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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
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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
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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.
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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.
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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
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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. Geographic or ecological isolation Genetic divergence and reproductive isolation
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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 even when their IS gene flow. (polymorphism)
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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 even when their IS gene flow. (polymorphism) - Selection can produce uniformity in absence of gene flow (convergence)
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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 even 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.
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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 even 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.
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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 even 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).
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Species and Speciation I. Species Concepts II. Recognizing Species A. Morphology
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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. H. erato H. melpomene Wing Pattern Wing Shape
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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. H. melpomene - 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. H. eratoH. melpomene Body Size Wing Shape
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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.
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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
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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.
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Coyne and Orr. 1989. Patterns of speciation in Drosophila. Evolution 43: 362-381. A summary of hybridization experiments involving 119 pairs of closely related Drosophila species. Prezygotic Isolation: Mate Selection: I = 1 - ( number of heterospecific matings) / (number of homospecific matings) Post-zygotic Isolation: avg: Offspring inviable or sterile (1) or viable and fertile (0)
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Species and Speciation I. Species Concepts II. Recognizing Species A. Morphology B. Genetic Analysis - Genetic Distance - Compute Nei's Genetic distance: D = -ln [ ∑p i 1p i 2/ √ ∑p i1 2 ∑ p i2 2 ] - So, for Population 1 and 2: - ∑p i 1p i 2 = (0.7*0.2) + (0.3*0.8) = 0.38 - denominator = √ (.49+.09) * (.04+.64) = 0.628 D 12 = -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
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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:
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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 differences can be hidden by morphological similarity (norms of reaction).
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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.
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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.
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Species and Speciation I. Species Concepts II. Recognizing Species A. Morphology B. Genetic Analysis C. Hybrid Analyses
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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.
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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.
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The only functional gametes are those that DID NOT cross over – and preserve the parental combination of alleles Inversion (changes the order of genes on a chromosome)
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Inversions in different populations of D. pseudoobscura (Dobzhansky& Sturtevant 1938)
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Relative frequencies (percentages) of five chromosomal inversions in D. pseudoobscura in different geographic regions.
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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.
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Species and Speciation I. Species Concepts II. Recognizing Species III. Making Species - Reproductive Isolation
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Species and Speciation I. Species Concepts II. Recognizing Species III. Making Species - Reproductive Isolation A. Pre-Zygotic Barriers
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Species and Speciation I. Species Concepts II. Recognizing Species III. Making Species - Reproductive Isolation A. Pre-Zygotic Barriers 1. Geographic Isolation (large scale or habitat)
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Drosophila speciation on the Hawaiian Islands. Obbard D J et al. Mol Biol Evol 2012;29:3459-3473 © The Author 2012. Published by Oxford University Press on behalf of the Society for Molecular Biology and Evolution.
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Species and Speciation I. Species Concepts II. Recognizing Species III. Making Species - Reproductive Isolation A. Pre-Zygotic Barriers 1. Geographic Isolation (large scale or habitat) 2. Temporal Isolation
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Species and Speciation I. Species Concepts II. Recognizing Species III. Making Species - Reproductive Isolation A. Pre-Zygotic Barriers 1. Geographic Isolation (large scale or habitat) 2. Temporal Isolation 3. Behavior Isolation - don't recognize one another as mates Western MeadowlarkEastern Meadowlark
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Species and Speciation I. Species Concepts II. Recognizing Species III. Making Species - Reproductive Isolation A. Pre-Zygotic Barriers 1. Geographic Isolation (large scale or habitat) 2. Temporal Isolation 3. Behavior Isolation - don't recognize one another as mates 4. Mechanical isolation - genitalia don't fit; limit pollinators
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Species and Speciation I. Species Concepts II. Recognizing Species III. Making Species - Reproductive Isolation A. Pre-Zygotic Barriers 1. Geographic Isolation (large scale or habitat) 2. Temporal Isolation 3. Behavior Isolation - don't recognize one another as mates 4. Mechanical isolation - genitalia don't fit 5. Gametic Isolation - gametes transfered but sperm can't fertilize egg; this is a common isolation mechanism in species that spawn at the same time
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Species and Speciation I. Species Concepts II. Recognizing Species III. Making Species - Reproductive Isolation A. Pre-Zygotic Barriers 1. Geographic Isolation (large scale or habitat) 2. Temporal Isolation 3. Behavior Isolation - don't recognize one another as mates 4. Mechanical isolation - genitalia don't fit 5. Gametic Isolation - gametes transfered but sperm can't fertilize egg B. Post-Zygotic Isolation
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Species and Speciation I. Species Concepts II. Recognizing Species III. Making Species - Reproductive Isolation A. Pre-Zygotic Barriers 1. Geographic Isolation (large scale or habitat) 2. Temporal Isolation 3. Behavior Isolation - don't recognize one another as mates 4. Mechanical isolation - genitalia don't fit 5. Gametic Isolation - gametes transfered but sperm can't fertilize egg B. Post-Zygotic Isolation 1. Genomic Incompatibility - zygote dies
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Species and Speciation I. Species Concepts II. Recognizing Species III. Making Species - Reproductive Isolation A. Pre-Zygotic Barriers 1. Geographic Isolation (large scale or habitat) 2. Temporal Isolation 3. Behavior Isolation - don't recognize one another as mates 4. Mechanical isolation - genitalia don't fit 5. Gametic Isolation - gametes transfered but sperm can't fertilize egg B. Post-Zygotic Isolation 1. Genomic Incompatibility - zygote dies 2. Hybrid Inviability - F1 has lower survival Crazy hybrids
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Species and Speciation I. Species Concepts II. Recognizing Species III. Making Species - Reproductive Isolation A. Pre-Zygotic Barriers 1. Geographic Isolation (large scale or habitat) 2. Temporal Isolation 3. Behavior Isolation - don't recognize one another as mates 4. Mechanical isolation - genitalia don't fit 5. Gametic Isolation - gametes transfered but sperm can't fertilize egg B. Post-Zygotic Isolation 1. Genomic Incompatibility - zygote dies 2. Hybrid Inviability - F1 has lower survival 3. Hybrid Sterility - F1 has reduced reproductive success Horse: 64 chromosomes Donkey: 62 chromosomes Mule: 63 chromosomes
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Species and Speciation I. Species Concepts II. Recognizing Species III. Making Species - Reproductive Isolation A. Pre-Zygotic Barriers 1. Geographic Isolation (large scale or habitat) 2. Temporal Isolation 3. Behavior Isolation - don't recognize one another as mates 4. Mechanical isolation - genitalia don't fit 5. Gametic Isolation - gametes transfered but sperm can't fertilize egg B. Post-Zygotic Isolation 1. Genomic Incompatibility - zygote dies 2. Hybrid Inviability - F1 has lower survival 3. Hybrid Sterility - F1 has reduced reproductive success 4. F2 breakdown - F1's survive but F2's have incompatible combo's of genes
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AABB x aabb F1: AaBb = ok F2: A-B- = ok A-bb = no aaB- = no aabb = ok
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Species and Speciation I. Species Concepts II. Recognizing Species III. Making Species - Reproductive Isolation IV. Speciation
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