Species and Speciation
D. melanogaster
D. simulans
Species and Speciation
I. Species Concepts
Species and Speciation
I. Species Concepts
How we define a species depends on the goal we have in mind.
Species and Speciation
I. Species Concepts
How we define a species depends on the goal we have in mind.
Are we categorizing existing or fossil organisms?
Species and Speciation
I. Species Concepts
How we define a species depends on the goal we have in mind.
Are we categorizing existing or fossil organisms?
Are we trying to understand correlates between populations adapting to
different environments?
Species and Speciation
I. Species Concepts
How we define a species depends on the goal we have in mind.
Are we categorizing existing or fossil organisms?
Are we trying to understand correlates between populations adapting to
different environments?
Are we trying to reconstruct phylogenies?
Species and Speciation
I. Species Concepts
A. Morphological Species Concept
Species and Speciation
I. Species Concepts
A. Morphological Species Concept
- Categorical/'essential' in a platonic sense; based on morphological similarity to a
'type' specimen
Species and Speciation
I. Species Concepts
A. Morphological Species Concept
- Categorical/'essential' in a platonic sense; based on morphological similarity to a
'type' specimen
- Useful, but:
Species and Speciation
I. Species Concepts
A. Morphological Species Concept
- Categorical/'essential' in a platonic sense; based on morphological similarity to a
'type' specimen
- Useful, but: many species are polymorphic
H. erato
Species and Speciation
I. Species Concepts
A. Morphological Species Concept
- Categorical/'essential' in a platonic sense; based on morphological similarity to a
'type' specimen
- Useful, but: many species are polymorphic and some sibling species are
indistinguishable morphologically.
H. erato
D. melanogaster (M)
Species and Speciation
I. Species Concepts
A. Morphological Species Concept
- Categorical/'essential' in a platonic sense; based on morphological similarity to a
'type' specimen
- Useful, but many species are polymorphic and some sibling species are
indistinguishable morphologically.
- Nonetheless, for dead or fossilized specimens, the phenotype is all we might have
to analyze. As such, there are ways of quantifying the phenotype and defining
"phenetic" species... by quantifying the within-group phenotypic variation, statistical
analysis can ascertain whether a novel individual lies within that typical range.
New Species!!
old species
Species and Speciation
I. Species Concepts
A. Morphological Species Concept
- Categorical/'essential' in a platonic sense; based on morphological similarity to a
'type' specimen
- Useful, but many species are polymorphic and some sibling species are
indistinguishable morphologically.
- Nonetheless, for dead or fossilized specimens, the phenotype is all we might have
to analyze. As such, there are ways of quantifying the phenotype and defining
"phenetic" species... by quantifying the within-group phenotypic variation, statistical
analysis can ascertain whether a novel individual lies within that typical range.
old species
New Species?
Problem... need a pretty good
sample to describe withingroup variation with
confidence.
Species and Speciation
I. Species Concepts
A. Morphological Species Concept
B. Biological Species Concept - Mayr 1942
Species and Speciation
I. Species Concepts
A. Morphological Species Concept
B. Biological Species Concept - Mayr 1942
"Groups of actually or potentially interbreeding populations that are reproductively
isolated from other such groups"
Ernst Mayr
(1904-2005)
Species and Speciation
I. Species Concepts
A. Morphological Species Concept
B. Biological Species Concept - Mayr 1942
"Groups of actually or potentially interbreeding populations that are reproductively
isolated from other such groups"
- Biological units are genetically defined; reproductive isolation makes populations
different from one another, creating new units. So, reproductive isolation is the key
characteristic of a species.
Species and Speciation
I. Species Concepts
A. Morphological Species Concept
B. Biological Species Concept - Mayr 1942
"Groups of actually or potetially interbreeding populations that are reproductively
isolated from other such groups"
- Biological units are genetically defined; reproductive isolation makes populations
different from one another, creating new units. So, reproductive isolation is the key
characteristic of a species.
- Limitations:
Species and Speciation
I. Species Concepts
A. Morphological Species Concept
B. Biological Species Concept - Mayr 1942
"Groups of actually or potetially interbreeding populations that are reproductively
isolated from other such groups"
- Biological units are genetically defined; reproductive isolation makes populations
different from one another, creating new units. So, reproductive isolation is the key
characteristic of a species.
