evolution and systematics

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EVOLUTION AND SYSTEMATICS SPECIES AND SPECIATION Ernst Mayr: "the greatest living evolutionary biologist“ -- S. J. Gould

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EVOLUTION AND SYSTEMATICS. Ernst Mayr: "the greatest living evolutionary biologist“ -- S. J. Gould. SPECIES AND SPECIATION. SPECIATION. Speciation connects micro- and macroevolution “Species“ is basic unit recognized for most life forms ~10 million species exist; ~1.4 million described - PowerPoint PPT Presentation

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Page 1: EVOLUTION AND SYSTEMATICS

EVOLUTION AND SYSTEMATICS

SPECIES AND SPECIATION

Ernst Mayr:"the greatest livingevolutionary biologist“

-- S. J. Gould

Page 2: EVOLUTION AND SYSTEMATICS

SPECIATION

• Speciation connects micro- and macroevolution• “Species“ is basic unit recognized for most life forms• ~10 million species exist; ~1.4 million described• Many additional extinct species assumed and known

(e.g. fossils)

Page 3: EVOLUTION AND SYSTEMATICS

• Living things tend to occur in classes/groups• Individuals in groups resemble one another more

than members of different groups• Species are important kind of natural group• Species differ in appearance, ecology, behaviour,

genetics, distribution, etc.• Why do natural groups exist? How do they evolve?• Diverse species concepts have been proposed

Page 4: EVOLUTION AND SYSTEMATICS

WHAT IS A SPECIES?EARLY PRACTICES

• Early research relied on morphological features, hence (1) Morphological Species Concept

• “A species is what a good taxonomist says it is“• Poulton (1904): interbreeding within species

defines them• Some workers also used non-anatomical

attributes, e.g. habitat, distribution

Page 5: EVOLUTION AND SYSTEMATICS

TRAITS VARY LESS WITHINTHAN AMONG SPECIES: SPECIES AREDISTINGUISHABLE BY THEIR TRAITS

Page 6: EVOLUTION AND SYSTEMATICS

SIBLING (CRYPTIC) SPECIESAND HYBRID ZONES

• Some species are difficult to distinguish

• Hybrid zones: zones of contact where adjacent (sub)species interbreed

cornix

corone

Subspecies of carrion crow(Corvus corone) hybridize

in contact zone

Page 7: EVOLUTION AND SYSTEMATICS

Species of fire-bellied toad(Bombina) hybridize

in complex contact zone

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CHANGING SPECIES CONCEPTS

• Genetics and evolution in 1930s, 1940s: Dobzhansky, Mayr, Fisher, Wright, Haldane

• Mayr (1942): “species are groups of actually or potentially interbreeding natural populations which are reproductively isolated from other such groups” = (2) Biological Species Concept

Page 9: EVOLUTION AND SYSTEMATICS

BSC: SPECIES DISCRETENESS

Interbreeding within species and absence of hybridization/interbreeding between them:

relative uniformity within species absence of intermediate forms

Barriers to reproduction essential for differentiation between populations speciation

Page 10: EVOLUTION AND SYSTEMATICS

SOME PROBLEMS WITH THE BSC

• Species may be morphologically similar yet isolated reproductively

• Morphologically different species may interbreed

American Black Duck(Anas rubripes)

Mallard (male)(Anas platyrhynchos)

Page 11: EVOLUTION AND SYSTEMATICS

Wintering

Nesting

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“REPRODUCTIVE ISOLATION”AND THE BSC

• Hybridization common in plants• Many plants reproduce mainly or solely by

asexual means such as apomixis• Apomixis in hundreds of species, > 30 families

of flowering plants (e.g., dandelion Taraxacum officinale)

Page 13: EVOLUTION AND SYSTEMATICS

Reproductive isolation:• Cannot be tested for fossils• Irrelevant to asexual forms• Hard to apply in groups with much

hybridization even between divergent forms

Page 14: EVOLUTION AND SYSTEMATICS

(3) PHYLOGENETIC SPECIES CONCEPT

• Monophyletic groups: groups with independent evolutionary histories; smallest group = species

• Testable and can be applied to any kind of organism• Problems: hard to apply, would lead to large increase

in number of recognized species• Nevertheless, cladistic approaches point to many

situations where current taxonomy/classification and recognition of species need to be revised

Page 15: EVOLUTION AND SYSTEMATICS

WHAT IS A SPECIES?

