BIOE 109 Summer 2009 Lecture 4- Part I Mutation and genetic variation
BIOE 109 Summer 2009 Lecture 11-Part I Species concepts
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Transcript of BIOE 109 Summer 2009 Lecture 11-Part I Species concepts
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BIOE 109Summer 2009
Lecture 11-Part ISpecies concepts
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How many species currently exist?
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How many species currently exist?
• about 3 million species have been described.
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How many species currently exist?
• about 3 million species have been described.
• only about 1.5 million in any detail.
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How many species currently exist?
• about 3 million species have been described.
• only about 1.5 million in any detail.
• estimates of the number of species present range from 5 million to 100 million.
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How many species currently exist?
• about 3 million species have been described.
• only about 1.5 million in any detail.
• estimates of the number of species present range from 5 million to 100 million.
Why the uncertainty?
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How many species currently exist?
1. Many groups are poorly studied.
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How many species currently exist?
1. Many groups are poorly studied.
• notably microorganisms and parasites.
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How many species currently exist?
1. Many groups are poorly studied.
• notably microorganisms and parasites.
2. Many environments are poorly sampled.
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How many species currently exist?
1. Many groups are poorly studied.
• notably microorganisms and parasites.
2. Many environments are poorly sampled.
• tropical environments - both terrestrial and aquatic.
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How many species currently exist?
1. Many groups are poorly studied.
• notably microorganisms and parasites.
2. Many environments are poorly sampled.
• tropical environments - both terrestrial and aquatic.
3. Molecular approaches are identifying more and more “cryptic species”.
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How many species currently exist?
1. Many groups are poorly studied.
• notably microorganisms and parasites.
2. Many environments are poorly sampled.
• tropical environments - both terrestrial and aquatic.
3. Molecular approaches are identifying more and more “cryptic species”.
• a cryptic species is indistinguishable from another species at the morphological level, but is distinguishable genetically.
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A list of some types of species!
Chronospecies SubspeciesCosmopolitan species SuperspeciesCryptic species Vicariant speciesEndemic species Sister speciesFugitive species Sibling speciesPolytypic species SemispeciesRelic species Ring speciesLazarus species
"... I was much struck how entirely vague and arbitrary is the distinction between species and varieties" Darwin 1859.
"The species problem is the long-standing failure of biologists to agree on how we should identify species and how we should define the word 'species'." Hey (2001)
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Species Concepts
1. The Typological Species Concept (TSC, Linnaeus)
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Species Concepts
1. The Typological Species Concept (TSC, Linnaeus)
Definition: a group of individuals that differ from other groups by possessing constant diagnostic characters.
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Species Concepts
1. The Typological Species Concept (TSC, Linnaeus)
Definition: a group of individuals that differ from other groups by possessing constant diagnostic characters.
• based on collecting and describing a “type” specimen for a given species.
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Problems with the TSC:
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Problems with the TSC:
1. Polymorphism within populations
Teagueia sancheziae
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Problems with the TSC:
1. Polymorphism within populations
2. Geographic variation among populations
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Problems with the TSC:
1. Polymorphism within populations
2. Geographic variation among populations
3. Sibling or cryptic species
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Problems with the TSC:
1. Polymorphism within populations
2. Geographic variation among populations
3. Sibling or cryptic species
• sibling species are reproductively isolated groups that are morphologically indistinguishable.
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2. The Biological Species Concept (BSC, Dobzhansky, Mayr)
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2. The Biological Species Concept (BSC, Dobzhansky, Mayr)
Mayr (1940): species are groups of actually or potentially interbreeding natural populations that are reproductively isolated from other such groups.
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2. The Biological Species Concept (BSC, Dobzhansky, Mayr)
Dobzhansky (1937): species are the largest and most inclusive reproductive community of sexual and cross-fertilizing individuals that share a common gene pool.
