Speciation Until recently over 500 species of cichlid

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Speciation ◦ Until recently, over 500 species of cichlid fishes lived in East Africa’s

Speciation ◦ Until recently, over 500 species of cichlid fishes lived in East Africa’s Lake Victoria Copyright © 2009 Pearson Education, Inc.

Africa Uganda Kenya Lake Victoria Lake Tanganyika Tanzania Lake Malawi

Africa Uganda Kenya Lake Victoria Lake Tanganyika Tanzania Lake Malawi

Speciation and the loss of species ◦ Lake Victoria’s cichlids diversified 100, 000 years

Speciation and the loss of species ◦ Lake Victoria’s cichlids diversified 100, 000 years ago (young species!) ◦ Why? ? – Specialized mouthparts that allow them to specialize on different food sources – Bright colors of the males vary with species, as females chose males with specific colors ◦ Groups isolated by diet or female mate choice may have lost the ability to interbreed Copyright © 2009 Pearson Education, Inc.

What is a species? Species: a group of organisms whose members can breed and

What is a species? Species: a group of organisms whose members can breed and produce fertile offspring, but who do not produce fertile offspring with members of other groups Copyright © 2009 Pearson Education, Inc.

What happened to the cichlids? ◦ Over the last 30 years, 200 species of

What happened to the cichlids? ◦ Over the last 30 years, 200 species of cichlids have disappeared from Lake Victoria – Introduced predator (perch) eats them up – Pollution makes it difficult for females to see colors Copyright © 2009 Pearson Education, Inc.

The origin of species is the source of biological diversity Speciation is the emergence

The origin of species is the source of biological diversity Speciation is the emergence of new species and increases diversity Millions of species all arose from ancestor that lived 3. 6 billion years ago Copyright © 2009 Pearson Education, Inc.

How do we categorize all these species? ◦ Taxonomy is the field of biology

How do we categorize all these species? ◦ Taxonomy is the field of biology that names and classifies species and groups them into broader categories ◦ Binomial system gives every organism a genus and species name Example: Homo sapien, Escherichia coli Copyright © 2009 Pearson Education, Inc.

Order Family Genus Species Felidae Felis catus (domestic cat) Mephitis Lutra Mustelidae Carnivora Mephitis

Order Family Genus Species Felidae Felis catus (domestic cat) Mephitis Lutra Mustelidae Carnivora Mephitis mephitis (striped skunk) Lutra lutra (European otter) Canis Canidae Canis latrans (coyote) Canis lupus (wolf)

But how do we decide what is actually a species? ? Copyright © 2009

But how do we decide what is actually a species? ? Copyright © 2009 Pearson Education, Inc.

For many eukaryotic organisms, we use … ◦ The biological species concept Species is

For many eukaryotic organisms, we use … ◦ The biological species concept Species is a population or group of populations whose members have the potential to interbreed in nature and produce fertile offspring ◦ Reproductive isolation prevents gene flow and maintains separate species Copyright © 2009 Pearson Education, Inc.

◦ Can the biological species concept always distinguish species from each other? Copyright ©

◦ Can the biological species concept always distinguish species from each other? Copyright © 2009 Pearson Education, Inc.

Other options for defining species… ◦ The morphological species concept : classifies organisms based

Other options for defining species… ◦ The morphological species concept : classifies organisms based on observable phenotypic traits It can be applied to asexual organisms, fossils, and when we don’t know about inbreeding Copyright © 2009 Pearson Education, Inc.

Other options for defining species… The ecological species concept: Defines a species by its

Other options for defining species… The ecological species concept: Defines a species by its ecological role or niche – Consider the cichlids, which are similar in appearance but feed at different depths in the lake Copyright © 2009 Pearson Education, Inc.

Other options for defining species… ◦ The phylogenetic species concept: Species as a set

Other options for defining species… ◦ The phylogenetic species concept: Species as a set of organisms representing a specific evolutionary lineage – Morphological or DNA similarities or differences can be used to define a species – Defining the amount of difference required to distinguish separate species is a problem Copyright © 2009 Pearson Education, Inc.

Why do species stay separate? ◦ Reproductive barriers serve to isolate a species gene

Why do species stay separate? ◦ Reproductive barriers serve to isolate a species gene pool and prevent interbreeding 1. Prezygotic (before sex) 2. Postzygotic (after sex) Copyright © 2009 Pearson Education, Inc.

Reproductive barriers keep species separate ◦ Prezygotic Barriers: prevent mating or fertilization between species

Reproductive barriers keep species separate ◦ Prezygotic Barriers: prevent mating or fertilization between species 1. Temporal isolation- two species breed at different times (seasons, times of day, years) Copyright © 2009 Pearson Education, Inc.

