Do you think Speciation can only be observed over millions of years? Explain.

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Do you think species are going extinct, but no new species are forming on Earth?

A. YesB. No

Explain your answer.

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What is a Species?A Case Study

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The Apple Maggot Fly Rhagoletis pomonella

Hawthorn trees are native to North America.

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The hawthorn fruit is eaten by the larvae of the hawthorn maggot fly, Rhagoletis pomonella.

13 mm averageSize fruit

Rhagoletis pomonella life cycle

1. The female lays fertilized eggs in the fruit.

2. Maggots (larvae) emerge from the egg, feed on the fruit, and grow .

3. Healthy maggots drop from the tree with the fruit and burrow in the soil. Pupation takes place in the soil.

4. Adult maggot flies emerge from the soil and fly to fruit trees, where they mate on the surface of the fruit.

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But there are parasites!

Parasitoid wasps try to lay eggs in the maggot’s body, paralyzing and ultimately killing the maggot.

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Apples

• Domesticated apples (Malus domesticus) were introduced to North America in the 1600s. They are now the most widely grown fruit in North America.

• A typical commercial apple has a diameter of 70 mm.

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Rhagoletis Host Shift

Rhagoletis pomonella

Hawthorn (Crataegus spp)

♀ lays eggs on fruit

1864: First notedappleInfestation(147 yearsAgo)

Apple (Malus domesticus)

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Apple vs. Hawthorn:The Maggot’s Viewpoint

• The large apple fruit provides 220 times more food than hawthorn fruit.

• But the nutritional quality of hawthorn fruit is superior:52% of hawthorn maggots survive vs. 27% of apple maggots.

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Apple vs. Hawthorn: The Risk of Attack

• Larger fruits of apples are much deeper than hawthorn fruits.

• Apple maggots can burrow to avoid parasitoid wasps.

• Apple maggots carry fewer parasitoid wasp eggs than hawthorn maggots do.

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Today: There are Hawthorn & Apple Maggot Flies

• Hawthorn and apple maggot flies are physically indistinguishable.

– However, they are genetically distinct, with different genetic profiles.

• There is no geographic isolation or physical separation between hawthorn and apple maggot flies.

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Hawthorn & Apple Maggot Flies

• Maggot flies tend to mate with their own kind.

– Hawthorn maggot flies strongly prefer to mate on and lay fertilized eggs in hawthorn fruit.

– Apple maggot flies strongly prefer to mate on and lay fertilized eggs in apple fruit.

• There is only a 4-6% hybridization rate between hawthorn and apple maggot flies.

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Rhagoletis Host Shift

Hybrids are viable and fertile. No post-zygotic barriers

Hawthorn-raised

Apple-raised

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Timing of Host Fruit RipeningDifferent ripening time of host fruit leads to temporal

separation of apple and hawthorn flies.

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Based on the information provided, are hawthorn and apple maggot flies separate species? Explain your reasoning.

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1. According to the biological species concept, are hawthorn and apple maggot flies separate species?

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Which information is relevant to the biological species definition?

A. Hawthorn and apple maggot flies are physically indistinguishable.

B. There is a 4-6% hybridization rate between hawthorn and apple maggot flies.

C. Hawthorn and apple maggot flies are genetically distinguishable and have a distinct genetic profiles.

D. Hawthorn and apple maggot flies strongly prefer to mate and lay fertilized eggs in hawthorns and apples, respectively.

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Ecological species concept

A species is a set of organisms exploiting a single niche.

The key aspects of this definition are the resources exploited and the habitat occupied by the members of a species.

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2. According to the ecological species concept, are hawthorn and apple maggot flies separate species?

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Which information is relevant to the ecological species definition? Explain.

A. Hawthorn and apple maggot flies are physically indistinguishable.

B. There is a 4-6% hybridization rate between hawthorn and apple maggot flies.

C. Hawthorn and apple maggot flies are genetically distinguishable and have a distinct genetic profiles.

D. Hawthorn and apple maggot flies strongly prefer to mate and lay fertilized eggs in hawthorns and apples, respectively.

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Morphological species concept

A species is a set of individuals with morphological features in common.

The key aspect of this definition is the morphology of the members of a species. Individuals of a species are morphologically similar to one another, yet morphologically distinct from individuals from another species.

3. According to the morphological species concept, are hawthorn and apple maggot flies separate species?

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Which information is relevant to the morphological species definition?

A. Hawthorn and apple maggot flies are physically indistinguishable.

B. There is a 4-6% hybridization rate between hawthorn and apple maggot flies.

C. Hawthorn and apple maggot flies are genetically distinguishable and have a distinct genetic profiles.

D. Hawthorn and apple maggot flies strongly prefer to mate and lay fertilized eggs in hawthorns and apples, respectively.

