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

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Presentation on theme: "Speciation & Reproductive Isolation in Columbines by J. Phil Gibson University of Oklahoma."— Presentation transcript:

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

2 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

3 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

4 What do the lines in this phylogeny represent? A.The passage of time B.Lineages of organisms C.Each line represents a single species D.Which species evolved first, second, third, etc. E.All of the above Clicker Question #

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 # G P R M

6 G P R M What does the point labeled R indicate? A.Species 5 in the past. B.Species 2 in the past C.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

7 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 occurring B.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

8 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?

9 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.

10 Flowering plants are a clade that share a unique feature, flowers. stamen filament anther { stigma ovary style { pistil petals sepals

11 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.

12 What do you think is the most important feature of a flower for attracting pollinators? A. Flower color B. Flower shape C. Flower orientation D. A reward, such as nectar E. A reward, such as pollen Clicker Question #6

13 POLLINATOR ATTRACTANTS PRIMARY 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)

14 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

15 Flowers and Pollinators: A structural-functional-behavioral interaction In 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).

16 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.

17 Aquilegia spp. (Columbines) - Spurs & Species All columbine flowers have nectar spurs and other structural similarities. nectar spurs anthers stigmas

18 In columbines, color would be an example of a _________ attractant and nectar would be an example of a _________ attractant. A.primary/secondary B.floral/pollinator C.secondary/primary D.bird/insect E.reward/visual Clicker Question #8

19 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 pollinated hummingbird pollinated hawkmoth pollinated hummingbird & hawkmoth pollinated

20 Aquilegia formosaAquilegia 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?

21 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

22 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.

23 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

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

25 Experimental Results Mean visits per flower per hour by different pollinators to A. formosa & A. pubescens

26 Aquilegia formosaAquilegia pubescens Selasphorus rufus Hyles lineata Experimental Results: Pollinators identified

27 Experimental Data: Pollinator preferences for A. formosana and A. pubescens What can the researchers conclude so far? Visits tohummingbirdshawkmothsbees A. formosa81085 A. pubescens Χ2Χ p<0.0001

28 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?

29 A. pubescens Flower Manipulations UnmanipulatedShortenedPendant Measure pollen removal as an indicator of effective pollinator visitation.

30 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

31 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. Clicker Question #11

32 Clicker Question #12 These results are consistent with the researchers prediction. A. True B. False Visits toNumber of observed visits upright51 pendent5 Χ2Χ p< Experimental Data: Visits by Hyles lineata to A. pubescens with differing floral orientation.

33 These results are consistent with the researchers prediction. A. True B. False Clicker Question #13 Visits toNumber of observed visits long17 short19 Χ2Χ pNot significant Experimental Data: Visits by Hyles lineata to A. pubescens with long or short nectar spurs.

34 These results are consistent with the researchers prediction. A. True B. False Clicker Question #14 Mean number of pollen grains remaining in A. pubescens anthers after hawkmoth visitation.

35 From these studies we can conclude that A. 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. Clicker Question #15

36 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.

37 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

38 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. Clicker Question #16

39 Based upon the data in the floral manipulation studies, spurs act to maintain separate Aquilegia species by... A.causing flowers to grow in different habitats B.offering different rewards to different pollinators C.influencing pollen removed from and depositing on flowers. D.attracting different pollinators. Clicker Question #17

40 Clicker Question #18 Based 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.

41 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.

42 Which species concept do you think is least applicable for A. formosa and A. pubescens? A. morphological B. biological C. ecological D. phylogenetic E. None of these really works. Clicker Question #19

43 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. Clicker Question #20

44 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.

45 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 ?

46 Image Credits Slide 1: Clump of columbines Copyright © 2006 J. Phil Gibson Slide 2: Aquilegia flower Copyright © 2006 J. Phil Gibson Slide 10: Kalmia latifolia flower Copyright © 2006 J. Phil Gibson Slide 11: Butterflies on a milkweed Copyright © 2012 J. Phil Gibson Slide 13: Cactus flower with bee Copyright © 2012 J. Phil Gibson Slide 17: Detail from Clump of columbines Copyright © 2006 J. Phil Gibson Slide 20: A. formosa: This file is licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license. A.pubescens: Copyright © 2009 Barry Breckling This image has a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 (CC BY-NC-SA 3.0) license.http://calphotos.berkeley.edu/cgi/img_query?enlarge= CC BY-NC-SA 3.0 Slide 26: A. formosa: This file is licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license. A. pubescens: Copyright © 2009 Barry Breckling This image has a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 (CC BY-NC-SA 3.0) license.http://calphotos.berkeley.edu/cgi/img_query?enlarge= Rufus hummingbird: Selasphorus rufus Hawkmoth: Hyles lineata This file is licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license. Slide 28: A. pubescens: Copyright © 2009 Barry Breckling This image has a Creative Commons Attribution- NonCommercial-ShareAlike 3.0 (CC BY-NC-SA 3.0) license. Slide 36: A. formosa: This file is licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license. A. pubescens: Copyright © 2009 Barry Breckling This image has a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 (CC BY-NC-SA 3.0) license.http://calphotos.berkeley.edu/cgi/img_query?enlarge= Slide 37: Figure from from Hodges, SA and ML Arnold Floral and Ecological isolation between Aquilegia formosa and Aquilegia pubescens. Poc Nat Acad. Sci USA 91: Permission needed.


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