Lecture #3 – Origin of Species

1. Lecture #3 – Origin of Species Cartoon – gentleman and ape

2. Key Concepts: • Species concepts • Development of reproductive isolation • Patterns of speciation • Macroevolution • Human evolution • Evolution continues…..

3. specie My pet peeve is…. “Species” is both singular and plural

4. Major Species Concepts • Biological • Morphological • Phylogenetic Diagram – variation in beaks between species

5. Biological species – the basic standard for separating species(Ernst Mayr, 1942) • Species are defined by natural reproductive isolation • Individuals that can produce successful offspring are considered the same species Image – Sarracenia rubra Image – Sarracenia flava ≠

6. Critical Thinking • Biological species are defined by natural reproductive isolation • Individuals that can produce successful offspring are considered the same species • Definition doesn't always work – why not???

7. Critical Thinking • Biological species are defined by natural reproductive isolation • Individuals that can produce successful offspring are considered the same species • Definition doesn't always work • Speciation often occurs as the gradual divergence of multiple populations • Fuzzy boundaries during divergence • Also, can’t be used to classify extinct species

8. Morphological species – the first way to separate species(Linnaeus, ~1750 & others) • Species are defined by differences in form • Individuals with the same morphology and/or anatomy are considered the same species Image – Hymenocallis coronaria Image – Hymenocallis floridana ≠

9. Critical Thinking • Morphological species are defined by differences in form • Individuals with the same morphology and/or anatomy are considered the same species • Definition doesn't always work – why not???

10. Critical Thinking • Morphological species are defined by differences in form • Individuals with the same morphology and/or anatomy are considered the same species • Definition doesn't always work • Some species have a lot of natural phenotypic variation • But, the only way to classify extinct species and species that lack sexual reproduction • Also important in describing new species

11. Phylogenetic species – the new standard for separating species??? • Species are defined based on evolutionary history • Species defined by the smallest monophyletic group in an evolutionary tree • Monophyletic = lineage is derived from a common ancestor • Definition doesn't always work • Don’t have good phylogenies for all species or groups • Also, imperfect agreement on interpretations

12. Development And Maintenance Of Reproductive Isolation: the essence of speciation • What constitutes a barrier to reproduction? • How do reproductive barriers develop? It is generally accepted that natural reproductive isolation defines and preserves separate species in sexually reproducing organisms

13. Pre-zygotic Barriers • Remember, the zygote is the fertilized egg cell • The first cell of the new offspring • Pre-zygotic barriers prevent the formation of the zygote • Natural, evolved incompatibilities prevent successful fertilization • Habitat isolation • Behavioral isolation • Temporal isolation • Structural isolation • Chemical isolation Image – blue-footed boobies mating behavior

14. Critical Thinking • Natural, evolved incompatibilities prevent successful fertilization • Think of some examples of: • Habitat isolation • Behavioral isolation • Temporal isolation • Structural isolation • Chemical isolation Euphorbia in very xeric habitat

15. Critical Thinking • Habitat isolation – different ecological niches • Behavioral isolation – changes in mating behaviors…. • Temporal isolation – the timing of reproductive events • Structural isolation – mutations that change morphology of reproductive structures • Chemical isolation – gametes must be compatible, pollen must “match”

16. Post-zygotic Barriers • Post-zygotic barriers prevent successful development of offspring • Hybrids don’t develop properly • Hybrids don’t reach sexual maturity • Hybrids don’t produce viable gametes • Hybrid lineages fail over time • Natural genetic incompatibilities prevent successful long-term reproduction Horse x Donkey = robust but sterile Mule

17. Critical Thinking The Darwinian fitness of an individual is measured by • its ability to reproduce. • how long it lives. • the number of mates it attracts. • the number of its offspring that survive to reproduce. • its physical strength.

18. Critical Thinking The Darwinian fitness of an individual is measured by • its ability to reproduce. • how long it lives. • the number of mates it attracts. • the number of its offspring that survive to reproduce. • its physical strength.

19. Patterns of SpeciationBarriers result from separations that persist long enough that eventually new species have developed Diagram – different species of fish in separated ponds

20. Patterns of Speciation • Pattern depends on the mechanism of gene flow interruption • Allopatric speciation occurs when populations are separated by a geographical barrier • Sympatric speciation occurs in the absence of a geographic barrier

21. Critical Thinking • Allopatric speciation occurs when populations are separated by a geographical barrier • Such as???? • How could such barriers form???

22. Critical Thinking • Allopatric speciation occurs when populations are separated by a geographical barrier • Such as rivers, canyons, mountains, oceans, glaciers….. • How could such barriers form??? Diagram showing development of a canyon

23. Critical Thinking • Allopatric speciation occurs when populations are separated by a geographical barrier • Such as rivers, canyons, mountains, oceans, glaciers….. • How could such barriers form??? • Geological processes • Mountain building • River erosion • Glaciation • Tectonic events • Cave formation

24. Critical Thinking • Also…. • Climate changes that cause large lakes to dry up or form smaller, isolated lakes • Colonization events that separate a group from the rest of the population (founder effect)

25. Allopatric Speciation • Once populations are physically isolated, speciation may occur due to all the evolutionary processes we talked about earlier • Selection • Drift • Selective mating • Mutation

26. Critical Thinking • What if the isolated population is small??? • What if the isolated population is from edge of the range of the original population???

