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Similaire à Bio413 07 sympatric_speciation_species concepts_allopatric_speciation_winter2012_posted
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Bio413 07 sympatric_speciation_species concepts_allopatric_speciation_winter2012_posted
- 1. Heliconius butterflies Real Example: Reproductive isolation + Sexual Selection + Natural Selection = sympatric species • live in various habitats in South America • Müllerian mimics to other Heliconius species in or close to their range, all are unpalatable (taste bad to predators)
- 2. Heliconius butterflies Real Example: Reproductive isolation + Sexual Selection + Natural Selection = sympatric species • live in various habitats in South America • Müllerian mimics to other Heliconius species, all unpalatable (taste bad to predators) • (incomplete) pre-zygotic isolation by habitat isolation H. cydno: live in forest understory H. melpomene: live in disturbed re-growth forest Species overlap in intermediate habitats and found flying together: rare hybrids found in wild
- 3. 1) Why aren’t hybrids more common? 2) How do overlapping (sympatric) species remain distinct species? Real Example: Reproductive isolation + Sexual Selection + Natural Selection
- 4. Experiment Real Example: Reproductive isolation + Sexual Selection + Natural Selection • Mating confirmed by identifying male spermatophore in female via dissection • Mate choice (and sexual selection pressure) is by MALES (male choice) & based on female color pattern • A male mates with a newly hatched female before her first flight • Males and females exposed to each other in no-choice trials (1 hr)
- 5. Real Example: Reproductive isolation + Sexual Selection + Natural Selection Results: Assortative mating in both species and their hybrid Males prefer to mate with females of their “type”
- 6. Results: Sexual Selection against hybrids because they don’t have attractive traits (in this case color pattern) Real Example: Reproductive isolation + Sexual Selection + Natural Selection Hybrids females are mated with 50% less often by males of either “parent” species
- 7. Results: Natural Selection: hybrids eaten by Jacamar birds (and other predators) more than parent species are. Real Example: Reproductive isolation + Sexual Selection + Natural Selection Hybrids aren’t protected from predators by Müllerian mimicry, thus more eaten by predators (N.S) =
- 8. Results: Natural Selection: hybrids eaten by Jacamar birds (and other predators) more than parent species are. Real Example: Reproductive isolation + Sexual Selection + Natural Selection Hybrids are eaten more by predators. The parent species are favored by N.S.: Disruptive selection
- 9. Darwin & The Modern Synthesis (Natural Selection, Heredity & Genetics) • Speciation was introduced by Darwin, in On the Origin of Species by Natural Selection (1859) • Darwin didn’t discuss allopatric speciation or genetic drift • The Modern Synthesis focused on geographical isolation and genetic drift (isolation + time ) Allopatric speciation =
- 10. Darwin & The Modern Synthesis (Natural Selection, Heredity & Genetics) •Allopatric speciation: evolution of reproductive isolation and divergence between populations that are geographically separate
- 11. Allopatric speciation: - requires geographic separation. - Most documented kind of speciation In this model, speciation results from differences in mating preference that arise from 2 possible sources: (1) genetic drift: Allopatric Speciation http://evolution.berkeley.edu/evosite/evo101/IIIDGeneticdrift.shtml
- 12. Allopatric speciation: - requires geographic separation. - Most documented kind of speciation In this model, speciation results from differences in mating preference that arise from 2 possible sources: (1) genetic drift: Change in allele frequencies due to chance. (2) disruptive selection: Natural Selection and/or Sexual Selection that favors more extreme phenotypes over the original average phenotype Allopatric Speciation
