Transcript Slide 1
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. Species and Speciation I. Species Concepts II. Recognizing Species III. Making Species - Reproductive Isolation Species and Speciation I. Species Concepts II. Recognizing Species III. Making Species - Reproductive Isolation A. Pre-Zygotic Barriers 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) 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 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 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 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 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 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 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 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 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 Species and Speciation I. Species Concepts II. Recognizing Species III. Making Species - Reproductive Isolation IV. Speciation Speciation Speciation is not a goal, or a selective product of adaptation. It is simply a consequence of genetic changes that occurred for other reasons (selection, drift, mutation, etc.). Speciation I. Modes: Speciation I. Modes: A. Allopatric: Divergence in geographically separate populations - Vicariance - range divided by new geographic feature A B C Speciation I. Modes: A. Allopatric: Divergence in geographically separate populations - Vicariance - range divided by new geographic feature - Peripatric - divergence of a small migrant population A B Speciation I. Modes: A. Allopatric: Divergence in geographically separate populations - Vicariance - range divided by new geographic feature - Peripatric - divergence of a small migrant population B. Parapatric - neighboring populations diverge, even with gene flow Speciation I. Modes: A. Allopatric: Divergence in geographically separate populations - Vicariance - range divided by new geographic feature - Peripatric - divergence of a small migrant population B. Parapatric - neighboring populations diverge, even with gene flow B. Parapatric - neighboring populations diverge, even with gene flow Hybrid Backcross?? Hybrid Speciation I. Modes: A. Allopatric: Divergence in geographically separate populations - Vicariance - range divided by new geographic feature - Peripatric - divergence of a small migrant population B. Parapatric - neighboring populations diverge, even with gene flow C. Sympatric: Divergence within a single population C. Sympatric: Divergence within a single population Maynard Smith (1966) - hypothesized this was possible if there was disruptive selection within a population - perhaps as a specialist herbivore/parasite colonized and adapted to a new host. C. Sympatric: Divergence within a single population Maynard Smith (1966) - hypothesized this was possible if there was disruptive selection within a population - perhaps as a specialist herbivore/parasite colonized and adapted to a new host. Example: Hawthorn/Apple Maggot Fly (Rhagoletis pomonella) Hawthorn maggot fly is a native species that breeds on Hawthorn (Crataegus sp.) C. Sympatric: Divergence within a single population Maynard Smith (1966) - hypothesized this was possible if there was disruptive selection within a population - perhaps as a specialist herbivore/parasite colonized and adapted to a new host. Example: Hawthorn/Apple Maggot Fly (Rhagoletis pomonella) Europeans brought apples to North America. They are in the same plant family (Rosaceae) as Hawthorn. C. Sympatric: Divergence within a single population Maynard Smith (1966) - hypothesized this was possible if there was disruptive selection within a population - perhaps as a specialist herbivore/parasite colonized and adapted to a new host. Example: Hawthorn/Apple Maggot Fly (Rhagoletis pomonella) Europeans brought apples to North America. They are in the same plant family (Rosaceae) as Hawthorn. In 1864, apple growers noticed infestation by Apple Maggot flies...which were actually just "hawthorn flies"... C. Sympatric: Divergence within a single population Maynard Smith (1966) - hypothesized this was possible if there was disruptive selection within a population - perhaps as a specialist herbivore/parasite colonized and adapted to a new host. Example: Hawthorn/Apple Maggot Fly (Rhagoletis pomonella) races breed on their own host plant, and have adapted to the different seasons of fruit ripening. Only a 4-6% hybridization rate. Temporal, not geographic, isolation. C. Sympatric: Divergence within a single population But can a generalist speciate sympatrically? Tauber and Tauber. 