Follow up on feedback & independent project drafts Follow up on minute papers Species concepts (cont.)

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Kristian Walker
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1 Spring 2014: Mondays 10:15am 12:05pm (Fox Hall, Room 204) Instructor: D. Magdalena Sorger Website: theantlife.com/teaching/bio295-islands-evolution LECTURE 10 Today: Follow up on feedback & independent project drafts Follow up on minute papers Species concepts (cont.) Give an example for how to deal with cryptic species diversity Speciation Compare and contrast different modes of speciation Explain the concept of ring species and give an example Discuss different mechanisms of speciation Guest speaker: Dr. Reade Roberts Summary 1

2 FOLLOW-UP ON FEEDBACK & INDEPENDENT PROJECT DRAFTS FOLLOW-UP MINUTE PAPERS 2

3 Follow up on minute papers Bootstrapping replaced by genome comparisons? How is DNA extracted from fossils? Why is biological species concept legal standard? Scientists using different species concepts how comparable? Species concepts overlap in ideas? Combining multiple species concepts? Why species not population considered smallest evolutionarily dependent unit? What defines a cryptic species? SPECIATION 3

4 Speciation 3 stages 1) Isolation of populations 2) Divergence in traits (e.g., mating system or habitat use) 3) Reproductive isolation (secondary contact) Modes of speciation Allopatric Peripatric Sympatric Parapatric 4

5 ALLOPATRIC SPECIATION Mayr 1942, 1963 physical isolation creates barrier to gene flow geographic isolation e.g.: VICARIANCE, DISPERSAL (and colonization of islands = PERIPATRIC SPECIATION) Modes of speciation VICARIANCE BEFORE Allopatric speciation 5

6 VICARIANCE DURING Allopatric speciation VICARIANCE AFTER Allopatric speciation 6

7 VICARIANCE AFTER Allopatric speciation VICARIANCE Former range is split into two or more distinct areas e.g., rise of mountain range, long term drying trend that fragments forests, lava flow, etc. Allopatric speciation 7

8 DISPERSAL BEFORE Allopatric speciation DISPERSAL DURING Allopatric speciation 8

9 DISPERSAL AFTER Allopatric speciation DISPERSAL AFTER Allopatric speciation 9

10 DISPERSAL Individuals colonize new habitat e.g.: islands, hot springs, deep sea vents, fens, bogs, caves, mountaintops, lakes, ponds, etc. Allopatric speciation PERIPATRIC SPECIATION (ALLOPATRIC) Divergence of small population from widely distributed ancestral form e.g.: FOUNDER EFFECT Modes of speciation 10

11 FOUNDER EFFECT Mainland Islands Peripatric speciation FOUNDER EFFECT Mainland Islands Peripatric speciation 11

12 FOUNDER EFFECT Mainland Islands Peripatric speciation SYMPATRIC SPECIATION Highly controversial Many examples are in fact micro allopatric speciation (e.g., different ecological niches, host shifts, example in Beak of the Finch Ch. 16 HW05) Modes of speciation 12

13 Sympatric speciation Sympatric speciation 13

14 PARAPATRIC SPECIATION Divergent selection at narrow environmental discontinuity may oppose gene flow and result in reproductive isolation Parapatric speciation Modes of speciation 14

15 HYBRID ZONE Parapatric speciation PARAPATRIC SPECIATION Example: Ring species Ring species: chain of intergrading populations encircles barrier terminal forms coexist without interbreeding Modes of speciation 15

16 Ring species: Dogs Ring species: Dogs 16

17 Ring species: Dogs SPECIES B SPECIES A Ring species: Dogs 17

18 SPECIES B SPECIES A Ring species: Dogs SPECIES B SPECIES A Ring species: Dogs 18

19 Ring species: Greenish warbler CASE STUDY Natural history Greenish warbler: Phylloscopus trochiloides Small, insectivorous leaf gleaning bird 5 subspecies encircling Tibetan Plateau Ring species: Greenish warbler Irwin et al