• “Smallest independent evolutionary unit” (text)• Lineages with independent evolutionary histories

and reproductive integrity• “Independence” follows from mutation, selection

gene flow, and drift operating on a population, separately from other populations

• In practice, parts of all three concepts often used jointly, with large roles of PSC and genetics

Page 16: EVOLUTION AND SYSTEMATICS

CONCEPTS AND PRACTICE

• More disagreement on concepts than practice• Four general species criteria in use:

1) Separation – Species must be separated from one another morphologically, behaviourally, genetically, or in other ways.

2) Cohesion – Populations must be internally cohesive, genetically and ecologically.

3) Monophyly – Individuals and populations within a species must share a single most recent common ancestor.

Page 17: EVOLUTION AND SYSTEMATICS

4) Distinguishability –

(a) Species diagnosable on morphological or genetic grounds: species possesses unique traits.

(b) Presence of phenetic or genetic clusters: single traits not unique, but overlap with other species. Multiple traits determination of clusters.

NOTE: Species may be morphologically indistinguishable but genetically different (cryptic species)

Page 18: EVOLUTION AND SYSTEMATICS

Japan

Caspian &Black Seas

Copepoda: Temoridae:Eurytemora affinis (Poppe 1880)-- morphospecies-- geographically widespread-- ecologically important in estuaries:

abundant grazer, prey species

Page 19: EVOLUTION AND SYSTEMATICS

Eurytemora affinis:Morphometrically-based phylogeny

Japan; Caspian & Black Seas

Remainder: California;Pacific Northwest; St. Lawrence R., U.S. Eastand Gulf Coasts

Page 20: EVOLUTION AND SYSTEMATICS

Eurytemora affinis:Molecularly-based phylogeny

Page 21: EVOLUTION AND SYSTEMATICS

SPECIATION IN AFRICAN ELEPHANTS• Genetics 58% difference between Asiatic (Elephas)

and African (Loxodonta) genera• Loxodonta from savannah/bush and tropical forests

differ in ecology, habitat, morphology, behaviour• Very limited gene flow detected• Divergence ~2.6 Ma• Recognize:-- L. africana (Blumenbach 1797)-- L. cyclotis (Matschie 1900)

Page 22: EVOLUTION AND SYSTEMATICS
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Pine marten

Page 24: EVOLUTION AND SYSTEMATICS

[From: Kyle & Strobeck (2003) Can. J. Zool. 81:57-66]

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PRACTICE vs. THEORY

• Life originated by descent with modification• Characters change over time• So speciation usually not in sharp steps• To expect only clearly defined species not realistic• Groups in varied states of divergence (Table 15.1)

Page 27: EVOLUTION AND SYSTEMATICS

MODES OF SPECIATION

Despite complications, many forms speciate by:A. Allopatric speciation: Due to geographic

separation of populationsB. Peripatric speciation: peripheral isolatesC. Parapatric speciation: speciation “beside”D. Sympatric speciation: speciation in “same

place“

Page 28: EVOLUTION AND SYSTEMATICS

allopatric peripatric parapatric sympatric

Modes of speciation

Page 29: EVOLUTION AND SYSTEMATICS

ALLOPATRIC SPECIATION• Speciation between geographically isolated

populations due to barrier (e.g., mountains)• Many kinds of barriers, scales of barriers• Small populations not assumed but may occur• Lack of gene flow permits adaptation to

different environments• Evolutionary divergence and reproductive

isolation follow• Can distinguish allopatric speciation due to

vicariance, founder events

Page 30: EVOLUTION AND SYSTEMATICS

Vicariance = splitting of area by appearance of barrier (e.g., mountain range, strait)

Page 31: EVOLUTION AND SYSTEMATICS
Page 32: EVOLUTION AND SYSTEMATICS

Kakapo (Strigops): nocturnal flightless ground parrot of New Zealand

Page 33: EVOLUTION AND SYSTEMATICS
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Kiwi (Apteryx): primitive nocturnal flightless ground bird of New Zealand

Page 35: EVOLUTION AND SYSTEMATICS

OCEANIC ISLANDS:MUCH SPECIATION, HIGH ENDEMISM

• Polynesia & Micronesia: ~50% of ~7,000 species of vascular plants are endemic

• Degeneriaceae with single tree species, (Degeneria vitiensis) endemic to Fiji

• Much endangerment: >60 species of endemic Hawaiian plants have <10 remaining wild individuals

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Endemic single-species family (Degeneriaceae), Fiji

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Hundreds of endemic plant taxa inhabit Socotra

