species and speciation d. melanogasterd. simulans

Species and Speciation

D. melanogaster D. simulans

Species and SpeciationI. Species Concepts


How we define a species depends on the goal we have in mind.



Are we categorizing existing or fossil organisms?



Are we categorizing existing or fossil organisms? Are we trying to understand correlates between populations adapting to different environments?



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?


A. Morphological Species Concept


A. Morphological Species Concept- Categorical/'essential' in a platonic sense; based on morphological similarity to a 'type' specimen


A. Morphological Species Concept- Categorical/'essential' in a platonic sense; based on morphological similarity to a 'type' specimen - Useful, but:


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


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.

D. melanogaster (M)

H. erato


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


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 speciesProblem... need a pretty good sample to describe within-group variation with confidence.

Species and SpeciationI. Species Concepts A. Morphological Species Concept B. Biological Species Concept - Mayr 1942

Species and SpeciationI. 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 SpeciationI. 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 SpeciationI. 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 SpeciationI. 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?


- not applicable to asexual species


- not applicable to asexual species

Bacteria, Archaeans, lots of Protists!!


- 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.

Species and SpeciationI. 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 SpeciationI. 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 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)


- Can't determine reproductive activity from a fossil; must rely on morphological criteria and patterns of change in a lineage.


- 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.


- 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".

http://www.oceansofkansas.com/sharks/Lederhos/P-whipplei2.jpg


- 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 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 SpeciationI. Species Concepts A. Morphological Species Concept B. Biological Species Concept - Mayr 1942 C. Evolutionary/Phylogenetic Species concepts D. Ecological Species Concept

Species and SpeciationI. 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


- 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.


- 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 SpeciationI. 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)



- Conundrums: - Selection can produce divergence when their IS gene flow. (polymorphism) - Selection can produce uniformity in absence of gene flow (convergence)



- 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.



- 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.



- 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 SpeciationI. Species ConceptsII. Recognizing SpeciesA. Morphology

Species and SpeciationI. Species ConceptsII. Recognizing SpeciesA. 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.

http://en.wikipedia.org/wiki/Image:Bimodal.png


Species and SpeciationI. Species ConceptsII. Recognizing SpeciesA. 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 SpeciationI. Species ConceptsII. Recognizing SpeciesA. 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 SpeciationI. Species ConceptsII. Recognizing SpeciesA. 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 SpeciationI. Species ConceptsII. Recognizing SpeciesA. MorphologyB. 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 SpeciationI. Species ConceptsII. Recognizing SpeciesA. MorphologyB. Genetic Analysis - Genetic Distance - Compute Nei's Genetic distance:

D = -ln [ ∑pi1pi2/ √ ∑pi12 ∑ pi2

2]

- 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 SpeciationI. Species ConceptsII. Recognizing SpeciesA. MorphologyB. 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:


- 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.




- 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 SpeciationI. Species ConceptsII. Recognizing SpeciesA. MorphologyB. Genetic AnalysisC. Hybrid Analyses

Species and SpeciationI. Species ConceptsII. Recognizing SpeciesA. MorphologyB. Genetic AnalysisC. 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 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.

species and speciation d. melanogasterd. simulans

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