- Limitations:
- Process may be continuous - where do you draw the "line" of isolation?
Species and Speciation
I. Species Concepts
A. Morphological Species Concept
B. Biological Species Concept - Mayr 1942
"Groups of actually or potetially interbreeding populations that are reproductively
isolated from other such groups"
- Biological units are genetically defined; reproductive isolation makes populations
different from one another, creating new units. So, reproductive isolation is the key
characteristic of a species.
- Limitations:
- not applicable to asexual species
Species and Speciation
I. Species Concepts
A. Morphological Species Concept
B. Biological Species Concept - Mayr 1942
"Groups of actually or potetially interbreeding populations that are reproductively
isolated from other such groups"
- Biological units are genetically defined; reproductive isolation makes populations
different from one another, creating new units. So, reproductive isolation is the key
characteristic of a species.
- Limitations:
- not applicable to asexual species
Bacteria, Archaeans, lots of Protists!!
Species and Speciation
I. Species Concepts
A. Morphological Species Concept
B. Biological Species Concept - Mayr 1942
"Groups of actually or potetially interbreeding populations that are reproductively
isolated from other such groups"
- Biological units are genetically defined; reproductive isolation makes populations
different from one another, creating new units. So, reproductive isolation is the key
characteristic of a species.
- Limitations:
- not applicable to asexual species
- hybridization occurs in nature, even between otherwise 'good' species.
Natural variability is not strictly discontinuous, so pigeon-holing on any grounds
will be wrong in some cases. It becomes a matter of degree. The best example
are "Ring Complexes"...series of species which breed with neighboring species
but the 'end' species do not. Salamanders in California, Gulls in circumpolar
regions.
Ring Species
Divergence that correlates with geographical
distance can create interesting patterns on a
spherical globe, or around a geographical
feature.
Ring Species
Divergence that correlates with geographical
distance can create interesting patterns on a
spherical globe, or around a geographical
feature.
Ring Species
Divergence that correlates with geographical
distance can create interesting patterns on a
spherical globe, or around a geographical
feature.
Species and Speciation
I. Species Concepts
A. Morphological Species Concept
B. Biological Species Concept - Mayr 1942
"Groups of actually or potentially interbreeding populations that are reproductively
isolated from other such groups"
- Biological units are genetically defined; reproductive isolation makes populations
different from one another, creating new units. So, reproductive isolation is the key
characteristic of a species.
- Limitations:
- not applicable to asexual species
- hybridization occurs in nature, even between otherwise 'good' species.
Natural variability is not strictly discontinuous, so pigeon-holing on any grounds
will be wrong in some cases. It becomes a matter of degree. The best example
are "Ring Complexes"...series of species which breed with neighboring species
but the 'end' species do not. Salamanders in California, Gulls in circumpolar
regions.
- Allopatric populations: Potential interbreeding means that populations that are
spatially separated and morphologically/genetically distinct may be in the same
species.
Species and Speciation
I. Species Concepts
A. Morphological Species Concept
B. Biological Species Concept - Mayr 1942
C. Evolutionary/Phylogenetic Species concepts
Species and Speciation
I. Species Concepts
A. Morphological Species Concept
B. Biological Species Concept - Mayr 1942
C. Evolutionary/Phylogenetic Species concepts
"A single lineage (ancestor-descendant sequence) of populations or organisms that
maintains an identity separate from other such lineages and which has its own
evolutionary tendancies and historical fate" - Wiley 1978
Species and Speciation
I. Species Concepts
A. Morphological Species Concept
B. Biological Species Concept - Mayr 1942
C. Evolutionary/Phylogenetic Species concepts
"A single lineage (ancestor-descendant sequence) of populations or organisms that
maintains an identity separate from other such lineages and which has its own
evolutionary tendancies and historical fate" - Wiley 1978
"Irreducible cluster of organisms diagnostically distinct from other such clusters, and
in which there is a parental pattern of ancestry and descent" - Cracraft - 1989
Species and Speciation
I. Species Concepts
A. Morphological Species Concept
B. Biological Species Concept - Mayr 1942
C. Evolutionary/Phylogenetic Species concepts
"A single lineage (ancestor-descendant sequence) of populations or organisms that
maintains an identity separate from other such lineages and which has its own
evolutionary tendancies and historical fate" - Wiley 1978
"Irreducible cluster of organisms diagnostically distinct from other such clusters, and
in which there is a parental pattern of ancestry and descent" - Cracraft - 1989
"The smallest monophyletic group of common ancestry" - (de Queiroz and
Donoghue - 1990).
