maintenance Natural selection optimizes energy allocation in a way that maximizes total lifetime reproduction Natural selection optimizes energy allocation in a way that maximizes total lifetime reproduction Differences among life history concern differences in energy allocation Differences among life history concern differences in energy allocation Other female opossums could mature earlier and reproduce earlier Other female opossums could mature earlier and reproduce earlier – Or devote less energy to reproduction and more to maintenance Natural selection optimizes energy allocation in a way that maximizes total lifetime reproduction Natural selection optimizes energy allocation in a way that maximizes total lifetime reproduction

32 Why Do Organisms Age and Die? Senescence = late life decline of fertility and probability of survival Senescence = late life decline of fertility and probability of survival Aging reduces an individual’s fitness and should be opposed by natural selection Aging reduces an individual’s fitness and should be opposed by natural selection Two theories on why aging persists Two theories on why aging persists Senescence = late life decline of fertility and probability of survival Senescence = late life decline of fertility and probability of survival Aging reduces an individual’s fitness and should be opposed by natural selection Aging reduces an individual’s fitness and should be opposed by natural selection Two theories on why aging persists Two theories on why aging persists

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34 Why Do Organisms Age and Die? Rate-of-Living Theory Rate-of-Living Theory – Senescence is caused by accumulation of irreparable damage to cells and tissues – Damage caused by errors during replication, transcription, and translation, and by accumulation of poisonous metabolic by products – All organisms have been selected to resist and repair damage as much as physiologically possible – Have reached limit of possible repair Rate-of-Living Theory Rate-of-Living Theory – Senescence is caused by accumulation of irreparable damage to cells and tissues – Damage caused by errors during replication, transcription, and translation, and by accumulation of poisonous metabolic by products – All organisms have been selected to resist and repair damage as much as physiologically possible – Have reached limit of possible repair

35 Why Do Organisms Age and Die? Rate-of-Living Theory Rate-of-Living Theory – Populations lack genetic variation needed to enable more effective repair mechanisms – Two predictions of theory: Because damage is partially caused by metabolic by products, aging rate should be correlated to metabolic rate Because damage is partially caused by metabolic by products, aging rate should be correlated to metabolic rate Because organisms have been selected to repair the maximum possible, species should not be able to evolve longer life spans Because organisms have been selected to repair the maximum possible, species should not be able to evolve longer life spans Rate-of-Living Theory Rate-of-Living Theory – Populations lack genetic variation needed to enable more effective repair mechanisms – Two predictions of theory: Because damage is partially caused by metabolic by products, aging rate should be correlated to metabolic rate Because damage is partially caused by metabolic by products, aging rate should be correlated to metabolic rate Because organisms have been selected to repair the maximum possible, species should not be able to evolve longer life spans Because organisms have been selected to repair the maximum possible, species should not be able to evolve longer life spans

36 Why Do Organisms Age and Die? Rate-of-Living Theory Rate-of-Living Theory – Austad and Fischer tested first prediction Calculated amount of energy expended per gram of tissue per lifetime for 164 mammal species Calculated amount of energy expended per gram of tissue per lifetime for 164 mammal species Should expend same amount regardless of length of life Should expend same amount regardless of length of life Found great variation in energy expenditure Found great variation in energy expenditure Found that bats expend three times the energy of other mammals their size Found that bats expend three times the energy of other mammals their size Rate-of-Living Theory Rate-of-Living Theory – Austad and Fischer tested first prediction Calculated amount of energy expended per gram of tissue per lifetime for 164 mammal species Calculated amount of energy expended per gram of tissue per lifetime for 164 mammal species Should expend same amount regardless of length of life Should expend same amount regardless of length of life Found great variation in energy expenditure Found great variation in energy expenditure Found that bats expend three times the energy of other mammals their size Found that bats expend three times the energy of other mammals their size

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38 Why Do Organisms Age and Die? Rate-of-Living Theory Rate-of-Living Theory – Luckinbill tested second prediction – Artificially selected for longevity in fruit flies – Increased life span from 35 days to 60 days – These long-lived fruit flies had lower metabolic rates during first 15 days of life Rate-of-Living Theory Rate-of-Living Theory – Luckinbill tested second prediction – Artificially selected for longevity in fruit flies – Increased life span from 35 days to 60 days – These long-lived fruit flies had lower metabolic rates during first 15 days of life

