Lecture 22 Speciation These facts seemed to me to throw some light on the origin of species that mystery of mysteries. C. Darwin The Origin
What is speciation? in Darwin s words, speciation is the multiplication of species.
What is speciation? in Darwin s words, speciation is the multiplication of species. according to the BSC, speciation occurs when populations evolve reproductive isolating mechanisms.
What is speciation? in Darwin s words, speciation is the multiplication of species. according to the BSC, speciation occurs when populations evolve reproductive isolating mechanisms. these barriers may act to prevent fertilization this is prezygotic isolation.
What is speciation? in Darwin s words, speciation is the multiplication of species. according to the BSC, speciation occurs when populations evolve reproductive isolating mechanisms. these barriers may act to prevent fertilization this is prezygotic isolation. may involve changes in location or timing of breeding, or courtship.
What is speciation? in Darwin s words, speciation is the multiplication of species. according to the BSC, speciation occurs when populations evolve reproductive isolating mechanisms. these barriers may act to prevent fertilization this is prezygotic isolation. may involve changes in location or timing of breeding, or courtship. barriers also occur if hybrids are inviable or sterile this is postzygotic isolation.
Modes of Speciation
Modes of Speciation 1. Allopatric speciation 2. Peripatric speciation 3. Parapatric speciation 4. Sympatric speciation
Modes of Speciation 1. Allopatric speciation 2. Peripatric speciation 3. Parapatric speciation 4. Sympatric speciation Ecological v.s. Mutation-order
1. Allopatric speciation Modes of Speciation
Allopatric Speciation The phenomenon of disjunction, or complete geographic isolation, is of considerable interest because it is almost universally believed to be a fundamental requirement for speciation. Endler (1977)
Allopatric Speciation Large ground finch Small ground finch
1. Allopatric speciation Modes of Speciation Allopatric speciation is the outcome of isolation and divergence. Isolation is created by reductions in gene flow. Divergence is created when mutation, genetic drift, and selection act on populations separately.
1. Allopatric speciation Modes of Speciation Allopatric speciation is the outcome of isolation and divergence. Isolation is created by reductions in gene flow. Divergence is created when mutation, genetic drift, and selection act on populations separately. Isolation may be caused by dispersal or vicariance.
Geographic isolation can rise from dispersal or vicariance
1. Allopatric speciation Modes of Speciation reproductive isolation occurs in complete geographic isolation (no gene flow). Example: Hawaiian Drosophila
Hawaiian Drosophila
Speciation by island-hopping
2. Peripatric speciation Modes of Speciation
3. Parapatric speciation Modes of Speciation
3. Parapatric speciation Modes of Speciation reproductive isolation occurs without complete geographic isolation (some gene flow).
3. Parapatric speciation Modes of Speciation reproductive isolation occurs without complete geographic isolation (some gene flow). Example: ring species of salamanders (Ensatina) in CA
Ensatina salamanders
Ring species evidence for parapatric speciation
Ring species evidence for parapatric speciation
4. Sympatric speciation Modes of Speciation
4. Sympatric speciation Modes of Speciation reproductive isolation evolves with complete geographic overlap.
Diploid parent (Two copies of each chromosome) Meiosis Tetraploid parent (Four copies of each chromosome) Mating Haploid gametes (One copy of each chromosome) Diploid gametes (Two copies of each chromosome) Meiosis Triploid zygote (Three copies of each chromosome) When these gametes combine, most offspring have incorrect number of chromosomes.
Soapberry bug Beak length correlates with fruit size. Flat-podded golden rain tree (non-native species) Balloon vine (native species) 12 8 Short-beaked population growing on non-native plants Long-beaked population growing on native plants Frequency 4 0 8 4 0 2 3 6 7 8 9 10 11 12 Non-native plant (small fruit) Beak length (mm) Native plant (large fruit) 2 3 6 7 8 9 10 11 12 Fruit radius (mm)
What evolutionary processes are involved in speciation?
What evolutionary processes are involved in speciation? 1. Natural selection
What evolutionary processes are involved in speciation? 1. Natural selection driven by different abiotic conditions (e.g., temperature, altitude) and biotic conditions (e.g., competitors, parasites).