Species and Speciation
I. Species Concepts
A. Morphological Species Concept
B. Biological Species Concept - Mayr 1942
C. Evolutionary/Phylogenetic Species concepts
"A single lineage (ancestor-descendant sequence) of populations or organisms that
maintains an identity separate from other such lineages and which has its own
evolutionary tendancies and historical fate" - Wiley 1978
"Irreducible cluster of organisms diagnostically distinct from other such clusters, and
in which there is a parental pattern of ancestry and descent" - Cracraft - 1989
"The smallest monophyletic group of common ancestry" - (de Queiroz and
Donoghue - 1990).
“A species is a lineage (an ancestral-descendant sequence of populations) evolving
separately from others and with its own unitary evolutionary roles and tendencies” (Simpson, 1961).
Species and Speciation
I. Species Concepts
A. Morphological Species Concept
B. Biological Species Concept - Mayr 1942
C. Evolutionary/Phylogenetic Species concepts
"A single lineage (ancestor-descendant sequence) of populations or organisms that
maintains an identity separate from other such lineages and which has its own
evolutionary tendancies and historical fate" - Wiley 1978
"Irreducible cluster of organisms diagnostically distinct from other such clusters, and
in which there is a parental pattern of ancestry and descent" - Cracraft - 1989
"The smallest monophyletic group of common ancestry" - (de Queiroz and
Donoghue - 1990).
“A species is a lineage (an ancestral-descendant sequence of populations) evolving
separately from others and with its own unitary evolutionary roles and tendencies” (Simpson, 1961).
“A species is a set of organisms (an evolutionary lineage) between two branch points
or between one branch point and an extinction event or a modern population” (Ridley 1993). (cladistic concept)
Species and Speciation
I. Species Concepts
A. Morphological Species Concept
B. Biological Species Concept - Mayr 1942
C. Evolutionary/Phylogenetic Species concepts
- Can't determine reproductive activity from a fossil;
must rely on morphological criteria and patterns of
change in a lineage.
Species and Speciation
I. Species Concepts
A. Morphological Species Concept
B. Biological Species Concept - Mayr 1942
C. Evolutionary/Phylogenetic Species concepts
- Can't determine reproductive activity from a fossil; must rely on morphological
criteria and patterns of change in a lineage.
- A single unique lineage is an evolutionary species. This is defined by the presence
of a unique derived character. Groups of populations that share the same suite of
characters are the same species. this can be based on morphometric or genetic
analysis.
Species and Speciation
I. Species Concepts
A. Morphological Species Concept
B. Biological Species Concept - Mayr 1942
C. Evolutionary/Phylogenetic Species concepts
- Can't determine reproductive activity from a fossil; must rely on morphological
criteria and patterns of change in a lineage.
- A single unique lineage is an evolutionary species. This is defined by the presence
of a unique derived character. Groups of populations that share the same suite of
characters are the same species. this can be based on morphometric or genetic
analysis.
- If it does not 'branch' but changes dramatically, stages can be distinguished as
"chronospecies".
Species and Speciation
I. Species Concepts
A. Morphological Species Concept
B. Biological Species Concept - Mayr 1942
C. Evolutionary/Phylogenetic Species concepts
- emphasize species as the product of evolution... not the process (reproductive
isolation) by which their identity is produced.
Species and Speciation
I. Species Concepts
A. Morphological Species Concept
B. Biological Species Concept - Mayr 1942
C. Evolutionary/Phylogenetic Species concepts
- emphasize species as the product of evolution... not the process (reproductive
isolation) by which their identity is produced.
- but identity is still critical... unique lineages are defined by the presence of a unique
derived character. Groups of populations that share the same suite of characters
are the same species. this can be based on morphometric or genetic analysis.
Species and Speciation
I. Species Concepts
A. Morphological Species Concept
B. Biological Species Concept - Mayr 1942
C. Evolutionary/Phylogenetic Species concepts
- emphasize species as the product of evolution... not the process (reproductive
isolation) by which their identity is produced.
