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CHAPTER 18 Interactions Among
Species
Coevolution
1.1. Two species that interact Two species that interact affecting the genetic structure affecting the genetic structure of one another. Each one acts of one another. Each one acts as a selective force on the as a selective force on the other (lineages change in other (lineages change in parallel)parallel)
2.2. Co-speciation – Do 2 lineages Co-speciation – Do 2 lineages speciate in the same pattern? speciate in the same pattern? Perhaps like a lichinous fungi Perhaps like a lichinous fungi and its algae symbiont. and its algae symbiont.
Concepts of Coevolution
• Coevolution as a process of reciprocal adaptive responseCoevolution as a process of reciprocal adaptive response1.1. Specific coevolution: Coevolution of two (or few) speciesSpecific coevolution: Coevolution of two (or few) species
2.2. Guild Coevolution (diffuse, or multispecific): Coevolution among Guild Coevolution (diffuse, or multispecific): Coevolution among sets of ecologically similar speciessets of ecologically similar species
3.3. Escape-and-radiate coevolutionEscape-and-radiate coevolution
4.4. Cospeciation (introduced by interaction)Cospeciation (introduced by interaction)
• Coevolution as a pattern, detected by phylogenetic Coevolution as a pattern, detected by phylogenetic analysisanalysis
1.1. Cospecieation (coincident speciation)Cospecieation (coincident speciation)
2.2. Parallel cladogenesisParallel cladogenesis
Co-evolution VS. Co-adaptation
• Co-evolution is when genetic composition of Co-evolution is when genetic composition of both species changes, each affecting the both species changes, each affecting the other. other.
• We assume co-evolution leads to co-We assume co-evolution leads to co-adaptation. adaptation.
• But you can have co-adaptation without co-But you can have co-adaptation without co-evolution (birds on same island with different evolution (birds on same island with different bill shapesbill shapes may have evolved in allopatry may have evolved in allopatry before sympatric overlap)before sympatric overlap)
• So, co-evolution should lead to co-adaptation So, co-evolution should lead to co-adaptation but co-adaptation is not necessarily the but co-adaptation is not necessarily the result of co-evolutionresult of co-evolution
Using Phylogenies to Answer Questions
• CoevolutionCoevolution– Leaf-cutting ants and fungi they farmLeaf-cutting ants and fungi they farm• Leaf cutters grow fungus on leaves that Leaf cutters grow fungus on leaves that
they cut for foodthey cut for food• 200 ant species of tribe Attini each farm a 200 ant species of tribe Attini each farm a
different fungus speciesdifferent fungus species• Did the two groups cospeciate?Did the two groups cospeciate?– Phylogenies should be congruentPhylogenies should be congruent
• Hinkle found congruence on all branches Hinkle found congruence on all branches but onebut one• Fungi were domesticated more than onceFungi were domesticated more than once
Evolution of Mimicry
• Complex interaction among multiple Complex interaction among multiple species believed to arise from co-species believed to arise from co-evolution, though it has not been evolution, though it has not been proven so. For sure, at least, this is co-proven so. For sure, at least, this is co-adaptation.adaptation.
• Major Types of Mimicry:Major Types of Mimicry:– Mullerian MimicryMullerian Mimicry
– Batesian MimicryBatesian Mimicry
– Mertensian MimicryMertensian Mimicry
Mullerian Mimicry• When a group of species that are distasteful, When a group of species that are distasteful,
poisonous, or otherwise noxious, resemble poisonous, or otherwise noxious, resemble each other in morphology or behavioreach other in morphology or behavior
• Often brightly colored and have some kind of Often brightly colored and have some kind of warning system warning system Aposematic TraitAposematic Trait
• They call attention to themselves and warn of They call attention to themselves and warn of danger. This warning is assumed to ward off danger. This warning is assumed to ward off potential predators or increase fitness in potential predators or increase fitness in some way.some way.
