Speciation & Reproductive Isolation in Columbines by J. Phil Gibson University of Oklahoma.

Speciation & Reproductive Isolation in Columbinesby J. Phil Gibson

University of Oklahoma

Columbine Case Questions:• How do flowers, pollinators, and pollination systems

work? • How can we identify and test different for

reproductive isolation in plants?• What mechanisms can act to unify members of a

species and maintain separatations between members of different species in plants?

Aquileqia caerulea – Colorado columbine

1 2 34 5

The diagram to the right is a phylogeny for 5 species in the same genus. This phylogeny shows. . .

A. the degree to which organisms look like one another.

B. how different organisms are related through common ancestors

C. the sequence in which species evolved from left to right.

D. the amount of change each species has experienced.

E. which species are most closely related to the species at point M.

Clicker Question #1

What do the lines in this phylogeny represent?

A. The passage of timeB. Lineages of organismsC. Each line represents a single

speciesD. Which species evolved first,

second, third, etc.E. All of the above

Clicker Question #2

1 2 34 5

What do the nodes (indicated by G, P, R, and M) represent in the phylogeny?

A. Where two species hybridized.

B. Lineages of organisms.C. Common ancestors of

different species.D. The sequence in which

species 1-5 evolved.E. None of the above.

Clicker Question #3

1 2 34 5 G

P

R

M

1 2 34 5 G

P

R

M

What does the point labeled R indicate? A. Species 5 in the past.B. Species 2 in the pastC. Where species 2 and species 5

hybridized.D. The common ancestor of species

2, 3, 4 & 5..E. Where species 5 became species

2.

Clicker Question #4

1 2 34 5 G

P

R

M

Which statement(s) below accurately describe what is happening at the nodes indicated by MRPG? (choose all that apply)

A. Speciation is occurringB. Mutation and natural selection are

making the best new species C. One species is turning into another

species.D. Gene pools are becoming separated

and isolated. E. Two species are coming together to

make a new species.

Clicker Question #5

Pre-case Thought Questions.

• How do flowers work? How do they play a role in maintaining separate species? Make a labeled diagram to summarize your thoughts.

• What are the important aspects of the interactions and relationship between flowering plants and their pollinators?

• What is the relationship among sister species, a common ancestor to the sister species, and reproductive isolation? Make a labeled diagram to summarize your thoughts.

• What is a phylogeny and what does it tell us about species?

1 2 34 5

Branches in a phylogeny are called clades. Members of a clade share a number of features, such as similar flower structure, due to common ancestry.

Nodes indicate common ancestors and points of lineage divergence (speciation).

Lines represent separate lineages. Traits can change in a lineage resulting in unique traits shared by members of that lineage.

Phylogenies are hypotheses about relationships among taxa.

Reproductive isolation maintains separate lineages.

Flowering plants are a clade that share a unique feature, flowers.

stamen

filament

anther

{

stigma

ovary

style

{ pistil

petals

sepals

What Do Pollinators Do?In flowering plants, pollination is the transfer of pollen

from an anther to a receptive stigma by an abiotic or biotic vector. Wind is a common means of abiotic pollination. Biotic pollination is typically a mutualistic relationship between a plant and an animal in which the plant attracts the animal to a flower to pick up pollen and then carry it to another flower for sexual reproduction.

What do you think is the most important feature of a flower for attracting pollinators?

A. Flower colorB. Flower shapeC. Flower orientationD. A reward, such as nectarE. A reward, such as pollen

Clicker Question #6

POLLINATOR ATTRACTANTSPRIMARY ATTRACTANTS• Food (nectar, pollen)• Shelter (solar tracking flowers)• Other needed materials (e.g. waxes,

pheromones, repellants)

SECONDARY ATTRACTANTS• Odor (scents & fragrances)• Visual cues (color, shape, nectar

guides)

Biotic Pollination Syndromes• Cantherophily (beetles): white or drab, sweet scent, open bowl

shape• Myophily (flies): variable• Sapromyophily (carion and dung flies): purple-brown, stink of

decaying protein, deep traps• Melittophily (bees): variable color/no pure red, sweet scent • Sphignopily (hawkmoths): white or pale green, strong sweet

scent, deep narrow tubes with nectar• Psychophily (butterflies): red, yellow, blue, moderately strong

sweet, deep narrow tubes with nectar• Ornithophily (birds): bright red, no scent, wide deep tubes with

nectar• Chiropterophily (bats): dull white or green, strong fermented

scent, brush or bowl shaped

Flowers and Pollinators:A structural-functional-behavioral interactionIn flowering plants, floral structure has been

suggested as an important mechanism for achieving reproductive isolation and promoting speciation by affecting either pollinator behavior (behavioral isolation) or pollen transfer (mechanical isolation) (Grant 1949).