What evolutionary processes are involved in speciation? 1. Natural selection driven by different abiotic conditions (e.g., temperature, altitude) and biotic conditions (e.g., competitors, parasites). 2. Sexual selection
What evolutionary processes are involved in speciation? 1. Natural selection driven by different abiotic conditions (e.g., temperature, altitude) and biotic conditions (e.g., competitors, parasites). 2. Sexual selection both female choice and male-male competition can promote rapid divergence (e.g., Hawaiian Drosophila).
What evolutionary processes are involved in speciation? 1. Natural selection driven by different abiotic conditions (e.g., temperature, altitude) and biotic conditions (e.g., competitors, parasites). 2. Sexual selection both female choice and male-male competition can promote rapid divergence (e.g., Hawaiian Drosophila). antagonistic sexual selection too!
Male-male competition in Hawaiian Drosophila
What evolutionary processes are involved in speciation? 3. Random genetic drift
What evolutionary processes are involved in speciation? 3. Random genetic drift may involve founder effects and genetic bottlenecks.
What evolutionary processes are involved in speciation? 3. Random genetic drift may involve founder effects and genetic bottlenecks. alleles that are neutral in one environment may not be neutral in another!
Ecological speciation in sticklebacks
Ecological speciation in sticklebacks Dolph Schluter
Ecological speciation in sticklebacks
Ecological speciation in sticklebacks
Ecological speciation in sticklebacks 1. Colonization by marine stickleback ~10,000 years ago
Ecological speciation in sticklebacks 1. Colonization by marine stickleback ~10,000 years ago 2. Adaptation to freshwater environment
Ecological speciation in sticklebacks 1. Colonization by marine stickleback ~10,000 years ago 2. Adaptation to freshwater environment 3. Secondary invasion by marine stickleback
Ecological speciation in sticklebacks 3. Secondary invasion by marine stickleback
Ecological speciation in sticklebacks 3. Secondary invasion by marine stickleback 4. Evolution of limnetic and benthic sticklebacks
Evidence for secondary invasion hypothesis
Evidence for secondary invasion hypothesis 1. Only low elevation lakes possess limnetic and benthic species pairs.
Evidence for secondary invasion hypothesis 1. Only low elevation lakes possess limnetic and benthic species pairs. 2. Cores from lakes with limnetic and benthic species pairs show evidence of salt water influx (e.g, clams, etc.).
Evidence for secondary invasion hypothesis 1. Only low elevation lakes possess limnetic and benthic species pairs. 2. Cores from lakes with limnetic and benthic species pairs show evidence of salt water influx (e.g, clams etc.). 3. Higher elevation lakes have neither limnetic and benthic species pairs nor evidence of salt water influx.
What types of genes are involved in speciation?
Sensory drive in Victoria Cichlids Ole Seehausen
Some generalities 1. The magnitude of prezygotic and postzygotic isolation both increase with the time.
Some generalities 1. The magnitude of prezygotic and postzygotic isolation both increase with the divergence time. in Drosophila, it takes about 1.5 to 3 million years for complete isolation to evolve.
Some generalities 1. The magnitude of prezygotic and postzygotic isolation both increase with the time. in Drosophila, it takes about 1.5 to 3 million years for complete isolation to evolve. in marine bivalves, it may take 4 to 6 million years!
Some generalities 1. The magnitude of prezygotic and postzygotic isolation both increase with the time. in Drosophila, it takes about 1.5 to 3 million years for complete isolation to evolve. in marine bivalves, it may take 4 to 6 million years! 2. Among recently separated groups, prezygotic isolation is generally stronger than postzygotic isolation.
Some generalities 3. In the early stages of speciation, hybrid sterility or inviability is almost always seen in the heterogametic sex.
Some generalities 3. In the early stages of speciation, hybrid sterility or inviability is almost always seen in the heterogametic sex. for example, D. simulans and D. mauritiana female hybrids are completely viable yet male hybrids are completely sterile!
Some generalities 3. In the early stages of speciation, hybrid sterility or inviability is almost always seen in the heterogametic sex. for example, D. simulans and D. mauritiana female hybrids are completely viable yet male hybrids are completely sterile! this is called Haldane s rule. J.B.S. Haldane (1892-1964)
What causes postzygotic isolation?