• The more these species look alike, the easier The more these species look alike, the easier it is for a predator to remember that one it is for a predator to remember that one warning pattern (eg. coral snakes bands) warning pattern (eg. coral snakes bands)
• Coral snakesCoral snakes all coral snakes all coral snakes are venomous. There are around are venomous. There are around 70 species in the new world. Over 70 species in the new world. Over 90% of them look extremely 90% of them look extremely similar, especially with respect similar, especially with respect to color and patternto color and pattern
• We assume that their similarity in We assume that their similarity in appearance allows predators to evolve the appearance allows predators to evolve the ability to identify them as poisonous and ability to identify them as poisonous and leave them alongleave them along
• Thus, there is an advantage that all share Thus, there is an advantage that all share from looking similarfrom looking similar
Examples of Mullerian Mimicry
Batesian Mimicry
• A non-noxious or non-poisonous mimic A non-noxious or non-poisonous mimic looks like a noxious modellooks like a noxious model
• For our coral snake example, the For our coral snake example, the venomous coral snakes would be the venomous coral snakes would be the model and non-venomous snakes model and non-venomous snakes looking like coral snakes are the looking like coral snakes are the mimicsmimics
Examples of Batesian Mimicry
In each picture, the snake to the right is the Venomous CoralSnake, while those to the left are the mimics (harmless)
Mertensian Mimicry• We have seen some examples of deadly We have seen some examples of deadly
poisonous snakes such as poisonous snakes such as MicrurusMicrurus (Elapidae) and non-poisonous snakes such (Elapidae) and non-poisonous snakes such asas Lampropeltus Lampropeltus and and PliocercusPliocercus (Colubridae). (Colubridae).
• But there are other snakes that are But there are other snakes that are moderately poisonous, such as members of moderately poisonous, such as members of the genera the genera RhinobothryumRhinobothryum, , ErthrolammprusErthrolammprus and and PseudoboaPseudoboa. .
• Mertens suggests that the moderately Mertens suggests that the moderately poisonous snakes could be the model, not poisonous snakes could be the model, not the poisonous snakes. the poisonous snakes.
Mertensian Mimicry
• If the moderately poisonous snakes bite a If the moderately poisonous snakes bite a predator, it would get sick and therefore would predator, it would get sick and therefore would learn to avoid those and similar snakes in the learn to avoid those and similar snakes in the future. future.
• But, if a deadly poisonous snake bites a predator, But, if a deadly poisonous snake bites a predator, it would die and never have a chance to learn. it would die and never have a chance to learn.
• So, Mertens proposes that the So, Mertens proposes that the moderately moderately poisonous snakes are the model and both the poisonous snakes are the model and both the poisonous and non-poisonous snakes are the poisonous and non-poisonous snakes are the mimicsmimics. This situation is termed Mertensian . This situation is termed Mertensian mimicrymimicry
Ecomorphs
• What is an ecomorph?What is an ecomorph?
• We can loosely define an ‘ecomorph’ We can loosely define an ‘ecomorph’ as a particular set or characters that as a particular set or characters that define a body plan commonly define a body plan commonly associated with living in a particular associated with living in a particular habitathabitat
• Eg. snakes that live in trees are Eg. snakes that live in trees are typically Green, slender, elongate... typically Green, slender, elongate...
Parallel Evolution of Anolis lizard ecomorphs on Caribbean islands
# species per island shown# species per island shown
There are 138 species in the Caribbean and There are 138 species in the Caribbean and about 340 species of anoline lizards overall.about 340 species of anoline lizards overall.
Parallel Evolution of Anolis lizard ecomorphs on Caribbean islands
Anolis l izards occupy many dif ferent ecological niches on Caribbean Islands
Ecomorphs are not closely related!! Each Island has independently
evolved ecomorphs!!!