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40 Why Do Organisms Age and Die? Rate-of-Living Theory Rate-of-Living Theory – Both of the predictions of the theory have been falsified – Examine energy expenditure on cells and chromosomes, not whole organism Normal animal cells are capable of a finite number of divisions before death Normal animal cells are capable of a finite number of divisions before death All cells except cancer cells, germ line cells, and stem cells All cells except cancer cells, germ line cells, and stem cells Senescence may result from chromosome damage Senescence may result from chromosome damage Rate-of-Living Theory Rate-of-Living Theory – Both of the predictions of the theory have been falsified – Examine energy expenditure on cells and chromosomes, not whole organism Normal animal cells are capable of a finite number of divisions before death Normal animal cells are capable of a finite number of divisions before death All cells except cancer cells, germ line cells, and stem cells All cells except cancer cells, germ line cells, and stem cells Senescence may result from chromosome damage Senescence may result from chromosome damage

41 Why Do Organisms Age and Die? Rate-of-Living Theory Rate-of-Living Theory – Telomeres of chromosomes consist of tandem repeats – Added by enzyme telomerase Overactive in cancer cells Overactive in cancer cells – During each replication pieces are lost – Progressive telomere loss is associated with senescence and death – Cells die because chromosomes are too damaged to function Rate-of-Living Theory Rate-of-Living Theory – Telomeres of chromosomes consist of tandem repeats – Added by enzyme telomerase Overactive in cancer cells Overactive in cancer cells – During each replication pieces are lost – Progressive telomere loss is associated with senescence and death – Cells die because chromosomes are too damaged to function

42 Why Do Organisms Age and Die? Rate-of-Living Theory Rate-of-Living Theory – Life spans of mammals are correlated with life spans of skin and blood cells – These results consistent with rate-of-living – Why doesn’t natural selection activate telomerase to add more telomeres? – Could be tradeoff between extending cell life and proliferating cancer Rate-of-Living Theory Rate-of-Living Theory – Life spans of mammals are correlated with life spans of skin and blood cells – These results consistent with rate-of-living – Why doesn’t natural selection activate telomerase to add more telomeres? – Could be tradeoff between extending cell life and proliferating cancer

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44 Why Do Organisms Age and Die? Evolutionary Theory of Aging Evolutionary Theory of Aging – If genetic variation for extending life spans does exist, why hasn’t natural selection produced this result in all species? – Aging is not caused by damage itself but the failure to repair the damage – Damage is not repaired because of deleterious mutations or tradeoffs between repair and reproduction Evolutionary Theory of Aging Evolutionary Theory of Aging – If genetic variation for extending life spans does exist, why hasn’t natural selection produced this result in all species? – Aging is not caused by damage itself but the failure to repair the damage – Damage is not repaired because of deleterious mutations or tradeoffs between repair and reproduction

45 Why Do Organisms Age and Die? Evolutionary Theory of Aging Evolutionary Theory of Aging – Hypothetical life history of individual with wild-type genotype Mature at age 3 Mature at age 3 Die at age 16 Die at age 16 Probability of survival from one year to the next is 0.8 Probability of survival from one year to the next is 0.8 Expected lifetime reproductive success = Expected lifetime reproductive success = – Will consider two mutations that alter life history strategy Evolutionary Theory of Aging Evolutionary Theory of Aging – Hypothetical life history of individual with wild-type genotype Mature at age 3 Mature at age 3 Die at age 16 Die at age 16 Probability of survival from one year to the next is 0.8 Probability of survival from one year to the next is 0.8 Expected lifetime reproductive success = Expected lifetime reproductive success = – Will consider two mutations that alter life history strategy