Clicker Question #7

Which form of reproductive isolation do you think would be most effective for flowering plants?

A. Ecological isolation due to plants growing in different habitats

B. Behavioral isolation due to floral traits influencing pollinator behavior

C. Hybrids being sterile and unable to produce functional gametes or not being able to survive in populations

D. Biochemical isolation due to failed interaction between pollen and stigma.

E. Mechanical isolation due to pollen not being successfully gathered or delivered.

Aquilegia spp. (Columbines) - Spurs & Species

All columbine flowers have nectar spurs and other structural similarities.

nectar spurs

anthers

stigmas

In columbines, color would be an example of a _________ attractant and nectar would be an example of a _________ attractant.

A. primary/secondaryB. floral/pollinatorC. secondary/primaryD. bird/insectE. reward/visual

Clicker Question #8

Floral nectar spurs are considered innovations

that have promoted speciation and

reproductive isolation in columbines through

shifts in pollinators related to changes in

nectar spur length. How could this work?

bee pollinatedhummingbird pollinatedhawkmoth pollinatedhummingbird & hawkmoth pollinated

Aquilegia formosa Aquilegia pubescens

Aquilegia fomosa and A. pubescens are species that evolved from a recent common ancestor. What differences between A. formosa and A. pubescens flowers may be important for interacting with pollinators?Why might their sharing a recent common ancestor be important?

Because they share a common ancestor. . .A. both columbine species share relatively few traits.B. both columbine species share some traits, but

also have other unique features that define and reinforce each species’ as a separate lineage.

C. both species are completely different from one another and share no traits.

D. both columbine species will attract the same pollinators and grow in the same places.

E. both columbine species are reproductively isolated from one another.

Clicker Question #9

Spurs & species

Given the proposed importance of nectar spurs, how would you test their influence on

columbine speciation?Develop an hypothesis and design an experiment to to explore potential causes and function of behavioral isolation and mechanical isolation in A. pubescens and A. formosa flowers.

In an initial study, researchers presented both columbine species in a hexagonal array with 9 of each spp. Arrays were placed near A. pubescens and A. formosa populations and

pollinator visits recorded.

Why did they do this?

A. pubescens

A. formosa

What would you expect?Mean visits per flower per hour by different pollinators to A.

formosa & A. pubescens

0

0.2

0.4

0.6

0.8

1

1.2

hummingbird hawkmoth fly bee

pollinator species

vis

its

/flo

we

r/h

ou

r (+

/- s

.e.)

A. formosa

A. pubescens

Experimental ResultsMean visits per flower per hour by different pollinators to A.

formosa & A. pubescens

0

0.05

0.1

0.15

0.2

0.25

0.3

hummingbird hawkmoth fly bee

pollinator species

vis

its

/flo

we

r/h

ou

r (+

/- s

.e.)

A. formosa

A. pubescens

Aquilegia formosa Aquilegia pubescens

Selasphorus rufus Hyles lineata

Experimental Results: Pollinators identified

Experimental Data: Pollinator preferences for A. formosana and A. pubescens

What can the researchers conclude so far?

Visits to hummingbirds hawkmoths bees

A. formosa 81 0 85

A. pubescens 9 115 19

Χ2 57.6 115 41.88

p <0.0001 <0.0001 <0.0001

Aquilegia pubescens

Next, the researchers focused on A. pubescens. In this study, they planted two arrays of modified and control (unmodified) flowers.

Array 1: pedicels for ½ of the A. pubescens flowers staked to make flowers pendant (point downwards)

Array 2: spurs for ½ of the A. pubescens flowers shortened (squeezed nectar from bottom of spurs, tied & clipped spur)

What data should they collect? Why?What will the data

tell them?

A. pubescens Flower Manipulations

Unmanipulated ShortenedPendant

Measure pollen removal as an indicator of effective pollinator

visitation.