- but identity is still critical... unique lineages are defined by the presence of a unique
derived character. Groups of populations that share the same suite of characters are
the same species. this can be based on morphometric or genetic analysis.
- but do we then differentiate populations with discrete differences in fixed alleles?
Species and Speciation
I. Species Concepts
A. Morphological Species Concept
B. Biological Species Concept - Mayr 1942
C. Evolutionary/Phylogenetic Species concepts
D. Ecological Species Concept
Species and Speciation
I. Species Concepts
A. Morphological Species Concept
B. Biological Species Concept - Mayr 1942
C. Evolutionary/Phylogenetic Species concepts
D. Ecological Species Concept
- In responding to selection, populations diverge and play unique roles in the
environment - filling different niches. This ecological specialization will be reflected in
physiological, morphological, or behavioral differences between populations.
Hawaiian Honeycreepers
Species and Speciation
I. Species Concepts
A. Morphological Species Concept
B. Biological Species Concept - Mayr 1942
C. Evolutionary/Phylogenetic Species concepts
D. Ecological Species Concept
- In responding to selection, populations diverge and play unique roles in the
environment - filling different niches. This ecological specialization will be reflected in
physiological, morphological, or behavioral differences between populations.
- Our classic example of "Character Displacement", where the morphology changes
as a function of the environment - most notably the presence of other species such
as competitors or predators.
Species and Speciation
I. Species Concepts
A. Morphological Species Concept
B. Biological Species Concept - Mayr 1942
C. Evolutionary/Phylogenetic Species concepts
D. Ecological Species Concept
- In responding to selection, populations diverge and play unique roles in the
environment - filling different niches. This ecological specialization will be reflected in
physiological, morphological, or behavioral differences between populations.
- Our classic example of "Character Displacement", where the morphology changes
as a function of the environment - most notably the presence of other species such
as competitors or predators.
- In the presence of a competitior, G. fortis
uses a different range of seeds and is a
different ecological species than where it
occurs alone. It plays a different role in the
environment and fills a different niche.
Species and Speciation
I. Species Concepts
A. Morphological Species Concept
B. Biological Species Concept - Mayr 1942
C. Evolutionary/Phylogenetic Species concepts
D. Striking a Balance
Species and Speciation
I. Species Concepts
A. Morphological Species Concept
B. Biological Species Concept - Mayr 1942
C. Evolutionary/Phylogenetic Species concepts
D. Striking a Balance
- So what preserves the integrity of species - reproductive isolation or ecological
isolation? These are often correlated, so it is tough to tease their independent
contributions apart.
Species and Speciation
I. Species Concepts
A. Morphological Species Concept
B. Biological Species Concept - Mayr 1942
C. Evolutionary/Phylogenetic Species concepts
D. Striking a Balance
- So what preserves the integrity of species - reproductive isolation or ecological
isolation? These are often correlated, so it is tough to tease their independent
contributions apart.
- Conundrums:
- Selection can produce divergence when their IS gene flow. (polymorphism)
Species and Speciation
I. Species Concepts
A. Morphological Species Concept
B. Biological Species Concept - Mayr 1942
C. Evolutionary/Phylogenetic Species concepts
D. Striking a Balance
- So what preserves the integrity of species - reproductive isolation or ecological
isolation? These are often correlated, so it is tough to tease their independent
contributions apart.
- Conundrums:
- Selection can produce divergence when their IS gene flow. (polymorphism)
- Selection can produce uniformity in absence of gene flow (convergence)
Species and Speciation
I. Species Concepts
A. Morphological Species Concept
B. Biological Species Concept - Mayr 1942
C. Evolutionary/Phylogenetic Species concepts
D. Striking a Balance
- So what preserves the integrity of species - reproductive isolation or ecological
isolation? These are often correlated, so it is tough to tease their independent
contributions apart.
- Conundrums:
- Selection can produce divergence when their IS gene flow. (polymorphism)
- Selection can produce uniformity in absence of gene flow (convergence)
- And, gene flow can also keep two populations in different environments similar.
Species and Speciation
I. Species Concepts
A. Morphological Species Concept
B. Biological Species Concept - Mayr 1942
C. Evolutionary/Phylogenetic Species concepts
D. Striking a Balance
- So what preserves the integrity of species - reproductive isolation or ecological
isolation? These are often correlated, so it is tough to tease their independent
contributions apart.