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47 Why Do Organisms Age and Die? Evolutionary Theory of Aging Evolutionary Theory of Aging – Mutation Accumulation Hypothesis – Mutation cause death at age 14 – Deleterious mutation, but how deleterious? – Expected lifetime reproductive success reduced to Still 96% of original Still 96% of original – Weakly selected against May persist in mutation-selection balance May persist in mutation-selection balance Evolutionary Theory of Aging Evolutionary Theory of Aging – Mutation Accumulation Hypothesis – Mutation cause death at age 14 – Deleterious mutation, but how deleterious? – Expected lifetime reproductive success reduced to Still 96% of original Still 96% of original – Weakly selected against May persist in mutation-selection balance May persist in mutation-selection balance

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49 Why Do Organisms Age and Die? Evolutionary Theory of Aging Evolutionary Theory of Aging – Deleterious mutations that affect individuals late in life can accumulate in populations and be the cause of aging – Cancers that usually occur late in life only slightly affect fitness of the individual – Not strongly selected against and can accumulate rapidly – Can cause senescence and death with few fitness consequences Evolutionary Theory of Aging Evolutionary Theory of Aging – Deleterious mutations that affect individuals late in life can accumulate in populations and be the cause of aging – Cancers that usually occur late in life only slightly affect fitness of the individual – Not strongly selected against and can accumulate rapidly – Can cause senescence and death with few fitness consequences

50 Why Do Organisms Age and Die? Evolutionary Theory of Aging Evolutionary Theory of Aging – Mutation of two different life history characters with pleiotropic action – Matures at 2 years – Dies at 10 years – Tradeoff between early reproduction and survival late in life Antagonistic pleiotropic effects Antagonistic pleiotropic effects – Expected lifetime reproductive success is 2.66 Mutation is beneficial Mutation is beneficial Evolutionary Theory of Aging Evolutionary Theory of Aging – Mutation of two different life history characters with pleiotropic action – Matures at 2 years – Dies at 10 years – Tradeoff between early reproduction and survival late in life Antagonistic pleiotropic effects Antagonistic pleiotropic effects – Expected lifetime reproductive success is 2.66 Mutation is beneficial Mutation is beneficial

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52 Why Do Organisms Age and Die? Evolutionary Theory of Aging Evolutionary Theory of Aging – Reproduce so much early that early death is not selected against – Mutation devotes less to repair and more to reproduction – Heat-shock protein hsp70 – Prevents damage due to denaturation – Heat-shock binding interferes with normal cellular functions – Heat-shock genes only expressed during environmental stress Proteins removed after stress passes Proteins removed after stress passes Evolutionary Theory of Aging Evolutionary Theory of Aging – Reproduce so much early that early death is not selected against – Mutation devotes less to repair and more to reproduction – Heat-shock protein hsp70 – Prevents damage due to denaturation – Heat-shock binding interferes with normal cellular functions – Heat-shock genes only expressed during environmental stress Proteins removed after stress passes Proteins removed after stress passes

53 Why Do Organisms Age and Die? Evolutionary Theory of Aging Evolutionary Theory of Aging – Expression of hsp70 in Drosophila causes longer life span but lower reproduction early in life – Tradeoff between early fecundity and late survival is mediated by hsp70 – Heat-shock proteins may mediate this tradeoff in many organisms Evolutionary Theory of Aging Evolutionary Theory of Aging – Expression of hsp70 in Drosophila causes longer life span but lower reproduction early in life – Tradeoff between early fecundity and late survival is mediated by hsp70 – Heat-shock proteins may mediate this tradeoff in many organisms

54 Why Do Organisms Age and Die? Evolutionary Theory of Aging Evolutionary Theory of Aging – Other examples of tradeoffs – Collared flycatchers are polymorphic in when they begin reproduction Birds that begin at age 1 have smaller clutch sizes throughout life Birds that begin at age 1 have smaller clutch sizes throughout life Birds that begin at age 2 have larger clutches throughout life Birds that begin at age 2 have larger clutches throughout life First year breeders still had higher reproductive success First year breeders still had higher reproductive success – 1.24 vs. 0.9 Evolutionary Theory of Aging Evolutionary Theory of Aging – Other examples of tradeoffs – Collared flycatchers are polymorphic in when they begin reproduction Birds that begin at age 1 have smaller clutch sizes throughout life Birds that begin at age 1 have smaller clutch sizes throughout life Birds that begin at age 2 have larger clutches throughout life Birds that begin at age 2 have larger clutches throughout life First year breeders still had higher reproductive success First year breeders still had higher reproductive success – 1.24 vs. 0.9