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Phylogenetic species conceptA species may be defined

by its unique genetic history as a tip of a phylogenetic tree.

Species are defined by their unique derived features and shared ancestry.

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4. According to the phylogenetic species concept, are hawthorn and apple maggot flies separate species?

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Which information is relevant to the phylogenetic species definition?

A. Hawthorn and apple maggot flies are physically indistinguishable.

B. There is a 4-6% hybridization rate between hawthorn and apple maggot flies.

C. Hawthorn and apple maggot flies are genetically distinguishable and have a distinct genetic profiles.

D. Hawthorn and apple maggot flies strongly prefer to mate and lay fertilized eggs in hawthorns and apples, respectively.

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Reproductive isolation

5. How do two similar species maintain genetic isolation if they come (or remain) in contact with each other?

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Reproductive isolation

Reproductive isolating mechanisms prevent two individuals from distinct species from interbreeding or produce viable and fertile hybrid offspring.

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Sympatric speciationIn sympatric speciation, there is no geographic barrier

to gene flow.

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6. Explain what type of Speciation is occuring or has occurred with Rhagoletis based on the evidence given.

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7. What reproductive barriers limit interbreeding between hawthorn and apple maggot flies? Explain.

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Timing of Host Fruit RipeningDifferent ripening time of host fruit leads to temporal

separation of apple and hawthorn flies.

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8. Are apple and hawthorn maggot flies a separate species?

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Genetic divergence

Genetic divergence is the accumulation of genetic differences between two populations.

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Evolutionary Significant Units

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Factors causing genetic divergence between isolated populations

• Founder effect • Mutation • Genetic drift • Differential selection

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Reproductive isolation

Reproductive isolating mechanisms prevent two individuals from distinct species from interbreeding or produce viable and fertile hybrid offspring.

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Reproductive isolation: Prezygotic barriers

• Habitat isolation• Behavioral isolation• Temporal isolation• Mechanical isolation• Gametic isolation

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• Obstacle to mating or to fertilization if mating occurs

PRE-reproduction barriers

behavioral isolation

geographic isolation ecological isolation temporal isolation

mechanical isolation gametic isolation

Ecological isolation• Species occur in same region, but occupy different

habitats so rarely encounter each other– reproductively isolated

2 species of garter snake, Thamnophis, occur in same area, but one lives in water & other is terrestrial

2 species of garter snake, Thamnophis, occur in same area, but one lives in water & other is terrestrial

Temporal isolation• Species that breed during different times of day, different

seasons, or different years cannot mix gametes– reproductive isolation– sympatric speciation

• “same country”

Eastern spotted skunk (L) & western spotted skunk (R) overlap in range but eastern mates in late winter & western mates in late summer

Eastern spotted skunk (L) & western spotted skunk (R) overlap in range but eastern mates in late winter & western mates in late summer

Behavioral isolation• Unique behavioral patterns & rituals isolate species

– identifies members of species – attract mates of same species �

• courtship rituals, mating calls• reproductive isolation

Blue footed boobies mate only after a courtship display unique to their species

Blue footed boobies mate only after a courtship display unique to their species

Mechanical isolation• Morphological differences can prevent successful

mating– reproductive isolation

Even in closely related species of plants, the flowers often have distinct appearances that attract different pollinators. These 2 species of monkey flower differ greatly in shape & color, therefore cross-pollination does not happen.

Even in closely related species of plants, the flowers often have distinct appearances that attract different pollinators. These 2 species of monkey flower differ greatly in shape & color, therefore cross-pollination does not happen.

Plants

sympatric speciation?

Mechanical isolation

• For many insects, male & female sex organs of closely related species do not fit together, preventing sperm transfer– lack of “fit” between sexual organs:

hard to imagine for us… but a big issue for insects with different shaped genitals!

Damsel fly penises

Animals

Gametic isolation• Sperm of one species may not be able to fertilize eggs of

another species– mechanisms

• biochemical barrier so sperm cannot penetrate egg– receptor recognition: lock & key between egg & sperm

• chemical incompatibility – sperm cannot survive in female reproductive tract

Sea urchins release sperm & eggs into surrounding waters where they fuse & form zygotes. Gametes of different species— red & purple —are unable to fuse.

Sea urchins release sperm & eggs into surrounding waters where they fuse & form zygotes. Gametes of different species— red & purple —are unable to fuse.

Reproductive isolation:Postzygotic barriers

• Reduced hybrid viability• Reduced hybrid fertility • Hybrid breakdown

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When a male donkey mates with a female horse, the hybrid offspring is an infertile mule. Explain what type of reproductive barrier this is.

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Mules are vigorous, but sterile

Reduced hybrid fertility• Even if hybrids are vigorous

they may be sterile– chromosomes of parents may differ in number or

structure & meiosis in hybrids may fail to produce normal gametes

Donkeys have 62 chromosomes(31 pairs)

Horses have 64 chromosomes(32 pairs) Mules have 63 chromosomes!

