Speciation

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Miskozi
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24272
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Speciation
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2010-06-20 14:17:15
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species evolution
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Questions covering Lecture 7: Speciation material from second year evolution course at UWO.
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  1. Where does microevolution occur?
    It occurs within populations and species.
  2. What does microevolution involve?
    It involves changes in gene frequencies, genetic drift, and phenotypic design for reproductive success. It occurs rapidly.
  3. Does macro or microevolution occur within populations and species?
    Microevolution
  4. What is a clade?
    A group of taxa or species that share features from a common ancestor
  5. Where does macroevolution occur?
    Occurs among species and clades.
  6. What does macroevolution involve?
    It involves speciation, extinction, and biogeography patterns. It occurs slowly.
  7. Macroevolution focuses on _______ while microevolution focuses on ________.
    Pattern; process
  8. Does macro or microevolution occur among species and clades?
    Macroevolution
  9. ____evolution we can watch happen before our eyes, but ______evolution must usually be inferred.
    Micro; macro
  10. How do micro and macro evolution influence each other?
    • Microevolution affects macroevolution by being the drive that creates new traits that ultimately affect speciation and extinction.
    • Macroevolution affects microevolution by constraining the direction that microevolution can go on (i.e. dolphins can’t suddenly evolve to live without an internal skeleton while forming an external skeleton).
  11. Speciation is a byproduct of _______ and ______.
    Selection; drift
  12. What are hybrid species?
    Populations of the same species that differ when distantly localized. May produce subspecies or races that meet and hybridize in a hybrid zone.
  13. What are sibling species? Name an example.
    Sibling species (aka: cryptic species) are species that resemble each other so closely that they cannot be distinguished by external morphology, but are reproductively isolated. D. melanogaster and D. simulans are nearly indistinguishable, but do not interbreed.
  14. What are the four species concepts?
    • Biological Species concept (BSC)
    • Phylogenetic Species Concept (PSC)
    • Ecological Species Concept (ESC)
    • Morphospecies Concept (MSC)
  15. What are some criteria we use to define a species?
    • Separation
    • Cohesion (both genetically and ecologically)
    • Monophyly
    • Distinguishability
  16. Define separation as a criteria of species.
    Morphological, behavioural, genetic; also includes mechanisms that produced separation 9geographic or behavioural).
  17. Define cohesion as a criteria of species.
    Population must be internally cohesive, both genetically (must interbreed) and ecologically (must actually or potentially occupy the same habitat at the same time). Ecological cohesion is necessary but not sufficient for genetic cohesion.
  18. Define monophyly as a criteria of species.
    The organisms and populations within a species must share a single most recent common ancestor.
  19. Define distinguishability as a criteria of species.
    • Three levels:
    • A diagnosable species trait
    • Phenetic cluster traits
    • Genetic cluster traits
  20. What is a diagnosable species trait?
    A level of distinguishability as a criteria of species that defines a trait that is fixed or distinct from other species.
  21. What is a phonetic cluster trait?
    A level of distinguishability as a criteria of species that defines a trait that is useful when several are considered together so that trait values for species forming a cluster will have different values and little or no overlap so that they may be distinguished.
  22. What is a genetic cluster trait?
    A level of distinguishability as a criteria of species that distinguishes morphologically identical species from one another with little or no overlap through the analysis of several different sequences of the genome.
  23. What is the most influential species concept?
    The Biological Species Concept (BSC).
  24. Define BSC.
    Species are groups of actually or potentially interbreeding natural populations that are reproductively isolated from other such groups (i.e. two individuals are of the same species if they can produce viable offspring with the opposite sex).
  25. Sexual reproduction promotes _________ within a species by genetic recombination, preventing strong genetic divergence.
    Uniformity
  26. If two groups do not interbreed, it allows natural selection and genetic drift to create further _____ ______ between groups.
    Genetic diversity
  27. What is sympatry?
    Two groups of organisms are exactly in the same habitat but refuse to interbreed.
  28. What are the types of reproductive isolating mechanisms?
    • Prezygotic
    • Postzygotic
  29. What is a prezygotic reproductive isolating mechanism?
    • Prevents formation of the zygote
    • Temporal habitat (i.e. mating at different times of year or day)
    • Behavioural (i.e. have different mating behaviours and strategies)
    • Mechanical (i.e. have incompatible reproductive organs between sexes)
  30. What is a postzygotic reproductive isolating mechanism?
    Acts after zygote formation. Hybrids produced but have low fitness.
  31. What are some postzygotic isolating mechanisms?
    • Hybrid inviability
    • Hybrid sterility
    • Hybrid breakdown
  32. What is hybrid inviability?
    A postzygotic reproductive isolating mechanism in which offspring do not live to adulthood.
  33. What is hybrid sterility?
    A postzygotic reproductive isolating mechanism in which first generation gonads fail to develop properly (i.e. sterile).
  34. What is hybrid breakdown?
    A postzygotic reproductive isolating mechanism in which F2 individuals have reduced viability due to the accumulation of lethal complementary alleles.
  35. What is Haldane’s Rule?
    When in the offspring of two different animal races one sex is absent, rare, or sterile, that sex is the heterozygous (heterogametic) sex.
  36. What is heterogametic sex? Name some examples.
    One sex may be absent, rare or sterile among F1 offspring of two animal races. Ligers (tiger x lion) have infertile males but fertile females.