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56 Why Do Organisms Age and Die? Natural Experiment in Aging Natural Experiment in Aging – High adult mortality rates should lead to earlier maturation – Austad compared Virginia opossums on mainland southeastern US and on a barrier island off of Georgia – In mainland, opossums have high ecological mortality rates – On island they have no predators – Two habitats and populations are similar otherwise Natural Experiment in Aging Natural Experiment in Aging – High adult mortality rates should lead to earlier maturation – Austad compared Virginia opossums on mainland southeastern US and on a barrier island off of Georgia – In mainland, opossums have high ecological mortality rates – On island they have no predators – Two habitats and populations are similar otherwise

57 Why Do Organisms Age and Die? Natural Experiment in Aging Natural Experiment in Aging – Populations separated years – Island population should have evolved delayed senescence – Island females showed delayed senescence in month-to-month probability of survival – Island females showed delayed senescence in reproductive performance – Island females showed delayed senescence in connective tissue physiology Natural Experiment in Aging Natural Experiment in Aging – Populations separated years – Island population should have evolved delayed senescence – Island females showed delayed senescence in month-to-month probability of survival – Island females showed delayed senescence in reproductive performance – Island females showed delayed senescence in connective tissue physiology

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59 Why Do Organisms Age and Die? Natural Experiment in Aging Natural Experiment in Aging – Results consistent with Evolutionary Theory of Senescence Evolutionary Theory of Senescence successful in explaining life history variation Evolutionary Theory of Senescence successful in explaining life history variation Natural Experiment in Aging Natural Experiment in Aging – Results consistent with Evolutionary Theory of Senescence Evolutionary Theory of Senescence successful in explaining life history variation Evolutionary Theory of Senescence successful in explaining life history variation

60 How Many Offspring to Have? The more offspring a parent attempts to raise at once, the less time and energy the parent can spend on each of them The more offspring a parent attempts to raise at once, the less time and energy the parent can spend on each of them How many eggs should a bird lay per clutch? How many eggs should a bird lay per clutch? David Lack’s Hypothesis David Lack’s Hypothesis – Selection will favor clutch size that produces the most surviving offspring – When researchers added eggs to nests, survival of all chicks decreased The more offspring a parent attempts to raise at once, the less time and energy the parent can spend on each of them The more offspring a parent attempts to raise at once, the less time and energy the parent can spend on each of them How many eggs should a bird lay per clutch? How many eggs should a bird lay per clutch? David Lack’s Hypothesis David Lack’s Hypothesis – Selection will favor clutch size that produces the most surviving offspring – When researchers added eggs to nests, survival of all chicks decreased

61 How Many Offspring to Have? David Lack’s Hypothesis David Lack’s Hypothesis – Number of surviving offspring reaches a maximum at intermediate clutch sizes David Lack’s Hypothesis David Lack’s Hypothesis – Number of surviving offspring reaches a maximum at intermediate clutch sizes

62 How Many Offspring to Have? Boyce and Perrins tested Lack’s hypothesis in a long-term great tit study Boyce and Perrins tested Lack’s hypothesis in a long-term great tit study – Mean clutch size was 8.53 – Greatest number of survivors came from clutches of 12 – Experimentally larger nests still had 12 survivors – All females could have lain 12 eggs and had higher fitness Boyce and Perrins tested Lack’s hypothesis in a long-term great tit study Boyce and Perrins tested Lack’s hypothesis in a long-term great tit study – Mean clutch size was 8.53 – Greatest number of survivors came from clutches of 12 – Experimentally larger nests still had 12 survivors – All females could have lain 12 eggs and had higher fitness

