CHAPTER 14: The Origin of Species NEW AIM: What is a species?

Name: CHAPTER 14: The Origin of Species NEW AIM: What is a species?
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Description: CHAPTER 14: The Origin of Species NEW AIM: What is a species?

CHAPTER 14: The Origin of Species NEW AIM: What is a species?
- Linnaeus used physical appearance to identify species when he developed the binomial system of naming organisms - established the basis for taxonomy (classification of living organisms) Swedish physician and Botanist - mid 1700’s Taxonomy = practice and science of classification Carolus Linnaeus Encyclopedia of life (

AIM: What is a species? - Problem: appearance is not always good at defining a species Swedish physician and Botanist Sturnella magna Sturnella neglecta (eastern meadowlark) (western meadowlark) Fig. 14.1A

AIM: What is a species? - Problem: appearance is not always good at defining a species Swedish physician and Botanist Fig. 14.1B Homo sapiens (Humans)

AIM: What is a species? - So how should we define a species?
The biological species concept - a population or group of populations whose members can interbreed and produce fertile offspring Swedish physician and Botanist

AIM: What is a species? Ring Species
Swedish physician and Botanist A Herring Gull, Larus argentatus (front) and a Lesser Black-backed Gull, Larus fuscus (behind) in Poland Reproductive isolation - prevents gene flow between species

AIM: What is a species? Ring Species - may illustrate the process of speciation in action. Swedish physician and Botanist A Herring Gull, Larus argentatus (front) and a Lesser Black-backed Gull, Larus fuscus (behind) in Poland Reproductive isolation - prevents gene flow between species

AIM: What is a species? Ring Species - may illustrate the process of speciation Fig. 14.1C Swedish physician and Botanist Reproductive isolation - prevents gene flow between species

AIM: What is a species? Ring Species - connected series of neighboring populations that can interbreed, but the two "end" populations are too distantly related to interbreed. Swedish physician and Botanist Reproductive isolation - prevents gene flow between species

AIM: What is a species? Does the biological species concept apply to all organisms? Does not apply to fossils or asexual organisms like bacteria. The morphological species concept - used when the biological species concept can’t be applied. Swedish physician and Botanist - classification based on observable and measurable phenotypic traits

AIM: What is a species? SUMMARY Linnaeus Biological species concept
- binomial system - Taxonomy Biological species concept - Ring species Swedish physician and Botanist Morphological species concept - Asexual, Fossils

NEW AIM: How do new species arise (speciation)?
EXAMPLE: Some mosquitoes (Culex pipiens) migrated into the London Underground (subway) during its construction.

AIM: How do new species arise?
Speciation - a gradual or rapid process? Mosquitos are isolated underground from parent population above ground. New environment - new prey, mating habits, stable temp., breeds all year long, etc… Natural selection, genetic drift, mutation, maybe SS - The two populations were diverging. Biologists considered this population a different species: Culex molestus Confirmed in 1999 when members of each population were put together…no offspring produced!

Speciation - a gradual or rapid process? In less than 150 years, a new species emerged = speciation. What had to happen for speciation to occur? Isolation of populations- need to block GENE FLOW between the populations! keep populations apart to prevent gene flow until enough genetic changes occur in each making them genetically incompatible (a reproductive barrier if formed)

Isolation of populations Mutations might** lead to a… Reproductive barrier speciation **Just because a population is split and the two populations are isolated from each other doesn’t mean that a reproductive barrier will arise.

NEW AIM: What types of reproductive barriers exist to keep species apart?
A biological feature of the organism that prevents it from interbreeding with closely related species Two general types: 1. Prezygotic barriers - prevent mating or fertilization Swedish physician and Botanist 2. Postzygotic barriers - prevent the development of fertile adults

AIM: What types of reproductive barriers exist to keep species apart?
Prezygotic barriers - prevent mating or fertilization 1. Temporal isolation - two species breed at different times (day, week, season) (mating or flowering) Eastern and Western spotted skunk territories overlap. - Eastern skunks breed only in late winter Swedish physician and Botanist - Western skunks breed only in fall Can they mate though if we put them together??? IMPORTANT: Populations may be able to breed successfully with each other if they were doing it at the same time.