- Conundrums:
- Selection can produce divergence when their IS gene flow. (polymorphism)
- Selection can produce uniformity in absence of gene flow (convergence)
- And, gene flow can also keep two populations in different environments similar.
- For bacteria/archaeans, lateral gene transfer (gene flow) creates new species,
with a new unique complement of genes.
Species and Speciation
I. Species Concepts
A. Morphological Species Concept
B. Biological Species Concept - Mayr 1942
C. Evolutionary/Phylogenetic Species concepts
D. Striking a Balance
- So what preserves the integrity of species - reproductive isolation or ecological
isolation? These are often correlated, so it is tough to tease their independent
contributions apart.
- Conundrums:
- Selection can produce divergence when their IS gene flow. (polymorphism)
- Selection can produce uniformity in absence of gene flow (convergence)
- And, gene flow can also keep two populations in different environments similar.
- For bacteria/archaeans, lateral gene transfer (gene flow) creates new species,
with a new unique complement of genes.
- Need to appreciate that the relative importance of different factors may vary
depending on the organism - does it have high dispersal and isolation probability?
Can it change rapidly? These things will vary with the type of organisms (large
mammals vs. insects).
Species and Speciation
I. Species Concepts
II. Recognizing Species
A. Morphology
Species and Speciation
I. Species Concepts
II. Recognizing Species
A. Morphology
- correlated phenotypic characters. Quantitative characteristics can have bimodal
distributions. However, it is unusual for a single species to be bimodal for lots of
characters.
Species and Speciation
I. Species Concepts
II. Recognizing Species
A. Morphology
- correlated phenotypic characters. Quantitative characteristics can have bimodal
distributions. However, it is unusual for a single species to be bimodal for lots of
characters.
- If you observe this (big ones are red, with wispy antenna, small wings and fast
flight; small ones are blue with short antenna, large wings and slow flight), then you
probably have two reproductively isolated groups.
Species and Speciation
I. Species Concepts
II. Recognizing Species
A. Morphology
- correlated phenotypic characters. Quantitative characteristics can have bimodal
distributions. However, it is unusual for a single species to be bimodal for lots of
characters.
- If you observe this (big ones are red, with wispy antenna, small wings and fast
flight; small ones are blue with short antenna, large wings and slow flight), then you
probably have two reproductively isolated groups.
- may miss morphologically similar sibling species, or lump polymorphic species.
Species and Speciation
I. Species Concepts
II. Recognizing Species
A. Morphology
- correlated phenotypic characters. Quantitative characteristics can have bimodal
distributions. However, it is unusual for a single species to be bimodal for lots of
characters.
- If you observe this (big ones are red, with wispy antenna, small wings and fast
flight; small ones are blue with short antenna, large wings and slow flight), then you
probably have two reproductively isolated groups.
- may miss morphologically similar sibling species, or lump polymorphic species.
- want to focus on traits of little selective value, or copulatory organs
Species and Speciation
I. Species Concepts
II. Recognizing Species
A. Morphology
B. Genetic Analysis
- Genetic Distance - distance correlates with divergence that can occur both before
and after reproductive isolation. So, there is a fairly continuous function of declining
similarity as reproductive isolation develops, dependent on average size of the
populations. Within a group, often we see 'species' associated with a particular
amount of genetic distance.
Species and Speciation
I. Species Concepts
II. Recognizing Species
A. Morphology
B. Genetic Analysis
- Genetic Distance
- Compute Nei's Genetic distance:
D = -ln [ ∑pi1pi2/ √ ∑pi12 ∑ pi22]
- So, for Population 1 and 2:
- ∑pi1pi2 = (0.7*0.2) + (0.3*0.8) = 0.38
- denominator = √ (.49+.09) * (.04+.64) = 0.628
D12 = -ln (0.38/0.62) = 0.50
- calculate these values FOR EACH locus, and
then average the I's or D's together to get the final Genetic
Distance. The more loci, the better.
p1 = 0.7
q1 = 0.3
p2 = 0.2
q2 = 0.8
Species and Speciation
I. Species Concepts
II. Recognizing Species
A. Morphology
B. Genetic Analysis
- Genetic Distance - distance correlates with divergence that can occur both before
and after reproductive isolation. So, there is a fairly continuous function of declining
similarity as reproductive isolation develops, dependent on average size of the
populations. Within a group, often we see 'species' associated with a particular
amount of genetic distance.