Which of these hypotheses are the researchers potentially testing?

If floral structural traits in A. pubescens are important for reproductive isolation, then we should expect. . .

A. the floral modifications will have no effect on pollinator visitation and pollen removal

B. hawkmoths will be better able to remove pollen from modified flowers.

C. hummingbirds will be attracted to the modified flowers less than unmodified flowers.

D. the unmodified flowers will have higher visitation and pollen removal by hawkmoths than modified flowers.

Clicker Question #10

In the floral manipulation experiment, you should expect . . .A. unmanipulated flowers will have more pollen removed by

hawkmoths than the others.B. unmanipulated flowers will have less pollen removed by

hawkmoths than the others.C. hawkmoths will visit pendant flowers more than the

others.D. hawkmoths will remove pollen from shortened spur

flowers more than the others.E. None of these are expected outcomes for this experiment.



These results are consistent with the researchers’ prediction.

A. True B. False

Visits to Number of observed visits

upright 51

pendent 5

Χ2 45.5

p <0.0001

Experimental Data: Visits by Hyles lineata to A. pubescens with differing floral orientation.

These results are consistent with the researchers’ prediction.

A. True B. False


Visits to Number of observed visits

long 17

short 19

Χ2 0.11

p Not significant

Experimental Data: Visits by Hyles lineata to A. pubescens with long or short nectar spurs.

These results are consistent with the researchers’

prediction.A. True B. False


0

500

1000

1500

2000

2500

3000

3500

4000

4500

control (long) shortened

treatment

mea

n po

llen

grai

ns re

mai

ning

in a

nthe

r (+/

- se)

Mean number of pollen grains remaining in A. pubescens anthers after hawkmoth visitation.

From these studies we can conclude thatA. Orientation and color promote mechanical isolation and

floral structure promotes behavioral isolation.B. The species have few floral features that would promote

reproductive isolation.C. Spur length is a primary attractant and color is a secondary

attractant.D. Orientation and color promote behavioral isolation and

floral structure promotes mechanical isolation.E. Floral structure causes reproductive isolation after

pollination occurs.


What about hybrids and habitats?

Although they have these differences, hybrid populations of viable, reproductively functioning plants with floral traits and molecular markers characteristic of both species have been identified at intermediate elevations and habitats!

How could that happen? What does it mean biologically? Evolutionarily?

A. pubescens typically grows at higher elevations and in more xeric habitats.

A. formosa tends to grow at lower elevations and in more mesic (moist) habitats.

Researchers measured floral (A & C) and genetic (B & D) traits in hybrid populations along elevation (A & B) and habitat transects (C & D). What do the data show?

A. formosa

A. pubescens

A. formosa genetic markers

A. formosa

A. pubescens genetic markers

A. pubescens

spur color

blade color

spur length

blade length

orientation

The occurrence of hybrids indicates. . .A. that A. formosa and A. pubescens are really just

one species.B. reproductive isolation does not matter for plant

species.C. pollinator behavior is not important for

maintaining species.D. reproductive isolating barriers are not always

absolute between species.E. that habitat is not important for maintaining

species.


Based upon the data in the floral manipulation studies, spurs act to maintain separate Aquilegia species by. . .

A. causing flowers to grow in different habitatsB. offering different rewards to different pollinatorsC. influencing pollen removed from and depositing

on flowers. D. attracting different pollinators.


Clicker Question #18Based upon the data in the hybrid studies, habitat

selection acts to maintain A. formosa and A. pubescens as separate species by. . .

A. causing plants of the separate species to grow better in distinct habitats.

B. offering different rewards to different pollinators based upon the habitat.

C. causing hybrid individuals to survive as well as non-hybrid individuals in any habaitat.

D. causing the pollinators living in different habitats to have access to different rewards.

Species Concepts• Morphological species concept

– Based on physical characteristics. – Simple, clear, but does not address mechanisms that separate or maintain species.

• Biological species concept– Species is a group of individuals whose members have the potential to interbreed

with one another in nature to produce viable, fertile offspring but cannot successfully interbreed with members of other species

– Not good for plants, asexual reproducers, hybrids, or extinct species.• Ecological species concept

– Each species occupies an ecological niche, which is the unique set of habitat resources that a species requires, as well as its influence on the environment and other species.