1977a and 1977b. Science. Two species of green lacewings - generalist insect predators Chrysopa downesi has one generation in early spring C. carnea breeds has three generations in summer C. Sympatric: Divergence within a single population But can a generalist speciate sympatrically? Tauber and Tauber. 1977a and 1977b. Science. Two species of green lacewings - generalist insect predators Chrysopa downesi has one generation in early spring, then diapause C. carnea breeds has three generations in summer, no diapause The differences are due to responses to photoperiod C. downesi stops reproducing and goes into diapause under long day length (summer), whereas C. carnea reproduces under long day length. C. Sympatric: Divergence within a single population But can a generalist speciate sympatrically? Tauber and Tauber. 1977a. Science 197:592. The species are completely interfertile in the lab: Did reciprocal matings: C. downesi x C. carea Reared F1 offspring under long day length (16L:8D). Found all F1 did not enter diapause (C. carnea photoperiod response is dominant). C. Sympatric: Divergence within a single population But can a generalist speciate sympatrically? Tauber and Tauber. 1977a. Science 197:592. Did F1 x F1 cross: Found 7% (~1/16) of F2 exhibited diapause at 16L:8D. This is consistent with a model of 2 independently assorting autosomal genes with complete dominance at each and an interactive effect. AABB x aabb F1 all A-B- phenotype F2 A-B- = 9/16 A-bb = 3/16 C. carnea photoperiod aaB- = 3/16 aabb = 1/16.... ~ 7% C. downesi photoperiod C. Sympatric: Divergence within a single population But can a generalist speciate sympatrically? Tauber and Tauber. 1977a. Science 197:592. F1 x C. downesi backcross had 3:1 ratio, as expected of model. AaBb x aabb AaBb = .25 Aabb = .25 C. carnea photoperiod aaBb = .25 aabb = .25 C. downesi photoperiod C. Sympatric: Divergence within a single population But can a generalist speciate sympatrically? Tauber and Tauber. 1977b. Science 197:1298. How did this temporal separation get established? C. downesi is dark green and prefers hemlock forests C. carnea is light green and prefers fields and meadows Difference governed by a single locus where dark is incompletely dominant. C. Sympatric: Divergence within a single population But can a generalist speciate sympatrically? Tauber and Tauber. 1977b. Science 197:1298. How did this temporal separation get established? C. downesi is dark green and prefers hemlock forests C. carnea is light green and prefers fields and meadows Difference governed by a single locus where dark is incompletely dominant. Hypothesize that selection for different morphs in different habitats created the stable dimorphism, reinforced by inbreeding within the habitats. intermediate heterozygote C. Sympatric: Divergence within a single population But can a generalist speciate sympatrically? Tauber and Tauber. 1977b. Science 197:1298. How did this temporal separation get established? C. downesi is dark green and prefers hemlock forests C. carnea is light green and prefers fields and meadows Difference governed by a single locus where dark is incompletely dominant. Hypothesize that selection for different morphs in different habitats created the stable dimorphism, reinforced by inbreeding within the habitats. Selection then favored early breeding in C. downesi, as that is when insects feeding on conifers are most abundant. Speciation I. Modes II. Mechanisms Speciation I. Modes II. Mechanisms A. Progressive Genomic Incompatibility Tilley et al. 1990. PNAS. Desmognathus ochrophaeus in western NC 1. correlation between geographic distance and genetic distance Tilley et al. 1990. PNAS. Desmognathus ochrophaeus in western NC 2. Placed sympatric and allopatric males and females (reciprocal mating