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64 How Many Offspring to Have? Boyce and Perrins’ test of Lack’s hypothesis Boyce and Perrins’ test of Lack’s hypothesis Not consistent with Lack’s hypothesis Not consistent with Lack’s hypothesis Many other studies have shown that birds have smaller clutches than predicted Many other studies have shown that birds have smaller clutches than predicted Why isn’t Lack’s hypothesis correct? Why isn’t Lack’s hypothesis correct? – Must be a violation of one of the underlying assumptions Boyce and Perrins’ test of Lack’s hypothesis Boyce and Perrins’ test of Lack’s hypothesis Not consistent with Lack’s hypothesis Not consistent with Lack’s hypothesis Many other studies have shown that birds have smaller clutches than predicted Many other studies have shown that birds have smaller clutches than predicted Why isn’t Lack’s hypothesis correct? Why isn’t Lack’s hypothesis correct? – Must be a violation of one of the underlying assumptions

65 How Many Offspring to Have? Assumptions of Lack’s hypothesis Assumptions of Lack’s hypothesis – No tradeoff between parent’s reproductive effort in one year and survival and reproduction in the future – Linden and Moller reviewed 60 bird studies and found that 26 showed a tradeoff between current and future reproductive effort – 4 of 16 studies found tradeoff between current reproduction and future survival – Optimal clutch size may be less than most productive clutch size Assumptions of Lack’s hypothesis Assumptions of Lack’s hypothesis – No tradeoff between parent’s reproductive effort in one year and survival and reproduction in the future – Linden and Moller reviewed 60 bird studies and found that 26 showed a tradeoff between current and future reproductive effort – 4 of 16 studies found tradeoff between current reproduction and future survival – Optimal clutch size may be less than most productive clutch size

66 How Many Offspring to Have? Assumptions of Lack’s hypothesis Assumptions of Lack’s hypothesis – Only effect of clutch size on offspring is determining whether offspring survive – Schluter and Gustafsson added or removed eggs from collared flycatcher nests – When those offspring had their own clutches, the ones from clutches that had been augmented produced smaller clutches and vice versa – Effects of clutch size extend further into future than thought Assumptions of Lack’s hypothesis Assumptions of Lack’s hypothesis – Only effect of clutch size on offspring is determining whether offspring survive – Schluter and Gustafsson added or removed eggs from collared flycatcher nests – When those offspring had their own clutches, the ones from clutches that had been augmented produced smaller clutches and vice versa – Effects of clutch size extend further into future than thought

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68 How Many Offspring to Have? Assumptions of Lack’s hypothesis Assumptions of Lack’s hypothesis – Clutch size is fixed by a particular genotype – Phenotypic plasticity of clutch size has been shown in many bird species – If birds predict good or bad environmental conditions, they can adjust their clutch size to the optimal value for that season Assumptions of Lack’s hypothesis Assumptions of Lack’s hypothesis – Clutch size is fixed by a particular genotype – Phenotypic plasticity of clutch size has been shown in many bird species – If birds predict good or bad environmental conditions, they can adjust their clutch size to the optimal value for that season

69 How Many Offspring to Have? Lack’s hypothesis applied to parasitoid wasps Lack’s hypothesis applied to parasitoid wasps – Although Lack’s hypothesis appears to be too simple to accurately predict clutch size, it serves as a valuable null model – Parasitoid wasps inject their eggs into a host insect The larvae eat the host, pupate, and emerge The larvae eat the host, pupate, and emerge – Host insect is analogous to a nest Lack’s hypothesis applied to parasitoid wasps Lack’s hypothesis applied to parasitoid wasps – Although Lack’s hypothesis appears to be too simple to accurately predict clutch size, it serves as a valuable null model – Parasitoid wasps inject their eggs into a host insect The larvae eat the host, pupate, and emerge The larvae eat the host, pupate, and emerge – Host insect is analogous to a nest

70 How Many Offspring to Have? Lack’s hypothesis for parasitoid wasps Lack’s hypothesis for parasitoid wasps – Trichogramma embryophagum deposits eggs in many different host species – Charnov and Skinner calculated optimal clutch sizes for three insect hosts Lack’s hypothesis for parasitoid wasps Lack’s hypothesis for parasitoid wasps – Trichogramma embryophagum deposits eggs in many different host species – Charnov and Skinner calculated optimal clutch sizes for three insect hosts