Common Ancestor
Island 1 Island 2
tree-top
tree-top
Trunk-dweller
Trunk-dweller Twig-
dwellerTwig-dweller
CHAPTER 19 Evolution of Life
History Characters
Reproduction Strategies
• Mice mature early and reproduce Mice mature early and reproduce quickly whereas bears mature late and quickly whereas bears mature late and reproduce latereproduce late
• Some plants live and flower for only Some plants live and flower for only one season, others live and flower for one season, others live and flower for centuriescenturies
• Some bivalves produce millions of tiny Some bivalves produce millions of tiny eggs at once, others less than 100 eggs at once, others less than 100 large eggs at a timelarge eggs at a time
Life History Analysis
• The branch of evolutionary biology that The branch of evolutionary biology that tries to sort our reproductive strategiestries to sort our reproductive strategies
• A “perfect” organism would mature at A “perfect” organism would mature at birth and produce many high quality birth and produce many high quality offspring throughout lifeoffspring throughout life
• No organism can do this because there No organism can do this because there are tradeoffs in time, size of offspring, are tradeoffs in time, size of offspring, and parental investmentand parental investment
Life History Analysis
• Life history extremesLife history extremes– Thrip egg mites are born already inseminated by Thrip egg mites are born already inseminated by
mating with brothers inside mother’s bodymating with brothers inside mother’s body• Adults have short livesAdults have short lives
• The offspring eat there way out of their mother The offspring eat there way out of their mother when she is four days oldwhen she is four days old
– Brown kiwis lay eggs 1/6 of their body weightBrown kiwis lay eggs 1/6 of their body weight• Chicks are self-reliant within a weekChicks are self-reliant within a week
• Takes one month for female to produce each eggTakes one month for female to produce each egg
Life History Analysis
• Organisms may grow to a large size to Organisms may grow to a large size to make large offspring or reproduce make large offspring or reproduce earlier at a smaller size to make smaller earlier at a smaller size to make smaller offspringoffspring
• For organisms that wait, chance of For organisms that wait, chance of dying before reproducing is highdying before reproducing is high
• Environmental variation creates life Environmental variation creates life history variationhistory variation
Life History Analysis
• Questions to ConsiderQuestions to Consider– Why do organisms age and die?Why do organisms age and die?
– How many offspring should an individual How many offspring should an individual produce in a year?produce in a year?
– How big should each offspring be?How big should each offspring be?
• Must balance among fitness aspectsMust balance among fitness aspects
• Conflicts arise between male and Conflicts arise between male and female parentsfemale parents
Life History Analysis
• Female Virginia opossumFemale Virginia opossum– Nursed for three months and then weanedNursed for three months and then weaned
– Continued to grow for several months until Continued to grow for several months until reaching sexual maturityreaching sexual maturity
– Had first litter of 8 offspringHad first litter of 8 offspring
– Months later had second litter of 7 Months later had second litter of 7 offspringoffspring
– At 20 months was killed by a predatorAt 20 months was killed by a predator
– Energy allocation changed through lifeEnergy allocation changed through life
Life History Analysis
• Differences among life history concern Differences among life history concern differences in energy allocationdifferences in energy allocation
• Other female opossums could mature Other female opossums could mature earlier and reproduce earlierearlier and reproduce earlier– Or devote less energy to reproduction and Or devote less energy to reproduction and
more to maintenancemore to maintenance
• Natural selection optimizes energy Natural selection optimizes energy allocation in a way that maximizes total allocation in a way that maximizes total lifetime reproductionlifetime reproduction
Why Do Organisms Age and Die?
• Senescence = late life decline of fertility Senescence = late life decline of fertility and probability of survivaland probability of survival
• Aging reduces an individual’s fitness Aging reduces an individual’s fitness and should be opposed by natural and should be opposed by natural selectionselection
• Two theories on why aging persistsTwo theories on why aging persists
Why Do Organisms Age and Die?