- 13. Allopatric speciation: - requires geographic separation. - Most documented kind of speciation Secondary contact: occurs after evolving in isolation, two populations come back into contact with each other •If the divergence is recent, these two species (or populations) may hybridize producing fertile offspring •If the divergence is substantial, the two species may hybridize producing unfertile offspring or may not hybridize at all Allopatric Speciation
- 14. Allopatric speciation: - requires geographic separation, Geographic separation of one population into two occurs by: (A) vicariance –separation of a population by geological forces Allopatric Speciation
- 15. Allopatric Speciation Allopatric speciation: - requires geographic separation, Geographic separation of one population into two occurs by: (A) vicariance –separation of a population by geological forces Examples: - a new river, glacier, or mountain range forms - a land bridge forms or is submerged - plate tectonics and continent movements
- 16. Allopatric speciation: - requires geographic separation, which causes reproductive isolation. Geographic separation of one population into two occurs by: (B) dispersal - colonization of a new habitat by founders Examples: - islands - postglacial lakes (Canada), rift lakes (Africa) Allopatric Speciation
- 17. Initially, there is migration between 2 nearby populations of a forest-dwelling animal with two alleles controlling color Allopatric speciation : Vicariance + Genetic drift because of gene flow, the allele frequencies will be the same in the two populations
- 18. Over time, a barrier to migration arises between populations: mountain range The allele frequencies in each population will start to change due to genetic drift (Step 1: gene flow has been interrupted) Allopatric speciation : Vicariance + Genetic drift
- 19. The populations will slowly diverge as different alleles become fixed at many loci throughout the genome (Step 2: populations differentiate) mountain range Different alleles may eventually fix in the 2 populations Allopatric speciation : Vicariance + Genetic drift
- 20. (Step 3: the populations become reproductively isolated) mountain range Differences accumulate BY CHANCE in alleles controlling mate preference: mating signals, genital shapes, etc. Allopatric speciation : Vicariance + Genetic drift
- 21. ... but because of assortative mating, the two types do not interbreed have formed sister species that will now evolve separately If the mountain range disappears, the two populations can mix = Secondary Contact. (Step 4: speciation has occurred) Allopatric speciation : Vicariance + Genetic drift
- 22. Consider a species found in a desert and a neighboring forest Hot, dry desert Cool, rainy forest Allopatric speciation : Vicariance + Disruptive Selection
- 23. Selection will favor different alleles in the desert and forest Hot, dry desert Cool, rainy forest Natural selection will favor forest-adapted individuals Natural selection will favor desert-adapted individuals Allopatric speciation : Vicariance + Disruptive Selection
- 24. After selection, the two populations will be genetically different Hot, dry desert Cool, rainy forest forest-adapted individuals have survived here desert-adapted individuals have survived here Allopatric speciation : Vicariance + Disruptive Selection
- 25. However, migration will keep mixing alleles between the populations Hot, dry desert Cool, rainy forest Allopatric speciation : Vicariance + Disruptive Selection Maybe some evolution, but NO SPECIATION unless there is reproductive isolation
- 26. Now: a barrier to gene flow arises between the 2 habitats Hot, dry desert Cool, rainy forest mountains Allopatric speciation : Vicariance + Disruptive Selection
- 27. Now: a barrier to gene flow arises between the 2 habitats Hot, dry desert Cool, rainy forest Natural selection will favor forest-adapted individuals Natural selection will favor desert-adapted individuals mountains Allopatric speciation : Vicariance + Disruptive Selection
- 28. Each population evolves into a distinct, well-adapted species Hot, dry desert Cool, rainy forest Forest-adapted population Desert-adapted population mountains Species #1 Species #2 Allopatric speciation : Vicariance + Disruptive Selection No migration
- 29. Hawaiian Drosophila Allopatric speciation : Dispersal & founders
