21 species concepts - university of california, santa...
TRANSCRIPT
Lecture 21 Species concepts
How many species currently exist?
How many species currently exist?
• about 3 million species have been described.
How many species currently exist?
• about 3 million species have been described.
• only about 1.5 million in any detail.
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.
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?
How many species currently exist?
1. Many groups are poorly studied.
How many species currently exist?
1. Many groups are poorly studied.
• notably microorganisms and parasites.
How many species currently exist?
1. Many groups are poorly studied.
• notably microorganisms and parasites.
2. Many environments are poorly sampled.
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.
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”.
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.
How many species currently exist?
Example: the mussels Mytilus trossulus and M. galloprovincialis in Monterey Bay.
Mytilus trossulus Mytilus galloprovincialis
A list of some types of species!
Chronospecies Subspecies Cosmopolitan species Superspecies Cryptic species Vicariant species Endemic species Sister species Fugitive species Sibling species Polytypic species Semispecies Relic species Ring species Lazarus species
Species Concepts
1. The Typological Species Concept (TSC, Linnaeus)
Species Concepts
1. The Typological Species Concept (TSC, Linnaeus)
Definition: a group of individuals that differ from other groups by possessing constant diagnostic characters.
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.
Problems with the TSC:
Problems with the TSC:
1. Polymorphism within populations
Teagueia sancheziae
Problems with the TSC:
1. Polymorphism within populations
2. Geographic variation among populations
Problems with the TSC:
1. Polymorphism within populations
2. Geographic variation among populations
3. Sibling or cryptic species
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.
2. The Biological Species Concept (BSC, Dobzhansky, Mayr)
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.
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.
Mayr divided the BSC into the “nondimensional” and the “multidimensional” species concept:
Mayr divided the BSC into the “nondimensional” and the “multidimensional” species concept:
Nondimensional species concept
Mayr divided the BSC into the “nondimensional” and the “multidimensional” species concept:
Nondimensional species concept
Species A
Species B
Mayr divided the BSC into the “nondimensional” and the “multidimensional” species concept:
Nondimensional species concept
species sympatric
and synchronous
Species A
Species B
Mayr divided the BSC into the “nondimensional” and the “multidimensional” species concept:
Nondimensional Multidimensional species concept species concept
species sympatric
and synchronous
Species A
Species B
Mayr divided the BSC into the “nondimensional” and the “multidimensional” species concept:
Nondimensional Multidimensional species concept species concept
species sympatric
and synchronous
Species A Species A
Species B Species B
Mayr divided the BSC into the “nondimensional” and the “multidimensional” species concept:
Nondimensional Multidimensional species concept species concept
species sympatric species are allopatric
and synchronous and/or allochronous
Species A Species A
Species B Species B
Problems with the BSC:
Problems with the BSC:
1. Not applicable to asexual species
Problems with the BSC:
1. Not applicable to asexual species
2. Reproductive isolation is often incomplete
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).
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 dad Middle: Dolphin mom Bottom: Baby wholphin
Wholphin mom Kekaimalu With daughter Kawili'Kai
Kawili'Kai
A “liger”
Hercules, the liger
A “tigon”
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
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”?
3. The Evolutionary Species Concept (ESC, George Gaylord Simpson, 1951)
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.
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.
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
Problems with the ESC
Problems with the ESC
1. Arbitrary
Problems with the ESC
1. Arbitrary
• how do you define independent roles and tendencies?
Problems with the ESC
1. Arbitrary
• how do you define independent roles and tendencies?
2. Does not provide a mechanism
4. The Phylogenetic Species Concept (PSC, Cracraft, 1983)
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.
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.
Phylogenetic species
A “cosmopolitan” copepod, Eurytemora affinis
Phylogenetic analyses reveals at least 8 cryptic species
Problems with the PSC
Problems with the PSC
1. What characters to use?
Problems with the PSC
1. What characters to use?
2. What level of divergence constitutes a species?
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.
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.
5. The Recognition Species Concept (RSC, Paterson, 1985)
5. The Recognition Species Concept (RSC, Paterson, 1985)
Definition: the most inclusive population of biparental organisms that share a common fertilization system.
5. The Recognition Species Concept (RSC, Paterson, 1985)
Definition: the most inclusive population of biparental organisms that share a common fertilization system. • this concept focuses on mate-recognition systems.
5. The Recognition Species Concept (RSC, Paterson, 1985)
• mate-recognition systems include:
5. The Recognition Species Concept (RSC, Paterson, 1985)
• mate-recognition systems include: • courtship displays
5. The Recognition Species Concept (RSC, Paterson, 1985)
• mate-recognition systems include: • courtship displays
• the timing of reproductive events
5. The Recognition Species Concept (RSC, Paterson, 1985)
• mate-recognition systems include: • courtship displays
• the timing of reproductive events
• neuroendocrine signals (e.g., pheromones)
5. The Recognition Species Concept (RSC, Paterson, 1985)
• mate-recognition systems include: • courtship displays
• the timing of reproductive events
• neuroendocrine signals (e.g., pheromones)
• design of copulatory organs
5. The Recognition Species Concept (RSC, Paterson, 1985)
• mate-recognition systems include: • courtship displays
• the timing of reproductive events
• neuroendocrine signals (e.g., pheromones)
• design of copulatory organs
• gamete compatibility (i.e., sperm and egg proteins)
Problems with the RSC
Problems with the RSC
1. Not applicable to asexual species
Problems with the RSC
1. Not applicable to asexual species
2. Recognition systems often go awry (i.e., hybridization occurs)
6. The Cohesion Species Concept (CSC, Templeton, 1989)
6. The Cohesion Species Concept (CSC, Templeton, 1989)
Definition: the most inclusive population of organisms having the potential for cohesion through intrinsic cohesive mechanisms.
6. The Cohesion Species Concept (CSC, Templeton, 1989)
Definition: the most inclusive population of organisms having the potential for cohesion through intrinsic cohesive mechanisms.
Two classes of cohesive mechanisms are identified:
6. The Cohesion Species Concept (CSC, Templeton, 1989)
Definition: the most inclusive population of organisms having the potential for cohesion through intrinsic cohesive mechanisms.
Two classes of cohesive mechanisms are identified:
1. Genetic cohesive mechanisms
6. The Cohesion Species Concept (CSC, Templeton, 1989)
Definition: the most inclusive population of organisms having the potential for cohesion through intrinsic cohesive mechanisms.
Two classes of cohesive mechanisms are identified:
1. Genetic cohesive mechanisms
• gene flow and stabilizing selection function to maintain species integrity.
6. The Cohesion Species Concept (CSC, Templeton, 1989) Two classes of cohesive mechanisms are identified:
1. Genetic cohesive mechanisms
• gene flow and stabilizing selection function to maintain species integrity.
2. Ecological cohesive mechanisms
6. The Cohesion Species Concept (CSC, Templeton, 1989) Two classes of cohesive mechanisms are identified:
1. Genetic cohesive mechanisms
• gene flow and stabilizing selection function to maintain species integrity.
2. Ecological cohesive mechanisms - abundance, demographic stability, strengths of interactions with other species, etc.
Problems with the CSC
1. Studying cohesive mechanisms is labor intensive!