71 How Many Offspring to Have? Lack’s hypothesis for parasitoid wasps Lack’s hypothesis for parasitoid wasps – Females shift behavior in response to different hosts – Lay smaller clutches than predicted by Lack’s hypothesis Lack’s hypothesis for parasitoid wasps Lack’s hypothesis for parasitoid wasps – Females shift behavior in response to different hosts – Lay smaller clutches than predicted by Lack’s hypothesis

72 How Many Offspring to Have? Lack’s hypothesis for parasitoid wasps Lack’s hypothesis for parasitoid wasps – Why are clutches smaller than optimal? – Larger clutches may reduce female fitness in unknown ways – There may be a tradeoff in current and future reproduction and survival – Parasitoids may lay two clutches in succession Fitness may be related to survival of all clutches, not just one Fitness may be related to survival of all clutches, not just one Lack’s hypothesis for parasitoid wasps Lack’s hypothesis for parasitoid wasps – Why are clutches smaller than optimal? – Larger clutches may reduce female fitness in unknown ways – There may be a tradeoff in current and future reproduction and survival – Parasitoids may lay two clutches in succession Fitness may be related to survival of all clutches, not just one Fitness may be related to survival of all clutches, not just one

73 How Many Offspring to Have? Lack’s hypothesis for parasitoid wasps Lack’s hypothesis for parasitoid wasps – While female searches for a host her fitness is 0 – Must incorporate fitness gained by the number of eggs lain on one host before leaving – May lay smaller clutches than predicted by Lack’s hypothesis because it may be more optimal to begin the search for a new host Lack’s hypothesis for parasitoid wasps Lack’s hypothesis for parasitoid wasps – While female searches for a host her fitness is 0 – Must incorporate fitness gained by the number of eggs lain on one host before leaving – May lay smaller clutches than predicted by Lack’s hypothesis because it may be more optimal to begin the search for a new host

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75 How Many Offspring to Have? Lack’s hypothesis is a good starting point for evolutionary analysis of clutch size Lack’s hypothesis is a good starting point for evolutionary analysis of clutch size Violations represent presence of tradeoffs Violations represent presence of tradeoffs Current parental effort may be negatively correlated with parent or offspring future reproductive success or survival Current parental effort may be negatively correlated with parent or offspring future reproductive success or survival Lack’s hypothesis is a good starting point for evolutionary analysis of clutch size Lack’s hypothesis is a good starting point for evolutionary analysis of clutch size Violations represent presence of tradeoffs Violations represent presence of tradeoffs Current parental effort may be negatively correlated with parent or offspring future reproductive success or survival Current parental effort may be negatively correlated with parent or offspring future reproductive success or survival

76 How Big Should Each Offspring Be? We have been assuming that size of offspring was fixed We have been assuming that size of offspring was fixed Principle of Allocation states that if organisms use energy for one function the amount of energy available for other functions is reduced Principle of Allocation states that if organisms use energy for one function the amount of energy available for other functions is reduced – Leads to trade-offs between functions such as number and size of offspring – Can either have many small young or few large young We have been assuming that size of offspring was fixed We have been assuming that size of offspring was fixed Principle of Allocation states that if organisms use energy for one function the amount of energy available for other functions is reduced Principle of Allocation states that if organisms use energy for one function the amount of energy available for other functions is reduced – Leads to trade-offs between functions such as number and size of offspring – Can either have many small young or few large young

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78 How Big Should Each Offspring Be? Smith and Fretwell’s analysis Smith and Fretwell’s analysis – Two assumptions – Tradeoff between size and number of offspring – Individual offspring survival correlated to size – Created a mathematical plot of expected parental fitness versus offspring size Smith and Fretwell’s analysis Smith and Fretwell’s analysis – Two assumptions – Tradeoff between size and number of offspring – Individual offspring survival correlated to size – Created a mathematical plot of expected parental fitness versus offspring size