– Can be hard to determine if species have broad habitat tolerances.• Evolutionary lineage (Phylogenetic) concept

– Species should be defined based on the separate evolution of lineages.– May be hard to draw delimitation.

Which species concept do you think is least applicable for A. formosa and A. pubescens?

A. morphologicalB. biologicalC. ecologicalD. phylogeneticE. None of these really works.


The two columbine species. . .A. are really just one species because their flowers are

not different enough to be separate species.B. represent different lineages that became isolated

from one another and diverged from a common ancestor.

C. are tentatively two species until the pollinators can differentiate them better.

D. represent different lineages but the pollinators’ inability to distinguish them will prevent further speciation.


Epilogue

There are floral differences that influence pollinator behavior.

However, there is some pollinator infidelity and hybrid offspring between the two species are produced and survive in habitats intermediate to the typical conditions for each species.

Although floral features maintain some reproductive isolation between species, habitat selection against hybrids is also a strong force maintaining reproductive isolation for both species.

End of Case Thought Questions• Prepare a diagram that uses these columbines to show the

relationship between pollinators and flower structure and function.

• Prepare a diagram that uses these columbines to demonstrate the evolutionary and ecological factors shaping the relationship between two sister species.

• Prepare a diagram that describes the history of these species and their common ancestor, how they may have become different, and how interactions with pollinators and habitat have shaped speciation.

• If we assume these species evolved from a common ancestor that was hummingbird pollinated, can you use a phylogenetic tree to diagram how traits diverged in the different ?

Image CreditsSlide 1: Clump of columbines Copyright © 2006 J. Phil GibsonSlide 2: Aquilegia flower Copyright © 2006 J. Phil GibsonSlide 10: Kalmia latifolia flower Copyright © 2006 J. Phil GibsonSlide 11: Butterflies on a milkweed Copyright © 2012 J. Phil GibsonSlide 13: Cactus flower with bee Copyright © 2012 J. Phil GibsonSlide 17: Detail from Clump of columbines Copyright © 2006 J. Phil GibsonSlide 20: A. formosa: http://species.wikimedia.org/wiki/File:Aquilegia_formosa_14962.JPG This file is licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license. A. pubescens: Copyright © 2009 Barry Breckling http://calphotos.berkeley.edu/cgi/img_query?enlarge=0000+0000+1209+2492.

This image has a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 (CC BY-NC-SA 3.0) license.Slide 26: A. formosa: http://species.wikimedia.org/wiki/File:Aquilegia_formosa_14962.JPG This file is licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license. A. pubescens: Copyright © 2009 Barry Breckling http://calphotos.berkeley.edu/cgi/img_query?enlarge=0000+0000+1209+2492 This image has a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 (CC BY-NC-SA 3.0) license. Rufus hummingbird: Selasphorus rufus http://en.wikipedia.org/wiki/File:Selasphorus_rufus.jpgHawkmoth: Hyles lineata http://en.wikipedia.org/wiki/File:White-lined_sphinx.JPG This file is licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license. Slide 28: A. pubescens: Copyright © 2009 Barry Breckling http://calphotos.berkeley.edu/cgi/img_query?enlarge=0000+0000+1209+2492 This image has a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 (CC BY-NC-SA 3.0) license. Slide 36: A. formosa: http://species.wikimedia.org/wiki/File:Aquilegia_formosa_14962.JPG This file is licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license. A. pubescens: Copyright © 2009 Barry Breckling http://calphotos.berkeley.edu/cgi/img_query?enlarge=0000+0000+1209+2492 This image has a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 (CC BY-NC-SA 3.0) license. Slide 37: Figure from from Hodges, SA and ML Arnold. 1994. Floral and Ecological isolation between Aquilegia formosa and Aquilegia pubescens. Poc Nat Acad. Sci USA 91: 2493-2496. Permission needed.

http://calphotos.berkeley.edu/cgi/img_query?enlarge=0000+0000+1209+2492

http://creativecommons.org/licenses/by-nc-sa/3.0/




Speciation & Reproductive Isolation in Columbines by J. Phil Gibson University of Oklahoma.

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Transcript of Speciation & Reproductive Isolation in Columbines by J. Phil Gibson University of Oklahoma.