Prezygotic barriers - prevent mating or fertilization 2. Habitat isolation - populations live in same general area, but not in the same kinds of places (do not meet) - Herbivorous insects feed and mate on different host plants. Swedish physician and Botanist

Prezygotic barriers - prevent mating or fertilization 3. Behavioral isolation - Little or no sexual attraction between males and females - Male fireflies - blink their light in particular patterns to attract females of their kind Swedish physician and Botanist - courtship rituals - pheromones

Prezygotic barriers - prevent mating or fertilization 4. Mechanical isolation - Structural differences in genitalia or flowers prevent copulation of pollen transfer - many insects have reproductive organs that fit like complicated puzzle pieces - only male and female of same species match up. Swedish physician and Botanist

Prezygotic barriers - prevent mating or fertilization 4. Mechanical isolation - Structural differences in genitalia or flowers prevent copulation or pollen transfer - many flowering plants have flower structures adapted for only a specific animal pollinator that will transfer pollen only between same species. Beak of humming bird perfect size for flower type and reaching nectar.

Prezygotic barriers - prevent mating or fertilization 5. Gametic isolation - Male or female gametes die before uniting or fail to unite - many mammals - sperm cannot survive in female of a different species - male and female sea urchins dump their sperm and eggs into the water. Only same species sperm and egg can fuse (appropriate ligand and receptor proteins). Beak of humming bird perfect size for flower type and reaching nectar.

Prezygotic barriers - prevent mating or fertilization SUMMARY 1. Temporal isolation 2. Habitat Isolation 3. Behavioral isolation 4. Mechanical isolation Beak of humming bird perfect size for flower type and reaching nectar. 5. Gametic isolation

Postzygotic barriers - prevent development of fertile adults 1. Hybrid inviability - Hybrid zygotes fail to develop or to reach sexual maturity - genes not compatible Ex. Hybrid between the frogs Rana pipiens and Rana sylvatica do not survive more than a day or so. Genus Rana frogs Rana pipiens Rana sylvetica

Postzygotic barriers - prevent development of fertile adults 2. Hybrid sterility - Hybrids make it to maturity, but fail to produce functional gametes a hinny (the offspring of a male horse and a female donkey). Horse (female) + donkey (male) = mule (sterile)

Postzygotic barriers - prevent development of fertile adults 3. Hybrid Breakdown - Hybrid mates, but offspring of hybrids are weak and infertile - hybrids can reproduce, but their offspring cannot (feeble or sterile). Happens more in plants than animals. Genus Rana frogs Ex. certain species of cotton plants

SUMMARY 1. Hybrid inviability 2. Hybrid sterility 3. Hybrid Breakdown Genus Rana frogs

Review: Genus Rana frogs

Question Two closely related tropical bird species live in the same forest, but one feeds and mates in the forest canopy and the other on the forest floor. What type of reproductive barrier is this an example of? Genus Rana frogs Habitat Isolation

NEW AIM: By what means do reproductive barriers (speciation) arise?
Isolation of populations Mutations might** lead to a… Reproductive barrier Genus Rana frogs speciation How might a population fragment and become isolated from each other?

AIM: By what means do reproductive barriers (speciation) arise?
1. allopatric speciation: Mode of speciation caused by a geographic barrier isolating populations: Allo – means alternate or other Patric means fatherland Explain why speciation does not always have to occur between allopatric populations. **Must establish a reproductive barrier!! Fig. 14.3

1. allopatric speciation: What types of geographic barriers can you think of? - Mountain range emerges - Large lakes break into smaller lakes - Land bridge may form or disappear Genus Rana frogs (all depends on the species) Fig. 14.3

1. allopatric speciation: What types of geographic barriers can you think of? Genus Rana frogs Geographically isolated antelope squirrels Fig. 14.3

1. allopatric speciation: What types of geographic barriers can you think of? Genus Rana frogs

1. allopatric speciation: When do you think allopatric speciation is most likely to occur? When the isolated population is SMALL. - genetic drift Genus Rana frogs - natural selection Ex. Galapagos finch species - all arose in less than 2 million years!

1. allopatric speciation: Fig. 14.4A Genus Rana frogs Galapagos - 14 finch species - all evolved from a single population that colonized one of the islands. How might this have happened?

1. allopatric speciation: Fig. 14.4A Fig. 14.4B Genus Rana frogs Galapagos - 14 finch species - all evolved from a single population that colonized one of the islands. How might this have happened?