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Mayr divided the BSC into the “nondimensional” and the “multidimensional” species concept:
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Mayr divided the BSC into the “nondimensional” and the “multidimensional” species concept:
Nondimensional species concept
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Mayr divided the BSC into the “nondimensional” and the “multidimensional” species concept:
Nondimensional species concept
Species A
Species B
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Mayr divided the BSC into the “nondimensional” and the “multidimensional” species concept:
Nondimensional species concept
species sympatric and synchronous
Species A
Species B
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Mayr divided the BSC into the “nondimensional” and the “multidimensional” species concept:
Nondimensional Multidimensional species concept species concept
species sympatricand synchronous
Species A
Species B
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Mayr divided the BSC into the “nondimensional” and the “multidimensional” species concept:
Nondimensional Multidimensional species concept species concept
species sympatricand synchronous
Species A Species A
Species BSpecies B
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Mayr divided the BSC into the “nondimensional” and the “multidimensional” species concept:
Nondimensional Multidimensional species concept species concept
species sympatric species are allopatricand synchronous and/or allochronous
Species A Species A
Species BSpecies B
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Problems with the BSC:
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Problems with the BSC:
1. Not applicable to asexual species
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Problems with the BSC:
1. Not applicable to asexual species
2. Reproductive isolation is often incomplete
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Problems with the BSC:
1. Not applicable to asexual species
2. Reproductive isolation is often incomplete
• hybridization is common among many groups (waterfowl, terrestrial plants, freshwater fishes).
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Problems with the BSC:
1. Not applicable to asexual species
2. Reproductive isolation is often incomplete
• hybridization is common among many groups (waterfowl, terrestrial plants, freshwater fishes).
Top: False killer whale dadMiddle: Dolphin momBottom: Baby wholphin
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Wholphin mom Kekaimalu With daughterKawili'Kai
Kawili'Kai
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A “liger”
Hercules, the liger
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A “tigon”
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Problems with the BSC:
1. Not applicable to asexual species
2. Reproductive isolation is often incomplete
• hybridization is common among many groups (waterfowl, terrestrial plants, freshwater fishes).
3. Multidimensional concept difficult to verify
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Problems with the BSC:
1. Not applicable to asexual species
2. Reproductive isolation is often incomplete
• hybridization is common among many groups (waterfowl, terrestrial plants, freshwater fishes).
3. Multidimensional concept difficult to verify
• how do we assess the “potential to interbreed”?
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3. The Evolutionary Species Concept (ESC, Simpson, 1951)
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3. The Evolutionary Species Concept (ESC, Simpson, 1951)
Definition: an evolutionary species is a lineage evolving separately from others with its own unitary evolutionary role and tendencies.
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3. The Evolutionary Species Concept (ESC, Simpson, 1951)
Definition: an evolutionary species is a lineage evolving separately from others with its own unitary evolutionary role and tendencies.
• initially developed to define fossil species.
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3. The Evolutionary Species Concept (ESC, Simpson, 1951)
Definition: an evolutionary species is a lineage evolving separately from others with its own unitary evolutionary role and tendencies.
• initially developed to define fossil species.
Time
Shell width
Species A
Species B
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Problems with the ESC
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Problems with the ESC
1. Arbitrary
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Problems with the ESC
1. Arbitrary
• how do you define independent roles and tendencies?
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Problems with the ESC
1. Arbitrary
• how do you define independent roles and tendencies?
2. Does not provide a mechanism
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4. The Phylogenetic Species Concept (PSC, Cracraft, 1983)
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4. The Phylogenetic Species Concept (PSC, Cracraft, 1983)
Definition: the smallest diagnosable monophyletic group of populations within which there is a parental pattern of ancestry and descent.
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4. The Phylogenetic Species Concept (PSC, Cracraft, 1983)
Definition: the smallest diagnosable monophyletic group of populations within which there is a parental pattern of ancestry and descent.
• two recent extensions are the internodal species concept and the genealogical species concept.
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Phylogenetic species
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A “cosmopolitan” copepod, Eurytemora affinis
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Phylogenetic analyses reveals at least 8 cryptic species
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Problems with the PSC
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Problems with the PSC
1. What characters to use?
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Problems with the PSC
1. What characters to use? 2. What level of divergence constitutes a species?
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Problems with the PSC
1. What characters to use? 2. What level of divergence constitutes a species? 3. Distinguishing between gene trees and species trees.
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Problems with the PSC
1. What characters to use? 2. What level of divergence constitutes a species? 3. Distinguishing between gene trees and species trees. 4. Does not address mechanism.
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5. The Recognition Species Concept (RSC, Paterson, 1985)
6. The Cohesion Species Concept (CSC, Templeton, 1989)
And many more……….