Reproductive barriers keep species separate ◦ Prezygotic Barriers: prevent mating or fertilization between species

Reproductive barriers keep species separate ◦ Prezygotic Barriers: prevent mating or fertilization between species 2. Habitat isolation: two species live in the same general area but not in the same kind of place Copyright © 2009 Pearson Education, Inc.

Reproductive barriers keep species separate ◦ Prezygotic Barriers: prevent mating or fertilization between species

Reproductive barriers keep species separate ◦ Prezygotic Barriers: prevent mating or fertilization between species 3. Behavioral isolation: there is little or no sexual attraction between species, due to specific behaviors Copyright © 2009 Pearson Education, Inc.

Reproductive barriers keep species separate ◦ Prezygotic Barriers: prevent mating or fertilization between species

Reproductive barriers keep species separate ◦ Prezygotic Barriers: prevent mating or fertilization between species 4. Mechanical isolation: female and male sex organs are not compatible Copyright © 2009 Pearson Education, Inc.

Reproductive barriers keep species separate ◦ Prezygotic Barriers: prevent mating or fertilization between species

Reproductive barriers keep species separate ◦ Prezygotic Barriers: prevent mating or fertilization between species 5. Gametic isolation: female and male gametes are not compatible Copyright © 2009 Pearson Education, Inc.

Reproductive barriers keep species separate ◦ Postzygotic Barriers: operate after hybrid zygotes are formed

Reproductive barriers keep species separate ◦ Postzygotic Barriers: operate after hybrid zygotes are formed 1. Zyogotic mortality 2. Reduced hybrid viability most hybrid offspring do not survive 3. Reduced hybrid fertility hybrid offspring are vigorous but sterile 4. Hybrid breakdown- first generation hybrid fertile, loss in second generation Copyright © 2009 Pearson Education, Inc.

Test yourself ◦ If two related species live in the same area, would natural

Test yourself ◦ If two related species live in the same area, would natural selection favor the evolution of prezygotic or postzygotic reproductive isolating mechanisms? Copyright © 2009 Pearson Education, Inc.

MECHANISMS OF SPECIATION Copyright © 2009 Pearson Education, Inc.

MECHANISMS OF SPECIATION Copyright © 2009 Pearson Education, Inc.

In allopatric speciation, geographic isolation leads to speciation ◦ In allopatric speciation, populations of

In allopatric speciation, geographic isolation leads to speciation ◦ In allopatric speciation, populations of the same species are geographically separated, separating their gene pools ◦ Changes in the allele frequencies of each population may be caused by _____? ? ? Copyright © 2009 Pearson Education, Inc.

In allopatric speciation, geographic isolation leads to speciation ◦ Gene flow between populations is

In allopatric speciation, geographic isolation leads to speciation ◦ Gene flow between populations is initially prevented by a geographic barrier – The Grand Canyon and Colorado River separate two species of antelope squirrels A. harrisi South Copyright © 2009 Pearson Education, Inc. A. leucurus North

In sympatric speciation, speciation takes place without geographic isolation ◦ In sympatric speciation, new

In sympatric speciation, speciation takes place without geographic isolation ◦ In sympatric speciation, new species may arise within the same geographic area as a parent species ◦ Gene flow between populations may be reduced by: 1. Polyploidy: multiplication of the chromosome number due to errors in cell division (plants) 2. Habitat differentiation (animals) 3. Sexual selection (animals) Copyright © 2009 Pearson Education, Inc.

a. b.

a. b.

How do you know if two species are reproductively isolated? ◦ Hybrid zones: regions

How do you know if two species are reproductively isolated? ◦ Hybrid zones: regions in which members of different species meet and mate producing some hybrid offspring New species Ancestral species 1 3 2 4 Gene flow Population (five individuals are shown) Copyright © 2009 Pearson Education, Inc. Hybrid zone Hybrid Barrier to gene flow

Outcomes of hybrid zones Reinforcement Stability Fusion

Outcomes of hybrid zones Reinforcement Stability Fusion

Speciation may occur rapidly or slowly ◦ What is the total length of time

Speciation may occur rapidly or slowly ◦ What is the total length of time between speciation events (between formation of a species and subsequent divergence of that species)? – In a survey of 84 groups of plants and animals, the time ranged from 4, 000 to 40 million years – Overall, the time between speciation events averaged 6. 5 million years and rarely took less than 50, 000 years Copyright © 2009 Pearson Education, Inc.

Zygote Gametes Prezygotic barriers • Temporal isolation • Habitat isolation • Behavioral isolation •

Zygote Gametes Prezygotic barriers • Temporal isolation • Habitat isolation • Behavioral isolation • Mechanical isolation • Gametic isolation Postzygotic barriers • Reduced hybrid viability • Reduced hybrid fertility • Hybrid breakdown Viable, fertile offspring