• Rate-of-Living TheoryRate-of-Living Theory– Senescence is caused by accumulation of Senescence is caused by accumulation of
irreparable damage to cells and tissuesirreparable damage to cells and tissues– Damage caused by errors during Damage caused by errors during
replication, transcription, and translation, replication, transcription, and translation, and by accumulation of poisonous and by accumulation of poisonous metabolic by productsmetabolic by products– All organisms have been selected to resist All organisms have been selected to resist
and repair damage as much as and repair damage as much as physiologically possiblephysiologically possible– Have reached limit of possible repairHave reached limit of possible repair
Why Do Organisms Age and Die?
• Rate-of-Living TheoryRate-of-Living Theory– Populations lack genetic variation needed to Populations lack genetic variation needed to
enable more effective repair mechanismsenable more effective repair mechanisms
– Two predictions of theory:Two predictions of theory:• Because damage is partially caused by metabolic Because damage is partially caused by metabolic
by products, aging rate should be correlated to by products, aging rate should be correlated to metabolic ratemetabolic rate
• Because organisms have been selected to repair Because organisms have been selected to repair the maximum possible, species should not be able the maximum possible, species should not be able to evolve longer life spansto evolve longer life spans
Why Do Organisms Age and Die?
• Rate-of-Living TheoryRate-of-Living Theory– Austad and Fischer tested first predictionAustad and Fischer tested first prediction• Calculated amount of energy expended per Calculated amount of energy expended per
gram of tissue per lifetime for 164 mammal gram of tissue per lifetime for 164 mammal speciesspecies• Should expend same amount regardless of Should expend same amount regardless of
length of lifelength of life• Found great variation in energy Found great variation in energy
expenditureexpenditure• Found that bats expend three times the Found that bats expend three times the
energy of other mammals their sizeenergy of other mammals their size
Why Do Organisms Age and Die?
• Rate-of-Living TheoryRate-of-Living Theory– Luckinbill tested second predictionLuckinbill tested second prediction
– Artificially selected for longevity in fruit Artificially selected for longevity in fruit fliesflies
– Increased life span from 35 days to 60 Increased life span from 35 days to 60 daysdays
– These long-lived fruit flies had lower These long-lived fruit flies had lower metabolic rates during first 15 days of lifemetabolic rates during first 15 days of life
Why Do Organisms Age and Die?
• Rate-of-Living TheoryRate-of-Living Theory– Both of the predictions of the theory have Both of the predictions of the theory have
been falsifiedbeen falsified– Examine energy expenditure on cells and Examine energy expenditure on cells and
chromosomes, not whole organismchromosomes, not whole organism• Normal animal cells are capable of a finite Normal animal cells are capable of a finite
number of divisions before deathnumber of divisions before death• All cells except cancer cells, germ line All cells except cancer cells, germ line
cells, and stem cellscells, and stem cells• Senescence may result from chromosome Senescence may result from chromosome
damagedamage
Why Do Organisms Age and Die?
• Rate-of-Living TheoryRate-of-Living Theory– Telomeres of chromosomes consist of Telomeres of chromosomes consist of
tandem repeatstandem repeats– Added by enzyme telomeraseAdded by enzyme telomerase• Overactive in cancer cellsOveractive in cancer cells
– During each replication pieces are lostDuring each replication pieces are lost– Progressive telomere loss is associated Progressive telomere loss is associated
with senescence and deathwith senescence and death– Cells die because chromosomes are too Cells die because chromosomes are too
damaged to functiondamaged to function
Why Do Organisms Age and Die?
• Rate-of-Living TheoryRate-of-Living Theory– Life spans of mammals are correlated with Life spans of mammals are correlated with
life spans of skin and blood cellslife spans of skin and blood cells
– These results consistent with rate-of-livingThese results consistent with rate-of-living
– Why doesn’t natural selection activate Why doesn’t natural selection activate telomerase to add more telomeres?telomerase to add more telomeres?
– Could be tradeoff between extending cell Could be tradeoff between extending cell life and proliferating cancerlife and proliferating cancer
Why Do Organisms Age and Die?
• Evolutionary Theory of AgingEvolutionary Theory of Aging– If genetic variation for extending life spans If genetic variation for extending life spans
does exist, why hasn’t natural selection does exist, why hasn’t natural selection produced this result in all species?produced this result in all species?