27. Critical Thinking • What if the isolated population is small??? • Speciation is likely to occur more rapidly • More genetic drift, less gene flow • What if the isolated population is from edge of the range of the original population???

28. Critical Thinking • What if the isolated population is small??? • Speciation is likely to occur more rapidly • More genetic drift, less gene flow • What if the isolated population is from edge of the range of the original population??? • It may be even more likely to diverge • Probably already adapting to frontier or edge conditions • Also, probably more likely to migrate

29. Allopatric Speciation due to geographic separation Birds???? Plants???? Images – different species of chipmunk on either side of the Grand Canyon

30. Speciation may, or may not, occur… Diagram – sympatric  allopatric  either sympatric again or not, as a population separates around a mountain range and then re-unites

31. Sympatric Speciation • Occurs when a population becomes reproductively isolated without geographic barriers • Mutations or selection pressures that lead to changes in behavior, habitat, food source, phenology…. • Errors in meiosis that lead to polyploidy (some plants can be self-fertile, vegetative reproduction) • Hybrids that develop into fertile populations through vegetative reproduction or multiple events (mostly plants) Diagram – sympatric speciation in a forest environment

32. Sympatric Speciation • Occurs when a population becomes reproductively isolated without geographic barriers • Mutations or selection pressures that lead to changes in behavior, habitat, food source, phenology…. • Errors in meiosis that lead to polyploidy (some plants can be self-fertile, vegetative reproduction) • Hybrids that develop into fertile populations through vegetative reproduction or multiple events (mostly plants) Diagram – meiosis errors

33. Polyploidy – one mechanism for sympatric speciation Diagram – errors in meiosis can lead to polyploids Some plants can self-pollinate, or vegetative reproduction can produce multiple fertile individuals

34. Sympatric Speciation • Occurs when a population becomes reproductively isolated without geographic barriers • Mutations or selection pressures that lead to changes in behavior, habitat, food source, phenology…. • Errors in meiosis that lead to polyploidy (some plants can be self-fertile, vegetative reproduction) • Hybrids that develop into fertile populations through vegetative reproduction or multiple events (mostly plants) Image showing hybrid asters

35. Speciation is NOT a Given • Must have an interruption to gene flow PLUS • Must have enough change in the separated populations to produce a barrier to reproduction

36. Endemic Species and Adaptive Radiation • Endemic species = restricted in distribution to a particular place, generally because they evolved in place • Volcanic island chains often contain many endemic species • No biota until they were colonized by a few individuals (founder effect) • These small populations then evolved into new species • Allopatric speciation due to the geographic barrier from the founder effect • But also……

37. Endemic Species and Adaptive Radiation • Many new species develop that are adapted to the diverse new habitats found in such islands • Sympatric speciation • No geographic barriers • Adaptive radiation into new habitats Diagram showing adaptive radiation

38. Adaptive Radiation Galapagos finches and Hawaiian honeycreepers Diagrams – adaptive radiation in birds

39. Adaptive Radiation is a common theme – both between and within lineages Diagram – mass extinctions over the past 2.5 billion years Diagram – diversification of mammals after extinction of the dinosaurs Mass Extinction Events Mammals

40. Critical Thinking • Humans have initiated a mass extinction event • Will life cease to exist on the planet??? • Can we destroy the planet???

41. Critical Thinking • Humans have initiated a mass extinction event • Will life cease to exist on the planet??? • Highly unlikely • There will just be a new set of species • Can we destroy the planet???

42. Critical Thinking • Humans have initiated a mass extinction event • Will life cease to exist on the planet??? • Highly unlikely • There will just be a new set of species • Can we destroy the planet??? • Highly unlikely • The earth has survived for at least 4 billion years! • Species come and go….

43. Speciation is a Constant • When migration, isolation or other selection pressures force divergence, reproductive isolation can eventually lead to speciation • Speciation might be gradual or abrupt (punctuated equilibrium) • Transitions (either gradual or abrupt) may or may not be captured in the fossil record

44. Macroevolution: larger-scale changes in organismsAlso contributes to speciation • Small, population-scale changes can accumulate • Exaptations – traits can be co-opted • Feathers for thermoregulation  feathers for flight • Large phenotypic changes can result from small changes in regulatory genes • Control over the timing and length of developmental events, or the spatial organization of body parts

45. Critical Thinking Was the evolution of the modern horse a series of directed events ???? Diagram – phylogeny of the modern horse

46. Critical Thinking Was the evolution of the modern horse a series of directed events??? • No, there are lots of lineages that are now extinct • Evolution may look directed, but it’s not....

47. Selection is a series of gates!!!

48. A Preview of the Taxonomic Hierarchy:this is how we classify diversity

49. Images – the yellow fringed orchid Platanthera ciliaris

50. Humans can also be classified! • Domain – eukarya • Kingdom – animal • Phylum – chordates • Sub-phylum – vertebrates • Class – mammals • Order – primates • Family – hominoids • Genus – Homo • Specific epithet – sapiens Image of human fossil