20 Natural history Greenish warbler: Phylloscopus trochiloides Small, insectivorous leaf gleaning bird 5 subspecies encircling Tibetan Plateau Gap because of recent deforestation Ring species: Greenish warbler Irwin et al Natural history Use song in species recognition Gradual variation in song around the ring Song and plumage used in courtship and territory defense Ring species: Greenish warbler Irwin et al

21 Methods mtdna 2 mircosatellite loci Wing bar size & body size Playback experiments Ring species: Greenish warbler Irwin et al Results Greenish warbler Irwin et al

22 Results 2 major clades (Western & Eastern individuals) Song and plumage (used in courtship and territory defense) differs between two reproductively isolated forms in Siberia Ring species: Greenish warbler Irwin et al Biogeographic history: 2 possibilities 1. Ancestral species split into 2 populations (west & east), then expanded and met each other in south (interbred) and in north (no interbreeding) Ring species: Greenish warbler Irwin et al

23 Biogeographic history: 2 possibilities 2. Ancestral species confined to Himalayas, developed genetic structure (isolation by distance), expanded northwards along two pathways (west & east) Ring species: Greenish warbler Irwin et al Conclusion Sexual selection played important role in speciation Sexual selection often favors novelty and/or complexity results in many possible outcomes Ring species: Greenish warbler Irwin et al

24 Modes of speciation Allopatric Peripatric Sympatric Parapatric Modes of speciation Allopatric no exchange of genes (m = 0) Sympatric exchange genes freely/randomly (m = 0.5) Parapatric exchange genes but not freely (0 < m < 0.5) m= fraction of genes exchanged Coyne & Orr

25 Mechanisms of speciation Genetic drift? Natural selection Sexual selection Sexual selection and speciation 33 species BIRDS OF PARADISE 5 species MANUCODES PROMISCUOUS MATING SYSTEMS 319 species HUMMINGBIRDS 103 species SWIFTS Higher speciation rate (or lower extinction rate) 25

26 CHARACTER DISPLACEMENT Characters differ more where two taxa are sympatric than where they are allopatric CHARACTER DISPLACEMENT Characters differ more where two taxa are sympatric than where they are allopatric 26

27 DIFFICULTIES WITH CONCEPT OF SPECIES? MORPHOSPECIES CONCEPT Phenotypic differences as basis for identification of morphospecies BIOLOGICAL SPECIES CONCEPT Evolutionary independence based on reproductive isolation PHYLOGENETIC SPECIES CONCEPT Smallest monophyletic group (lineages that contain all of known descendants of common ancestor) 27

28 3 stages to producing viable offspring PREMATING mating PREZYGOTIC zygote formed POSTZYGOTIC features that impede transfer of gametes to members of other species mating or gamete transfer occurs, but zygotes are not formed hybrid zygotes are formed but have reduced fitness There are barriers at each of these stages. PREMATING Ecological isolation Temporal isolation Habitat isolation Behavioral isolation Behavioral Pollinator isolation PREZYGOTIC Mechanical isolation Copulatory behavioral isolation Gametic isolation POSTZYGOTIC Extrinsic Ecological inviability Behavioral sterility Intrinsic Hybrid inviability Hybrid sterility Barriers to gene flow 28

29 Πάντα ῥεῖ (panta rhei) Everything flows. Characterizing Heraclitus thought (by Simplicius, & Plato) GUEST SPEAKER 29

30 Dr. Reade Roberts Recap Species concepts Give an example for how to deal with cryptic species diversity Speciation Compare and contrast different modes of speciation Explain the concept of ring species and give an example Discuss different mechanisms of speciation Cichlids 30

31 SUMMARY 1. What was the most important thing you learned during this class? 2. What important question regarding what you learned remains unanswered for you? (What would you like to know about next?) SUMMARY NAME & DATE 3/24/

32 For next week: The Beak of the Finch: Read Chapter 15 & 16 Read paper (will be posted)? Sign up sheet for independent project meeting 32

Summary. 16 1 Genes and Variation. 16 2 Evolution as Genetic Change. Name Class Date

Summary. 16 1 Genes and Variation. 16 2 Evolution as Genetic Change. Name Class Date Chapter 16 Summary Evolution of Populations 16 1 Genes and Variation Darwin s original ideas can now be understood in genetic terms. Beginning with variation, we now know that traits are controlled by