What causes postzygotic isolation? the underlying mechanism is called Dobzhansky- Muller incompatibility:
What causes postzygotic isolation? the underlying mechanism is called Dobzhansky- Muller incompatibility: Ancestral Pop: A 1 A 1 B 1 B 1
What causes postzygotic isolation? the underlying mechanism is called Dobzhansky- Muller incompatibility: Ancestral Pop: A 1 A 1 B 1 B 1 Derived Pops: A 2 A 2 B 1 B 1 A 1 A 1 B 2 B 2
What causes postzygotic isolation? the underlying mechanism is called Dobzhansky- Muller incompatibility: Ancestral Pop: A 1 A 1 B 1 B 1 Derived Pops: A 2 A 2 B 1 B 1 A 1 A 1 B 2 B 2 Hybrids: A 1 A 2 B 1 B 2 fitness
Differences between plant and animal speciation
Differences between plant and animal speciation in plants, polyploidization is a major mode of speciation.
Differences between plant and animal speciation in plants, polyploidization is a major mode of speciation. polyploidization refers to the retention of extra sets of chromosomes (i.e., tetraploids, octoploids, etc.)
Differences between plant and animal speciation in plants, polyploidization is a major mode of speciation. polyploidization refers to the retention of extra sets of chromosomes (i.e., tetraploids, octoploids, etc.) there are two types of polyploids: autopolyploids and allopolyploids.
Differences between plant and animal speciation autopolyploids add chromosomal sets from the same species:
Differences between plant and animal speciation autopolyploids add chromosomal sets from the same species: Species 1 x Species 1 Species 2 (2N = 4) (2N = 4) (4N = 8)
Differences between plant and animal speciation autopolyploids add chromosomal sets from the same species: Species 1 x Species 1 Species 2 (2N = 4) (2N = 4) (4N = 8) allopolyploids combine chromosomal sets from different species:
Differences between plant and animal speciation autopolyploids add chromosomal sets from the same species: Species 1 x Species 1 Species 2 (2N = 4) (2N = 4) (4N = 8) allopolyploids combine chromosomal sets from different species: Species 1 x Species 2 Species 3 (2N = 4) (2N = 6) (2N = 10)
Secondary contact and reinforcement
Secondary contact and reinforcement secondary contact occurs when two formerly allopatric populations meet.
Secondary contact and reinforcement secondary contact occurs when two formerly allopatric populations meet. Three outcomes are possible:
Secondary contact and reinforcement secondary contact occurs when two formerly allopatric populations meet. Three outcomes are possible: 1. No interbreeding occurs
Secondary contact and reinforcement secondary contact occurs when two formerly allopatric populations meet. Three outcomes are possible: 1. No interbreeding occurs isolating mechanisms in place speciation completed.
Secondary contact and reinforcement secondary contact occurs when two formerly allopatric populations meet. Three outcomes are possible: 1. No interbreeding occurs isolating mechanisms in place speciation completed. 2. Introgression
Secondary contact and reinforcement secondary contact occurs when two formerly allopatric populations meet. Three outcomes are possible: 1. No interbreeding occurs isolating mechanisms in place speciation completed. 2. Introgression no isolating mechanisms in place populations merge completely.
Secondary contact and reinforcement 3. Partial interbreeding occurs
Secondary contact and reinforcement 3. Partial interbreeding occurs some isolating mechanisms in place a hybrid zone forms (but hybrids are less fit).
Secondary contact and reinforcement 3. Partial interbreeding occurs some isolating mechanisms in place a hybrid zone forms (but hybrids are less fit). reinforcement should occur to complete the process by the evolution of additional prezygotic barriers.
Evidence for reinforcement in Drosophila
Evidence for reinforcement in Drosophila Coyne & Orr (1997) compared sister species of Drosophila that were either allopatric or sympatric.
Evidence for reinforcement in Drosophila Coyne & Orr (1997) compared sister species of Drosophila that were either allopatric or sympatric. For each species pair they estimated:
Evidence for reinforcement in Drosophila Coyne & Orr (1997) compared sister species of Drosophila that were either allopatric or sympatric. For each species pair they estimated: 1. The degree of premating isolation from mate choice experiments.
Evidence for reinforcement in Drosophila Coyne & Orr (1997) compared sister species of Drosophila that were either allopatric or sympatric. For each species pair they estimated: 1. The degree of premating isolation from mate choice experiments. 2. The degree of genetic divergence using allozymes.
Evidence for reinforcement in Drosophila