design) together for an evening and examined the cloaca of female in the morning for presence of sperm packet. Calculated "Coefficient of Isolation": (sum of % of sympatric matings) - (sum of % of allopatric matings) 2 = total isolation by sexual selection 0 = no differentiation by sexual selection Speciation I. Modes II. Mechanisms A. Progressive Genomic Incompatibility B. Hybrid Incompatibility - Dobzhansky and Müller (1930's) Pairs of genes that work together diverge in different populations Speciation I. Modes II. Mechanisms A. Progressive Genomic Incompatibility B. Hybrid Incompatibility - Dobzhansky and Müller (1930's) Pairs of genes that work together diverge in different populations A1A1B2B2 works A1A1B1B1 lethal A1 A2A2B2B2 works B1 A2A2B1B1 works B. Hybrid Incompatibility D. melanogaster and D. simulans B. Hybrid Incompatibility D. melanogaster and D. simulans Cross female D. mel. x male D. sim - no sons B. Hybrid Incompatibility D. melanogaster and D. simulans Cross female D. mel. x male D. sim - no sons - Watanabe - 1970 - isolated a mutant strain of D. simulans (w) that could make males with D. melanogaster.... B. Hybrid Incompatibility D. melanogaster and D. simulans Cross female D. mel. x male D. sim - no sons - Watanabe - 1970 - isolated a mutant strain of D. simulans (w) that could make males with D. melanogaster.... - Hypothesized that this strain had a mutant gene partner that reestablished function with the D. melanogaster partner gene... called it "lethal hybrid rescue" (lhr). B. Hybrid Incompatibility D. melanogaster and D. simulans Cross female D. mel. x male D. sim - no sons - Watanabe - 1970 - isolated a mutant strain of D. simulans (w) that could make males with D. melanogaster.... - Hypothesized that this strain had a mutant gene partner that reestablished function with the D. melanogaster partner gene... called it "lethal hybrid rescue" (lhr). - Ashburner - 1980 - isolated a mutant strain of D. melanogaster (a) females that could breed with D. simulans males and produce sons ...called it "hybrid male rescue" - hmr - X-linked B. Hybrid Incompatibility D. melanogaster and D. simulans SYSTEM: (s-lhr dominant) Ancestor: lhr, mhr Male D. simulans: s-lhr, mhr Female D. melanogaster: lhr, m-mhr(X) s-lhr/lhr, m-mhr(X) = INVIABLE SONS B. Hybrid Incompatibility D. melanogaster and D. simulans SYSTEM: (s-lhr dominant) D. sim = s-lhr, hmr (X) x D. mel = lhr, m-hmr (X) SONS GET : s-lhr/lhr, m-hmr/Y (only X) .... INVIABLE B. Hybrid Incompatibility D. melanogaster and D. simulans SYSTEM: D. sim = s-lhr, hmr (X) x D. mel = lhr, m-hmr (X) SONS GET : s-lhr/lhr, m-hmr (only X) .... INVIABLE (w)D. sim = lhr/s-lhr, hmr (X) x D. mel = lhr, m-hmr (X) 1/2 SONS GET lhr/lhr, m-hmr (ONLY X) = VIABLE B. Hybrid Incompatibility D. melanogaster and D. simulans SYSTEM: D. sim = s-lhr, hmr (X) x D. mel = lhr, m-hmr (X) SONS GET : s-lhr/lhr, m-hmr (only X) .... INVIABLE (w)D. sim = lhr/s-lhr, hmr (X) x D. mel = lhr, m-hmr (X) 1/2 SONS GET lhr/lhr, m-hmr (ONLY X) = VIABLE D. sim = s-lhr, hmr (X) x (a) D. mel = lhr, m-hmr(X)/hmr (X) 1/2 SONS GET: s-lhr/lhr, hmr (only X) = VIABLE B. Hybrid Incompatibility D. melanogaster and D. simulans SYSTEM: (s-lhr dominant) Ancestor: lhr, mhr D. simulans: s-lhr, mhr D. melanogaster: lhr, m-mhr s-lhr, m-mhr = INVIABLE B. Hybrid Incompatibility D. melanogaster and D. simulans Brideau et al. 2006. Science 314: 1292-1295 - isolated location of lhr gene. - put NORMAL D. simulans gene into D. melanogaster. - mated these D. melanogaster with Watanabe's mutant strain of D. simulans. - IF these two genes are partners, then 3/4 hybrids should die. (w) D. sim = lhr/s-lhr, hmr (X) x (b)D. mel = s-lhr/lhr, m-hmr (X) (doesn't die....) 1/4 SONS GET : lhr/lhr, m-hmr (only X) .... VIABLE 3/4 get some other combination including s-lhr and m-hmr.. INVIABLE Speciation I. Modes II. Mechanisms A. Progressive Genomic Incompatibility B. Hybrid Incompatibility C. Differential Selection C. Differential Selection - Assumed to be primary, but few studies documenting that reproductive isolation of phenotypes correlates with fitness differential in different environments. Rundle et al. (2000). Science 287:306. C. Differential Selection - Assumed to be primary, but few studies documenting that reproductive isolation of phenotypes correlates with fitness differential in different environments. Rundle et al. (2000). Science 287:306. Sticklebacks colonizing lakes...PHYLOGENY: limnetic benthic limnetic benthic limnetic benthic C. Differential Selection - Assumed to be primary, but few studies documenting that reproductive isolation of phenotypes correlates with fitness differential in different environments. Rundle et al. (2000). Science 287:306. Mate selection correlates with ecotype, not with genetic relatedness.... example of parallel evolution, too. Speciation I. Modes II. Mechanisms A. Progressive Genomic Incompatibility B. Hybrid Incompatibility C. Differential Selection D. Hybridization D. Hybridization - When hybridization occurs, it show increase gene flow between populations. How are hybrids stabilized as a reproductively isolated group? - adaptation to an extreme habitat Gompert et al. 2006. Science 314: 1923. - adaptation to an extreme habitat Gompert et al. 2006. Science 314: 1923. Two species of small western butterflies have overlapping ranges. - adaptation to an extreme habitat Gompert et al. 2006. Science 314: 1923. Two cluster Three cluster Probabilities of assigning individuals from these populations to a particular dendrogram "cluster" - adaptation to an extreme habitat Gompert et al. 2006. Science 314: 1923. Two cluster Three cluster Probabilities of assigning individuals from these populations to a particular dendrogram "cluster" Are the alpine populations simply in hybrid zone, or are they reproductively isolated? - adaptation to an extreme habitat Gompert et al. 2006. Science 314: 1923. Two cluster Three cluster Probabilities of assigning individuals from these populations to a particular dendrogram "cluster" Are the alpine populations simply in hybrid zone, or are they reproductively isolated? They are fixed for several alleles, suggesting no gene flow. - adaptation to an extreme habitat Gompert et al. 2006. Science 314: 1923. Two cluster Three cluster Probabilities of assigning individuals from these populations to a particular dendrogram "cluster" Are the alpine populations simply in hybrid zone, or are they reproductively isolated? They are fixed for several alleles, suggesting no gene flow. - Also used coalescence to estimate time since a common ancestor within each 'species". The alpine populations had a more recent history (400,000 yrs) than either of the others (1.2-1.9 my) - adaptation to an extreme habitat Gompert et al. 2006. Science 314: 1923. - What maintains this genetic uniqueness? - adaptation to an extreme habitat Gompert et al. 2006. Science 314: 1923. - What maintains this genetic uniqueness? Fidelity to Host Plant - adaptation to an extreme habitat Gompert et al. 2006. Science 314: 1923. - What maintains this genetic uniqueness? Fidelity to Host Plant Also, their eggs don't stick to the leaf; they drop off into litter. This may be adaptive, as winds blow leaves a long way from original plant at high elevations. The host plant is a perennial, so dropping into the leaf litter keeps it close to host plant. Other species, even if they used the plant, would have eggs dispersed from the host plant. That's bad for butterflies, 'cuz caterpillars don't disperse too far... D. Hybridization - When hybridization occurs, it show increase gene flow between populations. How are hybrids stabilized as a reproductively isolated group? - adaptation to extreme habitat - sexual selection - sexual selection Mavarez et al. 2006. Nature 441:868 X BACKCROSS BACKCROSS Offspring of H. heurippa x backcross B and Br loci are linked, so no recombinant types (white). Offspring of backcross x wild H. heurippa. Mating probabilities in no-choice experiments: strong Positive Assortative Mating female Male H. mel H. heur H. cyn H. mel 1.00 0.07 0.18 H. heur 0.10 1.00 0.44 H. cyn 0.12 0.02 1.00 Mate Pairing in Tetrads: strong Positive Assortative Mating Speciation I. Modes II. Mechanisms A. Progressive Genomic Incompatibility B. Hybrid Incompatibility C. Differential Selection D. Hybridization Several ways that new gene combinations can form and become stabilized.