- Compute Nei's Genetic Distance
- CAVEATS:
Species and Speciation
I. Species Concepts
II. Recognizing Species
A. Morphology
B. Genetic Analysis
- Genetic Distance - distance correlates with divergence that can occur both before
and after reproductive isolation. So, there is a fairly continuous function of declining
similarity as reproductive isolation develops, dependent on average size of the
populations. Within a group, often we see 'species' associated with a particular
amount of genetic distance.
- Compute Nei's Genetic Distance
- CAVEATS:
- Genetic diffs do not necessarily correlate with morphological diffs; small
genetic diffs can mean large morphological change (developmental genes), or large
genetic change can be hidden by morphological similarity (norms of reaction).
Species and Speciation
I. Species Concepts
II. Recognizing Species
A. Morphology
B. Genetic Analysis
- Genetic Distance - distance correlates with divergence that can occur both before
and after reproductive isolation. So, there is a fairly continuous function of declining
similarity as reproductive isolation develops, dependent on average size of the
populations. Within a group, often we see 'species' associated with a particular
amount of genetic distance.
- Compute Nei's Genetic Distance
- CAVEATS:
- Genetic diffs do not necessarily correlate with morphological diffs; small
genetic diffs can mean large morphological change (developmental genes), or large
genetic change can be hidden by morphological similarity (norms of reaction).
- Still, genetic similarity is a more direct measure of degree of isolation.
Species and Speciation
I. Species Concepts
II. Recognizing Species
A. Morphology
B. Genetic Analysis
- Genetic Distance - distance correlates with divergence that can occur both before
and after reproductive isolation. So, there is a fairly continuous function of declining
similarity as reproductive isolation develops, dependent on average size of the
populations. Within a group, often we see 'species' associated with a particular
amount of genetic distance.
- Compute Nei's Genetic Distance
- CAVEATS:
- Genetic diffs do not necessarily correlate with morphological diffs; small
genetic diffs can mean large morphological change (developmental genes), or large
genetic change can be hidden by morphological similarity (norms of reaction).
- Still, genetic similarity is a more direct measure of degree of isolation.
- Also, there is no suggestion that divergence in these loci CAUSE
speciation. Rather, these loci are simply used as 'markers' or indicators of general
genetic distance.
Species and Speciation
I. Species Concepts
II. Recognizing Species
A. Morphology
B. Genetic Analysis
C. Hybrid Analyses
Species and Speciation
I. Species Concepts
II. Recognizing Species
A. Morphology
B. Genetic Analysis
C. Hybrid Analyses
- Create hybrids and examine their fertility. Infertility may be due to:
- Epistatic interactions between loci derived from different parents. Maybe
species one has A1A1B1B1 and species 2 has A2A2B2B2, and maybe A1 and B1
don't work together. If one is a sex linked gene, then sterility might be sex-specific.
Species and Speciation
I. Species Concepts
II. Recognizing Species
A. Morphology
B. Genetic Analysis
C. Hybrid Analyses
- Create hybrids and examine their fertility. Infertility may be due to:
- Epistatic interactions between loci derived from different parents. Maybe
species one has A1A1B1B1 and species 2 has A2A2B2B2, and maybe A1 and B1
don't work together. If one is a sex linked gene, then sterility might be sex-specific.
- Hybrids that receive different inversion chromosomes may have lower
fitness because crossing over produces aneuploid gametes - with chromosomes that
lack centromeres and are lost from the cell line.
Species and Speciation
I. Species Concepts
II. Recognizing Species
A. Morphology
B. Genetic Analysis
C. Hybrid Analyses
- Create hybrids and examine their fertility. Infertility may be due to:
- Epistatic interactions between loci derived from different parents. Maybe
species one has A1A1B1B1 and species 2 has A2A2B2B2, and maybe A1 and B1
don't work together. If one is a sex linked gene, then sterility might be sex-specific.
- Hybrids that receive different inversion chromosomes may have lower
fitness because crossing over produces aneuploid gametes - with chromosomes that
lack centromeres and are lost from the cell line.
- Hybrids receiving chromosomes from parents with different reciprocal
translocations may not have neat homologous sets.