Species Concepts And Speciation


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Species Concepts And Speciation

  1. 1. Species Concepts and Speciation Mark McGinley Associate Professor Honors College and Department of Biological Sciences Texas Tech University
  2. 2. Species Concepts <ul><li>Defining “a species” is not as simple as you might hope </li></ul><ul><li>There are many different “species concepts”. </li></ul>
  3. 3. Historical Species Concepts <ul><li>Typological Species Concept </li></ul><ul><ul><li>species are a 'type' of organism </li></ul></ul><ul><li>Lineaeus </li></ul><ul><ul><li>&quot; Species are as many as were created in the beginning by the Infinite. “ </li></ul></ul><ul><ul><li>Systema Naturae , 10th ed. (1758) establishes a catalog of 4,162 &quot;types&quot; </li></ul></ul>
  4. 4. Historical Species Concepts <ul><li>Nominalistic Species Concept : </li></ul><ul><ul><li>a name given for convenience </li></ul></ul><ul><li>Darwin </li></ul><ul><ul><li>&quot; I look at the term species, as one arbitrarily given for the sake of convenience to a set of individuals closely resembling each other.... “ </li></ul></ul><ul><ul><li>philosophical Essentialism </li></ul></ul><ul><ul><li>Only individuals exist, not universal classes. </li></ul></ul>
  5. 5. Historial/Modern Species Concepts <ul><li>Morphospecies Concept </li></ul><ul><ul><li>Species traditionally have been described and identified on the basis of morphological criteria </li></ul></ul><ul><ul><li>According to this concept, species are “groups of individuals that are morphologically similar and clearly distinguishable from individuals of other groups” </li></ul></ul>
  6. 6. Modern Species Concepts <ul><li>Biological Species Concept </li></ul><ul><ul><li>a reproductively isolated population </li></ul></ul><ul><li>Mayr </li></ul><ul><ul><li>&quot; Species are groups of interbreeding natural populations that are reproductively isolated from other such groups. &quot;       </li></ul></ul><ul><ul><ul><li>Historically, the most widely used concept among ecologists       </li></ul></ul></ul>
  7. 7. Biological Species Concept- Key Concepts <ul><li>&quot; Interbreeding : => a genetic unit </li></ul><ul><ul><li>species are gene pools : a coadapted gene complex </li></ul></ul><ul><ul><li>Members of the same species resemble each other because they have common ancestors </li></ul></ul>
  8. 8. Biological Species Concept- Key Concepts <ul><li>&quot; Natural Populations &quot; => an ecological unit            </li></ul>
  9. 9. Biological Species Concept- Key Concepts <ul><li>&quot; Reproductively isolated &quot; => a reproductive unit </li></ul><ul><ul><li>Reproductive Isolating Mechanisms </li></ul></ul><ul><ul><ul><li>features that prevent mating outside the species </li></ul></ul></ul><ul><ul><li>Species Recognition Mechanisms </li></ul></ul><ul><ul><ul><li>features that allow recognition of potential mates </li></ul></ul></ul>
  10. 10. Premating or prezygotic mechanisms <ul><li>Ecological or habitat isolation </li></ul><ul><li>Seasonal or temporal isolation </li></ul><ul><li>Sexual or ethological isolation </li></ul><ul><li>Mechanical isolation </li></ul><ul><li>Isolation by different pollinators </li></ul><ul><li>Gametic isolation </li></ul>
  11. 11. Habitat Isolation- Geese
  12. 12. Seasonal Isolation- Frogs
  13. 13. Behavioral Isolation- Crabs
  14. 14. Mechanical Isolation- Insects
  15. 15. Postmating or post-zygotic mechanisms <ul><li>Hybrid inviability </li></ul><ul><li>Hybrid sterility </li></ul><ul><ul><li>F1 fails to produce viable gametes </li></ul></ul><ul><li>Hybrid breakdown </li></ul><ul><ul><li>F2s or backcrosses have reduced viability </li></ul></ul>
  16. 16. Hybrid sterility- Mule
  17. 17. Reproductive Isolation Summary
  18. 18. Identifying Species Using the Biological Species Concept <ul><li>Biological Species Concept </li></ul><ul><ul><li>suggests a research program that will allow scientists to identify species using this concept </li></ul></ul><ul><ul><ul><li>the mark of a good theory </li></ul></ul></ul><ul><li>    </li></ul>
  19. 19. Identifying Species Using the Biological Species Concept <ul><li>(1) Experiment: test cross </li></ul><ul><ul><li>A and B interbreed, but neither with C => A & B are conspecific </li></ul></ul><ul><ul><li>C is a separate species </li></ul></ul>
  20. 20. Identifying Species Using the Biological Species Concept <ul><li>(2) Field observations : a &quot; species gap&quot; exists </li></ul><ul><ul><li>Populations maintain identity when sympatric (occuring in the same place) &   synchronic (occuring at the same time) </li></ul></ul><ul><li>          </li></ul>
  21. 21. Odocoileus hemionus Mule Deer
  22. 22. Odocoileus virginianus White-tailed Deer
  23. 23. Odocoileus Distribution
  24. 24. Variation in Morphology
  25. 25. Variation in Behavior O. hemionus O. virginianus
  26. 26. Lacewings Chrysoperla plorabunda
  27. 27. Lightening Bugs Lampyridae: Hemiptera: Insecta
  28. 28. Firefly Flashing Patterns