- 31. Speciation and the Isthmus of Panama RESULTS of mating experiments: (1) Sister-species shrimp snapped at each other instead of mating! This is pre-zygotic reproductive isolation (sexual isolation): mating signals not understood by potential mates (2) when a male of one species was held with a female of its sister species [from the other side of Panama] for a month, no offspring were produced except for one single pair This is either pre-zygotic isolation (gamete isolation) or post-zygotic reproductive isolation: zygote does not develop. For snapping shrimp: 3.5 million years is enough time for complete reproductive isolation to occur Allopatric speciation: Vicariance
- 32. Caribbean and Pacific oceans were linked until the Isthmus of Panama formed ~3.5 million years ago Prevented any more gene flow between marine organisms on each side of the new land barrier Did this result in the evolution of new sister species pairs separated by the Isthmus? Speciation and the Isthmus of Panama Google maps Allopatric speciation : Vicariance
- 33. Speciation and the Isthmus of Panama Knowlton et al. studied pairs of snapping shrimps that were morphologically similar, where one member of the pair was found on the Caribbean side and the other on the Pacific side Knowlton & Weight 1998 Alphaeus cylindricus The sister species still closely resembled each other – were they different species? Sequenced part of a gene and also compared allele frequencies Finally, did mating crosses to assess reproductive compatibility would shrimp mate or fight with their sister species? Allopatric speciation : Vicariance
- 34. Knowlton & Weigt 1998 • based on DNA sequences, the members of each pair were indeed each other’s closest relatives - That is, each sister-group pair were were descendants of a common ancestor Allopatric speciation: Vicariance
- 35. What is a species? • Species are the fundamental units of biodiversity • Note: one species, two species http://carabidae.pro/carabidae/elaphrinae.html Elaphrus beetles
- 36. Importance of recognizing species • Survival depends on our ability to recognize species What is a species?
- 37. Universality of recognizing species
- 38. What is a species?Time Amount of divergence (morphology)
- 39. What is a species? • Races • Varieties • “kinds” • Incipient species • Ecotypes • Morphs • Subspecies • Cultivars (Artificial Selection) • Breeds (Artificial Selection)
- 40. Time Amount of divergence What is a species?
- 41. What is a species?
- 42. What is a species? 1) speciation by cladogenesis 2) speciation by anagenesis between a & b a b
- 45. Anagenesis + Cladogenesis A B C D E A B C D Most of the time we don’t know the ancestral states for sure
- 46. What is a species? • Biologists do not agree on ONE way to define a species – thus, “species concepts” Why?
- 47. At least 22 different definitions have been proposed to explain what a “species” is. Three main ones: 1. Morphological 2. Biological 3. Phylogenetic Species concepts
- 48. Morphological species concept : Two organisms that display “substantial” and consistent morphological differences are different species • Advantages: Easy to apply, can be used with fossil species – Disadvantages: It is not testable, the definition of “substantial” is subjective. Problems with convergence, cryptic species, hybridization (= gene flow) & intermediate phenotype
- 49. Morphological species concept : Chronospecies: a morphology that can be identified as a stage in an evolving lineage (anagenesis) Note increasing number of pleura (or “ribs”) on trilobites
- 50. Biological species concept : a group of actually or potentially inter- breeding individuals • Advantages: testable in many cases, objective • Disadvantages: difficult to apply and test (impractical), cannot be used with fossils, irrelevant to asexual populations
- 51. Fertile Hybrids: Violations of both the Morphological v. Biological species Concepts
- 52. Phylogenetic species concept : Lineages with different evolutionary histories are different species – these lineages must be the smallest units of evolution • Advantage: it is testable, objective and can be applied to living and fossil species – Disadvantage: it requires comprehensive phylogenetic analyses = need a cladogram!