– Aging is not caused by damage itself but Aging is not caused by damage itself but the failure to repair the damagethe failure to repair the damage
– Damage is not repaired because of Damage is not repaired because of deleterious mutations or tradeoffs between deleterious mutations or tradeoffs between repair and reproductionrepair and reproduction
Why Do Organisms Age and Die?
• Evolutionary Theory of AgingEvolutionary Theory of Aging– Hypothetical life history of individual with Hypothetical life history of individual with
wild-type genotypewild-type genotype• Mature at age 3Mature at age 3• Die at age 16Die at age 16• Probability of survival from one year to the Probability of survival from one year to the
next is 0.8next is 0.8• Expected lifetime reproductive success = Expected lifetime reproductive success =
2.4192.419
– Will consider two mutations that alter life Will consider two mutations that alter life history strategyhistory strategy
Why Do Organisms Age and Die?
• Evolutionary Theory of AgingEvolutionary Theory of Aging– Mutation Accumulation HypothesisMutation Accumulation Hypothesis– Mutation cause death at age 14Mutation cause death at age 14– Deleterious mutation, but how Deleterious mutation, but how
deleterious?deleterious?– Expected lifetime reproductive success Expected lifetime reproductive success
reduced to 2.340reduced to 2.340• Still 96% of originalStill 96% of original
– Weakly selected againstWeakly selected against• May persist in mutation-selection balanceMay persist in mutation-selection balance
Why Do Organisms Age and Die?
• Evolutionary Theory of AgingEvolutionary Theory of Aging– Deleterious mutations that affect Deleterious mutations that affect
individuals late in life can accumulate in individuals late in life can accumulate in populations and be the cause of agingpopulations and be the cause of aging– Cancers that usually occur late in life only Cancers that usually occur late in life only
slightly affect fitness of the individualslightly affect fitness of the individual– Not strongly selected against and can Not strongly selected against and can
accumulate rapidlyaccumulate rapidly– Can cause senescence and death with few Can cause senescence and death with few
fitness consequencesfitness consequences
Why Do Organisms Age and Die?
• Evolutionary Theory of AgingEvolutionary Theory of Aging– Mutation of two different life history characters Mutation of two different life history characters
with pleiotropic actionwith pleiotropic action
– Matures at 2 yearsMatures at 2 years
– Dies at 10 yearsDies at 10 years
– Tradeoff between early reproduction and survival Tradeoff between early reproduction and survival late in lifelate in life• Antagonistic pleiotropic effectsAntagonistic pleiotropic effects
– Expected lifetime reproductive success is 2.66Expected lifetime reproductive success is 2.66• Mutation is beneficialMutation is beneficial
Why Do Organisms Age and Die?
• Evolutionary Theory of AgingEvolutionary Theory of Aging– Reproduce so much early that early death is not Reproduce so much early that early death is not
selected againstselected against– Mutation devotes less to repair and more to Mutation devotes less to repair and more to
reproductionreproduction– Heat-shock protein hsp70Heat-shock protein hsp70– Prevents damage due to denaturationPrevents damage due to denaturation– Heat-shock binding interferes with normal cellular Heat-shock binding interferes with normal cellular
functionsfunctions– Heat-shock genes only expressed during Heat-shock genes only expressed during
environmental stressenvironmental stress• Proteins removed after stress passesProteins removed after stress passes
Why Do Organisms Age and Die?
• Evolutionary Theory of AgingEvolutionary Theory of Aging– Expression of hsp70 in Expression of hsp70 in DrosophilaDrosophila causes causes
longer life span but lower reproduction longer life span but lower reproduction early in lifeearly in life
– Tradeoff between early fecundity and late Tradeoff between early fecundity and late survival is mediated by hsp70survival is mediated by hsp70
– Heat-shock proteins may mediate this Heat-shock proteins may mediate this tradeoff in many organismstradeoff in many organisms
