Download Lecture 21 Species concepts

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
Cosmopolitan species
Cryptic species
Endemic species
Fugitive species
Polytypic species
Relic species
Lazarus species
Subspecies
Superspecies
Vicariant species
Sister species
Sibling species
Semispecies
Ring 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 B
Species A
Mayr divided the BSC into the “nondimensional”
and the “multidimensional” species concept:
Nondimensional
species concept

Species A

Species B
species sympatric
and synchronous
Mayr divided the BSC into the “nondimensional”
and the “multidimensional” species concept:
Nondimensional
Multidimensional
species concept
species concept

Species A

Species B
species sympatric
and synchronous
Mayr divided the BSC into the “nondimensional”
and the “multidimensional” species concept:
Nondimensional
Multidimensional
species concept
species concept

Species A

Species B


Species B
species sympatric
and synchronous
Species A
Mayr divided the BSC into the “nondimensional”
and the “multidimensional” species concept:
Nondimensional
Multidimensional
species concept
species concept

Species A

Species B

Species A

Species B
species sympatric
and synchronous
species are allopatric
and/or allochronous
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.



Species A
Time
Species B


Shell width
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!