- 53. Phylogenetic species concept : Lineages with different evolutionary histories are different species – these lineages must be the smallest units of evolution •Instead of depending on reproductive isolation, this concept revolves around fixed differences between populations •Species are the smallest population that you don’t have any reason to divide into even smaller clades or populations
- 55. Issues & Solutions Issue: How genetically different do species have to be? Solutions: - from a single DNA base change that only exists in one population, to many consistent genetic differences across genes, also consistent measurable phenotypic differences - Ideally, multiple fixed differences should be used - Need a well-supported cladogram. Phylogenetic Species Concept
- 56. High level of cryptic species diversity revealed by sympatric lineages of Southeast Asian forest frogs Bryan L Stuart, Robert F Inger, and Harold K Voris Biol Lett. 2006 September 22; 2(3): 470–474. Odorrana livida Cryptic species by the phylogenetic species concept cf. = similar to
- 57. High level of cryptic species diversity revealed by sympatric lineages of Southeast Asian forest frogs Bryan L Stuart, Robert F Inger, and Harold K Voris Biol Lett. 2006 September 22; 2(3): 470–474. Odorrana livida Cryptic species by the phylogenetic species concept Cryptic species: organisms that appear identical or almost identical to close relatives, but are genetically distinct- they are their own lineage Odorrana livida
- 58. High level of cryptic species diversity revealed by sympatric lineages of Southeast Asian forest frogs Bryan L Stuart, Robert F Inger, and Harold K Voris Biol Lett. 2006 September 22; 2(3): 470–474. Odorrana livida Cryptic species by the phylogenetic species concept cf. = similar to Odorrana livida
- 59. Rana chalconota cf. = similar to Cryptic species by the phylogenetic species concept
- 60. Cryptic species by the phylogenetic species concept Morphology + DNA Forest habitat Savanna habitat
- 61. Cryptic species by the phylogenetic species concept LoxodontiaafricanaElephas maximus
- 62. Cryptic species by the phylogenetic species concept + extinct organisms! 6 mya
- 63. Ring species by the phylogenetic & morphological & biological species concepts
- 65. Ring species by the phylogenetic & morphological & biological species concepts
- 66. How do you describe a species? 1. Compare it to all similar described species 2. Name it • Must be latinized & binominal 3. Designate a type • Designate a holotype • Designate paratypes (if possible) 4. Describe it 5. Provide a picture or illustration 6. Designate a type locality 7. Deposit it (the type or types) into a museum 8. Publish the description in a peer-reviewed journal
Notes de l'éditeur
- Seasonal/temporal isolation: timing of gamete release (sperm and eggs don’t meet)
- Seasonal/temporal isolation: timing of gamete release (sperm and eggs don’t meet)
- Seasonal/temporal isolation: timing of gamete release (sperm and eggs don’t meet)
- Seasonal/temporal isolation: timing of gamete release (sperm and eggs don’t meet)
- Seasonal/temporal isolation: timing of gamete release (sperm and eggs don’t meet)
- Seasonal/temporal isolation: timing of gamete release (sperm and eggs don’t meet)
- The model of allopatric speciation says nothing more is needed for 2 populations to evolve into separate species but geographical isolation + time - this remains the dominant view of how most speciation has taken place over earth’s history - notice: there is no requirement for natural selection to play a role in species formation Because drift is a random process, it may take a very long time for enough fixed differences to build up to prevent two populations from interbreeding - according to this model, species should only co-exist if they were 1st isolated from each other for a long time
- As these photos of Drosophila suzukii, D. macrothrix, and D. nigribasis (top to bottom) show, the Drosophila found in Hawaii are remarkably diverse in body size, wing coloration, and other traits.
- All human cultures recognize and name species. Because we eat other species of living organisms it is very important that we can properly recognize species with different characteristics and that we have names for them, so we can communicate about the characteristics of the different species.
- A wholphin or wolphin is a rare hybrid, born from a mating of bottlenose dolphin. Polar-Grizzly Bear Hybrid. An example of a sheep-goat chimera. A Cama is a hybrid between a camel and a llama. A jaglion, Jaguar-Lion Hybrid. Würdemann's Heron, a great blue heron white egret hybrid.
- The taxa labeled A-G on the tips of this phylogeny represent distinct species. Groups labeled G1, G2 etc. represent populations of the same species.
- In West Africa, elephants that live in forest habitats (left) have morphological characteristics that distinguish them from savanna-dwelling elephants (right) from west, central, and east Africa.
- This evolutionary tree indicates that forest-dwelling elephants are a distinct phylogenetic species.