Lecture 22: Specialization,

Coevolution• Species interactions

• Specialization

• Coevolution:

– Competitors

– Predators-prey

– Cospeciation

• When is it coevolution?

Can species interactions

drive the evolution of

biological diversity?

Cuckoos: brood parasites

• Lay eggs in nest of other birds

• Nestlings eject host egg/nestling

• Specialists

– Different races each specialized on

different host

• Coevolution:

– reciprocal adaptation:evolutionary change ininteracting species owing tonatural selection imposed byeach on the other

• Specialization:

– Not all highly specializedinteractions are coevolved:environmental tracking

Sp1 Sp2

Sp1 Sp2

Types of species interactions

++ Mutualisms: pollinator-plant, plant-seed disperser

+- Antagonistic interactions:Brood parasitism, Predator-prey, Plant-herbivore

-- Competitive

Reciprocal Selection:

• The fitness ofSpecies 1individuals isdecreased byinteracting withSpecies 2

• And the converse!• Reciprocal selection

favors traits thatreduce theinteraction

Coevolution in competitive interactions

Phenotype

(e.g., body size)

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Coevolution and competition

Sticklebacks: Is

divergent body

morphs due to

coevolution?

Limnetic (open water)

Benthic (bottom)

An experiment: competition and

coevolution

Paxton Lake: limnetic and benthic

Cranby Lake: 1 intermediate species

An experiment: competition and

coevolution

Paxton Lake: limnetic and benthic

Cranby Lake: 1 intermediate species

• Measured thefitness effect ofPaxton Limneticspecies on CranbyLake intermediatespecies

• w/ limnet species:expect selectiontoward benthics

Fitne

ss (gr

owth

)

Body size: More Limnetic

w/o Paxton limnetics

w/ Paxton limnetics

• Directional

selection w/

limnetic species

• Stabilizing

selection w/o

• When species

coexist,

reciprocal

selection for

divergence in

body size

Predator-Prey coevolution:

garter snakes and newts

• Brodie and Brodie, et al.

• Rough-skinned newt:TTX tetrodotoxin in skin– Paralytic

• Snake T. spiralis– Amphibian specialist

– Resistance: overcomeparalytic effects

• Snake resistance

varies

• Have these

predators evolved

in response to prey?

• Snakes vary in

resistance

– Snake

population w/o

newts:

Susceptible to

TTX

• Abilities

matched in

areas of

sympatry

Red Crossbills: predator-prey

coevolution• Specialists: seeds

from conifer trees

• Different “species”

feed on different

trees: pine, spruce,

fir, hemlock

Red Crossbills: predator-prey

coevolution• Use bill to extract

seeds

• “species” differ in

bill size

• Is this

specialization due

to coevolution?

• Compare billdepth withfeedingefficiency in alab study

• Compare billdepth withsurvivorship innature

• E.g. Lodgepolepine

• For 4 conifer species

• Disruptive selection on bill depth, groove

• Reciprocal adaptation?

• Crossbills and

lodgepole pine

• Cones evolve inresponse to crossbills,

squirrels

• Crossbill adaptation

differ in presence and

absence of squirrels

Does coevolution promote

biodiversity?

• Bacteria Buchneraendosymbiotic withaphids

• Bacteria supplynutrients to aphid(mutualism)

• Vertical bacteriatransfer: mother tooffspring via eggs

• Strong cospeciationpattern

•Fig 14.14

• Trait matching:

e.g. plant-

polinator

mutualism

• HA: Ecological

sorting?

• Floral traits evolved,

insects use flowers

with matching trait

Is it coevolution?

Is it coevolution?

Host

Parasite/

mutualist

• cospeciation

• HA: sharedpatterns of

vicariance or

limited dispersal!

When is it coevolution?Common misconception #2: parasite adaptation to host defenses

Evolutionary tracking is an equally plausible explanation!

• Plant evolved phototoxic compounds at

some point in time

• Moth evolved UV shielding web making

behavior at some point in time

• Is this coevolution?