Page 38: EVOLUTION AND SYSTEMATICS

HAWAIIAN SILVERSWORDS (ARGYROXIPHIUM)• 5 endemic species on slopes of

highest volcanoes• At 10-15 yr of age, grow

high stalks with flowers, die

Page 39: EVOLUTION AND SYSTEMATICS

HAWAIIAN DROSOPHILIDAE

• Adaptive radiation: allopatric speciation by geographic isolation

• ~900 species (described and undescribed)• Diverse in morphology, ecology, behaviour

Page 40: EVOLUTION AND SYSTEMATICS

Hawaiian Drosophila:Successive founder events andspeciation as new land masses arose

Page 41: EVOLUTION AND SYSTEMATICS

PERIPATRIC SPECIATION

• Speciation between geographically isolated main and peripheral populations

• Small peripheral population assumed (founder effect)

• Lack of gene flow permits adaptation to different environment; main divergence in peripheral population

• Small founding and existing population• Peripheral populations with low population

densities, extreme and unpredictable environments

• Peripheral populations also at range extremes

Page 42: EVOLUTION AND SYSTEMATICS

allopatric peripatric parapatric sympatric

Page 43: EVOLUTION AND SYSTEMATICS

• Peripheral populations differ in environment• Peripheral populations differ demographically

Page 44: EVOLUTION AND SYSTEMATICS

allopatric peripatric parapatric sympatric

Page 45: EVOLUTION AND SYSTEMATICS

PARAPATRIC SPECIATION

*selection must be strong mate choice must be correlated with cause of divergence

*

Page 46: EVOLUTION AND SYSTEMATICS

Kwando R.

Zambesi R.

Linyanti Swamp

Pollimyrus spp.(Mormyridae)

Page 47: EVOLUTION AND SYSTEMATICS

P. castelnaui

Page 48: EVOLUTION AND SYSTEMATICS

P. marianne Kwando/Linyanti fish P. castelnaui

EOD discharge patterns

voltage

Page 49: EVOLUTION AND SYSTEMATICS

Electric organ discharge (EOD) characteristics ofP. castelnaui and Pollimyrus captured in Kwando/Linyanti system

Page 50: EVOLUTION AND SYSTEMATICS

P. castelnaui

P. marianne

Semi-isolatedintermediate population

intermittent

Page 51: EVOLUTION AND SYSTEMATICS

• Okavango vs. Zambesi samples differ in:-- EOD discharge patterns-- mtDNA-- allozymes-- morphometrics

• Kwando/Linyanti vs. Zambesi samples differ in EOD discharge patterns and morphometrics

• Okavango (P. castelnaui) genetically distant from P. marianne; in latter, K/L vs. Z likely different biological species

Page 52: EVOLUTION AND SYSTEMATICS

allopatric peripatric parapatric sympatric

“Speciation in the same place”: selection must be strong, mate choice must be correlated with cause of divergence

Page 53: EVOLUTION AND SYSTEMATICS

APPLE AND HAWTHORN FLIES

Apple and hawthorn flies (Rhagoletis) classic example:• Courtship, mating on or near fruits; eggs laid on and

larvae develop within fruits; drop to pupate in soil• Apple trees introduced < 300 yr ago (hawthorn

native)• Apple fruits ~3 weeks earlier than hawthorn fruitDivergent selection:• Hawthorn flies should develop rapidly so pupation

takes place before ground freezes• Apple fly larvae should develop slowly so they do not

emerge as adults too early

Page 54: EVOLUTION AND SYSTEMATICS

REPRODUCTIVE ISOLATIONWITHIN SPECIES: RASSENKREIS

• Geographic variation and gene exchange may occur throughout geographic range

• Populations at range extremes may be reproductively isolated

Page 55: EVOLUTION AND SYSTEMATICS

GEOGRAPHIC VARIATION WITHIN SPECIES

• Much geographic and other spatial variation described within species, especially early in systematics

• Many forms, races, varieties, subspecies described• Lines often drawn to depict boundaries between

subspecies

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Subspecies of Song Sparrow(Melospiza melodia)

Page 57: EVOLUTION AND SYSTEMATICS

Proportion of corolla tube + pedicel

Variation in flowers along transect in mountains of southern California(Mimulus longiflorus)

Page 58: EVOLUTION AND SYSTEMATICS

Pleistocene isolates

post-Pleistocenedispersal

reproductive isolationbetween

“Circle of races” ring species

Herring Gull(Larus argentatus)

Page 59: EVOLUTION AND SYSTEMATICS

Ring species (Ensatina salamanders):forms at end of intergrading “ring”

are reproductively isolated