  37. Two different species of birds produce hybrid offspring on occasion. If males are the heterogametic sex, what is the result?
    The male hybrid offspring will be absent, rare, or sterile.
  38. What are three challengers of BSC?
    • Hybrids
    • Asexual organisms
    • Ring species
  39. Why are asexual organisms a challenge for BSC?
    BSC defines species based on their sexual compatibility. However, some species of plant and fungi have somehow lost the ability to sexually reproduce … so you might find a “species” in which you have several strains of unique but very much related individuals that only reproduce asexually. According to BSC, you could not group these individuals into the same species because they do not interbreed, and yet they are practically the same species.
  40. Why are interspecies hybrids a challenge for BSC?
    BSC defines species based o their sexual compatibility, and yet some distinct species may result in fertile hybrids, more commonly in plants.
  41. Why are ring species a challenge to BSC?
    Ring species may form a ring around some given natural habitat (for example, around Hudson’s Bay). Populations along the ring will interbreed with other populations along the gradient, but on occasion scientists will find that the species on the ends of the ring will not and cannot interbreed. Since BSC defines species as a group of individuals that can interbreed, this poses a challenge to defining these individuals as members of the same species.
  42. What is the core genome hypothesis? Why is it useful?
    It predicts that barriers to interspecies recombination for core genes are not shared by auxiliary genes. This means that we can focus on differences between core genes and ignore auxiliary genes when trying to determine if cryptic species are unique from one another.
  43. What is the mosaic gene structure?
    Individual bacterial or viral genes composed of bits and pieces of very different origin (conflicts with BSC).
  44. What are core genes?
    Core genes are involved in cell metabolism, are rarely transferred, and are divergent between taxa.
  45. What are auxiliary genes?
    Auxiliary genes are involved in adapting to local conditions, including genes for pathogenicity, antibiotic resistance toxins, and novel metabolic functions. There are advantages to exchanging these.
  46. What are three mechanisms of population divergence?
    • Genetic drift
    • Natural selection
    • Sexual selection
  47. Define the PSC.
    A monophyletic group composed of the ‘smallest diagnosable cluster of individual organisms within which there is a parental pattern of ancestry and descent’.
  48. How many stages of speciation are there?
    4
  49. Define the ESC.
    The ecological species concept involves defining a species based on a shared adaptation to acquire a particular set of resources (niche).
  50. What are two problems with ESC?
    • It’s difficult to measure niche overlap between individuals.
    • Also breaks down when different sexes or different morphs occupy different niches.
  51. Define the MSC.
    The morpho species concept defines as a species as those groups of organisms that show the same phenotype.
  52. What are some problems with MSC?
    Doesn’t take into account sibling species which look the same but are reproductively isolated. Also doesn’t consider that a lot variation can be found within a species.
  53. Which species concept can you not use when considering asexual species and the fossil record?
    BSC
  54. Which species concept can you not use when considering species with males and females that have non-overlapping niches?
    ESC
  55. Which species concept can you not use when considering species that lack reliable phylogenic data?
    PSC
  56. Which species concept can you not use when considering cryptic species or different morphs?
    MSC
  57. What is the Three-Step Model of Speciation?
    • Isolation (usually geographic, allopatric)
    • Populations diverge (drift, natural selection, sexual selection)
    • Secondary contact (either reinforcement which completes speciation, or resume gene-flow which is despeciation)
  58. Why is the Three-Step Model of Speciation oversimplified?
    • Speciation sometimes happens in sympatry.
    • Secondary contact isn’t necessary.
    • There other possible outcomes besides just one or two species.
  59. What are the forms of isolation
    • Temporal
    • Behavioral
    • Habitat
  60. What is temporal isolation?
    Occupy same area but don’t interbreed because they mate at different times.
  61. What is behavioral isolation?
    Courtship rituals can differ greatly between species, and females or males will only respond to the “right one”.
  62. What is habitat isolation?
    Different species can prefer different breeding grounds.
  63. What are the two types of allopatry?
    • Peripatry
    • Parapatry
  64. What is peripatry?
    Occurs when a small peripheral population gets separated from a large central population.
  65. What is parapatry?
    Occurs when you have two populations that have adjacent geographic ranges with some contact.
  66. What are the two mechanisms of peripatry?
    • Dispersal
    • Vicariance
  67. What is dispersal at it relates to allopatry?
    Dispersal is the way in which allopatry can occur when a sub-set of a population expands into a separate range such as an island, moutaintop, or swamp.
  68. What is vicariance as it relates to allopatry?
    It’s the splitting of a population into two populations by some geographic event (ex. Newly formed river or lake can split a population into two, or a new mountain range, a new valley, etc).
  69. What is an example of parapatric isolation?
    Ring species
  70. How can isolation/speciation occur in sympatry?
    • Polyploidy in plants
    • Disruptive selection that selects for extremes over intermediates
  71. Is drift indicated as a major source of speciation?
    No
  72. What is Dobzhansky’s Reinforcement Hypothesis?
    When populations re-establish contact after a period of divergence, hybrids usually less fit than ’parental’ (pure) forms. If populations have become postzygotically isolated (low hybrid fitness) selection should now favour evolution of prezygotic isolating mechanisms. This reinforcement of parental forms is a necessary final step in speciation (according to Dobzhansky).

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