1. allopatric speciation: Fig. 14.4A Fig. 14.4B Isabela, Santa Cruz, Santiago, Fernandina Adaptive radiation - emergence of numerous species from a common ancestor introduced to new and diverse environments

1. allopatric speciation: 700 km north of the galapagos Why do you think that only ONE finch species is found on Cocos Island?

1. allopatric speciation: 700 km north of the galapagos There is only one isolated island without geographic barriers to split the population in contrast to the Galapagos.

? AIM: By what means do reproductive barriers (speciation) arise?
Genus Rana frogs speciation

1. allopatric speciation: Geographic Isolation of populations Mutations might** lead to a… Reproductive barrier (isolation) 700 km north of the galapagos speciation **Just because a population is split and the two populations are isolated from each other doesn’t mean that a reproductive barrier will arise.

Can you think of another way that speciation might occur other than through allopatric speciation? Genus Rana frogs

2. Sympatric speciation: - when reproductive isolation (barriers) arises without geographic separation. - not widespread among animals - very important in plants How might reproductive isolation arise within a population? Herbivorous insects eating and mating around different vegetation Sym - together, at the same time *genetic change produces a reproductive barrier between new mutants and parent population

2. Sympatric speciation: Plants - - If this plant cell undergoes meiosis, what would be the ploidy of the resulting cells? Haploid Genus Rana frogs

2. Sympatric speciation: Plants - - What if an “accident” occurred during meiosis (total nondisjunction in meiosis II)? Genus Rana frogs

2. Sympatric speciation: Plants - - What if an “accident” occurred during meiosis (total nondisjunction in meiosis II)? Diploid cells form Genus Rana frogs

2. Sympatric speciation: Plants - If it happens in ovum and sperm, these gametes can now self fertilize… Genus Rana frogs

2. Sympatric speciation: Plants - - Result: A Polyploid (tetraploid, 4n) offspring (Plants are better able to deal with polyploidy than animals) Genus Rana frogs Fig. 14.5A

2. Sympatric speciation: Plants - How can the tetraploid reproduce? Genus Rana frogs Fig. 14.5A

2. Sympatric speciation: Plants - Meiosis of a tetraploid cell would generate diploid gametes. Genus Rana frogs Fig. 14.5A

2. Sympatric speciation: Plants - - What if the tetraploid were to breed with the parent-type (diploid) organism? Diploid (2n) gametes + haploid (n) gamete = triploid (3n) zygote (sterile) Genus Rana frogs Fig. 14.5A

Result: INSTANT SPECIATION
AIM: By what means do reproductive barriers (speciation) arise? 2. Sympatric speciation: Plants - - What if new tetraploid were to initially self fertilize and then the offspring mate? Diploid (2n) ovum + Diploid (2n) sperm = tetraploid (4n) zygote Genus Rana frogs Result: INSTANT SPECIATION Fig. 14.5A

Evolution of reproductive barriers in the lab: Type of reproductive barrier? Behavioral isolation Genus Rana frogs - Perhaps alleles that enhance digestion of starch or maltose also effect (or are linked to) the alleles that code for enzymes that make molecules that function in mate recognition (pheromones). Diana Dodd - Yale University

SUMMARY 1. Allopatric Speciation - speciation due to geographic isolation 2. Sympatric Speciation - speciation event within the population - polyploidy in plants Genus Rana frogs - From a single individual 1. meiotic error (diploid becomes tetraploid) - Cross fertilization of different species 1. cross fertilization (new haploid) 2. meiotic error (becomes diploid)

Punctuated vs. Gradualistic model
Evidence of evolution mainly from fossil record Punctuated model Gradualistic model

Punctuated vs. Gradualistic model
Evidence of evolution mainly from fossil record Question: Which model would account for the relative rarity of transition fossils linking newer species to older ones?

2. Sympatric speciation: Plants - - What if instead of a single species mating with itself to make a polyploid, two somewhat related species were to mate? Result: Plant is usually sterile (chromosomes are not homologous) Result: SPECIATION (How many sets of chromosomes does this new plant have?) Genus Rana frogs However: The plant may be able to reproduce asexually What if: the “haploid” cell has an accident during MITOSIS or MEIOSIS (total nondisjunction)? Your now diploid (2n) and fertile!

2. Sympatric speciation: Genus Rana frogs

CHAPTER 14: The Origin of Species NEW AIM: What is a species?

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CHAPTER 14: The Origin of Species NEW AIM: What is a species?

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