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80 How Big Should Each Offspring Be? Smith and Fretwell’s analysis Smith and Fretwell’s analysis – Optimal offspring size for parents is often small than optimal offspring size for offspring Offspring always want to be bigger to survive better Offspring always want to be bigger to survive better Parents want to ration out resources to all offspring, current and future Parents want to ration out resources to all offspring, current and future – Can only test Smith and Fretwell’s analysis if there is high polymorphism in offspring size in a population Smith and Fretwell’s analysis Smith and Fretwell’s analysis – Optimal offspring size for parents is often small than optimal offspring size for offspring Offspring always want to be bigger to survive better Offspring always want to be bigger to survive better Parents want to ration out resources to all offspring, current and future Parents want to ration out resources to all offspring, current and future – Can only test Smith and Fretwell’s analysis if there is high polymorphism in offspring size in a population

81 How Big Should Each Offspring Be? Offspring Size Selection in Uta Offspring Size Selection in Uta – Side-blotched lizards live in western US – Show heritable variation in egg size – Sinervo surgically manipulated egg size variation further Got lizards to lay unusually small eggs by removing some yolk from each Got lizards to lay unusually small eggs by removing some yolk from each Got lizards to lay unusually large eggs by destroying all but two follicles so that yolk would be transferred to remaining eggs Got lizards to lay unusually large eggs by destroying all but two follicles so that yolk would be transferred to remaining eggs Offspring Size Selection in Uta Offspring Size Selection in Uta – Side-blotched lizards live in western US – Show heritable variation in egg size – Sinervo surgically manipulated egg size variation further Got lizards to lay unusually small eggs by removing some yolk from each Got lizards to lay unusually small eggs by removing some yolk from each Got lizards to lay unusually large eggs by destroying all but two follicles so that yolk would be transferred to remaining eggs Got lizards to lay unusually large eggs by destroying all but two follicles so that yolk would be transferred to remaining eggs

82 How Big Should Each Offspring Be? Offspring Size Selection in Uta Offspring Size Selection in Uta – Found tradeoff in number and size of eggs – Probability of juvenile survival was a function of egg mass – In 1989, selection favored larger eggs – In 1990, selection favored intermediate eggs – Maternal fitness always favored medium eggs – Conflict of interest between mother and offspring for egg size Offspring Size Selection in Uta Offspring Size Selection in Uta – Found tradeoff in number and size of eggs – Probability of juvenile survival was a function of egg mass – In 1989, selection favored larger eggs – In 1990, selection favored intermediate eggs – Maternal fitness always favored medium eggs – Conflict of interest between mother and offspring for egg size

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84 How Big Should Each Offspring Be? Phenotypic Plasticity in Beetle Egg Size Phenotypic Plasticity in Beetle Egg Size – Seed beetle lays eggs on various seeds – Larvae burrow inside, feed, and pupate – Fox studied seed beetle grown on acacia and palo verde seeds – Acacia is a good host Most larvae survive Most larvae survive – Palo verde is a poor host Less than half survive Less than half survive – Females lay larger eggs on palo verde than acacia Phenotypic Plasticity in Beetle Egg Size Phenotypic Plasticity in Beetle Egg Size – Seed beetle lays eggs on various seeds – Larvae burrow inside, feed, and pupate – Fox studied seed beetle grown on acacia and palo verde seeds – Acacia is a good host Most larvae survive Most larvae survive – Palo verde is a poor host Less than half survive Less than half survive – Females lay larger eggs on palo verde than acacia

85 How Big Should Each Offspring Be? Phenotypic Plasticity in Beetle Egg Size Phenotypic Plasticity in Beetle Egg Size – Phenotypic plasticity selected for in this generalist species – Researchers switched the host seed mid- way through oviposition and the females switched egg sizes – 0.3% of larvae from small eggs on palo verde survived – 24% of larvae from large eggs on acacia survived – Poor environment forces females to expend more energy on large egg size Phenotypic Plasticity in Beetle Egg Size Phenotypic Plasticity in Beetle Egg Size – Phenotypic plasticity selected for in this generalist species – Researchers switched the host seed mid- way through oviposition and the females switched egg sizes – 0.3% of larvae from small eggs on palo verde survived – 24% of larvae from large eggs on acacia survived – Poor environment forces females to expend more energy on large egg size

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