  29. 29. Identifying Species Using the Biological Species Concept <ul><li>(3) Inference : forms 'look different' </li></ul><ul><li>      Many new species are described from single 'skin & skull' or small series.       Most commonly used criterion: inference is often weak. </li></ul>
  30. 30. Morphological Differences
  31. 31. Geographic Variation in Weasels Mustela erminea
  32. 32. Feloid ( Panthera ) and Canoid ( Canis)
  33. 33. Identifying Species Using the Biological Species Concept <ul><li>4) Genetic studies indicate no gene flow between forms        </li></ul><ul><li>- fixation for alternative alleles                    </li></ul><ul><li>- distinct DNA sequences </li></ul><ul><li>             </li></ul><ul><li>- distinct karyotypes                     </li></ul>
  34. 34. Evolutionary Species Concept <ul><li>an evolving lineage </li></ul><ul><ul><li>&quot; An evolutionary species is a single lineage of ancestor-descendant populations which maintains its identity from other such lineages and which has its own evolutionary tendencies and historical fate. &quot; </li></ul></ul><ul><ul><li>  Historically, the most popular concept among paleontologists . </li></ul></ul><ul><ul><li>Used extensively in comparative biology & phylogenetic systematics </li></ul></ul>
  35. 35. Evolutionary Species Concept <ul><li>(1) &quot; Lineage &quot;: an ancestor-descendent series </li></ul><ul><ul><li>genealogy is crucial: members of a species have a common ancestor </li></ul></ul><ul><ul><li>Research program of paleontology is inferrence of genealogy         </li></ul></ul>Pelycodus an early Eocene Primate
  36. 36. Evolutionary Species Concept <ul><li>(2) &quot; Identity &quot;: a biologically distinct entity </li></ul><ul><ul><li>Includes concepts associated with Biological Species, </li></ul></ul><ul><ul><li>the Biological Species Concept is the broadest general case of the Evolutionary Species Concept </li></ul></ul><ul><ul><ul><li>  [ i.e. , a biological species is an evolutionary species at a partcular point in time]        </li></ul></ul></ul>
  37. 37. Evolutionary Species Concept <ul><li>(3) &quot; Tendencies & Fate &quot;: a species is a historical entity </li></ul><ul><ul><li>Species have an origin (by cladogenesis = ' splitting ' of lineages) </li></ul></ul><ul><ul><li>undergo evolution (by anagenesis = change within lineages) </li></ul></ul><ul><ul><li>disappear (by extinction = termination of lineage). </li></ul></ul>
  38. 38. Other Species Concepts <ul><li>Phylogenetic Species Concept </li></ul><ul><li>Recognition Species Concept </li></ul><ul><li>Cohesion Species Concept </li></ul><ul><li>Ecological Species Concept </li></ul><ul><li>Internodal Species Concept </li></ul><ul><li>Why so many species concepts??? </li></ul>
  39. 39. Problems with the Biological Species Concept <ul><li>(1) Reproductive isolation is a &quot;typological criterion&quot; (an either / or rule).       Does one successful hybridization invalidate species distinction?       Extent & consequences of hybridization may vary:              <  4% of Alberta deer show hybrid ancestry, including F1 s (Hughes & Carr 1993)              > 50% in West Texas (Ballinger et al . 1996): no F1 s </li></ul>
  40. 40. Problems with the Biological Species Concept <ul><li>(2) Reproductive isolation evolves gradually: species distinctions somewhat arbitrary       Rassenkreis   (''race circle'): a geographically convergent series of species </li></ul><ul><ul><li>adjacent forms are reproductively compatible & morphologically similar </li></ul></ul><ul><ul><li>ends of circle are reproductively isolated & morphologically distinct </li></ul></ul>
  41. 41. Ensatina - salamanders
  42. 42. Ring species in Gulls ( Larus )
  43. 43. Problems with the Biological Species Concept <ul><li>Reproductive isolation arises without morphological differentiation:        Sibling species are morphologically identical species pairs        </li></ul>
  44. 44. Tree Creepers Sibling Species
  45. 45. Sibling Species Empidonax flycatchers
  46. 46. Problems with the Biological Species Concept <ul><li>(3) Reproductive criterion does not work well with asexual species. </li></ul><ul><li>      parthenogenesis  is common in plants                 Plant species hybridize widely outside 'species' boundary:         </li></ul>
  47. 47. Hybridization <ul><li>Raphanus radish X Brassica cabbage => “ Raphanobrassica &quot; (radish leaves & cabbage root ) </li></ul>
  48. 48. Problems with the Biological Species Concept <ul><li>(4) Genetic differences may not indicate reproductive isolation or morphological divergence .       Fixed allelic differences may indicate local adaptation or genetic drift.        </li></ul>
  49. 49. Problems with the Biological Species Concept <ul><li>(5) What to do with paleospecies </li></ul><ul><ul><li>(extinct or fossil species)? </li></ul></ul><ul><ul><li>fragmentary ecological evidence : only by inference              </li></ul></ul><ul><li>      </li></ul>
  50. 50. Problems with the Biological Species Concept <ul><li>Are dinosaurs ? </li></ul><ul><ul><li>'hot-blooded', </li></ul></ul><ul><ul><li>'maternal', </li></ul></ul><ul><ul><li>‘ colorful'       </li></ul></ul><ul><ul><li>fragmentary physical evidence </li></ul></ul>