Reduced hybrid viability• Genes of different parent species may interact

& impair the hybrid’s development

Species of salamander genus, Ensatina, may interbreed, but most hybrids do not complete development & those that do are frail.

Species of salamander genus, Ensatina, may interbreed, but most hybrids do not complete development & those that do are frail.

Hybrid breakdown• Hybrids may be fertile & viable in first

generation, but when they mate offspring are feeble or sterile

In strains of cultivated rice, hybrids are vigorous but plants in next generation are small & sterile.On path to separate species.

In strains of cultivated rice, hybrids are vigorous but plants in next generation are small & sterile.On path to separate species.

sympatric speciation?

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The antennae of male moths can only detect sex pheromones released by a female in his species. Explain this reproductive barrier.

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Question

Would you expect natural selection to favor pre-zygotic or post-zygotic isolating mechanisms between sympatric species?

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Graphic of salamanders - ring species idea, or other.

Suppose two long separated populations had an opportunity for renewed contact with each other. explain the possible outcomes?

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In terms of post and prezygotic reproductive barriers, Habitat isolation and temporal isolation are:

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Notes and outs

• Follow will go on an information sheet that students will have at each table.

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Rhagoletis pomonella life cycle• The female lays fertilized eggs in the fruit.

• Maggots (larvae) emerge from the egg, feed on the fruit, and grow through several molts.

• Healthy maggots drop from the tree with the fruit and burrow in the soil. Pupation takes place in the soil.

• Adult maggot flies emerge from the soil and fly to fruit trees, where they mate on the surface of the fruit.

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Rhagoletis Host Shift

• Hybrids are viable and fertile. No post-zygotic barriers

Hawthorn-raised

Apple-raised

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Rhagoletis Speciation

Small fruit (13 mm) Large fruit (70 mm)High nutritional quality Low nutritional quality

Shallow burrows Deep burrowsMore parasitoid wasps Fewer wasps

Fruit available later Fruit available early

HawthornApple

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Timing of Host Fruit Ripening

Different ripening time of host fruit leads to temporal separation of apple and hawthorn flies.

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Which information is relevant to the biological species definition? Explain why you chose your answer.

A. Hawthorn and apple maggot flies are physically indistinguishable.

B. There is a 4-6% hybridization rate between hawthorn and apple maggot flies.

C. Hawthorn and apple maggot flies are genetically distinguishable and have a distinct genetic profiles.

D. Hawthorn and apple maggot flies strongly prefer to mate and lay fertilized eggs in hawthorns and apples, respectively.

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Three outcomes…

With renewed or continued contact between two populations, there are three possible outcomes:

1. Individuals can hybridize readily.

2. Individuals do not hybridize at all.

3. Individuals hybridize but offspring have reduced fitness.

No speciation

Full speciation

Speciation in progress. Selection for evolution of strongreproductive barriers.

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CQ#1: Speciation can only be observed over millions of years:

A. TrueB. False

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CQ#2: Species are going extinct, but no new species are forming on Earth:

A. TrueB. False

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Q#1: What would the best salmon look like?

Boys: Imagine you are a male salmon. Pick the characteristics you want. Write them down.

Girls: Imagine you are a female salmon. Pick the characteristics you want. Write them down.

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Q#2 How did you determine what were the best characteristics?

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Which are the lucky few who make it to reproduce?

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The most dominant males (usually largest and most aggressive) successfully defend their redds and inseminate the eggs. Smaller males that also have the kype lose out in head-to-head competition with larger males.

Q#3: Are we seeing natural selection in action here?

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Q#4: Why do these non-dominant males persist in the population

over time?

Why don’t female mimics get weeded out through natural selection if they are not fit?

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Q#5: Even though female mimics are not dominant, are they fit?

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Q#6: Given the fitness data, what selection pattern would you expect for the salmon?

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Fre

qu

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Body Size of Salmon

Q#7: Do individuals have to be the “strongest” to be fit?

A. YesB. No

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What selection pattern would you expect for the moths?

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Fre

qu

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Moth Pigmentation

Hawthorns

Hawthorns are native North American shrubs.

Hawthorn fruits range between 5 mm and 20 mm in diameter, with an average of 12.6 mm.

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Rhagoletis Host Shift

When apples were introduced to North America, the larva of Rhagoletis pomonella started feeding on them.

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Rhagoletis Speciation

Small fruit (13 mm) Large fruit (70 mm)High nutritional quality Low nutritional quality

Shallow burrows Deep burrowsMore parasitoid wasps Fewer wasps

Fruit available later Fruit available early

HawthornApple

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Modes of speciation

Allopatric speciation is initiated by a geographic barrier between individuals from two natural populations.

Sympatric speciation takes place in a single geographic area.

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